Metabolic resistance in Nilaparvata lugens to etofenprox, a non-ester pyrethroid insecticide

Insecticidal activity of the spider neurotoxin PPTX-04 through modulating insect voltage-gated sodium channel

Ion channels on cell membrane are molecular targets of more than half peptide neurotoxins from spiders. From Pardosa pseudoannulata, a predatory spider on a range of insect pests, we characterized a peptide neurotoxin PPTX-04 with an insecticidal activity. PPTX-04 showed high toxicity to Nilaparvata lugens, a main prey of P. pseudoannulata, and the toxicity was not affected by the resistance to etofenprox (IUPAC chemical name:1-ethoxy-4-[2-methyl-1-[(3-phenoxyphenyl)methoxy]propan-2-yl]benzene, purity: 99%). On N. lugens voltage-gated sodium channel NlNav1 expressed in Xenopus oocytes, PPTX-04 prolonged the channel opening and induced tail currents, which is similar to pyrethroid insecticides. However, PPTX-04 potency on NlNav1 was not affected by mutations conferring pyrethroid resistance in insects, which revealed that PPTX-04 and pyrethroids should act on different receptors in NlNav1. In contrast, two mutations at the extracellular site 4 significantly reduced PPTX-04 potency, which indicated that PPTX-04 would act on a potential receptor containing the site 4 in NlNav1. The result from the molecular docking supported the conclusion that the binding pocket of PPTX-04 in NlNav1 should contain the site 4. In summary, PPTX-04 had high insecticidal activity through acting on a distinct receptor site in insect Nav, and was a potential resource to control insect pests and manage resistance to pyrethroids.

Risk of resistance and the metabolic resistance mechanism of Laodelphax striatellus (Fallén) to cyantraniliprole

Cyantraniliprole is a highly effective diamide insecticide used to control of Laodelphax striatellus (Fallén). This study aimed to assess the insecticide resistance risk of L. striatellus and its metabolic resistance mechanisms. After 25 continuous generations of selection, the resistance of L. striatellus to cyantraniliprole increased by 17.14-fold. The realistic heritability of resistance was 0.0751. After successive rearing for five generations without exposure to insecticides, the resistance ratio for the resistant strain of L. striatellus decreased by 3.47-fold, and the average resistance decline rate per generation was 0.0266. Cyantraniliprole-resistant strains did not exhibit cross-resistance to triflumezopyrim, pymetrozine, flonicamid, sulfoxaflor, dinotefuran, clothianidin, thiamethoxam, nitenpyram, or imidacloprid. Compared to those of the sensitive strain, the 2nd, 3rd, and 4th instars, nymphal stage durations, total preoviposition period, and average generation time of the resistant strain were markedly reduced. Furthermore, the activity of cytochrome P450 monooxygenase (P450) and carboxylesterase (CarE) were markedly increased. The upregulation of CYP419A1v2 expression was most evident among the P450 genes, with a 6.10-fold increase relative to that in the sensitive strain. The CarE gene LsCarE5 was significantly upregulated by 1.94-fold compared with that in the sensitive strain. With the continuous use of cyantraniliprole, L. striatellus may develop resistance to this insecticide. This resistance may be related to the increase in metabolic enzyme activities regulated by the overexpression of P450 and CarE genes.

Insecticidal toxicity of ω-Atypitoxin-Cs1a and its inhibitory effects on insect voltage-gated calcium channels

BACKGROUND

Excessive use of chemical insecticides raises concerns about insecticide resistance, urging the development of novel insecticides. Peptide neurotoxins from spider venom are an incredibly rich source of ion channel modulators with potent insecticidal activity. A neurotoxin U1-Atypitoxin-Cs1a from the spider Calommata signata was annotated previously. It was of interest to investigate its insecticidal activity and potential molecular targets.

RESULTS

Cs1a was heterologously expressed, purified and pharmacologically characterized here. The recombinant neurotoxin inhibited high-voltage-activated calcium channel currents with an median inhibitory concentration (IC50 ) value of 0.182 ± 0.026 μm on cockroach DUM neurons and thus was designated as ω-Atypitoxin-Cs1a. The recombinant Cs1a was toxic to three insect pests of agricultural importance, Nilaparvata lugens, Spodoptera frugiperda and Plutella xylostella with median lethal concentration (LD50 ) values of 0.121, 0.172 and 0.356 nmol g-1 , respectively, at 24 h postinjection. Cs1a was equivalently toxic to both insecticide-susceptible and -resistant insects. Cs1a exhibited low toxicity to Danio rerio with an LD50 of 2.316 nmol g-1 .

