Status of insecticide resistance and selection for imidacloprid resistance in the ladybird beetle Propylaea japonica (Thunberg)

Field populations or strains of Propylaea japonica collected from four places in southern China (Guangzhou, Nanning, Guilin, and Yuxi) were tested for susceptibility to four insecticides (abamectin, imidacloprid, beta-cypermethrin, and chlorpyrifos) by the Petri-dish Potter tower method and compared with an insecticide-susceptible strain. Concentrations that proved lethal for 50% of the tested individuals (LC50) were estimated by probit analysis, and resistance factors (RF) were calculated at the LC50 level, which ranged from 1.6 to 10.1, depending on the insecticide. In addition, the Guangzhou strain formed the original population for imidacloprid resistance selection. After selection for 20 generations, the resistance had increased 39.3-fold. Fitness analysis in terms of such traits as fecundity, days to maturity, and survival showed that although both resistant and susceptible populations developed at comparable rates, the resistant strain was less fecund (it laid fewer eggs and a smaller proportion of those eggs hatched and resulted in adults), attaining a fitness score of only 0.56 relative to the susceptible strain. These observations suggest that it is possible to detect strains of P. japonica highly resistant to insecticides under laboratory conditions, and that resistance to imidacloprid carries considerable fitness costs to P. japonica. The study served to expand our understanding of the impact of imidacloprid resistance on biological parameters of P. japonica in more detail and to facilitate the deployment of natural enemies resistant to insecticides in integrated pest management.

Imidacloprid impairs the post-embryonic development of the midgut in the yellow fever mosquito Stegomyia aegypti (=Aedes aegypti)

The mosquito Stegomyia aegypti (=Aedes aegypti) (Diptera: Culicidae) is a vector for the dengue and yellow fever viruses. As blood digestion occurs in the midgut, this organ constitutes the route of entry of many pathogens. The effects of the insecticide imidacloprid on the survival of St. aegypti were investigated and the sub-lethal effects of the insecticide on midgut development were determined. Third instar larvae were exposed to different concentrations of imidacloprid (0.15, 1.5, 3.0, 6.0 and 15.0 p.p.m.) and survival was monitored every 24 h for 10 days. Midguts from imidacloprid-treated insects at different stages of development were dissected and processed for analyses by transmission electron microscopy, immunofluorescence microscopy and terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) assays. Imidacloprid concentrations of 3.0 and 15.0 p.p.m. were found to affect midgut development similarly. Digestive cells of the fourth instar larvae (L4) midgut exposed to imidacloprid had more multilamellar bodies, abundantly found in the cell apex, and more electron-lucent vacuoles in the basal region compared with those from untreated insects. Moreover, imidacloprid interfered with the differentiation of regenerative cells, dramatically reducing the number of digestive and endocrine cells and leading to malformation of the midgut epithelium in adults. The data demonstrate that imidacloprid can reduce the survival of mosquitoes and thus indicate its potentially high efficacy in the control of St. aegypti populations.

Inactivation of Staphylococcus aureus in Oat and Soya Drinks by Enterocin AS-48 in Combination with Other Antimicrobials

The presence of toxicogenic Staphylococcus aureus in foods and the dissemination of methicillin-resistant S. aureus (MRSA) in the food chain are matters of concern. In the present study, the circular bacteriocin enterocin AS-48, applied singly or in combination with phenolic compounds (carvacrol, eugenol, geraniol, and citral) or with 2-nitro-1-propanol (2NPOH), was investigated in the control of a cocktail made from 1 methicillin-sensitive and 1 MRSA strains inoculated on commercial oat and soya drinks. Enterocin AS-48 exhibited low bactericidal activity against staphylococci in the drinks investigated when applied singly. The combinations of sub-inhibitory concentrations of enterocin AS-48 (25 μg/mL) and phenolic compounds or 2NPOH caused complete inactivation of staphylococci in the drinks within 24 h of incubation at 22 °C. When tested in oat and soya drinks stored for 7 d at 10 °C, enterocin AS-48 (25 μg/mL) in combination with 2NPOH (5.5 mM) reduced viable counts rapidly in the case of oat drink (4.2 log cycles after 12 h) or slowly in soya drink (3.8 log cycles after 3 d). The same combined treatment applied on drinks stored at 22 °C achieved a fast inactivation of staphylococci within 12 to 24 h in both drinks, and no viable staphylococci were detected for up to 7 d of storage. Results from the study highlight the potential of enterocin AS-48 in combination with 2NPOH for inactivation of staphylococci.

Maize (Zea mays) seeds can detect above-ground weeds; thiamethoxam alters the view

BACKGROUND

Far red light is known to penetrate soil and delay seed germination. Thiamethoxam as a seed treatment has been observed to enhance seed germination. No previous work has explored the effect of thiamethoxam on the physiological response of buried maize seed when germinating in the presence of above-ground weeds. We hypothesised that the changes in red:far red reflected from above-ground weeds would be detected by maize seed phytochrome and delay seed germination by decreasing the level of GA and increasing ABA. We further hypothesised that thiamethoxam would overcome this delay in germination.

RESULTS

Thiamethoxam enhanced seed germination in the presence of above-ground weeds by increasing GA signalling and downregulating DELLA protein and ABA signalling genes. An increase in amylase activity and a degradation of starch were also observed.

CONCLUSIONS

Far red reflected from the above-ground weeds was capable of penetrating below the soil surface and was detected by maize seed phytochrome. Thiamethoxam altered the effect of far red on seed germination by stimulating GA and inhibiting ABA synthesis. This is the first study to suggest that the mode of action of thiamethoxam involves both GA synthesis and ABA inhibition.

Reproductive parameters of Tetranychus urticae (Acari: Tetranychidae) affected by neonicotinoid insecticides

Two-spotted spider mite is a major pest of many agricultural and ornamental crops worldwide. Some reports have indicated that application of neonicotinoid insecticides may lead to increased fecundity of this pest. If this is found to be true, the use of these pesticides may cause an outbreak of spider mite populations. Sublethal effects of three neonicotinoids, namely thiacloprid, acetamiprid and thiamethoxam were studied on T. urticae adults at field recommended doses. The experiments were carried out using bean leaf pieces in plastic Petri dishes. The adult mites were treated using two methods: (1) drench application and (2) spraying of leaves with Potter Spray Tower. Our results indicated that all neonicotinoids tested increased T. urticae population. In both treatment methods, acetamiprid treated mites had the highest intrinsic rate of population increase (rm) and finite rate of population increase (λ); and the lowest mean generation time (T) and doubling time among the treatments. If similar results are obtained from greenhouse and field trials, the use of these insecticides requires necessary precautions such as avoiding repeated use of neonicotinoid insecticide for controlling insect pests.

Mitochondrial succinate dehydrogenase is involved in stimulus-secretion coupling and endogenous ROS formation in murine beta cells

AIMS/HYPOTHESIS

Generation of reduction equivalents is a prerequisite for nutrient-stimulated insulin secretion. Mitochondrial succinate dehydrogenase (SDH) fulfils a dual function with respect to mitochondrial energy supply: (1) the enzyme is part of mitochondrial respiratory chains; and (2) it catalyses oxidation of succinate to fumarate in the Krebs cycle. The aim of our study was to elucidate the significance of SDH for beta cell stimulus-secretion coupling (SSC).

METHODS

Mitochondrial variables, reactive oxygen species (ROS) and cytosolic Ca(2+) concentration ([Ca(2+)]c) were measured by fluorescence techniques and insulin release by radioimmunoassay in islets or islet cells of C57Bl/6N mice.

