Cross-resistance and genetics of field-evolved resistance to chlorfenapyr in Plutella xylostella

Chlorfenapyr is a broad-spectrum halogenated pyrrole insecticide with a unique mode of action. Due to the misuse and overuse of this chemical, resistance has been reported in several arthropods, including Plutella xylostella, which is one of the most destructive insect pests afflicting crucifers worldwide. A better understanding of the cross-resistance and genetics of field-evolved chlorfenapyr resistance could effectively guide resistance management practices. Here, the chlorfenapyr resistance of a field-derived population of P. xylostella was introgressed into the susceptible IPP-S strain using a selection-assisted multigenerational backcrossing approach. The constructed near-isogenic strain, TH-BC5F2, shared 98.4% genetic background with the recurrent parent IPP-S strain. The TH-BC5F2 strain showed 275-fold resistance to chlorfenapyr, but no significant cross-resistance to spinosad, abamectin, chlorpyrifos, β-cypermethrin, indoxacarb, chlorantraniliprole, or broflanilide (no more than 4.2-fold). Genetic analysis revealed that resistance was autosomal, incompletely dominant, and conferred by 1 major gene or a few tightly linked loci. The synergism of metabolic inhibitors (PBO, DEM, and DEF) to chlorfenapyr was very weak (<1.7-fold), and the metabolic enzyme activities in the TH-BC5F2 strain were not significantly elevated compared with the IPP-S strain. The results enhances our understanding of the genetic traits of chlorfenapyr resistance, and provides essential information for improving resistance management strategies.

An investigation of the acaricidal activity of benzyl alcohol on Rhipicephalus annulatus and Rhipicephalus sanguineus and its synergistic or antagonistic interaction with commonly used acaricides

The most economically significant ectoparasites in the tropics and subtropics are ixodid ticks, especially Rhipicephalus annulatus and Rhipicephalus sanguineus. Years of extensive use of the readily available acaricides have resulted in widespread resistance development in these ticks, as well as negative environmental consequences. Benzyl alcohol (BA) has been frequently used to treat pediculosis and scabies, and it may be an effective alternative to commonly used acaricides. The main aim of the present study was to evaluate the acaricide activity of BA and its combination with the regularly used chemical acaricides against R. annulatus and R. sanguineus. Different concentrations of BA alone and in combination with deltamethrin, cypermethrin and chlorpyrifos were tested in vitro against adult and larvae of both tick species. The results showed that BA is toxic to R. annulatus and R. sanguineus larvae, with 100% larval mortality at concentrations of ≥50 mL/L, and LC50 and LC90 attained the concentrations of 19.8 and 33.8 mL/L for R. annulatus and 18.8 and 31.8 mL/L for R. sanguineus, respectively. Furthermore, BA in combination with deltamethrin, cypermethrin and chlorpyrifos exhibited synergistic factors of 2.48, 1.26 and 1.68 against R. annulatus larvae and 1.64, 11.1 and 1.14 against R. sanguineus larvae for deltamethrin + BA, cypermethrin + BA and chlorpyrifos + BA, respectively. BA induced 100% mortality in adult R. annulatus at concentrations of ≥250 mL/L with LC50 and LC90 reached the concentrations of 111 and 154 mL/L, respectively. Additionally, BA had ovicidal activity causing complete inhibition of larval hatching at 100 mL/L. The combination of BA with deltamethrin and cypermethrin increased acetylcholinesterase inhibition, whereas the combination of BA with chlorpyrifos decreased glutathione (GSH) activity and malondialdehyde levels. In the field application, the combination of BA 50 mL/L and deltamethrin (DBA) resulted in a significant reduction in the percentage of ticks by 30.9% 28 days post-treatment when compared with groups treated with deltamethrin alone. In conclusion, BA causes mortality in laboratory and field studies alone and in combination with cypermethrin or deltamethrin. BA can be used for control of ticks of different life stages, that is, eggs and larvae, through application to the ground.

Grape seed extract prevents chlorpyrifos-induced toxicity in rat liver through the modulation of phase I detoxification pathway

Chlorpyrifos (CPF) poisoning is a public health problem for which there is not currently any effective prophylaxis. In this study, we investigated the protective effect of grape seed extract (GSE) against CPF-induced hepatotoxicity. Rats were daily treated either with CPF (2 mg/kg) or CPF and GSE (20 mg/kg) for 1 week, sacrificed, and their livers dissected for biochemical, molecular, and histopathological analyses. CPF generated liver dysfunction by altering carbohydrate, lipid, amino acid, ammonia and urea metabolism, and provoked mitochondrial impairment through disturbing tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS), and mitochondrial viability. CPF also induced cholinergic excitotoxicity along with oxidative stress and histopathological alterations. Interestingly, treatment with GSE prevented all the detrimental effects of CPF through the regulation of cytochrome P450 (CYP450) gene expression. Molecular docking analysis indicated that GSE-containing polyphenols acted as epigenetic modulators through inhibiting DNA (cytosine-5)-methyltransferase 1 (DNMT1), thus favoring the CYP2C6 detoxification pathway. Thereby, GSE might be a promising strategy in the protection of the liver against CPF toxicity.

Does Leptinotarsa decemlineata larval survival after pesticide treatment depend on microbiome composition?

BACKGROUND

The microbiomes of some arthropods are believed to eliminate pesticides by chemical degradation or stimulation of the host immune system. The Colorado potato beetle (CPB; Leptinotarsa decemlineata) is an important agricultural pest with known resistance to used pesticides. We sought to analyze microbiome composition in CPB larvae from different sites and to identify the effect of pesticides on the microbiome of surviving and dead larvae after chlorpyrifos treatment in laboratory. Changes in the Lactococcus lactis community in larvae treated with chlorpyrifos and fed by potato leaves with L. lactis cover were studied by manipulative experiment. The microbiome was characterized by sequencing the 16S RNA gene.

RESULTS

The microbiome of L. decemlineata larvae is composed of a few operational taxonomic units (OTUs) (Enterobacteriaceae, Pseudocitrobacter, Acinetobacter, Pseudomonas, L. lactis, Enterococcus, Burkholderia and Spiroplasma leptinotarsae). The microbiome varied among the samples from eight sites and showed differences in profiles between surviving and dead larvae. The survival of larvae after chlorpyrifos treatment was correlated with a higher proportion of L. lactis sequences in the microbiome. The S. leptinotarsa profile also increased in the surviving larvae, but this OTU was not present in all sampling sites. In manipulative experiments, larvae treated with L. lactis had five-fold lower mortality rates than untreated larvae.

CONCLUSION

These results indicate that the microbiome of larvae is formed from a few bacterial taxa depending on the sampling site. A member of the gut microbiome, L. lactis, is believed to help overcome the toxic effects of chlorpyrifos in the larval gut. © 2023 Society of Chemical Industry.

Assessing phytotoxicity and cyto-genotoxicity of two insecticides using a battery of in-vitro biological assays

Intensive use of chemical pesticides in agriculture poses environmental risks and may have negative impacts on agricultural productivity. The potential phytotoxicity of two chemical pesticides, chlorpyrifos (CPS) and fensulfothion (FSN), were evaluated using Cicer arietinum and Allium cepa as model crops. Different concentrations (0-100 μgmL-1) of both CPS and FSN decreased germination and biological attributes of C. arietinum. High pesticide doses significantly (p ≤ 0.05) caused membrane damage by producing thiobarbituric acid reactive substances (TBARS) and increasing proline (Pro) content. Pesticides elevated ROS levels and substantially increased the superoxide anions and H2O2 concentrations, thus aggravating cell injury. Plants exposed to high pesticide dosages displayed significantly higher antioxidant levels to combat pesticide-induced oxidative stress. Ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) increased by 48%, 93%, 71%, 52% and 94%, respectively, in C. arietinum roots exposed to 100 µgFSNmL-1. Under CLSM, pesticide-exposed C. arietinum and 2',7'-dichlorodihydrofluorescein diacetate (2'7'-DCF) and 3,3'-diaminobenzidine stained roots exhibited increased ROS production in a concentration-dependent manner. Additionally, enhanced Rhodamine 123 (Rhd 123) and Evan's blue fluorescence in roots, as well as changes in mitochondrial membrane potential (ΔΨm) and cellular apoptosis, were both associated with high pesticide dose. Allium cepa chromosomal aberration (CAs) assay showed a clear reduction in mitotic index (MI) and numerous chromosomal anomalies in root meristematic cells. Additionally, a-dose-dependent increase in DNA damage in root meristematic cells of A. cepa and conversion of the super-coiled form of DNA to open circular in pBR322 plasmid revealed the genotoxic potential of pesticides. The application of CPS and FSN suggests phytotoxic and cyto-genotoxic effects that emphasize the importance of careful monitoring of current pesticide level in soil before application and addition at optimal levels to soil-plant system. It is appropriate to prepare both target-specific and slow-release agrochemical formulations for crop protection with concurrent safeguarding of agroecosystems.

Tubermycin B coated on Galactosylated Chitosan Nanoparticles synthesized by eco-friendly method ameliorates intracellular free radical production and reduces oxidative stress, reducing phosphorylation of IKKα/β/pIкBα/NF-кB pathway

OBJECTIVE

The objective of the current study was to investigate the cytotoxic potentials of Galactosylated Chitosan Nanoparticles. Specifically, the study aimed to develop Tubermycin B coated on Galactosylated Chitosan Nanoparticles using a new green method that replaces sodium borohydride in the reduction process.

MATERIALS AND METHODS

The study synthesized Tubermycin B coated on Galactosylated Chitosan Nanoparticles through a new green method. The cytotoxicity of these nanoparticles was evaluated in a mice intestinal tract model that had been induced with chlorpyrifos, which causes oxidative stress-related enterotoxicity. Multiple activities, including the apoptosis of intestinal macrophages and the activation of Ikappa α/β kinase (IKKα/β), were examined as indicators of the nanoparticles' efficacy. The stability of the synthesized Chitosan Nanoparticles was also assessed. Additionally, the encapsulation efficiency of Boscia angustifalia and Boscia senegalensis extracts within the nanoparticles was determined.