CONCLUSION

Our results suggest that ω-Atypitoxin-Cs1a is a potent CaV channel inhibitor and an attractive candidate reagent for pest control and resistance management. © 2023 Society of Chemical Industry.

Roles of GFAT and PFK genes in energy metabolism of brown planthopper, Nilaparvata lugens

Glutamine:fructose-6-phosphate aminotransferases (GFATs) and phosphofructokinase (PFKs) are the principal rate-limiting enzymes involved in hexosamine biosynthesis pathway (HBP) and glycolysis pathway, respectively. In this study, the NlGFAT and NlPFK were knocked down through RNA interference (RNAi) in Nilaparvata lugens, the notorious brown planthopper (BPH), and the changes in energy metabolism were determined. Knockdown of either NlGFAT or NlPFK substantially reduced gene expression related to trehalose, glucose, and glycogen metabolism pathways. Moreover, trehalose content rose significantly at 72 h after dsGFAT injection, and glycogen content increased significantly at 48 h after injection. Glucose content remained unchanged throughout the experiment. Conversely, dsPFK injection did not significantly alter trehalose, but caused an extreme increase in glucose and glycogen content at 72 h after injection. The Knockdown of NlGFAT or NlPFK significantly downregulated the genes in the glycolytic pathway, as well as caused a considerable and significant decrease in pyruvate kinase (PK) activity after 48 h and 72 h of inhibition. After dsGFAT injection, most of genes in TCA cycle pathway were upregulated, but after dsNlPFK injection, they were downregulated. Correspondingly, ATP content substantially increased at 48 h after NlGFAT knockdown but decreased to an extreme extent by 72 h. In contrast, ATP content decreased significantly after NlPFK was knocked down and returned. The results have suggested the knockdown of either NlGFAT or NlPFK resulted in metabolism disorders in BPHs, highlighting the difference in the impact of those two enzyme genes on energy metabolism. Given their influence on BPHs energy metabolism, developing enzyme inhibitors or activators may provide a biological control for BPHs.

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.

Insecticide resistance associated overexpression of two sigma GST genes assists Nilaparvata lugens to remedy oxidative stress from feeding on resistant rice variety

Insect glutathione S-transferases (GSTs) participate in detoxifying insecticides and plant metabolites in two different ways, metabolizing toxic components and remedying oxidative stress. Here in Nilaparvata lugens, a major insect pest on rice, the roles of cytosolic GSTs in resistance to insecticides and to plant defences were evaluated. The over-expression in four resistant strains indicated that NlGSTs1 and NlGSTs2 were essential to resistances to four test insecticides and H₂O₂ through an antioxidation mechanism. RNAi verified the antioxidation function of NlGSTs1 and NlGSTs2 in the resistances as a common mechanism, regardless of the structural differences among insecticides and H₂O₂. NlGSTs1 and NlGSTs2 also provided protection for N. lugens against rice defense by the same mechanism, reducing H₂O₂ levels when N. lugens were fed on the resistant rice variety Mudogo. The antioxidation activity of recombinant NlGSTs1 and NlGSTs2 is higher than their direct detoxification, which supported the ability of these two GSTs to remedy oxidative stress. For oxidative stress remediation as a common mechanism of NlGSTs1 and NlGSTs2 in both insecticide resistance and host adaptability, the development of insecticide resistance might enhance the ability of insects to remedy oxidative stress from feeding on resistant rice variety and thus to lower the resistance level of rice variety to N. lugens. The results call for careful assessment on N. lugens control when both insecticides and resistant rice variety are applied.