RESULTS

Inhibition of SDH with 3-nitropropionic acid (3-NPA) or monoethyl fumarate (MEF) reduced glucose-stimulated insulin secretion. Inhibition of the ATP-sensitive K(+) channel (KATP channel) partly prevented this effect, whereas potentiation of antioxidant defence by superoxide dismutase mimetics (TEMPOL and mito-TEMPO) or by nuclear factor erythroid 2-related factor 2 (Nrf-2)-mediated upregulation of antioxidant enzymes (oltipraz, tert-butylhydroxyquinone) did not diminish the inhibitory influence of 3-NPA. Blocking SDH decreased glucose-stimulated increase in intracellular FADH2 concentration without alterations in NAD(P)H. In addition, 3-NPA and MEF drastically reduced glucose-induced hyperpolarisation of mitochondrial membrane potential, indicative of decreased ATP production. As a consequence, the glucose-stimulated rise in [Ca(2+)]c was significantly delayed and reduced. Acute application of 3-NPA interrupted glucose-driven oscillations of [Ca(2+)]c. 3-NPA per se did not elevate intracellular ROS, but instead prevented glucose-induced ROS accumulation.

CONCLUSIONS/INTERPRETATION

SDH is an important regulator of insulin secretion and ROS production. Inhibition of SDH interrupts membrane-potential-dependent SSC, pointing to a pivotal role of mitochondrial FAD/FADH2 homeostasis for the maintenance of glycaemic control.

Sitona lineatus (Coleoptera: Curculionidae) Larval Feeding on Pisum sativum L. Affects Soil and Plant Nitrogen

Adults of Sitona lineatus (pea leaf weevil, PLW) feed on foliage of several Fabaceae species but larvae prefer to feed on nodules of Pisum sativum L. and Vicia faba L. Indirectly, through their feeding on rhizobia, weevils can reduce soil and plant available nitrogen (N). However, initial soil N can reduce nodulation and damage by the weevil and reduce control requirements. Understanding these interactions is necessary to make integrated pest management recommendations for PLW. We conducted a greenhouse study to quantify nodulation, soil and plant N content, and nodule damage by weevil larvae in relation to soil N amendment with urea, thiamethoxam insecticide seed coating and crop stage. PLWs reduced the number of older tumescent (multilobed) nodules and thiamethoxam addition increased them regardless of other factors. Nitrogen amendment significantly increased soil available N (>99% nitrate) as expected and PLW presence was associated with significantly lower levels of soil N. PLW decreased plant N content at early flower and thiamethoxam increased it, particularly at late flower. The study illustrated the complexity of interactions that determine insect herbivory effects on plant and soil nutrition for invertebrates that feed on N-fixing root nodules. We conclude that effects of PLW on nodulation and subsequent effects on plant nitrogen are more pronounced during the early growth stages of the plant. This suggests the importance of timing of PLW infestation and may explain the lack of yield depression in relation to this pest observed in many field studies. Also, pea crops in soils with high levels of soil N are unlikely to be affected by this herbivore and should not require insecticide inputs.

Imidacloprid sorption kinetics, equilibria, and degradation in sandy soils of Florida

Imidacloprid (IMD) is a neonicotinoid insecticide soil-drenched on sandy soils of southwest Florida for the control of Diaphorina citri Kuwayama or Asian citrus psyllid (ACP). The ACP vectors causal pathogens of a devastating citrus disease called citrus greening. Understanding the behavior of IMD in these soils and plants is critical to its performance against target pests. Samples from Immokalee fine sand (IFS) were used for sorption kinetics and equilibria experiments. IMD kinetics data were described by the one-site mass transfer (OSMT) model and reached equilibrium between 6 and 12 h. Batch equilibrium and degradation studies revealed that IMD was weakly sorbed (K(OC) = 163-230) and persistent, with a half-life of 1.0-2.6 years. Consequently, IMD has the potential to leach below the citrus root zone after the soil-drench applications.

Thiamethoxam Resistance in the House Fly, Musca domestica L.: Current Status, Resistance Selection, Cross-Resistance Potential and Possible Biochemical Mechanisms

The house fly, Musca domestica L., is an important ectoparasite with the ability to develop resistance to insecticides used for their control. Thiamethoxam, a neonicotinoid, is a relatively new insecticide and effectively used against house flies with a few reports of resistance around the globe. To understand the status of resistance to thiamethoxam, eight adult house fly strains were evaluated under laboratory conditions. In addition, to assess the risks of resistance development, cross-resistance potential and possible biochemical mechanisms, a field strain of house flies was selected with thiamethoxam in the laboratory. The results revealed that the field strains showed varying level of resistance to thiamethoxam with resistance ratios (RR) at LC50 ranged from 7.66-20.13 folds. Continuous selection of the field strain (Thia-SEL) for five generations increased the RR from initial 7.66 fold to 33.59 fold. However, resistance declined significantly when the Thia-SEL strain reared for the next five generations without exposure to thiamethoxam. Compared to the laboratory susceptible reference strain (Lab-susceptible), the Thia-SEL strain showed cross-resistance to imidacloprid. Synergism tests revealed that S,S,S-tributylphosphorotrithioate (DEF) and piperonyl butoxide (PBO) produced synergism of thiamethoxam effects in the Thia-SEL strain (2.94 and 5.00 fold, respectively). In addition, biochemical analyses revealed that the activities of carboxylesterase (CarE) and mixed function oxidase (MFO) in the Thia-SEL strain were significantly higher than the Lab-susceptible strain. It seems that metabolic detoxification by CarE and MFO was a major mechanism for thiamethoxam resistance in the Thia-SEL strain of house flies. The results could be helpful in the future to develop an improved control strategy against house flies.

3-Nitroasterric Acid Derivatives from an Antarctic Sponge-Derived Pseudogymnoascus sp. Fungus

Four new nitroasterric acid derivatives, pseudogymnoascins A-C (1-3) and 3-nitroasterric acid (4), along with the two known compounds questin and pyriculamide, were obtained from the cultures of a Pseudogymnoascus sp. fungus isolated from an Antarctic marine sponge belonging to the genus Hymeniacidon. The structures of the new compounds were determined by extensive NMR and MS analyses. These compounds are the first nitro derivatives of the known fungal metabolite asterric acid. Several asterric acid derivatives isolated from other fungal strains have shown antibacterial and antifungal activities. However, the new compounds described in this work were inactive against a panel of bacteria and fungi (MIC > 64 μg/mL).

Sublethal and hormesis effects of imidacloprid on the soybean aphid Aphis glycines

The soybean aphid, Aphis glycines Matsumura, is a major pest in soybean crop. Current management of this pest relies mainly on insecticides applications, and the neonicotinoid imidacloprid has been proposed as an effective insecticide to control A. glycines in soybean field. Imidacloprid at lethal concentrations not only exerts acute toxicity to A. glycines, but also cause various biological changes when aphids are chronically exposed to lower concentrations. In this study, we assessed the effects of a low-lethal (0.20 mg L(-1)) and two sublethal (0.05 and 0.10 mg L(-1)) imidacloprid concentrations on various A. glycines life history traits. Aphid exposure to 0.20 mg L(-1) imidacloprid caused slower juvenile development, shorter reproductive period, and reduced adult longevity, fecundity and total lifespan. Stimulatory effects, i.e. hormesis, on reproduction and immature development duration were observed in aphids exposed to the lower sublethal imidacloprid concentrations. Consequently, the net reproduction rate (R 0) was significantly higher than in the control aphids. These findings stress the importance of the actual imidacloprid concentration in its toxicological properties on A. glycines. Therefore, our results would be useful for assessing the overall effects of imidacloprid on A. glycines and for optimizing integrated pest management programs targeting this pest.