RESULTS

The results of the study showed that Tubermycin B coated on Galactosylated Chitosan Nanoparticles effectively alleviated the oxidative stress-related enterotoxicity in the mice intestinal tract induced by chlorpyrifos. The nanoparticles prevented the apoptosis of intestinal macrophages and inhibited the activation of IKKα/β. The synthesized chitosan nanoparticles exhibited high stability. The encapsulation efficiency of Boscia angustifalia extract was recorded as 46.58%, whereas for Boscia senegalensis extract, it was 9.77%. The nanoparticles showed no cytotoxicity at all tested concentrations and demonstrated a medium-level anticancer effect.

CONCLUSIONS

Based on the findings, it can be concluded that Tubermycin B coated on Galactosylated Chitosan Nanoparticles has the potential to alleviate oxidative stress-related enterotoxicity in the mice intestinal tract. The nanoparticles showed high stability and exhibited a medium-level anticancer effect. Furthermore, the study demonstrated that Boscia angustifalia extract exhibited higher anti-hepatitis C virus antibodies (anti-HCV) activity compared to Boscia senegalensis extract in an in-vitro system. Therefore, Boscia angustifalia could be considered a promising candidate for the development of an anti-HCV drug for future in-vivo studies.

Thirty-minute test to detect insecticide resistance under field conditions: the case of the Asian citrus psyllid

BACKGROUND

Diaphorina citri Kuwayama is one of the most destructive citrus pests worldwide. It is controlled mainly through applications of conventional insecticides. Methodologies used to estimate resistance to insecticides do not correlate with field efficacy, and do not provide timely and reliable information to make decisions at a site where spraying is needed. The use of diagnostic doses with 30-min exposure is proposed for estimating the resistance of D. citri to imidacloprid, spinosad, malathion and chlorpyrifos at the orchard level.

RESULTS

Under laboratory conditions, we estimated the lowest doses that caused 100% mortality within 30 min of exposure (diagnostic dose) in a susceptible D. citri colony. The diagnostic doses for imidacloprid, spinosad, malathion and chlorpyrifos were 7.4, 4.2, 1.0 and 5.5 mg a.i. L-1 , respectively. Under field conditions, we applied the diagnostic doses to D. citri feeding on Citrus aurantifolia Swingle at five localities in Michoacan state, Mexico (Nueva Italia, Santo Domingo, El Varal, Gambara and El Ceñidor). Additionally, the field efficacy of these insecticides against these populations was evaluated. A significant correlation between field efficacy and mortality was observed with the diagnostic doses for imidacloprid, malathion and chlorpyrifos (R2  ≥ 0.93). The correlation for spinosad could not be estimated because the mortality caused by the diagnostic dose and its field efficacy at all study sites was consistently >98%.

CONCLUSIONS

Field efficacy and resistance were estimated based on the field diagnostic doses with 30-min exposure for all tested insecticides. Consequently, growers and pest management technicians can estimate the performance of the evaluated insecticides at the orchard level and before insecticide application. © 2023 Society of Chemical Industry.

Chlorpyrifos and chlorfenapyr resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae) relies on UDP-glucuronosyltransferases

Fall armyworm, Spodoptera frugiperda (J. E. Smith), has become an important agricultural pest worldwide. S. frugiperda is mainly controlled by the chemical insecticides, whereas the frequent application of insecticides would result in the resistance development. Insect uridine diphosphate-glucuronosyltransferases (UGTs), as phase II metabolism enzymes, play vital roles in the breakdown of endobiotic and xenobiotics. In this study, 42 UGT genes were identified by RNA-seq, including 29 UGT genes were elevated compared to the susceptible population, and the transcript levels of 3 UGTs (UGT40F20, UGT40R18, and UGT40D17) were increased by more than 2.0-fold in the field populations. Expression pattern analysis revealed that S. frugiperda UGT40F20, UGT40R18, and UGT40D17 were increased by 6.34-, 4.26-, and 8.28-fold, compared the susceptible populations, respectively. The expression of UGT40D17, UGT40F20, and UGT40R18 was affected after exposure to phenobarbital, chlorpyrifos, chlorfenapyr, sulfinpyrazone, and 5-nitrouracil. The induced expression of UGT genes may have improved UGT enzymatic activity, while the inhibition of UGTs genes expression may decreased UGT enzymatic activity. Sulfinpyrazone, and 5-nitrouracil, significantly increased the toxicity of chlorpyrifos and chlorfenapyr, as well as phenobarbital significantly reduced the toxicity of chlorpyrifos and chlorfenapyr against the susceptible populations and field populations of S. frugiperda. The suppression of UGTs (UGT40D17, UGT40F20, and UGT40R18) significantly increased the insensitivity of the field populations to chlorpyrifos and chlorfenapyr. These findings strongly supported our viewpoint that UGTs may play a critical role in insecticide detoxification. This study provides a scientific basis for the management of S. frugiperda.

Susceptibility monitoring and comparative gene expression of susceptible and resistant strains of Spodoptera frugiperda to lambda-cyhalothrin and chlorpyrifos

BACKGROUND

Spodoptera frugiperda (J. E. Smith) is a widespread agricultural pest with several records of resistance to different insecticides and Bt proteins, including the neurotoxic insecticides chlorpyrifos (organophosphate) and lambda-cyhalothrin (pyrethroid). Here, we (i) characterized and monitored the susceptibility of field populations of S. frugiperda to chlorpyrifos (194 populations) and lambda-cyhalothrin (197 populations) collected from major maize-growing regions of Brazil from 2003 to 2016, and (ii) compared gene expression levels of laboratory-selected, chlorpyrifos- and lambda-cyhalothrin-resistant strains to a susceptible reference strain (Sf-ss) of S. frugiperda.

RESULTS

The susceptibility monitoring detected average survival ranging from 29.3% to 36.0% for chlorpyrifos, and 23.1% to 68.0% for lambda-cyhalothrin. The resistance ratio of the chlorpyrifos-resistant strain (Clo-rr) was 25.4-fold and of the lambda-cyhalothrin-resistant strain (Lam-rr) was 21.5-fold. We identified 1098 differentially expressed genes (DEGs) between Clo-rr and Sf-ss, and 303 DEGs between Lam-rr and Sf-ss. Functional analyses of the DEGs revealed the up-regulation of several detoxification enzymes, mainly cytochrome P450 belonging to CYP3 and CYP6 clans. Genes associated with regulatory processes, such as the forkhead box class O (FoxO) transcription factor were also up-regulated. Variant analysis of target-site mutations for both pesticides identified the A201S and F290V mutations in acetylcholinesterase-1, both occurring in heterozigosis in the Clo-rr S. frugiperda strain.

CONCLUSION

Our data show that the overexpression of the enzymatic detoxification machinery is the main difference to explain the resistance of Clo-rr and Lam-rr strains of S. frugiperda to chlorpyrifos and lambda-cyhalothrin, although a target-site mutation also contributes to the Clo-rr resistance to chlorpyrifos. © 2023 Society of Chemical Industry.

CRISPR/Cas9-mediated knockout of NlCYP6CS1 gene reveals its role in detoxification of insecticides in Nilaparvata lugens (Hemiptera: Delphacidae)

BACKGROUND

The brown planthopper (Nilaparvata lugens) is one of the major rice insect pests in Asia. Recently, high levels of insecticide resistance have been frequently reported and cytochrome P450 monooxygenase (P450)-mediated metabolic detoxification is a common resistance mechanism in N. lugens. However, there has been no persuasive genetic method to prove the role of P450s in insecticide resistance in N. lugens.

RESULTS

Here, CRISPR/Cas9 system was used to disrupt the P450 gene NlCYP6CS1 to elucidate its role in insecticide resistance in field populations of N. lugens. We successfully constructed a homozygous strain (Nl6CS1-KO) with a 5-bp deletion and 1-bp insertion mutation of NlCYP6CS1. Compared with a background resistant strain (Nl-R), the susceptibility of knockout strain Nl6CS1-KO to imidacloprid, nitenpyram, thiamethoxam, dinotefuran, and pymetrozine was increased by 2.3-, 3.4-, 7.0-, 4.2- and 3.9-fold, respectively, but not significantly changed to triflumezopyrim, chlorpyrifos and buprofezin. Life table analysis demonstrated that the Nl6CS1-KO strain resembled the Nl-R strain in terms of egg and nymph developmental duration and adult lifespan, but differed from the Nl-R strain in the survival rate of eggs and nymphs, reproduction, and body weight.

CONCLUSIONS

Our study demonstrates the effect of functional deletion of NlCYP6CS1 on multiple insecticide resistance in N. lugens. For the first time, we applied CRISPR/Cas9 system to reveal the mechanism of insecticide resistance in N. lugens, which may shed light on similar studies in other hemipteran insects. © 2023 Society of Chemical Industry.

Contribution of UDP-glycosyltransferases to chlorpyrifos resistance in Nilaparvata lugens

As a multigene superfamily of Phase II detoxification enzymes, uridine diphosphate (UDP)-glycosyltransferases (UGTs) play important roles in the metabolism of xenobiotics including insecticides. In this study, 5-nitrouracil, an inhibitor of UGT enzyme activity, effectively increased the toxicity of chlorpyrifos to the chlorpyrifos-resistant strain of Nilaparvata lugens, one of the most resistant rice pests. The enzyme content of UGT in the resistant strain was significantly higher than that in the susceptible strain. Among 20 identified UGT genes, UGT386H2, UGT386J2, UGT386N2 and UGT386P1 were found significantly overexpressed in the resistant strain and can be effectively induced by chlorpyrifos. These four UGT genes were most highly expressed in the midgut and/or fat body, two main insect detoxification tissues. Amino acid sequence alignments revealed that these four UGTs contained a variable N-terminal substrate-binding domain and a conserved C-terminal sugar donor-binding domain. Furthermore, homology modeling and molecular docking analyses showed that these UGTs could stably bind to chlorpyrifos and chlorpyrifos oxon, with the binding free energies from -19.4 to -110.62 kcal mol^-1. Knockdown of UGT386H2 or UGT386P1 by RNA interference dramatically increased the susceptibility of the resistant strain to chlorpyrifos. These findings suggest that overexpression of these two UGT genes contributes to chlorpyrifos resistance in N. lugens.