Characterization of two kdr mutations at predicted pyrethroid receptor site 2 in the sodium channels of Aedes aegypti and Nilaparvata lugens

Pyrethroid insecticides prolong the opening of insect sodium channels by binding to two predicted pyrethroid receptor sites (PyR), PyR1 and PyR2. Many naturally-occurring sodium channel mutations that confer pyrethroid resistance (known as knockdown resistance, kdr) are located at PyR1. Recent studies identified two new mutations, V253F and T267A, at PyR2, which co-exist with two well-known mutations F1534C or M918T, at PyR1, in pyrethroid-resistant populations of Aedes aegypti and Nilaparvata lugens, respectively. However, the role of the V253F and T267A mutations in pyrethroid resistance has not been functionally examined. Here we report functional characterization of the V253F and T267A mutations in the Ae. aegypti sodium channel AaNa_v2-1 and the N. lugens sodium channel NlNa_v1 expressed in Xenopus oocytes. Both mutations alone reduced channel sensitivity to pyrethroids, including etofenprox. We docked etofenprox in a homology model of the pore module of the NlNa_v1 channel based on the crystal structure of an open prokaryotic sodium channel NavMs. In the low-energy binding pose etofenprox formed contacts with V253, T267 and a previously identified L1014 within PyR2. Combining of V253F or T267A with F1534C or M918T results in a higher level of pyrethroid insensitivity. Furthermore, both V253F and T267A mutations altered channel gating properties. However, V253F- and T267A-induced gating modifications was not observed in the double mutant channels. Our findings highlight the first example in which naturally-found combinational mutations in PyR1 and PyR2 not only confer higher level pyrethroid insensitivity, but also reduce potential fitness tradeoff in pyrethroid-resistant mosquitoes caused by kdr mutation-induced sodium channel gating modifications.

Role of Insect Gut Microbiota in Pesticide Degradation: A Review

Insect pests cause significant agricultural and economic losses to crops worldwide due to their destructive activities. Pesticides are designed to be poisonous and are intentionally released into the environment to combat the menace caused by these noxious pests. To survive, these insects can resist toxic substances introduced by humans in the form of pesticides. According to recent findings, microbes that live in insect as symbionts have recently been found to protect their hosts against toxins. Symbioses that have been formed are between the pests and various microbes, a defensive mechanism against pathogens and pesticides. Insects' guts provide unique conditions for microbial colonization, and resident bacteria can deliver numerous benefits to their hosts. Insects vary significantly in their reliance on gut microbes for basic functions. Insect digestive tracts are very different in shape and chemical properties, which have a big impact on the structure and composition of the microbial community. Insect gut microbiota has been found to contribute to feeding, parasite and pathogen protection, immune response modulation, and pesticide breakdown. The current review will examine the roles of gut microbiota in pesticide detoxification and the mechanisms behind the development of resistance in insects to various pesticides. To better understand the detoxifying microbiota in agriculturally significant pest insects, we provided comprehensive information regarding the role of gut microbiota in the detoxification of pesticides.

Current Status of Pyrethroids Resistance in Aedes aegypti (Culicidae: Diptera) in Lahore District, Pakistan: A Novel Mechanistic Insight

Aedes aegypti (Linnaeus, 1762) is a major vector responsible for dengue transmission. Insecticides are being used as the most effective tool to control vector populations in Lahore, Pakistan. Control of Ae. aegypti is threatened by the development of resistance against insecticides. The current status of insecticide resistance was evaluated against pyrethroids (deltamethrin, cypermethrin, and lambda-cyhalothrin) in different populations of Lahore (Model Town, Mishri Shah, Sadar Cantt, Walton, and Valencia). The susceptibility of the larval and adult populations was tested following the standard WHO guidelines. Moderate to high levels of resistance were found against pyrethroids in the larval (RR50: 3.6-27.2 and RR90: 5-90) and adult populations (percentage mortality < 98%). Biochemical assays revealed a statistically significant increase in the enzyme level in all field populations compared to the laboratory strain. The value of esterase was one-fold higher, monooxygenase was 3.9- to 4.7-fold higher, and glutathione S-transferases was 1.9- to 2.6-fold higher in field populations compared to the laboratory strain. These results depict the presence of resistance against deltamethrin, cypermethrin, and lambda-cyhalothrin in field populations of Lahore mediated by metabolic enzymes i.e. esterases, monooxygenases, and glutathione S-transferase.