Thiamethoxam as a seed treatment alters the physiological response of maize (Zea mays) seedlings to neighbouring weeds

BACKGROUND

Thiamethoxam is a broad-spectrum neonicotinoid insecticide that, when applied to seed, has been observed to enhance seedling vigour under environmental stress conditions. Stress created by the presence of neighbouring weeds is known to trigger the accumulation of hydrogen peroxide (H2 O2 ) in maize seedling tissue. No previous work has explored the effect of thiamethoxam as a seed treatment on the physiological response of maize seedlings emerging in the presence of neighbouring weeds.

RESULTS

Thiamethoxam was found to enhance seedling vigour and to overcome the expression of typical shade avoidance characteristics in the presence of neighbouring weeds. These results were attributed to maintenance of the total phenolics content, 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging activity and anthocyanin and lignin contents. These findings were also associated with the activation of scavenging genes, which reduced the accumulation of H2 O2 and the subsequent damage caused by lipid peroxidation in maize seedlings originating from treated seeds even when exposed to neighbouring weeds.

CONCLUSIONS

These results suggest the possibility of exploring new chemistries and modes of action as novel seed treatments to upregulate free radical scavenging genes and to maintain the antioxidant system within plants. Such an approach may provide an opportunity to enhance crop competitiveness with weeds.

Does behaviour play a role in house fly resistance to imidacloprid-containing baits?

The objective of this research was to examine the role and type of behavioural mechanisms that function in house fly, Musca domestica L. (Diptera: Muscidae), resistance to an imidacloprid-containing commercial fly bait, QuickBayt(®) , using an insecticide-susceptible and an imidacloprid-resistant strain. Mortality and feeding behaviour were observed through choice bioassays of three post-imidacloprid selected house fly generations to determine whether flies would consume the bait in the presence of an alternative food source. Mortality rates in choice containers progressively decreased in post-selection flies as QuickBayt(®) no-choice selections proceeded. There were no differences between the proportions of flies observed contacting QuickBayt(®) and sugar, respectively, a finding that eliminates repellency as a mechanism of stimulus-dependent behavioural resistance. However, differences in QuickBayt(®) consumption and subsequent mortality between choice and no-choice containers provided strong support for the evolution of consumption irritancy- or taste aversion-related behavioural resistance. The results of this study support the responsible rotation of insecticide bait formulations for house fly control.

Pre-treatment of Stegomyia aegypti mosquitoes with a sublethal dose of imidacloprid impairs behavioural avoidance induced by lemon oil and DEET

The present study was conducted to determine whether imidacloprid can impair the avoidance behaviour of the mosquito Stegomyia aegypti. Laboratory investigations using a T-maze apparatus showed that St. aegypti mosquitoes present long term avoidance behaviour when they are exposed to repetitive trials with lemon oil and DEET. The present study tested the effect of a sublethal dose of imidacloprid on the avoidance behaviour of St. aegypti mosquitoes over a 48 h period. Data suggest that 0.5 ng of imidacloprid/mosquito reduces the avoidance behaviour of mosquitoes exposed to lemon oil, on the first day of exposure, after the second trial; whereas imidacloprid affected DEET repellency only the first day of exposure, after the second trial. Imidacloprid was toxic against St. aegypti mosquitoes, and at sublethal doses was able to impair the repellency induced by lemon oil and DEET. The present data were consistent with the finding that St. aegypti mosquitoes exhibit long term avoidance behaviour, and treatment of mosquitoes with a sublethal dose of imidacloprid under DEET application can affect the repellency of DEET against St. aegypti.

DFT calculations, spectroscopy and antioxidant activity studies on (E)-2-nitro-4-[(phenylimino)methyl]phenol

We have reported synthesis and characterization of (E)-2-nitro-4-[(phenylimino)methyl]phenol by using X-ray crystallographic method, FT-IR and UV-vis spectroscopies and density functional theory (DFT). Optimized geometry and vibrational frequencies of the title compound in the ground state have been computed by using B3LYP with the 6-311G+(d,p) basis set. HOMO-LUMO energy gap, Non-linear optical properties and NBO analysis of the compound are performed at B3LYP/6-311G+(d,p) level. Additionally, as remarkable properties, antioxidant activity of the title compound (CMPD) has been determined by using different antioxidant test methods i.e. ferric reducing antioxidant power (FRAP), hydrogen peroxide scavenging (HPSA), free radical scavenging (FRSA) and ferrous ion chelating activities (FICA). When compared with standards (BHA, BHT, and α-tocopherol), we have concluded that CPMD has effective FRAP, HPSA, FRSA and FICA.

Allium cepa and Tradescantia pallida bioassays to evaluate effects of the insecticide imidacloprid

The indiscriminate use of pesticides has become a serious environmental concern. Of them, imidacloprid (IMI) is one of the most widely used worldwide. In 2010 in Brazil, 1.934 tonnes of IMI were sold and mainly used for sugarcane crops. Several studies have examined the toxicity of IMI as well as its possible ecological effects. However, few studies have examined its toxicity at the genetic level. This is one of the biggest challenges for the scientific community, which is concerned about the impacts of these contaminants on the environment and human health. In this study, we evaluated the effects of IMI above the genetic material in Allium cepa and Tradescantia pallida following exposure to different concentrations of this insecticide. The results demonstrated that the concentrations tested induced chromosomal alterations and increased the frequency of micronuclei. Therefore, IMI in these concentrations was genotoxic to the tested organisms. These factors should be taken into account when applying this pesticide.

Identification of key amino acid differences contributing to neonicotinoid sensitivity between two nAChR α subunits from Pardosa pseudoannulata

Chemical insecticides are still primary methods to control rice planthoppers in China, which not only cause environmental pollution, insecticide residue and insecticide resistance, but also have negative effects on natural enemies, such as Pardosa pseudoannulata (the pond wolf spider), an important predatory enemy of rice planthoppers. Neonicotinoids insecticides, such as imidacloprid and thiacloprid, are insect-selective nAChRs agonists that are used extensively in the areas of crop protection and animal health, but have hypotoxicity to P. pseudoannulata. In the present study, two nAChR α subunits, Ppα1 or Ppα8, were found to be successfully expressed with rβ2 in Xenopus oocytes, but with much different sensitivity to imidacloprid and thiacloprid on two recombinant receptors Ppα1/rβ2 and Ppα8/rβ2. Key amino acid differences were found in and between the important loops for ligand binding. In order to well understand the relationship between the amino acid differences and neonicotinoid sensitivities, different segments in Ppα8 or Ppα1 with key amino acid differences were introduced into the corresponding regions of Ppα1 or Ppα8 to construct chimeras and then co-expressed with rβ2 subunit in Xenopus oocytes. The results from chimeras of both Ppα8 and Ppα1 showed that segments Δ5, Δ6, and Δ7 contributed to neonicotinoid sensitivities directly between two receptors. Although the segment Δ4 including all loop B region had no direct influences on neonicotinoid sensitivities, it could more remarkably influence neonicotinoid sensitivities when co-introductions with Δ5, Δ6 or Δ7. So, key amino acid differences in these four segments were important to neonicotinoid sensitivities, but the difference in Δ4 was likely ignored because of its indirect effects.

Transcriptional response of soybean to thiamethoxam seed treatment in the presence and absence of drought stress

BACKGROUND

Neonicotinoid insecticides are widely known for their broad-spectrum control of arthropod pests. Recently, their effects on plant physiological mechanisms have been characterized as producing a stress shield, which is predicted to enhance tolerance to adverse conditions. Here we investigate the molecular underpinnings of the stress shield concept using the neonicotinoid thiamethoxam in two separate experiments that compare gene expression. We hypothesized that the application of a thiamethoxam seed treatment to soybean would alter the expression of genes involved in plant defensive pathways and general stress response in later vegetative growth. First, we used next-generation sequencing to examine the broad scale transcriptional effects of the thiamethoxam seed treatment at three vegetative stages in soybean. Second, we selected ten target genes associated with plant defense pathways in soybean and examined the interactive effects of thiamethoxam seed treatment and drought stress on expression using qRT-PCR.