Chlorpyrifos induces apoptosis and necroptosis via the activation of CYP450s pathway mediated by nuclear receptors in LMH cells

Chlorpyrifos (CPF), an organophosphorus pesticide, is detected commonly in environments, where it is thought to be highly toxic to non-target organisms. However, the mechanism of CYP450s pathway mediated by nuclear receptors on CPF-induced apoptosis and necroptosis at the cellular level and the effect of CPF on the cytotoxicity of the chicken hepatocarcinoma cell line (LMH) has also not been reported in detail. Therefore, this experiment aims to explore whether CPF can improve apoptosis and necroptosis in LMH cells by activating the nuclear receptors/CYP450s axis. LMH cells, the subject of this study, were exposed to 5 μg/mL, 10 μg/mL, and 15 μg/mL doses of CPF. With the increase of CPF concentration, the increase of nuclear receptor level led to the up-regulation of CYP450s activity. With the massive production of ROS, the expression of apoptotic pathway genes (Bax, Caspase9, and Caspase3) enhanced, while Bcl-2 expression dropped sharply. The expression of programmed necroptosis genes (RIPK1, RIPK3, and MLKL) heightened, and Caspase8 reduced considerably. In short, our data suggests that excessive activation of nuclear receptors and CYP450s induced by CPF promotes ROS production, which directs apoptosis and programmed necroptosis in LMH cells.

Evaluation of chemical and microbial control options for Pangaeus bilineatus (Say) (Hemiptera: Cydnidae) infesting peanut crop

BACKGROUND

The peanut burrower bug, Pangaeus bilineatus is a major crop pest of peanuts in the southern United States. Peanuts infested by P. bilineatus exhibit weight and quality losses and could be discounted by ≤50% of the prevailing market price. Control of this pest is difficult because it attacks peanut pods underground, thus rendering foliar pesticide applications ineffective. Integration of entomopathogenic fungi and nematodes (EPF/EPNs) with chemical insecticides in the management of P. bilineatus was investigated as a potential integrated pest management containment tool.

RESULTS

The nymphs were less susceptible than adults of P. bilineatus to EPNs. Comparison of six strains of both Heterorhabditis spp. and Steinernema spp. demonstrated that Steinernema carpocapsae (All) was the most virulent EPN, causing 75.54% mortality of P. bilineatus adults after 7 days postinoculation (dpi), whereas the mortality generated by the application of the rest of the nematodes ranged between 17.03% (H. bacteriophora - Lewis) and 50% (H. bacteriophora VS). Application of imidacloprid by itself at ½FR (field rate) did not result in any significant mortality of P. bilineatus adults but application of chlorpyrifos at 1/8FR caused significant mortality (27.41-61.35%) at 7-14 dpi. However, combined applications of S. carpocapsae and imidacloprid resulted in significant mortality starting at 3 dpi. The interactions between S. carpocapsae and imidacloprid were synergistic at 3-5 dpi, but became additive at 7-14 dpi. Both chlorpyrifos and imidacloprid did not negatively impact the reproduction of S. carpocapsae.

CONCLUSION

The compatibility between S. carpocapsae and imidacloprid makes a case for the combination to be used for the management of P. bilineatus. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Chlorpyrifos stimulates ABCC-mediated transport in the intestine of the rainbow trout Oncorhynchus mykiss

The organophosphorus pesticide chlorpyrifos, detected in water and food worldwide, has also been found in the Río Negro and Neuquén Valley, North Patagonia, Argentina, where the rainbow trout, Oncorhynchus mykiss, is one of the most abundant fish species. We analyzed whether chlorpyrifos affects the transport activity of the ATP-binding cassette protein transporters from the subfamily C (ABCC), which are critical components of multixenobiotic resistance. We exposed ex vivo O. mykiss middle intestine strips (non-polarized) and segments (polarized) for one hour to 0 (solvent control), 3, 10, and 20 μg L^-1 and to 0, 10, and 20 μg L^-1 chlorpyrifos, respectively. We estimated the Abcc-mediated transport rate by measuring the transport rate of the specific Abcc substrate 2,4-dinitrophenyl-S-glutathione (DNP-SG). In addition, we measured the enzymatic activity of cholinesterase, carboxylesterase, glutathione-S-transferase, and 7-ethoxyresorufin-O-deethylase (EROD, indicative of the activity of cytochrome P450 monooxygenase 1A, CYP1A). We also measured lipid peroxidation using the thiobarbituric acid reactive substances method and the gene expression of Abcc2 and genes of the AhR pathway, AhR, ARNT, and cyp1a, by qRT-PCR. Chlorpyrifos induced the DNP-SG transport rate in middle intestine strips in a concentration-dependent manner (49-71%). In polarized preparations, the induction of the DNP-SG transport rate was observed only in everted segments exposed to 20 μg L^-1 chlorpyrifos (40%), indicating that CPF only stimulated the apical (luminal) transport flux. Exposure to chlorpyrifos increased GST activity by 42% in intestine strips and inhibited EROD activity (47.5%). In addition, chlorpyrifos exposure inhibited cholinesterase (34-55%) and carboxylesterase (33-42.5%) activities at all the concentrations assayed and increased TBARS levels in a concentration-dependent manner (71-123%). Exposure to 20 μgL^-1 chlorpyrifos did not affect the mRNA expression of the studied genes. The lack of inhibition of DNP-SG transport suggests that chlorpyrifos is not an Abcc substrate. Instead, CPF induces the activity of Abcc proteins in the apical membrane of enterocytes, likely through a post-translational pathway.

Herbivore-induced tomato plant volatiles lead to the reduction of insecticides susceptibility in Spodoptera litura

Herbivore-induced plant volatiles (HIPVs) have been associated with plant-plant-herbivorous-natural enemies communication and an enhanced response to the subsequent attack. Spodoptera litura is a serious cosmopolitan pest that has developed a high level of resistance to many insecticides. However, the underlying molecular and biochemical mechanism by which HIPV priming reduces S. litura larval sensitivity to insecticides remains largely unknown. This study was conducted to explore the potential of volatile from undamaged, or artificially damaged, or S. litura-damaged tomato plants on the susceptibility of S. litura to the insecticides beta-cypermethrin indoxacarb and chlorpyrifos. We found that larvae exposed to volatile from S. litura-damaged or artificially damaged tomato plants were significantly less susceptible to the three insecticides than those exposed to volatile from undamaged tomato plants. Elevated activities of detoxifying enzymes [cytochrome P450 monooxygenases (P450s), glutathione S-transferases (GSTs), and esterases (ESTs)], were expressed in S. litura larvae exposed to volatile from S. litura-damaged tomato plants than those exposed to volatile from undamaged tomato plants. Similarly, seven detoxification-related genes [GSTs (SlGSTe1, SlGSTo1, and SlGSTe3) and P450s (CYP6B48, CYP9A40, CYP321A7, and CYP321B1)] in the midgut and fat body of larvae were up-regulated under exposure to volatile from S. litura-damaged tomato plants. Increased volatile organic compounds emissions were detected in the headspace of tomato plants damaged by S. litura compared to the undamaged plants. Collectively, these findings suggest that HIPVs can considerably reduce caterpillar susceptibility to insecticides, possibly through induction-enhanced detoxification mechanisms, and provide valuable information for implementing an effective integrated pest management strategy.

CRISPR/Cas9-Mediated Knockout Reveals the Involvement of CYP304F1 in β-Cypermethrin and Chlorpyrifos Resistance in Spodoptera litura

Functions of insect CYP2 clan P450s in insecticide resistance are relatively less reported. In Spodoptera litura, a gene from the CYP2 clan (CYP304F1) was validated to be up-regulated significantly in a pyrethroid- and organophosphate-resistant population (QJ) than a susceptible population by RNA-Seq and qRT-PCR. Spatial-temporal expression indicated the high expression of CYP304F1 in the fourth, fifth, and sixth instar larvae and the metabolism-related tissue fat body and malpighian tubules. CYP304F1 was knocked out by CRISPR/Cas9, and a homozygous population (QJ-CYP304F1) with a G-base deletion at exon 2 was obtained after selection. Bioassay results showed that the LD₅₀ values to β-cypermethrin and chlorpyrifos in the QJ-CYP304F1 population decreased significantly, and the resistance ratio was both 1.81-fold in the QJ population compared with that in the QJ-CYP304F1 population. The toxicity of fenvalerate, cyhalothrin, or phoxim showed no significant change. These results suggested that CYP304F1 is involved in β-cypermethrin and chlorpyrifos resistance in S. litura.

Green synthesis of rGO-AgNP composite using Curcubita maxima extract for enhanced photocatalytic degradation of the organophosphate pesticide chlorpyrifos

In this study, Curcubita maxima leaves are used as a novel source for green synthesis of reduced graphene oxide - silver nanoparticle composite in a single pot. Characterization of the novel phyto source-driven composite was performed by UV-visible spectroscopy, Fourier transform infrared analysis, X-ray diffraction analysis, and field emission scanning electron microscopic methods. The assessment of degradation effect of chlorpyrifos by the synthesized nanocomposite was performed. The photocatalytic activity of the composite was demonstrated through two different processes as adsorption under room temperature and photocatalysis in the presence of sunlight. Different parameters such as pH, time, photocatalyst dose and pesticide concentration were optimized. The adsorption isotherms governing the photocatalytic adsorption process were investigated to predict the adsorption capacity of the synthesized nanocomposite. In addition, the results of antimicrobial activity of the nanocomposite against gram-positive, gram-negative bacteria and antifungal activity were also been found to be highly promising to utilize this composite for the removal of microbial contaminations in wastewater treatment.