Carboxylesterase genes in nitenpyram-resistant brown planthoppers, Nilaparvata lugens

Carboxylesterases (CarEs) represent one of the major detoxification enzyme families involved in insecticide resistance. However, the function of specific CarE genes in insecticide resistance is still unclear in the insect Nilaparvata lugens (Stål), a notorious rice crop pest in Asia. In this study, a total of 29 putative CarE genes in N. lugens were identified, and they were divided into seven clades; further, the β-esterase clade was significantly expanded. Tissue-specific expression analysis found that 17 CarE genes were abundantly distributed in the midgut and fat body, while 12 CarE genes were highly expressed in the head. The expression of most CarE genes was significantly induced in response to the challenge of nitenpyram, triflumezopyrim, chlorpyrifos, isoprocarb and etofenprox. Among these, the expression levels of NlCarE2, NlCarE4, NlCarE9, NlCarE17 and NlCarE24 were increased by each insecticide. Real-time quantitative polymerase chain reaction and RNA interference assays revealed the NlCarE1 gene to be a candidate gene mainly involved in nitenpyram resistance, while simultaneously silencing NlCarE1 and NlCarE19 produced a stronger effect than silencing either one individually, suggesting a cooperative relationship in resistance formation. These findings lay the foundation for further clarification of insecticide resistance mediated by CarE in N. lugens.

Cytochrome P450s Are Essential for Insecticide Tolerance in the Endoparasitoid Wasp Meteorus pulchricornis (Hymenoptera: Braconidae)

With the widespread application of insecticides, parasitoid wasps may also be under risk when exposed to insecticides directly at their free-living stages. The endoparasitoid wasp Meteorus pulchricornis is the predominant natural enemy of many lepidopteran pests, such as Spodoptera litura and Helicoverpa armigera. The cytochrome P450 monooxygenases constitute a ubiquitous and complex superfamily of hydrophobic, haem-containing enzymes. P450s are involved in the detoxification of many xenobiotics. However, their exact roles in the tolerance mechanism in parasitoids toward insecticides has received less attention. Here, 28 P450 genes in M. pulchricornis were identified from a previously constructed transcriptome dataset. These P450 genes belonged to CYP2, -3, and -4, and mitochondrial clans. Subsequently, eight candidate MpulCYPs were selected from four CYP clans to validate their expression patterns under phoxim, cypermethrin, and chlorfenapyr exposure by qRT-PCR. The results showed that all three insecticides had significant effects on the expression of MpulCYPs. To further study the function of P450s, CYP369B3 was silenced, and its expression levels of CYP369B3 were significantly decreased. Survival analysis indicated that after dsRNA injection, the mortality rate of wasps was significantly increased when M. pulchricornis females were exposed to insecticides compared to control groups. Our findings provide a theoretical base for elucidating the mechanism of insecticide tolerance and promote functional research on P450 genes in parasitoid wasps.

Knockdown of AMP-activated protein kinase increases the insecticidal efficiency of pymetrozine to Nilaparvata lugens

Insecticides are the main tools used to control Nilaparvata lugens (Stål), a serious pest of rice in Asia. However, repeated application of insecticides has caused many negative effects. Reducing the amount of insecticide used, while maintaining good pest population control, would be valuable. AMP-activated protein kinase (AMPK), a sensor of cellular energy status, helps to maintain insect energy balance at the cellular and whole-body level. The role of AMPK in insect response to insecticide stimulation is unknown. We studied the functions of AMPK catalytic subunit alpha (NlAMPKα) in the development of N. lugens and in response to pymetrozine, an insecticide used to control insect pests with piercing-sucking mouthparts. A phylogenetic analysis of protein sequences from 12 species in six orders showed that insects have only the AMPKα 2 subtype. RNA interference against NlAMPKα demonstrated that blocking the AMPK pathway led to a decrease in the systemic ATP level and an increase in N. lugens mortality. NlAMPKα responded to the energy stress caused by pymetrozine treatment, which activated downstream energy metabolic pathways to compensate for the energy imbalance. However, the ATP level in pymetrozine- treated nymphs was not increased, suggesting that ATP is consumed more than synthesized. When NlAMPKα expression was reduced in pymetrozine-treated nymphs by RNAi, the ATP level was decreased and the mortality was significantly increased. At day eight post 0.5 g/3 L of pymetrozine and dsNlAMPKα treatment, nymph survival was 29.33%, which was similar to the 27.33% survival of 1 g/3 L pymetrozine-treated nymphs. Addition of dsNlAMPKα can reduce the concentration of pymetrozine used by 50% while providing comparable efficacy. These results indicate that AMPK helps maintain the energy metabolism of N. lugens in response to pymetrozine treatment. Knockdown of NlAMPKα increases the insecticidal efficiency of pymetrozine to N. lugens.