RESULTS

Direct comparison of thiamethoxam-treated and untreated soybeans revealed minor transcriptional differences. However, when examined across vegetative stages, the thiamethoxam seed treatment induced substantial transcriptional changes that were not observed in untreated plants. Genes associated with photosynthesis, carbohydrate and lipid metabolism, development of the cell wall and membrane organization were uniquely upregulated between vegetative stages in thiamethoxam-treated plants. In addition, several genes associated with phytohormone and oxidative stress responses were downregulated between vegetative stages. When we examined the expression of a subset of ten genes associated with plant defense and stress response, the application of thiamethoxam was found to interact with drought stress by enhancing or repressing expression. In drought stressed plants, thiamethoxam induced (upregulated) expression of a thiamine biosynthetic enzyme (THIZ2) and gibberellin regulated protein (GRP), but repressed (downregulated) the expression of an apetala 2 (GmDREB2A;2), lipoxygenase (LIP), and SAM dependent carboxyl methyltransferase (SAM).

CONCLUSIONS

We found evidence that a thiamethoxam seed treatment alters the expression soybean genes related to plant defense and stress response both in the presence and absence of drought stress. Consistent with the thiamethoxam stress shield concept, several genes associated with phytohormones showed enhanced expression in drought stressed plants.

Botanicals, selective insecticides, and predators to control Diaphorina citri (Hemiptera: Liviidae) in citrus orchards

The Asian citrus psyllid (ACP) Diaphorina citri Kuwayama vectors pathogens that cause huanglongbing (HLB) or citrus greening devastating and economically important disease present in most citrus growing regions. Young citrus shoots are required for psyllid reproduction and development. During winter citrus trees produce little or no new growth. Overwintering adults reproduce in spring on newly emerging shoots also attractive to other pests and beneficial insects. Botanicals and relatively selective insecticides could help to conserve beneficial insects and reduce pest resistance to insecticides. Sprays of Azadirachtin (Neem), Tropane (Datura), Spirotetramat, Spinetoram, and broad-spectrum Imidacloprid were evaluated to control ACP in spring and summer on 10-year-old "Kinow" Citrus reticulata Blanco trees producing new growth. Psyllid populations were high averaging 5-9 nymphs or adults per sample before treatment application. Nymphs or adults were significantly reduced to 0.5-1.5 per sample in all treatments for 3 weeks, average 61%-83% reduction. No significant reduction in ladybeetles Adalia bipunctata, Aneglei scardoni, Cheilomenes sexmaculata, and Coccinella septempunctata was observed. Syrphids, spiders and green lacewings were reduced in treated trees except with Tropane. Studies are warranted to assess impact of these predators on ACP and interaction with insecticides. Observed reduction in ACP populations may not be enough considering its reproductive potential and role in the spread of HLB. Follow-up sprays may be required to achieve additional suppression using rotations of different insecticides.

Identification of promoter polymorphisms in the cytochrome P450 CYP6AY1 linked with insecticide resistance in the brown planthopper, Nilaparvata lugens

Imidacloprid resistance in the brown planthopper, Nilaparvata lugens, is primarily the result of the over-expression of cytochrome P450 monooxygenases. Here, a field-collected strain of N. lugens was shown to be highly resistant to both imidacloprid and buprofezin. Insecticide exposure and quantitative real-time PCR revealed that its resistance was mainly associated with a cytochrome P450 gene, CYP6AY1. CYP6AY1 is known to metabolize imidacloprid but its effect on buprofezin is unclear. In the 5'-untranslated region of CYP6AY1, a novel alternative splicing was detected. After a 1990-bp promoter region was cloned, its basal luciferase activity was assessed. Furthermore, genotyping studies identified 12 variations in the promoter region that discriminated between the field-collected and control strain. Finally, survival bioassays revealed a single nucleotide polymorphism and an insertion-deletion polymorphism linked to buprofezin and imidacloprid resistance. Mutagenesis of these sites enhanced the promoter activity of CYP6AY1. These results suggest that promoter polymorphisms may affect P450-mediated multiple insecticide resistance of pests.

Variable concentration of soil-applied insecticides in potato over time: implications for management of Leptinotarsa decemlineata

BACKGROUND

Select populations of Colorado potato beetle, Leptinotarsa decemlineata, in Wisconsin have recently become resistant to soil-applied neonicotinoids in potato. Sublethal insecticide concentrations persisting in foliage through the growing season may select for resistance over successive years of use. Over the 2 years of this study, the aim was to document the in-plant insecticide concentrations over time that result from four different types of soil-applied insecticide delivery for thiamethoxam and imidacloprid in potato, and to measure the impact upon L. decemlineata populations following treatments. After plant emergence, insect life stages were counted and plant tissue was assayed weekly for nine consecutive weeks using ELISA.

RESULTS

Peak concentration of both imidacloprid and thiamethoxam occurred in the first sample week following plant emergence. The average concentration of both insecticides dissipated sharply over time as the plant canopy expanded 50 days after planting in all delivery treatments. Both insecticides were detected at low levels during the later weeks of the study. Among-plant concentrations of both neonicotinoids were highly variable throughout the season. Populations of L. decemlineata continued to develop and reproduce throughout the period of declining insecticide concentrations.

CONCLUSION

Sublethal, chronic exposure to soil-applied systemic insecticides resulting from these delivery methods may accelerate selection for resistant insects in potato.

[Stress effects of imidacloprid on RSV in rice plants]

The rice stripe disease is a viral disease transmitted by small brown planthopper, Laodelphax striatellus, which outbroke a few years ago in the Yangtze River basin, especially Jiangsu region, China. To study the effects of imidacloprid stress on rice stripe virus (RSV) in rice plants, the rice seedlings were treated with imidacloprid 1, 2, 3 and 4 times (B1, B2, B3 and B4), respectively, after artificial inoculation by L. striatellus for 48 h, and the expression levels of relative genes including RSV NS3, CP, SP and NSvc4, as well as the protein concentrations of CP and SP were detected at different stages by real-time PCR and Western blotting. The results showed that the effects of imidacloprid treatment on the expression levels of four genes were gene-specific and correlated with application frequencies of imidacloprid. The expression levels of NS3 gene were upregulated in three treatments, and the highest expression level (10.86) was observed 16 days after inoculation in B4 treatment, but a significant down-regulation of NS3 gene was found in all other treatments. The expression levels of CP, SP and NSvc4 genes were down-regulated significantly (0-0.74) in almost all B2 and B3 treatments, while a significant up-regulation was found in half of B1 and B4 treatments, and the highest expression levels of SP gene were observed 16 days after inoculation in B1 (258.89) and B4 (730.54) treatment, respectively. On the other hand, the effects of imidacloprid stress on the expression patterns of CP and SP genes were different from those of CP and SP proteins. For example, the expression level of CP gene was almost no expression (0) 19 days after inoculation in B1 treatment, while significantly up-regulated (23.08) was observdd for CP protein.