Daily temperature fluctuations can magnify the toxicity of pesticides

We review the effect of daily temperature fluctuations (DTF), a key thermal factor predicted to increase under climate change, on pesticide toxicity. The effect of DTF on pesticide toxicity may be explained by: (i) a DTF-specific mechanism (caused by Jensen's inequality) and (ii) general mechanisms underlying an increased pesticide toxicity at both higher (increased energetic costs, pesticide uptake and metabolic conversion) and lower constant temperatures (lower organismal metabolic and associated elimination rates, increased sodium channel modulated nervous system vulnerability and energetic costs). Furthermore, DTF may enhance pesticide-induced reductions in heat tolerance due to stronger effects on oxygen demand (increase) and oxygen supply (decrease). Our literature review showed considerable support that DTF increase the negative impact of pesticides on insects, especially in terms of decreased survival. Therefore, we suggest that considering DTF in ecotoxicological studies may be of great importance to better protect biodiversity in our warming world.

Associations between acetylcholinesterase-1 mutations and chlorpyrifos resistance in beet armyworm, Spodoptera exigua

Control of the beet armyworm, Spodoptera exigua depends heavily on chemical insecticides. Chlorpyrifos, an acetylcholinesterase (AChE) inhibitor, has been used in beet armyworm control for many years in China. Here we describe high level resistance to chlorpyrifos in a S. exigua strain, FX19-R, which was developed from a field-collected Chinese strain (FX) by selection with chlorpyrifos in the laboratory. FX19-R showed 1001-fold resistance to chlorpyrifos compared with the laboratory reference strain WH-S. The esterase inhibitor triphenyl phosphate (TPP) provided significant but small synergism (only 3.5-fold) for chlorpyrifos and neither of the glutathione s-transferase depletor diethyl maleate and the cytochrome P450s inhibitor piperonyl butoxide provided any detectable synergism, indicating that AChE insensitivity may play the major role in the resistance in FX19-R. Consistent with this, an amino acid substitution, F443Y (F331Y in standard Torpedo californica numbering) in AChE1 was identified in the FX19-R strain and shown to be tightly linked to chlorpyrifos resistance. Precisely homologous substitutions have been associated with organophosphate resistance in other pest species. A novel amino acid substitution, G311S (or G198S in standard numbering), was also identified in the reference strain WH-S. Recombinantly expressed AChE1 proteins carrying the G311S and F443Y substitutions were about 4.2-fold and 210-fold less sensitive to inhibition by chlorpyrifos oxon than wild-type AChE1, respectively. These results enhance our understanding of the mechanisms of chlorpyrifos resistance and provide a basis for resistance management based on monitoring the F443Y and G311S substitutions.

Antagonistic effects and mechanisms of carbendazim and chlorpyrifos on the neurobehavior of larval zebrafish

Residues from multiple pesticides are frequently detected on vegetables, which may produce combined toxicity not predicted by individual toxicity data. As these combined effects present additional dangers to food safety, we have compared individual to combined effects for a variety of pesticides. Carbendazim and chlorpyrifos are the two most commonly detected pesticides in vegetables, and previous studies reported that combined exposure results in synergistic developmental toxicity to zebrafish embryos. In this study, individual and combined effects on zebrafish motor activity were examined following individual and combined exposure to assess nervous system toxicity. Further, transcriptomics methods were used to identify potential molecular mechanisms for individual and combined toxicity. Carbendazim alone induced a disorganized swim pattern characterized by increased angular velocity, turn angle, meander, and acceleration during light-dark transition, while chlorpyrifos alone reduced average swim speed and light-dark acceleration. Combined treatment significantly reduced average swim velocity and total distance traveled. Combination indices indicated strong antagonism between compounds for average speed and light-dark acceleration. Transcriptomics (RNA-seq) showed that carbendazim significantly altered the expression of genes involved in antigen processing and presentation, apoptosis, autophagy, and metabolism, including ctslb, cyp7a1, hsp70l, and ugt1a1. Alternatively, chlorpyrifos significantly altered genes involved in various nervous system-related pathways, including glutamatergic, GABAergic, dopaminergic, and calcium signaling. Protein-protein interaction (PPI) network analysis suggested that chlorpyrifos significantly downregulated genes related to light transduction, resulting in decreased sensitivity to light-dark transitions, while antagonism mainly reflected divergent effects on phototransduction and retinol metabolism. Carbendazim had no significant effects on vision-related genes such as gnat1 and gngt1, while chlorpyrifos downregulated expression, an effect reversed by the combination. Comprehensive toxicity analyses must include joint effects of co-applied pesticides for enhanced food safety.

Field-evolved resistance to chlorpyrifos by Spodoptera frugiperda (Lepidoptera: Noctuidae): Inheritance mode, cross-resistance patterns, and synergism

BACKGROUND

Fall armyworm (FAW), Spodoptera frugiperda (Smith), is an economically important pest worldwide. In this study, we selected a genotype of FAW resistant to chlorpyrifos from a field-collected population, characterized the genetic basis of resistance, and evaluated cross-resistance and mechanisms of resistance using synergists.

RESULTS

The LD₅₀ values of chlorpyrifos for the resistant (Clorp-R) and susceptible (Sus) FAW genotypes were 24.26 and 0.023 μg per larva, respectively, representing a resistance ratio > 1050-fold. The LD₅₀ values of chlorpyrifos against heterozygotes were 3.34 and 4.00 μg per larva, suggesting that resistance is autosomally inherited. The chlorpyrifos resistance in FAW was influenced by few genes, with the minimum numbers of segregations being 1.74 and 1.88. On chlorpyrifos-sprayed plants and leaves, Clorp-R and heterozygote genotypes showed >95% and >52% survival, respectively, whereas the Sus genotype had no survival, indicating that the resistance is incompletely dominant at the field rate of chlorpyrifos. The Clorp-R genotype presented some cross-resistance to acephate, but low cross-resistance to thiodicarb, methomyl, chlorfenapyr, flubendiamide, methoxyfenozide, spinetoram, and teflubenzuron. The synergists piperonyl butoxide, diethyl maleate, and S,S,S-tributyl phosphorotrithiotate did not have relevant effects on the Clorp-R genotype, suggesting a minor role for metabolic resistance.

CONCLUSIONS

The inheritance of chlorpyrifos resistance in FAW was characterized as autosomal, incompletely dominant, and polygenic, with metabolic resistance playing a small role in the detoxification of chlorpyrifos. Low cross-resistance between chlorpyrifos and other mode of action (MoA) insecticides occurs in FAW, highlighting the importance of considering the rotation of MoA as a strategy to delay resistance. © 2021 Society of Chemical Industry.

SlGSTE9 participates in the stability of chlorpyrifos resistance in Spodoptera litura

BACKGROUND

Spodoptera litura is an important agricultural pest and has developed serious resistance to multiple insecticides. The resistance level to several insecticides is reported to be unstable, but the mechanism is less reported.

RESULTS

Chlorpyrifos and phoxim resistance level in a field-collected population of S. litura declined continuously from the first to the tenth generation and remained stable at the 11th and 12th generations without insecticide exposure. Synergist experiment showed that diethyl maleate and piperonyl butoxide significantly increased mortality to chlorpyrifos and phoxim in the first and sixth generations, but not in the 12th generation. The expression of 31 identified glutathione S-transferase (GST) genes in the third-instar larvae of S. litura in the first, sixth and 12th generations was determined, and eight genes were seen to decrease significantly in the sixth and 12th generations compared with the first generation. SlGSTe9 was selected for further functional study as it had higher abundance and significantly higher expression in the chlorpyrifos-resistant population than in the susceptible population. The recombinant protein of SlGSTE9 showed metabolism activity to chlorpyrifos in vitro and in Escherichia coli, but not to phoxim. Silencing of SlGSTe9 increased the cumulative mortality to chlorpyrifos significantly. SlGSTE9 also showed antioxidant activity to cumene hydroperoxide.

CONCLUSION

Our results suggest that SlGSTe9 is directly involved in chlorpyrifos resistance stability, but not in phoxim. SlGSTE9 may also participate in insecticides resistance by relieving the oxidase stress induced by insecticides. © 2021 Society of Chemical Industry.

Susceptibility of different developmental stages of Trichogramma parasitoids to insecticides commonly used in the Mediterranean olive agroecosystem

Insecticide application and augmentative parasitoid releases are often considered incompatible. However, pesticide applications and parasitoid releases can be integrated into a pest management scheme if there is careful time scheduling of these interventions. In this study, we assessed the influence of commonly used insecticides (chlorpyrifos-methyl, deltamethrin, pyriproxyfen, thiamethoxam) in olive agroecosystems to two currently present Trichogramma parasitoids in the Mediterranean basin. Exposure to insecticides in relation to parasitoid's development was also tested. Both, insecticide type and application time influenced parasitism and the emergence rates of the two parasitoid species. Chlorpyrifos-methyl had the strongest impact on parasitoids resulting in low numbers of emerged adults followed by deltamethrin. The two parasitoids also exhibited different levels of susceptibility to the insecticides used. Potential integration of insecticides to integrated pest management using Trichogramma parasitoids is discussed.