GFAT and PFK genes show contrasting regulation of chitin metabolism in Nilaparvata lugens

Glutamine:fructose-6-phosphate aminotransferase (GFAT) and phosphofructokinase (PFK) are enzymes related to chitin metabolism. RNA interference (RNAi) technology was used to explore the role of these two enzyme genes in chitin metabolism. In this study, we found that GFAT and PFK were highly expressed in the wing bud of Nilaparvata lugens and were increased significantly during molting. RNAi of GFAT and PFK both caused severe malformation rates and mortality rates in N. lugens. GFAT inhibition also downregulated GFAT, GNPNA, PGM1, PGM2, UAP, CHS1, CHS1a, CHS1b, Cht1-10, and ENGase. PFK inhibition significantly downregulated GFAT; upregulated GNPNA, PGM2, UAP, Cht2-4, Cht6-7 at 48 h and then downregulated them at 72 h; upregulated Cht5, Cht8, Cht10, and ENGase; downregulated Cht9 at 48 h and then upregulated it at 72 h; and upregulated CHS1, CHS1a, and CHS1b. In conclusion, GFAT and PFK regulated chitin degradation and remodeling by regulating the expression of genes related to the chitin metabolism and exert opposite effects on these genes. These results may be beneficial to develop new chitin synthesis inhibitors for pest control.

Cross-resistance and biochemical characterization of buprofezin resistance in the white-backed planthopper, Sogatella furcifera (Horvath)

Buprofezin is a chitin synthesis inhibitor that is very effective against Homopteran pests, such as the white-backed planthopper (WBPH), S. furcifera (Horvath). In the present study, resistance selection, cross-resistance and mechanisms of buprofezin resistance were investigated in this planthopper species. However, the mechanism associated with resistance to growth regulator insecticides (IGRs) remains largely unknown. A resistant strain (Bup-R) with a resistance level (22-fold) to buprofezin was developed through continuous selection for 47 generations from a laboratory susceptible strain (Bup-S). The results showed that the Bup-R exhibited no cross-resistance to other tested insecticides. Synergism tests showed that piperonyl butoxide (PBO) (SR = 3.9-fold) and diethyl maleate (DEM) (SR = 1.8-fold) had synergistic effects on buprofezin toxicity in the resistant strain (F₄₇). Enzyme activity results revealed an approximate 5.7-fold difference in cytochrome P450 monooxygenase and a 2-fold difference in glutathione S-transferase (GST) between the resistant and susceptible strains, suggesting that the increased activity of these two enzymes is likely the main detoxification mechanism involved in resistance to buprofezin in this species. Furthermore, the mRNA expression levels of cytochrome P450 (CYP) and GST genes by quantitative real-time PCR results indicated that sixteen P450 and one GST gene were significantly overexpressed in the Bup-R strain, among which thirteen P450 genes and one GST gene were >2-fold higher than in the Bup-S strain. The present study increases our knowledge of the buprofezin resistance mechanism in S. furcifera and provides a useful reference for integrated pest management (IPM) strategies.

Characterization of nitenpyram resistance in Nilaparvata lugens (Stål)

Nitenpyram is very effective in controlling Nilaparvata lugens (brown planthopper, BPH), and its resistance has been reported in field populations; however, the resistance mechanism remains unclear. In the present study, cross-resistance and resistance mechanisms in nitenpyram-resistant BPH were investigated. A resistant strain (NR) with a high resistance level (164.18-fold) to nitenpyram was evolved through successive selection for 42 generations from a laboratory susceptible strain (NS). The bioassay results showed that the NR exhibited cross-resistance to imidacloprid (37.46-fold), thiamethoxam (71.66-fold), clothianidin (149.17-fold), dinotefuran (98.13-fold), sulfoxaflor (47.24-fold), cycloxaprid (9.33-fold), etofenprox (10.51-fold) and isoprocarb (9.97-fold) but not to triflumezopyrim, chlorpyrifos and buprofezin. The NR showed a 3.21-fold increase in cytochrome P450 monooxygenase (P450) activity compared to that in the NS, while resistance was also synergized (4.03-fold) with the inhibitor piperonyl butoxide (PBO), suggesting a role of P450. Furthermore, the mRNA expression levels of cytochrome P450 (CYP) genes by quantitative real-time PCR results indicated that twelve P450 genes were significantly overexpressed in the NR strain, especially CYP6ER1 (203.22-fold). RNA interference (RNAi) suppression of CYP6ER1 through injection of dsCYP6ER1 led to significant susceptibility in the NR strain. The current study expands our understanding of the nitenpyram resistance mechanism in N. lugens, provides an important reference for integrated pest management (IPM), and enriches the theoretical system of insect toxicology.