Suppression of Cpn10 increases mitochondrial fission and dysfunction in neuroblastoma cells

To date, several regulatory proteins involved in mitochondrial dynamics have been identified. However, the precise mechanism coordinating these complex processes remains unclear. Mitochondrial chaperones regulate mitochondrial function and structure. Chaperonin 10 (Cpn10) interacts with heat shock protein 60 (HSP60) and functions as a co-chaperone. In this study, we found that down-regulation of Cpn10 highly promoted mitochondrial fragmentation in SK-N-MC and SH-SY5Y neuroblastoma cells. Both genetic and chemical inhibition of Drp1 suppressed the mitochondrial fragmentation induced by Cpn10 reduction. Reactive oxygen species (ROS) generation in 3-NP-treated cells was markedly enhanced by Cpn10 knock down. Depletion of Cpn10 synergistically increased cell death in response to 3-NP treatment. Furthermore, inhibition of Drp1 recovered Cpn10-mediated mitochondrial dysfunction in 3-NP-treated cells. Moreover, an ROS scavenger suppressed cell death mediated by Cpn10 knockdown in 3-NP-treated cells. Taken together, these results showed that down-regulation of Cpn10 increased mitochondrial fragmentation and potentiated 3-NP-mediated mitochondrial dysfunction in neuroblastoma cells.

Comparative susceptibility of Bemisia tabaci to imidacloprid in field- and laboratory-based bioassays

BACKGROUND

Bemisia tabaci biotype B is a resistance-prone pest of protected and open agriculture. Systemic uptake bioassays used in resistance monitoring programs have provided important information on susceptibility to neonicotinoid insecticides, but have remained decoupled from field performance. Simultaneous bioassays conducted in field and laboratory settings were compared and related to concentrations of imidacloprid in plant tissue for clearer interpretation of resistance monitoring data.

RESULTS

Mean mortalities of adult whiteflies confined on cantaloupe leaves field-treated with three rates of imidacloprid did not exceed 40% in two trials. In contrast, laboratory bioassays conducted on different subsets of the same whitefly populations yielded concentration-response curves suggestive of susceptibility to imidacloprid in five populations (LC50 values from 1.02 to 6.4) relative to a sixth population (LC50  = 13.8). In the field, densities of eggs and nymphs were significantly lower on the imidacloprid-treated cantaloupes compared with the untreated control, but the margin of control was greater in 2006 than in 2007. The potential impact of imidacloprid on whitefly eggs was explored in a greenhouse test that showed egg mortality occurring in both early (one-day-old) and late (three-day-old) eggs on cotton leaves systemically treated with imidacloprid. Quantification of imidacloprid residues in cotton leaves used routinely in systemic uptake bioassays revealed concentrations that greatly exceeded concentrations found in the field-treated cantaloupe leaves, at least at the three highest solution concentrations used for uptake.

CONCLUSION

Systemic uptake bioassays have been widely used for monitoring B. tabaci resistance to imidacloprid, but without knowledge of imidacloprid concentrations that occur in test leaves relative to field concentrations. Higher mortality observed in systemic uptake bioassays relative to field-treated cantaloupes in this study suggests that field rates of imidacloprid are only partially effective against B. tabaci adults, in contrast to systemic uptake bioassays that showed susceptibility to imidacloprid. The discrepancy between field- and laboratory-based mortalities is probably due to extraordinarily high concentrations of imidacloprid that can occur in leaves of systemic uptake bioassays, potentially skewing perception of susceptibility to imidacloprid. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Differential protein expression in the susceptible and resistant Myzus persicae (Sulzer) to imidacloprid

Myzus persicae, a serious economic agricultural pest, has developed resistance to imidacloprid (IMI), which was widely used to control this aphid worldwide. To gain a better understanding of the mechanisms of IMI resistance in M. persicae, we carried out a comparative proteomic analysis. Total proteins of the IMI-susceptible and resistant strains were extracted and separated by two-dimensional gel electrophoresis. More than 1300 protein spots were reproducibly detected, including 14 that were more abundant and 14 less abundant. Mass spectrometry analysis and database searching helped us to identify 25 differentially abundant proteins. The identified proteins were categorized into several functional groups including signal transduction, RNA processing, protein processing, transport processing, stress response, metabolisms, and cytoskeleton structure, etc. This study is the first analysis of differentially expressed proteins in IMI-susceptible and resistant M. Persicae, and gives new insights into the mechanisms of IMI resistance in M. persicae.

Variation in mortality among populations is higher for pymetrozine than for imidacloprid and spiromesifen in Trialeurodes vaporariorum in greenhouses in Finland

BACKGROUND

Insecticide resistance in Trialeurodes vaporariorum W. is unknown in the species' northern distribution range where it inhabits mainly commercial greenhouses. Resistance development in whiteflies feeding on year-round crops in greenhouses is possible owing to the use of chemical treatments to back up biocontrol. The authors tested the response levels to spiromesifen, pymetrozine and imidacloprid in whiteflies collected from seven greenhouses within a 35 km radius in western Finland.

RESULTS

All except one (PR) population had LC50 values below the recommended concentrations for the tested compounds. However, some populations showed reduced susceptibility to pymetrozine in comparison with the reference susceptible population. Resistance ratios to pymetrozine were highly variable (resistance ratio 0.5-39.7), even among closely located greenhouses, and higher than those for imidacloprid (resistance ratio 1.05-10.5) and spiromesifen (resistance ratio 0.8-11.5). LC50 values and application frequencies of pymetrozine correlated positively among the sampled populations.

CONCLUSION

High variation in resistance levels to pymetrozine among populations within natural whitefly dispersal limits reflects variation in the usage of this compound among individual greenhouse crop producers. Thus, resistance management is recommended at the individual greenhouse crop producer level, even in a dense production cluster. © 2014 Society of Chemical Industry.

Is imidacloprid an effective alternative for controlling pyrethroid-resistant populations of Triatoma infestans (Hemiptera: Reduviidae) in the Gran Chaco ecoregion?

The prevention of Chagas disease is based primarily on the chemical control of Triatoma infestans (Klug) using pyrethroid insecticides. However, high resistance levels, correlated with control failures, have been detected in Argentina and Bolivia. A previous study at our laboratory found that imidacloprid could serve as an alternative to pyrethroid insecticides. We studied the delayed toxicity of imidacloprid and the influence of the blood feeding condition of the insect on the toxicity of this insecticide; we also studied the effectiveness of various commercial imidacloprid formulations against a pyrethroid-resistant T. infestans population from the Gran Chaco ecoregion. Variations in the toxic effects of imidacloprid were not observed up to 72 h after exposure and were not found to depend on the blood feeding condition of susceptible and resistant individuals. Of the three different studied formulations of imidacloprid on glass and filter paper, only the spot-on formulation was effective. This formulation was applied to pigeons at doses of 1, 5, 20 and 40 mg/bird. The nymphs that fed on pigeons treated with 20 mg or 40 mg of the formulation showed a higher mortality rate than the control group one day and seven days post-treatment (p < 0.01). A spot-on formulation of imidacloprid was effective against pyrethroid-resistant T. infestans populations at the laboratory level.

Thiamethoxam resistance selected in the western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae): cross-resistance patterns, possible biochemical mechanisms and fitness costs analysis

The western flower thrips (WFT) Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), an important pest of various crops in the world, has invaded China since 2003. To understand the risks and to determine possible mechanisms of resistance to thiamethoxam in WFT, a resistant strain was selected under the laboratory conditions. Cross-resistance and the possible biochemical resistance mechanisms were investigated in this study. A 15.1-fold thiamethoxam-resistant WFT strain (TH-R) was established after selection for 55 generations. Compared with the susceptible strain (TH-S), the selected TH-R strain showed extremely high level cross-resistance to imidaclothiz (392.1-fold) and low level cross-resistance to dinotefuran (5.7-fold), acetamiprid (2.9-fold) and emamectin benzoate (2.1-fold), respectively. No cross-resistance to other fourteen insecticides was detected. Synergism tests showed that piperonyl butoxide (PBO) and triphenyl phosphate (TPP) produced a high synergism of thiamethoxam effects in the TH-R strain (2.6- and 2.6-fold respectively). However, diethyl maleate (DEM) did not act synergistically with thiamethoxam. Biochemical assays showed that mixed function oxidase (MFO) activities and carboxylesterase (CarE) activity of the TH-R strain were 2.8- and 1.5-fold higher than that of the TH-S strain, respectively. When compared with the TH-S strain, the TH-R strain had a relative fitness of 0.64. The results show that WFT develops resistance to thiamethoxam after continuous application and thiamethoxam resistance had considerable fitness costs in the WFT. It appears that enhanced metabolism mediated by cytochrome P450 monooxygenases and CarE was a major mechanism for thiamethoxam resistance in the WFT. The use of cross-resistance insecticides, including imidaclothiz and dinotefuran, should be avoided for sustainable resistance management.