Mechanisms for multiple resistances in field populations of rice stem borer, Chilo suppressalis (Lepidoptera: Crambidae) from Sichuan Province, China

Chilo suppressalis Walker (Lepidoptera: Crambidae) is a widely destructive pest occurring in rice, particularly in the rice-growing regions of Asia. In recent years, C. suppressalis has developed resistance to several insecticides because of the extensive use of insecticides. The resistance levels to four insecticides were determined among populations from different regions of Sichuan Province, China, using a drop-method bioassay. Based on LC₅₀ values of a laboratory susceptible strain, all field populations showed moderate level of resistance to triazophos (23.9- to 83.5-fold) and were either susceptible or had a low level of resistance to abamectin (2.1- to 5.8-fold). All field-collected populations had a low or moderate level of resistance to chlorpyrifos (1.7- to 47.1-fold) and monosultap (2.7- to 13.5-fold). The synergism experiment indicated that the resistance of the XW19 to triazophos may be associated with cytochrome P450 monooxygenases (P450s), with the highest synergistic ratio (SR) of 3.05-fold and increased ratio (IR) of 2.28-fold for piperonylbutoxide (PBO). The P450 activity of the TJ19 population was the greatest among the six field populations. Moreover, the relative expression levels of four resistance-related P450 genes were detected with qRT-PCR, and the results indicated that CYP324A12, CYP321F3 and CYP9A68 were overexpressed in the resistant population, especially in the XW19 population (by 1.2-, 3.4 -, and 18.0-fold, respectively). In addition, the relative expression levels of CYP9A68 among the CZ19 and TJ19 populations were also enhanced 10.5- and 24.9-fold, respectively. These results suggested that CYP324A12, CYP321F3 and CYP9A68 may be related to the resistance development of C. suppressalis to triazophos.

Genetic analysis and molecular detection of resistance to chlorpyrifos mediated by the A216S substitution in acetylcholinesterase-1 in the plant bug Apolygus lucorum

The green plant bug Apolygus lucorum is a major pest of Bacillus thuringiensis cotton in China. Previously, we reported that chlorpyrifos resistance in a laboratory-selected strain of A. lucorum (BZ-R) is associated with the homozygosis of an allele in the ace-1 gene encoding an alanine to serine substitution at position 216 of acetylcholinesterase-1. Here we describe the results of crosses between the resistant BZ-R strain (41-fold to chlorpyrifos) and the unselected susceptible BZ-S strain homozygous for the wild type alanine allele at position 216. Resistance to chlorpyrifos was inherited as a semi-dominant trait mainly controlled by a single autosomal gene and co-segregates strongly but not completely with the serine substitution in ace-1. Synergism bioassays and enzyme assays showed that minor contributions to resistance are also made by enhanced cytochrome P450 and carboxylesterase activities. A survey of 25 field populations from five Chinese provinces showed strong positive correlations between 50% lethal concentration against chlorpyrifos and S216 allele and genotype frequencies, although the most tolerant populations still only show 40%-50% S216 allele frequencies. The results above provide important information for designing effective resistance monitoring and management strategies for A. lucorum in China.

Adipokinetic hormone enhances CarE-mediated chlorpyrifos resistance in the brown planthopper, Nilaparvata lugens

Adipokinetic hormone (AKH), the principal stress-responsive neurohormone in insects, has been implicated in insect responses to insecticides. However, the functionality of AKH and its mode of signalling in insecticide resistance are unknown. Herein, we demonstrated that the enhanced activity of carboxylesterases (CarEs) is involved in the chlorpyrifos resistance in Nilaparvata lugens [brown planthopper (BPH)]. Chlorpyrifos exposure significantly induced the expression of AKH and its receptor AKHR in the susceptible BPH (Sus), and these two AKH signalling genes were over-expressed in the chlorpyrifos-resistant strain (Res) compared to Sus. RNA interference (RNAi) against AKH or AKHR decreased the CarE activity and suppressed the BPH's resistance to chlorpyrifos in Res. Conversely, AKH peptide injection elevated the CarE activity and enhanced the BPH's survival against chlorpyrifos in Sus. Furthermore, five CarE genes were identified to be positively affected by the AKH pathway using RNAi and AKH injection. Among these CarE genes, CarE and Esterase E4-1 were found to be over-expressed in Res compared to Sus, and knockdown of either gene decreased the BPH's resistance to chlorpyrifos. In conclusion, AKH plays a role in enhancing chlorpyrifos resistance in the BPH through positive influence on the expression of CarE genes and CarE enzyme activity.

Biochemical mechanism, inheritance and cross-resistance to cyromazine in a non-target Chrysoperla carnea: A potential predator of whiteflies and aphids

Developing an eco-friendly Integrated Pest Management (IPM) approach is only possible by minimizing the use of insecticides and their effects on non-targets such as natural enemies. Chrysoperla carnea is a potential predator of several economic pests including whiteflies and aphids. C. carnea selected with cyromazine for 15 generations indicated a great increase in resistance to this Insect Growth Regulator (IGR). There was no cross-resistance to chlorpyrifos, cypermethrin and nitenpyram in Cyro-SEL population. Inheritance to cyromazine was autosomal, incompletely dominant, and polygenic. A high realized heritability (h₂) value (0.37) confirmed more genetic variability. Synergists piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF) showed a significant involvement of P-450 monooxygenase and esterase in cyromazine resistance development. These findings are helpful to design a natural enemy-friendly IPM strategy resulting in increased survival and performance of C. carnea controlling economic pests.

Assessment of Resistance to Organophosphates and Pyrethroids in Aedes aegypti (Diptera: Culicidae): Do Synergists Affect Mortality?

Aedes aegypti (L.) is the primary vector of Zika, dengue, yellow fever, and chikungunya viruses. Insecticides used in mosquito control can help prevent the spread of vector-borne diseases. However, it is essential to determine insecticide resistance (IR) status before control measures are undertaken. Only the most effective insecticides should be used to avoid ineffective control and/or promotion of IR. Pyrethroids and organophosphates are the most commonly used insecticides for mosquito control. Here, the efficacy of two active ingredients (AIs; permethrin [pyrethroid], chlorpyrifos [organophosphate]), two formulated products (FPs; Biomist [AI: permethrin]) and (Mosquitomist [AI: chlorpyrifos]), and three synergists (piperonyl butoxide, diethyl maleate, S-S-S-tributyl phosphorotrithioate) was evaluated in two Ae. aegypti colonies (pyrethroid resistant and susceptible). Mosquitomist was most effective against the pyrethroid-resistant colony (100% mortality at diagnostic time). Pre-exposure to synergists did not increase the efficacy of AIs against the pyrethroid-resistant colony. Further research is needed to discover how synergists may affect the efficacy of insecticides when used on pyrethroid-resistant mosquitoes.

Effects of chlorpyrifos on growth and aflatoxin B1 production by Aspergillus section Flavi strains on maize-based medium and maize grains

Chlorpyrifos is one of the most used insecticides in agro-ecosystems and is repeatedly applied due to the increase in pest resistance, which leads to environmental accumulation. The aim of this work was to evaluate the effect of chlorpyrifos on growth and aflatoxin B₁ (AFB₁) production by four Aspergillus section Flavi strains, under different water conditions-a_W (0.93, 0.95 and 0.98)-on maize-based medium (MMEA) and maize grains supplied with 0.06 to 1.4 mmol/L of chlorpyrifos. MMEA plates were incubated at 18, 28, and 37 °C and plates with maize grains at 25 °C during 21 days. Chlorpyrifos stimulated the growth and AFB₁ production of non-target organisms, such as Aspergillus section Flavi strains, both at low (0.06 mmol/L) and at high concentrations (1.4 mmol/L) on MMEA and maize grains. Stimulation occurred over a wide range of temperature and a_w conditions. The toxin concentration produced by the two strains on MMEA at 18 °C increased when the concentration of chlorpyrifos also increased, being most significant at 0.6 mmol/L. In conclusion, the presence of chlorpyrifos should be considered as a factor, together with environmental conditions, for the development of effective production practices of maize grains, in order to avoid fungal growth and AFB₁ production, to prevent both economic losses and risks to human and animal health.

Glutathione in Chlorpyrifos-and Chlorpyrifos-Oxon-Induced Toxicity: a Comparative Study Focused on Non-cholinergic Toxicity in HT22 Cells

Chlorpyrifos (CPF) is a neurotoxic organophosphorus (OP) insecticide widely used for agricultural purposes. CPF-mediated neurotoxicity is mainly associated with its anticholinesterase activity, which may lead to a cholinergic syndrome. CPF metabolism generates chlorpyrifos-oxon (CPF-O), which possesses higher anticholinesterase activity and, consequently, plays a major role in the cholinergic syndrome observed after CPF poisoning. Recent lines of evidence have also reported non-cholinergic endpoints of CPF- and CPF-O-induced neurotoxicities, but comparisons on the non-cholinergic toxic properties of CPF and CPF-O are lacking. In this study, we compared the non-cholinergic toxicities displayed by CPF and CPF-O in cultured neuronal cells, with a particular emphasis on their pro-oxidant properties. Using immortalized cells derived from mouse hippocampus (HT22 line, which does present detectable acetylcholinesterase activity), we observed that CPF-O was 5-fold more potent in decreasing cell viability compared with CPF. Atropine, a muscarinic acetylcholine receptor antagonist, protected against acetylcholine (ACh)-induced toxicity but failed to prevent the CPF- and CPF-O-induced cytotoxicities in HT22 cells. CPF or CPF-O exposures significantly decreased the levels of the antioxidant glutathione (GSH); this event preceded the significant decrease in cell viability. Pretreatment with N-acetylcysteine (NAC, a GSH precursor) protected against the cytotoxicity induced by both CPF and CPF-O. The present study indicates that GSH depletion is a non-cholinergic event involved in CPF and CPF-O toxicities. The study also shows that in addition of being a more potent AChE inhibitor, CPF-O is also a more potent pro-oxidant molecule when compared with CPF, highlighting the role of CPF metabolism (bioactivation to CPF-O) in the ensuing non-cholinergic toxicity.