Characterization of sulfoxaflor resistance in the brown planthopper, Nilaparvata lugens (Stål)

BACKGROUND

Sulfoxaflor is a new insecticide for controlling Nilaparvata lugens in the field. This study was conducted to investigate the risk of resistance development, the cross-resistance spectrum and the mechanisms of sulfoxaflor resistance in N. lugens.

RESULTS

A sulfoxaflor-resistant strain was obtained from a field population by successive selection with sulfoxaflor for 39 generations in the laboratory. Sulfoxaflor-resistant populations showed significant levels of cross-resistance to dinotefuran, nitenpyram, thiamethoxam, clothianidin, imidacloprid and cycloxaprid. However, they exhibited only minor or no cross-resistance to isoprocarb, etofenprox, chlorpyrifos, triflumezopyrim and buprofezin. Sulfoxaflor was synergized by the inhibitor piperonyl butoxide (PBO) in the sulfoxaflor-resistant strain (SFX-SEL) with 2.69-fold relative synergistic ratios compared with the unselected strain (UNSEL). Compared with UNSEL, the P450 enzyme activity of SFX-SEL was increased 3.50 times, and eight P450 genes were upregulated more than 2.0-fold in SFX-SEL. RNAi reduced the expression of CYP6ER1 (36.87-fold change) and significantly enhanced the susceptibility of SFX-SEL to sulfoxaflor.

CONCLUSION

Resistance development and cross-resistance risk of sulfoxaflor-resistance in N. lugens is evident. The enhanced detoxification of P450 enzymes caused by upregulation of several P450 genes is considered to be the metabolic resistance mechanism. These results suggest that CYP6ER1 might play an important role in sulfoxaflor resistance in N. lugens. © 2018 Society of Chemical Industry.

Effects of single exposure and binary mixtures of ultraviolet filters octocrylene and 2-ethylhexyl 4-(dimethylamino) benzoate on gene expression in the freshwater insect Chironomus riparius

Ultraviolet filters are used extensively in the production of many personal care and industrial products. These products can inadvertently pollute the environment through recreational activities. They have been associated with endocrine disruption in vertebrates but their effects in invertebrates are poorly understood. Chironomus riparius is a species of the dipteran order, with aquatic larvae that are frequently used in toxicity tests. Previously, we showed that octocrylene (OC) and 2-ethylhexyl 4-(dimethylamino) benzoate (OD-PABA) differentially affected the mRNA levels of the ecdysone receptor and Hsp70 genes. For a better understanding of their mode of action, transcriptional activity by real-time PCR was analyzed in fourth instar larvae exposed to OC, OD-PABA, or a binary mixture of both. We studied 16 genes related to the endocrine system, stress, the immune system, and biotransformation mechanisms to elucidate the putative interactions between these compounds. No response was observed for the genes involved in biotransformation, suggesting that enzymes other than cytochromes P450 and glutathione-S-transferases (GSTs) could get involved in transformation of these compounds. Similarly, no response was observed for endocrine-related genes while the stress gene HYOU1 was inhibited by OD-PABA, suggesting an effect in response to hypoxia. In addition, no significant interactions were observed following exposure to a binary mixture of these compounds. Overall, the results suggest a weak, acute response in different metabolic pathways and a lack of interaction between the compounds. Finally, new genes are identified in this organism, opening the possibility to analyze new cellular pathways as targets of toxicants.