Characterizing heat shock protein 90 gene of Apolygus lucorum (Meyer-Dür) and its expression in response to different temperature and pesticide stresses

In this study, we cloned a full-length cDNA of heat shock protein (HSP) gene of Apolygus lucorum (Meyer-Dür) [AlHSP90, KC109781] and investigated its expression in response to temperature and pesticide stresses. The open reading frame (ORF) of AlHSP90 is 2,169 bp in length, encoding a 722 amino acid polypeptide with a predicted molecular weight of 82.99 kDa. Transcriptional and translational expression profiles of AlHSP90 under extreme temperature or pesticide stresses were examined by fluorescent real-time quantitative PCR and Western blot. Results showed that the expression profiles of AlHSP90 protein were in high agreement with those of AlHSP90 RNA and indicated that AlHSP90 was not only an important gene for A. lucorum adults in response to extremely high temperature, but also involved in the resistance or tolerance to cyhalothrin, imidacloprid, chlorpyrifos, and emamectin benzoate, especially for female adults to emamectin benzoate and for male adults to cyhalothrin. Transcriptional results of AlHSP90 also confirmed that AlHSP90 was an important gene involved in the resistance or tolerance to both temperature and pesticide stresses. In addition, our study also revealed that ∼24 °C may be the suitable temperature range for A. lucorum survival, which is also confirmed by the results of the expression of AlHSP90, the nymph mortality, and the intrinsic rate of increase (r m) when A. lucorum is reared at six different temperatures. Therefore, these studies are significant in elucidating the AlHSP90 in response to temperature and pesticide stresses and would provide guidance for A. lucorum management with different pesticides or temperatures in fields.

Synthesis and biological activity of fluorescent neonicotinoid insecticide thiamethoxam

Here, we describe the synthesis of two new fluorescent derivatives of thiamethoxam and compared their toxicity on aphid Acyrthosiphon pisum and their mode of action on insect nicotinic acetylcholine receptors expressed on the sixth abdominal ganglion. The compound 3 with two 2-chlorothiazole moieties was found to be more toxic using toxicological bioassays 24 h and 48 h after exposure while compound 4 appeared more active using cockroach ganglionic depolarization. Interestingly, thiamethoxam appeared more effective than component 3 and 4, respectively. Our results demonstrated that component 3 and 4 act as agonists of insect nicotinic acetylcholine receptors.

Susceptibility of cat fleas (Siphonaptera: Pulicidae) to fipronil and imidacloprid using adult and larval bioassays

The monitoring of the susceptibility offleas to insecticides has typically been conducted by exposing adults on treated surfaces. Other methods such as topical applications of insecticides to adults and larval bioassays on treated rearing media have been developed. Unfortunately, baseline responses of susceptible strains of cat flea, Ctenocephalides felis (Bouchè), except for imidacloprid, have not been determined for all on-animal therapies and new classes of chemistry now being used. However, the relationship between adult and larval bioassays of fleas has not been previously investigated. The adult and larval bioassays of fipronil and imidacloprid were compared for both field-collected isolates and laboratory strains. Adult topical bioassays of fipronil and imidacloprid to laboratory strains and field-collected isolates demonstrated that LD50s of fipronil and imidacloprid ranged from 0.11 to 0.40 nanograms per flea and 0.02 to 0.18 nanograms per flea, respectively. Resistance ratios for fipronil and imidacloprid ranged from 0.11 to 2.21. Based on the larval bioassay published for imidacloprid, a larval bioassay was established for fipronil and reported in this article. The ranges of the LC50s of fipronil and imidacloprid in the larval rearing media were 0.07-0.16 and 0.11-0.21 ppm, respectively. Resistance ratios for adult and larval bioassays ranged from 0.11 to 2.2 and 0.58 to 1.75, respectively. Both adult and larval bioassays provided similar patterns for fipronil and imidacloprid. Although the adult bioassays permitted a more precise dosage applied, the larval bioassays allowed for testing isolates without the need to maintain on synthetic or natural hosts.

Use of honeydew production to determine reduction in feeding by Bemisia tabaci (Hemiptera: Aleyrodidae) adults when exposed to cyantraniliprole and imidacloprid treatments

Bemisia tabaci (Gennadius) whitefly populations produce economically important damage to crops by their direct feeding and also by transmitting plant viruses. Although there are several methods to reduce B. tabaci damage, most growers rely on the use of insecticides to decrease populations of this pest. Insecticides that reduce feeding of whitefly adults may also reduce the transmission of viruses that are harmful to crop plants. However, demonstrating the feeding reduction has proved challenging. In this study, water-sensitive paper was used to determine whitefly adult feeding, indirectly through honeydew production, when insects were placed on insecticide-treated and untreated plants. Plant treatments with two formulations of cyantraniliprole (Cyazypyr) showed a reduction in the amount of honeydew produced by B. tabaci adults equivalent to imidacloprid. The reduction in the amount of honeydew produced indicates reduced insect feeding and the possibility for a reduction in virus transmission. Plant treatments with two formulations of cyantraniliprole also resulted in higher mortality than imidacloprid.

Polyacrylamide hydrogels: an effective tool for delivering liquid baits to pest ants (Hymenoptera: Formicidae)

Ant management in urban and natural areas often relies on toxic baits. Liquid baits are highly attractive to pest ants because they mimic natural food sources such as honeydew and nectar, the principal dietary components of many ants. However, liquid bait use has been limited owing to the lack of bait dispensers that are effective, inexpensive, and easy to service. The current study evaluated the potential of water-storing crystals (polyacrylamide spheres) to effectively deliver liquid thiamethoxam baits to laboratory colonies of Argentine ants, Linepithema humile Mayr. Results of laboratory trials show that bait crystals saturated in 25% sucrose solution containing 0.007% thiamethoxam are highly attractive to Argentine ants and highly effective against all castes and life stages, including workers, queens, and brood. Fresh bait crystals were highly effective and required approximately 2 d to kill all workers and approximately 6 d to achieve complete mortality in queens and brood. Results of bait aging tests show that the crystals lose approximately 70% of moisture in 8 h and the duration of outdoor exposure has a significant effect on moisture loss and subsequently bait acceptance and bait efficacy. A gradual decrease in mortality was observed for all castes and life stages as bait age increased. In general, fresh baits and those aged for < 8 h retained their efficacy and caused substantial mortality. Baits aged longer than 8 h were substantially less attractive and less effective. Horizontal transfer tests examined the transfer of thiamethoxam from live treated donors to live untreated recipients. The results show that donor ants that obtain thiamethoxam by feeding on bait crystals effectively transfer it to untreated recipient ants. The level of secondary mortality depended on the donor:recipient ratio, with approximately 40% recipient worker mortality with the 1:5 ratio and 15% recipient worker mortality with 1:10 or 1:20 ratios. However, no queens died in any transfer tests, suggesting that multiple feedings from multiple donors may be necessary to produce queen mortality. The results of the transfer tests demonstrate the role of trophallaxis in the distribution of thiamethoxam and confirm that thiamethoxam is effectively transferred in Argentine ant colonies. The distribution of thiamethoxam within Argentine ant colonies was further examined using protein marking coupled with an enzyme-linked immunosorbent assay to detect the marker. The distribution of thiamethoxam was highly efficient, with 79 +/- 13% of workers testing positive at 15 min and 100 +/- 0% of workers testing positive at 6 h. In summary, the results of this study demonstrate that water-storing crystals effectively deliver thiamethoxam to all castes and life stages of Argentine ants and may offer an effective tool for Argentine ant management.