Morphological and biochemical traits and mortality in Physalaemus gracilis (Anura: Leptodactylidae) tadpoles exposed to the insecticide chlorpyrifos

Organophosphate insecticides such as chlorpyrifos are commonly detected in surface waters around the world, where they are highly toxic to many organisms. The frog Physalaemus gracilis uses water sources located in open fields as reproductive sites, where it is exposed to insecticides. The study aimed to evaluate the lethal and sublethal effect of a commercial chlorpyrifos formulation on P. gracilis tadpoles (Anura: Leptodactylidae). In acute toxicity tests, five chlorpyrifos concentrations between 750 and 2,000 μg L^-1 were tested. Chronic toxicity, swimming activity, morphological and enzymatic changes, as well as levels of non-protein thiols (NPSH), carbonyl proteins and lipid peroxidation were evaluated at five insecticide concentrations between 11 and 500 μg L^-1. The highest mortality rate of P. gracilis tadpoles occurred at 24 and 48 h, with an LC₅₀ of 893.59 μg L^-1. At all chlorpyrifos concentrations, tadpoles displayed reduced mobility and spasms. Morphological anomalies were observed in the mouth and intestine, especially at the highest concentrations used. Acetylcholinesterase activity decreased at 250 and 500 μg L^-1, catalase activity increased at all concentrations, and superoxide dismutase and glutathione S-transferase increased from 90 μg L^-1 to 30 μg L^-1, respectively. We also observed increases in NPSH levels at chlorpyrifos concentration starting at 30 μg L^-1 and increases in carbonyl proteins from 90 μg L^-1 of pesticide. Taken together, these data suggest that the insecticide chlorpyrifos presents acute and chronic risks for P. gracilis, causing neurotoxic effects and oxidative damage, culminating in high risk for this species.

A commentary on some epidemiology data for chlorpyrifos

Extensive animal and human studies on chlorpyrifos (CPF) point to changes in a blood enzyme as its first biological effect, and governments and health groups around the world have used this effect in the determination of its safe dose. Preventing this first biological effect, referred to in risk assessment parlance as the critical effect, is part and parcel of chemical regulation in general and of CFP specifically. Rauh et al. (2011), one of the published studies from the Columbia Center for Children's Environmental Health (CCCEH), reported evidence of deficits in Working Memory Index and Full-Scale IQ in children at 7 years old as a function of prenatal CPF exposures that are much lower than levels causing cholinesterase inhibition. Since the raw data on which Rauh et. al. (2011) publicly-funded (in part) findings were based have not been made available despite repeated requests, we show extracted data in Fig. 1A and 1E of Rauh et al. (2011), and plotted these extracted data as response versus log dose, a common risk assessment approach. Surprisingly, a significant portion of the data stated to be available in Rauh et al. (2011) were not found in these published figures, perhaps due to data point overlay. However, the reported associations of chlorpyrifos levels with Working Memory and Full Scale IQ were also not replicated in our analysis due perhaps to this missing data. Multiple requests were made to Rauh et al. (2011) for access to data from this, in part, publicly funded study, so that confirmation could be attempted. This general lack of data and inconsistency with cholinergic responses in other researches raises concerns about the lack of data transparency.

Resistance profile and molecular characterization of pyrethroid resistance in a Rhipicephalus microplus strain from Colombia

Intensive use of chemical acaricides for the control of cattle ticks (Rhipicephalus microplus) has led to the development of multiple acaricide resistance in Colombia. The present study aimed to characterize, using toxicological bioassays and molecular biology techniques, the resistance profile of a tick strain isolated from the Arauca state, Northeast Colombia. Commercial acaricides were used in adult immersion tests to determine its in vitro efficacies. Deltamethrin showed very low activity (4-7.3%), a mixture of cypermethrin and chlorpyrifos had intermediate efficacy (64-75.2%), and ethion presented the highest activity (88.5-100%). A colony (Arauquita strain) was established and larval immersion tests confirmed high resistance level to deltamethrin (241-fold) and susceptibility to ivermectin. A quantitative polymerase chain reaction-high resolution melt technique was used to identify single nucleotide polymorphisms (SNPs) in the para-sodium channel gene. All of the genotyped individuals were mutant, presenting one (n = 7), two (n = 7) or three (n = 9) SNPs previously associated with pyrethroid resistance. Sequencing revealed a novel mutation (F712L), that was found for the first time in R. microplus ticks from South America. This is the first description of mutations associated with pyrethroid resistance in R. microplus from Colombia. The acaricide resistance pattern found in the Arauquita strain is similar to other parts of Colombia.

Walnut Polyphenol Extract Protects against Malathion- and Chlorpyrifos-Induced Immunotoxicity by Modulating TLRx-NOX-ROS

Malathion (MT) and chlorpyrifos (CPF) are immunotoxic organophosphate pesticides that are used extensively in agriculture worldwide. Dietary polyphenols protect against a variety of toxins. In this study, walnut polyphenol extract (WPE) prevents MT- or CPF-induced toxicity to splenic lymphocytes in vitro. WPE promotes the proliferation of MT-exposed splenocytes, as indicated by increases in the proportions of splenic T-lymphocyte subpopulations (CD3+, CD4+, and CD8+ T cells) and levels of T-cell-related cytokines interleukin (IL)-2, interferon-γ, IL-4, and granzyme B, and decreases the apoptosis-associated proteins Bax and p53. WPE also significantly enhances the proliferation of CPF-exposed splenic B lymphocytes (CD19+ B cells) and levels of the B-cell-related cytokine IL-6, leading to decreases of the apoptosis-associated proteins Bax and p53. These effects are related to reduced production of reactive oxygen species (ROS), as evidenced by normalized hydroxyl radical (•OH), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), and glutathione (GSH) levels, which are associated with decreased expression of NADPH oxidase 2 (NOX2) and dual oxidase 1 (DUOX1). WPE inhibits the production of ROS and expression of NOX by regulating toll-like receptors 4 and 7 in MT- and CPF-exposed splenic lymphocytes. In conclusion, WPE protects against MT- or CPF-mediated immunotoxicity and inhibits oxidative damage by modulating toll-like receptor (TLR)x-NOX-ROS.

Do you smell the danger? Effects of three commonly used pesticides on the olfactory-mediated antipredator response of zebrafish (Danio rerio)

Fish are warned about the presence of predators via an alarm cue released from the skin of injured conspecifics. The detection of this odor inherently initiates an antipredator response, which increases the chance of survival for the individual. In the present study, we assessed the effect of three commonly used pesticides on the antipredator response of zebrafish (Danio rerio). For this, we analyzed the behavioral response of zebrafish to a conspecific skin extract following 24 h of exposure to the respective contaminants. Results demonstrate that fish exposed to 20 μg/L of the organophosphate insecticide chlorpyrifos significantly reduced bottom-dwelling and freezing behavior, suggesting an impairment of the antipredator response. For the urea-herbicide linuron and the pyrethroid insecticide permethrin, no statistically significant effects could be detected. However, linuron-exposed fish appeared to respond in an altered manner to the skin extract; some individuals failed to perform the inherent behaviors such as erratic movements and instead merely increased their velocity. Furthermore, we determined whether zebrafish would avoid the pesticides in a choice maze. While fish avoided permethrin, they behaved indifferently to chlorpyrifos and linuron. The study demonstrates that pesticides may alter the olfactory-mediated antipredator response of zebrafish in distinct ways, revealing that particularly fish exposed to chlorpyrifos may be more prone to predation.

Aryl hydrocarbon receptor regulates the expression of LmGSTd7 and is associated with chlorpyrifos susceptibility in Locusta migratoria

BACKGROUND

The aryl hydrocarbon receptor (AhR) belongs to the bHLH-PAS (basic Helix-Loop-Helix - Period/ARNT/Single minded) family of transcription factors. AhR is a ligand-activated transcription factor, which participates in the sensing and transmitting stimuli of endogenous and exogenous chemicals, and subsequently activates the transcription of genes related to various physiological and detoxification functions.

RESULT

In this study, a single full-length LmAhR sequence was cloned and characterized. RNA interference (RNAi) and insecticide bioassays showed that LmAhR plays a vital role in chlorpyrifos susceptibility. To better identify aryl hydrocarbon receptor from locusta migratoria (LmAhR)-regulated genes involved in chlorpyrifos susceptibility, a comparative transcriptome analysis was performed using double-stranded (ds)GFP- and dsLmAhR-injected Locusta migratoria. Differential gene expression analysis identified 145 down-regulated and 67 up-regulated genes (P ≤ 0.05 and fold change ≥2) in dsLmAhR-knockdown insects. We selected 27 down-regulated genes and verified their expression levels using reverse transcription quantitative PCR. Finally, one glutathione S-transferase (GST) gene (LmGSTd7) was selected as a candidate detoxification gene and was further validated via RNAi and chlorpyrifos bioassays.

CONCLUSION

Our data suggest that AhR is associated with chlorpyrifos susceptibility via the regulation of LmGSTd7 expression in L. migratoria. © 2019 Society of Chemical Industry.

Enzymatic degradation of extracellular DNA exposed to chlorpyrifos and chlorpyrifos-methyl in an aqueous system

The persistence of extracellular DNA (eDNA) is crucial for ensuring species diversity and ecological function in aquatic systems. However, scarce information exists about the impact of pesticides on eDNA, although they often co-exist in the aquatic environment. Using a variety of spectroscopic analyses, eDNA degradation and the associated alterations in DNA secondary structure was investigated by exposing DNase I to tested DNA in the presence of chlorpyrifos, a commonly used organophosphate pesticide. Molecular dynamics simulation was used to explore the weak interactions between the tested DNA and chlorpyrifos. The results indicated that chlorpyrifos significantly enhanced DNA degradation without affecting the enzyme activity of DNase I in an aqueous system. Spectroscopic experiments confirmed that chlorpyrifos and the analog chlorpyrifos-methyl could bind with DNA to cause the bases noncovalent stacking interaction. Molecular simulations further demonstrated that pesticide binding with DNA molecules caused widening of the DNA grooves and destruction of the hydrated layer, which enhanced DNA degradation. The findings presented herein provide novel insight into the genotoxicity and ecotoxicity of chlorpyrifos and chlorpyrifos-methyl, as well as their impacts on DNA persistence in aquatic environments.