Impaired reproduction and individual growth of the water flea Daphnia magna as consequence of exposure to the non-ester pyrethroid etofenprox

The effect of the pesticide etofenprox (0.76, 0.95, 1.18, 1.48, and 1.85 μg L^-1) on survival, reproduction, and growth of Daphnia magna organisms was monitored using 21-day exposure tests. In order to test pesticide effects on D. magna, survival, length, mean total neonates per female, mean brood size, time to first reproduction, mean number broods per female, cumulative molting, and the population parameter intrinsic rate of natural increase (r) were used. Reproduction was seriously affected by etofenprox. Concentrations of etofenprox higher than 1.18 μg L^-1affected all the reproductive parameters analyzed as well as individual length. However, daphnids' survival after 21 days of pesticide exposure did not exhibited differences among experimental and control groups. The no observed effect concentration (NOEC), the lowest observed effect concentration (LOEC), and the maximum acceptable toxicant concentration (MATC) were calculated for the different parameters. A MATC estimation of 1.32 μg L^-1 was calculated for mean brood size, mean number of broods per female, mean number of neonates per female, and the intrinsic rate of growth population. Etofenprox effect on the algae Nannochloris oculata was also evaluated. The selected etofenprox concentrations did not affect algal growth rate (μ) after 24 h; however, N. oculata exposed during 48 and 72 h to the highest etofenprox concentration showed a decreased in its population rate.

Transcriptional activity of detoxification genes is altered by ultraviolet filters in Chironomus riparius

Ultraviolet (UV) filters are compounds used to prevent the damage produced by UV radiation in personal care products, plastics, etc. They have been associated with endocrine disruption, showing anti-estrogen activity in vertebrates and altering the ecdysone pathway in invertebrates. Although they have attracted the attention of multiple research teams there is a lack of data about how animals activate detoxification systems, especially in invertebrates. Here, analysis of the effects of two UV filters, benzophenone-3 (BP3) and 4-methylbenzylidene camphor (4MBC), on the transcriptional activity of nine genes covering the three steps of the detoxification process has been performed. Four cytochrome P450 genes belonging to different members of this family, five GST genes, and the multidrug resistance protein 1 (MRP1) gene were studied by RT-PCR to analyze their transcriptional activity in fourth instar larvae exposed to the UV filters for 8 and 24h. The obtained results show a differential response with downregulation of the different Cyp450s tested by 4MBC while BP3 seems not to modify their expression. On the other hand, some of the GST genes were affected by one or other of the filters, showing a less homogenous response. Finally, MRP1 was activated by both filters but at different times. These results demonstrate for first time that UV filters alter the expression of genes involved in the different steps of the detoxification process and that they can be processed by phase I enzymes other than Cyp450s. They also suggest that UV filters affect biotransformation processes, compromising the ability of the individual to respond to chemical stress, so further research is needed to know the extent of the damage that they can produce in the resistance of the cell to chemicals.

Imidacloprid-susceptible Nilaparvata lugens individuals exceeded resistant individuals in a mixture population with density pressure

BACKGROUND

Fitness costs associated with insecticide resistance in pest insects have mainly been studied under optimal laboratory conditions. However, resistant insects face more stressors than just insecticides in the field, and how the resistant population reacts to these stressors is of practical importance for the control of pest insects such as the brown planthopper Nilaparvata lugens. The aim of the present study was to explore the impact of population density on the competitiveness of resistant and susceptible individuals.

RESULTS

Two isogenic N. lugens populations, a highly imidacloprid-resistant population (HZ-R) with a resistance ratio (RR) of 227.10 and a relatively susceptible population (HZ-S) with an RR of 2.99, were created from a field-resistant population (HZ; RR 62.51). The high resistance levels of HZ-R and HZ were mainly attributable to the overexpression of multiple cytochrome P450 (CYP) genes such as CYP6ER1, CYP6AY1, CYP6CW1 and CYP4CE1 compared with HZ-S, this being supported by piperonyl butoxide synergism. HZ-R was observed to be more resistant to thiacloprid and etofenprox compared with HZ and HZ-S. Most interestingly, in high population density treatments, HZ-S individuals were much more competitive than HZ-R individuals.

CONCLUSION

Imidacloprid-resistant individuals of N. lugens are less competitive than their susceptible counterparts under density pressure. © 2017 Society of Chemical Industry.