Intrastriatal transplantation of adenovirus-generated induced pluripotent stem cells for treating neuropathological and functional deficits in a rodent model of Huntington's disease

Induced pluripotent stem cells (iPSCs) show considerable promise for cell replacement therapies for Huntington's disease (HD). Our laboratory has demonstrated that tail-tip fibroblasts, reprogrammed into iPSCs via two adenoviruses, can survive and differentiate into neuronal lineages following transplantation into healthy adult rats. However, the ability of these cells to survive, differentiate, and restore function in a damaged brain is unknown. To this end, adult rats received a regimen of 3-nitropropionic acid (3-NP) to induce behavioral and neuropathological deficits that resemble HD. At 7, 21, and 42 days after the initiation of 3-NP or vehicle, the rats received intrastriatal bilateral transplantation of iPSCs. All rats that received 3-NP and vehicle treatment displayed significant motor impairment, whereas those that received iPSC transplantation after 3-NP treatment had preserved motor function. Histological analysis of the brains of these rats revealed significant decreases in optical densitometric measures in the striatum, lateral ventricle enlargement, as well as an increase in striosome size in all rats receiving 3-NP when compared with sham rats. The 3-NP-treated rats given transplants of iPSCs in the 7- or 21-day groups did not exhibit these deficits. Transplantation of iPSCs at the late-stage (42-day) time point did not protect against the 3-NP-induced neuropathology, despite preserving motor function. Transplanted iPSCs were found to survive and differentiate into region-specific neurons in the striatum of 3-NP rats, at all transplantation time points. Taken together, these results suggest that transplantation of adenovirus-generated iPSCs may provide a potential avenue for therapeutic treatment of HD.

Neonicotinoids interfere with specific components of navigation in honeybees

Three neonicotinoids, imidacloprid, clothianidin and thiacloprid, agonists of the nicotinic acetylcholine receptor in the central brain of insects, were applied at non-lethal doses in order to test their effects on honeybee navigation. A catch-and-release experimental design was applied in which feeder trained bees were caught when arriving at the feeder, treated with one of the neonicotinoids, and released 1.5 hours later at a remote site. The flight paths of individual bees were tracked with harmonic radar. The initial flight phase controlled by the recently acquired navigation memory (vector memory) was less compromised than the second phase that leads the animal back to the hive (homing flight). The rate of successful return was significantly lower in treated bees, the probability of a correct turn at a salient landscape structure was reduced, and less directed flights during homing flights were performed. Since the homing phase in catch-and-release experiments documents the ability of a foraging honeybee to activate a remote memory acquired during its exploratory orientation flights, we conclude that non-lethal doses of the three neonicotinoids tested either block the retrieval of exploratory navigation memory or alter this form of navigation memory. These findings are discussed in the context of the application of neonicotinoids in plant protection.

Transcriptome analyses of the honeybee response to Nosema ceranae and insecticides

Honeybees (Apis mellifera) are constantly exposed to a wide variety of environmental stressors such as parasites and pesticides. Among them, Nosema ceranae and neurotoxic insecticides might act in combination and lead to a higher honeybee mortality. We investigated the molecular response of honeybees exposed to N. ceranae, to insecticides (fipronil or imidacloprid), and to a combination of both stressors. Midgut transcriptional changes induced by these stressors were measured in two independent experiments combining a global RNA-Seq transcriptomic approach with the screening of the expression of selected genes by quantitative RT-PCR. Although N. ceranae-insecticide combinations induced a significant increase in honeybee mortality, we observed that they did not lead to a synergistic effect. According to gene expression profiles, chronic exposure to insecticides had no significant impact on detoxifying genes but repressed the expression of immunity-related genes. Honeybees treated with N. ceranae, alone or in combination with an insecticide, showed a strong alteration of midgut immunity together with modifications affecting cuticle coatings and trehalose metabolism. An increasing impact of treatments on gene expression profiles with time was identified suggesting an absence of stress recovery which could be linked to the higher mortality rates observed.

Pharmacological inhibition of cochlear mitochondrial respiratory chain induces secondary inflammation in the lateral wall: a potential therapeutic target for sensorineural hearing loss

Cochlear lateral wall has recently been reported as a common site of inflammation, yet precise molecular mechanisms of the inflammatory responses remain elucidated. The present study examined the inflammatory responses in the lateral wall following acute mitochondrial dysfunction induced by a mitochondrial toxin, 3-nitropropionic acid (3-NP). Reverse-transcription (RT)-PCR revealed increases in the expression of the proinflammatory cytokines interleukin (IL)-1β and IL-6. Immunohistochemistry showed an increase in the number of activated cochlear macrophages in the lateral wall, which were in close proximity to IL-6-expressing cells. A genome-wide DNA microarray analysis of the lateral wall revealed that 35% and 60% of the genes showing >2-fold upregulation at 1 d and 3 d post-3-NP administration, respectively, were inflammatory genes, including CC- and CXC-type chemokine genes. High expression of CCL-1, 2, and 3 at 1 d, and of CCL-1, 2, 3, 4, and 5, CCR-2 and 5, and CX3CR1 at 3 d post-3-NP administration, coupled with no change in the level of CX3CL1 expression suggested that macrophages and monocytes may be involved in the inflammatory response to 3-NP-mediated injury. Quantitative (q)RT-PCR showed a transient induction of IL-1β and IL-6 expression within 24 h of 3-NP-mediated injury, followed by sustained expression of the chemoattractants, CCL-2, 4 and 5, up until 7 d after injury. The expression of CCL-2 and IL-6 was higher in animals showing permanent hearing impairment than in those showing temporary hearing impairment, suggesting that these inflammatory responses may be detrimental to hearing recovery. The present findings suggest that acute mitochondrial dysfunction induces secondary inflammatory responses in the lateral wall of the cochlear and that the IL-6/CCL-2 inflammatory pathway is involved in monocyte activation. Therefore, these secondary inflammatory responses may be a potential post-insult therapeutic target for treatments aimed at preventing the damage caused by acute mitochondrial dysfunction in the cochlear lateral wall.

Evaluation of three neonicotinoid insecticides against the common pistachio psylla, Agonoscena pistaciae, and its natural enemies

The common pistachio psylla, Agonoscena pistaciae Burckhardt and Lauterer (Hemiptera: Psyllidae), is a key pest in pistachio orchards in Iran. Chemical control is a common method to manage this pest. Compatibility between natural enemies and pesticides is a primary concern in programs of integrated pest management of the psyllid pest. In this research, susceptibility of fifth instar nymphs of Ag. pistaciae and fourth instar larvae of the two most common predators of this pest, Adalia bipunctata L. (Coleoptera: Coccinellidae) and Coccinella undecimpunctata aegyptiaca Reiche, to acetamiprid, thiamethoxam, and imidacloprid was investigated. Probit analysis of concentration-mortality data was conducted to estimate the LC50 value. The results showed that thiamethoxam with an LC50 value of 56.35 mg a.i./L was more toxic to fifth instar nymphs of Ag. pistaciae in comparison to acetamiprid (60.75 mg a.i/L) and imidacloprid (138.21 mg a.i/L) . Imidacloprid with an LC50 value of 218.89 mg a.i/L compared to acetamiprid (222.65 mg a.i/L) and thiamethoxam (232.37 mg a.i/L) had more lethal effects on fourth instar larvae of Ad. bipunctata. However, on the fourth instar larvae of C. undecimpunctata aegyptica, acetamiprid with an LC50 value of 263.44 mg a.i/L was more toxic than thiamethoxam (296.62 mg a.i/L) and imidacloprid (447.82 mg a.i/L). The laboratory findings showed that the three tested insecticides were more toxic to the common pistachio psylla than to its natural predators. Thiamethoxam was the most toxic against Ag. pistaciae. However, its toxicity to the predators was lower than imidacloprid and acetamiprid. This result suggests that thiamethoxam is the best insecticide for control of Ag. pistaciae in combination with predatory lady beetles.