Chlorpyrifos and its metabolite modulates angiogenesis in the chorioallantoic membrane of chick embryo

Background Chlorpyrifos (CPF) is an organophosphate insecticide, acaricide, and miticide used primarily to control foliage and soilborne insect pests on a variety of food and feed crops. Since trace amounts of these compounds are found in water and food products, they easily enter into the organ system unnoticed. In the same way, the compound or its metabolite gets transmitted from the parent to the embryo mainly through blood vessels. Since blood vessels form the major route of transport, it is pertinent to study the effect of these compounds during angiogenesis. The effect of CPF and 3,5,6-trichloro-2-pyridinol (TCPy) on the angiogenesis of chick embryo was evaluated in the chorioallantoic membrane (CAM) using an ex vivo model. Methods Nine-day-old incubated eggs where inoculated with various doses of CPF and TCPy. After 48 h of incubation, the CAM layers were retrieved and analyzed using angiogenesis software to obtain the density of blood vessels. Histomorphometric studies were performed to measure the thickness of vessel walls. The expression of VEGF, VEGFR2, and N-cadherin genes responsible for angiogenesis were analyzed. Results The exposure to the parent compound CPF and its metabolite TCPy promoted angiogenesis in groups administered with lower concentration of the pesticide and its metabolite, whereas a decline in angiogenesis was observed at higher concentrations. These observations were made by analyzing the density, histomorphometry results, and semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) results. The density, thickness, and lumen size of blood vessels in the groups with low concentration of CPF and TCPy were 28.34, 9 μm, and 30 μm, respectively, whereas in the groups with higher CPF and TCPy concentrations, they were 12, 3 μm, and 9 μm, respectively. Conclusions Hence, CPF and its metabolites interfere with angiogenesis in the CAM of chick embryos. Because of their estrogen-mimicking ability, pesticides are the prime etiological suspects of increasing alteration in blood vessel formation. These results may be of help in future studies on the effect of CPF in embryonic growth, wound healing, diabetes, and tumors.

Gut microbiota: An underestimated and unintended recipient for pesticide-induced toxicity

Pesticide pollution residues have become increasingly common health hazards over the last several decades because of the wide use of pesticides. The gastrointestinal tract is the first physical and biological barrier to contaminated food and is therefore the first exposure site. Interestingly, a number of studies have shown that the gut microbiota plays a key role in the toxicity of pesticides and has a profound relationship with environmental animal and human health. For instance, intake of the pesticide of chlorpyrifos can promote obesity and insulin resistance through influencing gut and gut microbiota of mice. In this review, we discussed the possible effects of different kinds of widely used pesticides on the gut microbiota in different experimental models and analyzed their possible subsequent effects on the health of the host. More and more studies indicated that the gut microbiota of animals played a very important role in pesticides-induced toxicity, suggesting that gut micriobita was also the unintended recipient of pesticides. We hope that more attention can focus on the relationship between pesticides, gut microbiota and environmental health risk assessment in near future.

The effect of copper and chlorpyrifos co-exposure on biomarkers in the marine mussel Mytilus galloprovincialis

Metals and organophosphorous pesticides commonly co-occur in marine environment, but the effect of their mixtures on non-target organisms is still poorly understood. This study investigated the combined effect of the essential metal copper (Cu) and organophosphorous pesticide chlorpyrifos (Chp) in mussels (Mytilus galloprovincialis) after short-term exposure to their sublethal concentrations. Mussels were exposed for four days to 5 and 15 μg L^-1 Cu and 0.05 and 5 μg L^-1 Chp, and to their binary mixtures. The investigated biomarkers, namely acetylcholinesterase activity (AChE), glutathione S-transferase activity (GST), metallothioneins content (MTs) and lipid peroxide levels (LPO) displayed unspecific and inconsistent response patterns that varied depending on the concentration of chemicals and composition of mixtures. The exposure to Cu or Chp alone did not induce AChE activity changes, whereas only Cu provoked a significant GST activity increase. Exposure to lower and higher concentration of Chp resulted in MTs content and LPO level increase, respectively. Response of biomarkers to mixtures was generally inconsistent. Data integration by IBR index and PCA revealed different stress levels for given exposure conditions, but no explicit differentiation between single and joint exposures was found. The present results showed that low and environmentally relevant concentrations of Cu and Chp in mixtures may result in a detectable biological response, stressing the need for further investigation of joint effects of widespread marine contaminants in sentinel organisms.

Demonstrating the need for chemical exposure characterisation in a microplate test system: toxicity screening of sixteen pesticides on two marine microalgae

Pesticides used in viticulture create a potential risk for the aquatic environment due to drift during application, runoff and soil leaching. The toxicity of sixteen pesticides and one metabolite were evaluated on the growth of two marine microalgae, Tisochrysis lutea and Skeletonema marinoi, in 96-h exposure assays conducted in microplates. For each substance, concentrations of stock solutions were analytically measured and abiotic assays were performed to evaluate the chemical stability of pesticides in microplates. For two chemicals, microalgae exposures were run simultaneously in microplates and culture flasks to compare EC₅₀ calculated from the two exposure systems. Results from chemical analyses demonstrated the low stability of hydrophobic pesticides (log K_OW > 3). For such chemicals, EC₅₀ values calculated using measured pesticide concentrations were two-fold lower than those first estimated using nominal concentrations. Photosystem II inhibitors were the most toxic herbicides, with EC₅₀ values below 10 μg L^-1 for diuron and around double this for isoproturon. Chlorpyrifos-methyl was the only insecticide to significantly affect the growth of T. lutea, with an EC₅₀ around 400 μg L^-1. All fungicides tested were significantly toxic to both species: strobilurins showed low overall toxicity, with EC₅₀ values around 400 μg L^-1, whereas quinoxyfen, and spiroxamine, showed high toxicity to both species, especially to T. lutea, with an EC₅₀ below 1 μg L^-1 measured for spiroxamine in culture flasks. This study highlights the need to perform chemical analyses for reliable toxicity assessment and discusses the advantages and disadvantages of using microplates as a toxicity screening tool.

Sublethal concentrations of chlorpyrifos induce changes in the thermal sensitivity and tolerance of anuran tadpoles in the toad Rhinella arenarum?

Amphibians are considered one of the groups most susceptible to chemical contamination, therefore are good bio-indicators of aquatic pollution. Synergistic effects of temperature and pesticides have been found in amphibians determining amplified toxicity effect on survival and malformations with increasing temperatures. We studied the sensitivity of sublethal concentrations of chlorpyrifos in Rhinella arenarum tadpoles over on two fitness related thermal traits: locomotor swimming performance and thermal tolerance limits (CT_max = critical thermal maximum and CT_min = critical thermal minimum). Our result shows a decrease in the locomotor performance of R. arenarum tadpoles with increasing sublethal chlorpyrifos concentrations. The experimental temperature increased locomotor performance but this being only significant for the control whereas tadpoles raised at any sublethal chlorpyrifos concentration did not increase their total swimming distance with temperature (Concentration × Temperature interaction, P < 0.019). Chlorpyrifos toxicity decreases maximum swimming distance but this reduction not compensated at high temperatures that do enhance swimming performance in the control treatment. On the other hand, higher chlorpyrifos sensitivity in CT_max than CT_min since tadpoles exposed to all polluted treatments exhibits a significant decline in CT_max but not in CT_min. Current global warming and the increase of atypical climatic events, such as heat waves may put at risk the larval chlorpyrifos polluted populations of R. arenarum. Our results show that the sublethal concentrations of the chlorpyrifos pesticide may affect the fitness and survival of the larvae of R. arenarum.

Resistance development and insecticide susceptibility in Culex pipiens pipiens, an important vector of human diseases, against selection pressure of temephos and its relationship to cross-resistance towards organophosphates and pyrethroids insecticides

Background

Culex pipiens pipiens is an important vector of human diseases.

Objective

To determine the insecticide resistance development in Culex pipiens pipiens against selection pressure of temephos..

Methods

A field population of Culex pipiens pipiens was collected from Northwestern Tunisia with a medium level of temephos resistance (LC₅₀ = 0.0069). It was subjected to six generations of temephos pressure selection to evaluate its relationship to cross-resistance towards organophosphates (OPs) and pyrethroids (PYR) insecticides.

Results

The selection was initiated at the dose 0.0266, 0.0748 and 0.0069 which were increased during successive generations up to 0.1488, 3.8747 and 0.0086 after sixth generation for temephos, chlorpyrifos and permethrin insecticides, respectively. It is important to noted that high cross-resistance to chlorpyrifos insecticide (OP) was detected (51.88×). However, little or no cross-resistance to the pyrethroid permethrin (PYR) was recorded (1.24×). Contrary to metabolic resistance, it seemed that acetylcholinesterases AChE 1 was fixed under pressure selection.

Conclusion

The high cross-resistance to temephos and chlorpyrifos is reasonable because they belong to the same class of insecticide (OP). However, the little cross-resistance to the pyrethroid permethrin could support its use alternately for Culex pipiens pipiens control.

Assessment of acute toxicity tests and rhizotron experiments to characterize lethal and sublethal control of soil-based pests

BACKGROUND

Characterizing lethal and sublethal control of soil-based pests with plant protection products is particularly challenging due to the complex and dynamic interplay of the system components. Here, we present two types of studies: acute toxcity experiments (homogenous exposure of individuals in soil) and rhizotron experiments (heterogeneous exposure of individuals in soil) to investigate their ability to strengthen our understanding of mechanisms driving the effectivness of the plant protection product. Experiments were conducted using larvae of the western corn rootworm Diabrotica virgifera LeConte and three pesticide active ingredients: clothianidin (neonicotinoid), chlorpyrifos (organophosphate) and tefluthrin (pyrethroid).

RESULTS

The order of compound concentrations needed to invoke a specific effect intensity (EC₅₀ values) within the acute toxicity tests was chlorpyrifos > tefluthrin > clothianidin. This order changed for the rhizotron experiments because application type, fate and transport of the compounds in the soil profile, and sublethal effects on larvae also influence their effectiveness in controlling larval feeding on corn roots.

CONCLUSION

Beyond the pure measurement of efficacy through observing relative changes in plant injury to control plants, the tests generate mechanistic understanding for drivers of efficacy apart from acute toxicity. The experiments have the potential to enhance efficacy testing and product development, and might be useful tools for assessing resistance development in the future. © 2018 Society of Chemical Industry.

Effects of sequential exposure to water accommodated fraction of crude oil and chlorpyrifos on molecular and biochemical biomarkers in rainbow trout

Fish can be simultaneously or sequentially exposed to various kinds of pollutants, resulting in combined effects. Polycyclic aromatic hydrocarbons induce cytochrome P450 monooxygenase 1A (CYP1A) expression, which catalyzes the conversion of the organophosphorus insecticide chlorpyrifos (CPF) into its most active derivative, CPF-oxon. CPF-oxon inhibits CYP1A and other enzymes, including carboxylesterases (CEs) and acetylcholinesterase (AChE). We studied the effects of an in vivo exposure to crude oil water accommodated fraction (WAF) followed by an ex vivo exposure of liver tissue to CPF on the expression of Cyp1a, AhR and ARNT mRNA, CYP1A protein and on the activity of biomarker enzymes in the rainbow trout (Oncorhynchus mykiss). Juvenile rainbow trout were exposed to WAF (62 μg L^-1 TPH) for 48 h. Then, liver was dissected out, sliced and exposed to 20 μg L^-1 CPF ex vivo for 1 h. Liver tissue was analyzed for mRNA and protein expression and for CEs, AChE, glutathione S-transferase (GST) and CYP1A (EROD) activity. WAF induced Cyp1a mRNA and CYP1A protein expression by 10-fold and 2.5-8.3-fold, respectively, with no effect of CPF. WAF induced AhR expression significantly (4-fold) in control but not in CPF treated liver tissue. ARNT mRNA expression was significantly lowered (5-fold) by WAF. CPF significantly reduced liver EROD activity, independently of WAF pre-treatment. CEs activity was significantly inhibited in an additive manner following in vivo exposure to WAF (42%) and ex vivo exposure to CPF (19%). CPF exposure inhibited AChE activity (37%) and increased GST activity (42%).

The use of carboxylesterases as biomarkers of pesticide exposure in bivalves: A methodological approach

Bivalves are worldwide sentinels of anthropogenic pollution. The inclusion of biomarker responses in chemical monitoring is a recommended practise that has to overcome some difficulties. One of them is the time frame between sample collection and sample processing in order to ensure the preservation of enzymatic activities. In the present study, three bivalve species of commercial interest (mussel, Mytilus galloprovincialis, razor shell, Solen marginatus, and cockle, Cerastoderma edule) were processed within <2 h after being retrieved from their natural habitat, and 24 h after being transported in air under cold conditions (6-8 °C) to laboratory facilities. The enzymatic activities were compared in the three species submitted to both conditions revealing no differences in terms of carboxylesterase dependent activities (CEs) using different substrates: p-nitrophenyl acetate (pNPA), p-nitrophenyl butyrate (pNPB), 1-naphthyl acetate (1-NA), 1-naphthyl butyrate (1-NB) and 2-naphthyl acetate (2-NA). In mussels, three tissues were selected (haemolymph, gills and digestive gland). For comparative purposes, in razor shell and cockle only digestive gland was considered as it is the main metabolic organ. Baseline enzymatic activities for CEs were characterised in the digestive gland of the three bivalves using four out of the five selected CE substrates as well as the kinetic parameters (V_max and K_m) and catalytic efficiency. The in vitro sensitivity to the organophosphorus metabolite chlorpyrifos oxon was also calculated. IC₅₀ values (pM-nM range) were lower than those obtained for vertebrate groups which suggest that bivalves have high protection efficiency against this pesticide as well as species dependent particularities.

Activity of acetylcholinesterase and acid and alkaline phosphatases in different insecticide-treated Helicoverpa armigera (Hübner)

Helicoverpa armigera is a major devastating insect pest on a wide range of vegetables and cash crops. Insecticides are presently indispensable for its control in nearly all crops. H. armigera has acquired resistance against almost all insecticides because of the activity of detoxification enzymes used for the defensive mechanism. The current research was carried out to evaluate the activity of detoxification enzymes, i.e., acetylcholinesterase and alkaline and acid phosphatases in chlorpyrifos-, bifenthrin-, lufenuron-, lambda cyhalothrin-, and emamectin benzoate-treated larvae of H. armigera. The maximum AChE activity was recorded in emamectin benzoate-treated larval samples followed by chlorpyrifos, lufenuron, lambda cyhalothrin and bifenthrin, respectively, while the highest alkaline phosphatases' activity was recorded in emamectin and the lowest in bifenthrin-treated H. armigera. As far as acid phosphatases' activity is concerned, the highest activity was noted in lufenuron samples while the lowest in lambda cyhalothrin samples, respectively. Comparatively, activities of alkaline and acid phosphatases were higher than AChE. The elevated activities of detoxification enzymes can possibly lead to increase in resistance development against synthetic chemical insecticides.

Effect of exposition to chlorpyrifos upon plasmatic cholinesterases, hematology and blood biochemistry values in Bothrops asper (Serpentes: Viperidae)

The terciopelo (Bothrops asper), is one of the most important venomous snakes in Costa Rica and common on agriculture where insecticides are frequently used for pest control. To assess the exposure to organophosphates on captive B. asper, an experiment using chlorpyrifos and butyrylcholinesterase (BChE), as a biomarker was conducted. In addition to BChE, hematology, aspartate aminotransferase (AST), total proteins (TP) and albumin were measured after exposure. Different concentrations of chlorpyrifos were used in Group A (0.1%) and B (1%), while the Control Group received distilled water; each group was composed of 5 snakes. Values of BChE, AST, TP, and albumin were measured before exposure, and at 6, 12, 24, 196, 360 and 528 h post-exposure. Hematology values were measured after 24 h post-exposure. As result, an important variation between subjects in all groups before exposure was obtained. Moreover, BChE activity showed 37% inhibition of Group A when compared to Control Group at 12 h post-exposure, and a higher inhibition of Group B (97%) related to Control Group, at 6 h post-exposure. Recovery of BChE occurred towards 528 h, never reaching initial values. Despite some variation in the rest of parameters used, a marked relative lymphopenia and monocytosis occurred at 24 h, assuming stress as the main cause.

Resistance to commonly used insecticides and phosphine fumigant in red palm weevil, Rhynchophorus ferrugineus (Olivier) in Pakistan

The red palm weevil Rhynchophorus ferrugineus (Olivier) is an important pest of date palms in many regions of the world. This paper reports the first survey of insecticide resistance in field populations of R. ferrugineus in Pakistan which were collected from seven date palm growing areas across Punjab and Khyber Pakhtunkhwa (KPK) provinces, Pakistan. The resistance was assessed by the diet incorporation method against the formulated commonly used chemical insecticides profenophos, imidacloprid, chlorpyrifos, cypermethrin, deltamethrin, spinosad, lambda-cyhalothrin and a fumigant phosphine. Elevated levels of resistance were recorded for cypermethrin, deltamethrin and phosphine after a long history of insecticide use in Pakistan. Resistance Ratios (RRs) were 63- to 79-fold for phosphine, 16- to 74-fold for cypermethrin, 13- to 58-fold for deltamethrin, 2.6- to 44-fold for profenophos, 3- to 24-fold for chlorpyrifos, 2- to 12-fold for lambda-cyhalothrin and 1- to 10-fold for spinosad compared to a susceptible control line. Resistant R. ferrugineus populations were mainly found in southern Punjab and to some extent in KPK. The populations from Bahawalpur, Vehari, Layyah and Dera Ghazi Khan were most resistant to chemical insecticides, while all populations exhibited high levels of resistance to phosphine. Of the eight agents tested, lower LC50 and LC90 values were recorded for spinosad and lambda-cyhalothrin. These results suggest that spinosad and lambda-cyhalothrin exhibit unique modes of action and given their better environmental profile, these two insecticides could be used in insecticide rotation or assist in phasing out the use of older insecticides. A changed pattern of both insecticides can be used sensibly be recommended without evidence of dose rates and frequencies used.

Development and removal ability of non-toxigenic Aspergillus section Flavi in presence of atrazine, chlorpyrifos and endosulfan

This study evaluated the in vitro effect of three concentrations of atrazine, chlorpyrifos and endosulfan on the growth parameters of four non-toxigenic Aspergillus section Flavi strains. The ability of the strains to remove these pesticides in a synthetic medium was also determined. Growth parameters were measured on soil extract solid medium supplied with 5, 10 and 20mg/l of each pesticide, and conditioned to -0.70, -2.78, -7.06 and -10.0 water potential (MPa). Removal assays were performed in Czapek Doc medium (CZD) supplied with 20mg/l of each pesticide under optimal environmental conditions (-2.78 of MPa and 25°C). The residual levels of each pesticide were detected by the reversed-phase HPLC/fluorescence detection system. The lag phases of the strains significantly decreased in the presence of the pesticides with respect to the control media. This result indicates a fast adaptation to the conditions assayed. Similarly, the mycelial growth rates in the different treatments increased depending on pesticide concentrations. Aspergillus oryzae AM 1 and AM 2 strains showed high percentages of atrazine degradation (above 90%), followed by endosulfan (56 and 76%) and chlorpyrifos (50 and 73%) after 30 days of incubation. A significant (p<0.001) correlation (r=0.974) between removal percentages and growth rate was found. This study shows that non-toxigenic Aspergillus section Flavi strains from agricultural soils are able to effectively grow in the presence of high concentrations of atrazine, chlorpyrifos and endosulfan under a wide range of MPa conditions. Moreover, these strains have the ability to remove high levels of these pesticides in vitro in a short time.