Biotype expression and insecticide response of Bemisia tabaci chemosensory protein-1

Chemosensory proteins (CSPs) are a group of small soluble proteins found so far exclusively in arthropod species. These proteins act in chemical communication and perception. In this study, a gene encoding the Type 1 CSP (BtabCSP1) from the agricultural pest Bemisia tabaci (whitefly) was analyzed to understand sequence variation and expression specificity in different biotypes. Sequence analysis of BtabCSP1 showed significant differences between the two genetically characterized biotypes, B and Q. The B-biotype had a larger number of BtabCSP1 mutations than the Q-biotype. Similar to most other CSPs, BtabCSP1 was more expressed in the head than in the rest of the body. One-step RT-PCR and qPCR analysis on total messenger RNA showed that biotype-Q had higher BtabCSP1 expression levels than biotype-B. Females from a mixed field-population had high levels of BtabCSP1 expression. The interaction of BtabCSP1 with the insecticide thiamethoxam was investigated by analyzing the BtabCSP1 expression levels following exposure to the neonicotinoid, thiamethoxam, in a time/dose-response study. Insecticide exposure increased BtabCSP1 expression (up to tenfold) at 4 and 24 h following 50 or 100 g/ml treatments.

3-Nitropropionic acid induces ovarian oxidative stress and impairs follicle in mouse

Oxidative stress induces many serious reproductive diseases in female mammals and thus poses a serious threat to reproductive health. However, the relationship between reactive oxygen species (ROS)-induced oxidative stress and follicular development, oocyte and embryo quality is not clear. The aim of this study was to investigate the effect of ovarian oxidative stress on the health of follicle and oocyte development. Female ICR mice were dosed with 3-nitropropionic acid (3-NPA) at three different concentrations (6.25, 12.5 and 25 mg/kg) and saline (control) via continuous intraperitoneal injection for 7 days. The treatment with 12.5 mg/kg reduced the weight of mouse ovaries, and significantly increased ROS levels and the activities of antioxidant enzymes--total superoxide dismutase (T-SOD), glutathione peroxidase (GPx) and catalase (CAT)--in granulosa cells and ovarian tissues, but not in other tissues (brain, liver, kidney and spleen). The same treatment significantly increased the percentage of atretic large follicles, and reduced the number of large follicles, the number of ovulated oocytes, and the capacity for early embryonic development compared with controls. It also significantly decreased the ratio of Bcl-2 to Bax, while causing an increase in the mRNA expression of (SOD2, CAT and GP X) and ROS levels in granulosa cells. Collectively, these data indicate that 3-NPA induces granulosa cell apoptosis, large follicle atresia, and an increase of ROS levels in the ovary. Therefore, we have established an in vivo model of ovarian oxidative stress for studying the mechanism of resulting damage induced by free radicals and for the screening of novel antioxidants.

Activity of chlorantraniliprole and thiamethoxam seed treatments on life stages of the rice water weevil as affected by the distribution of insecticides in rice plants

BACKGROUND

The systemic insecticides chlorantraniliprole (CAP) and thiamethoxam (TMX), applied to rice as seed treatments, may affect multiple life stages of the rice water weevil, Lissorhoptrus oryzophilus. Effects of CAP and TMX on adult survival, egg-laying and first- and late-instar survivals were determined by infesting plants treated as seeds with different rates of insecticides. The biological activity was related to insecticidal concentrations in leaves, shoots and roots.

RESULTS

CAP did not affect adult survival but decreased egg numbers and reduced the survival of the first and late instars. The greatest reduction in weevil population occurred in late instars feeding on roots. In contrast, TMX reduced adult survival and egg and larval numbers. The high biological activity of CAP on root-feeding stages was consistent with the accumulation of CAP in roots, whereas in TMX-treated plants the high activity on adults correlated with high concentrations of TMX in leaves and stems.

CONCLUSIONS

The differential activity of insecticides on adults suggests poor inherent potency of CAP as an adulticide and/or its limited systemicity in foliage. The distribution of insecticide in specific plant parts can be attributed to the different physicochemical properties of CAP and TMX. The field implications of this research on management of L. oryzophilus are discussed.

CONTROL OF DIABROTICA VIRGIFERA VIRGIFERA LE CONTE IN MAIZE SEED TREATMENT

During the last decade of XX century, Diabrotica virgifera virgifera Le Conte became an important introduced harmful species in maize production in the northern Serbia region. The aim of this work was to assess the efficacy of imidacloprid based insecticides formulated for seed treatment in the control of D. v. virgifera. Experiments were set at two localities (Čurug--two-year maize culturing; Bečej--four-year maize culturing) in 2013, according to OEPP (PP 1/212(1) 2004) method. Imidacloprid based insecticide (600 g a.i./L) was applied at rates 0.36; 0.55; 0,7 and 0.8 L/100 kg of maize seeds (hybrids NS 5041 and NS 640 Ultra). The degree of maize root damage was determined according to scale 1-6 (http://www.ent.iastate.edu/-pest/rootworm/nodeinjury/nodeinjury.htm). A number of damaged plants was also registered and expressed in percents, as well as the development of adventitious roots. Significance of differences between root damages and number of damaged plants between treatments was tested using ANOVA. Regardless on localities and applied rates, maize roots in treatments with imidacloprid were significantly less damaged by larvae D. v. virgifera (1.1-1.4) compared to the control (3.7-4.1). Also, a significant reduction in percent of damaged plants (5.0-20%) was registered compared to the control (90-97.5%). At both localities in treatments with imidacloprid adventitious roots were well developed in 60.5 to 91% of plants compared to the control were it was the case in 10-27.5% plants. It is important to emphasize that roots were significantly more developed in treated variants compared to the control. Based on the obtained results it can be concluded that imidacloprid, regardless on its future status and restraints/limitations in maize seed treatment, provided efficient protection of maize roots from D. v. virgifera larvae, even at rate twice lower (0.36) than recommended (0.8 L/100 kg seeds), which justifies the application of lower quantities of imidacloprid in practice.

Behavioural avoidance and enhanced dispersal in neonicotinoid-resistant Myzus persicae (Sulzer)

BACKGROUND

The peach potato aphid Myzus persicae is a major agricultural pest capable of transmitting over 100 plant viruses to a wide range of crops. Control relies largely upon treatment with neonicotinoid insecticides such as thiamethoxam (TMX). In 2009, a strain denoted FRC, which exhibits between 255- and 1679-fold resistance to current neonicotinoids previously linked to metabolic and target site resistance, was discovered in France. Dispersal behaviour may potentially further enhance the resistance of this strain. This study investigated this possibility and is the first to compare the dispersal behaviour of aphid clones of the same species with differing levels of neonicotinoid resistance.

RESULTS

Comparing the dispersal behaviour of the FRC strain with that of a clone of lower neonicotinoid resistance (5191A), and a susceptible clone (US1L) highlighted several differences. Most importantly, the FRC strain exhibited an increased ability to locate untreated areas when presented with an environment consisting of both TMX-treated and untreated plant tissue.

CONCLUSION

The altered dispersal behaviour of the FRC may partially account for the high level of neonicotinoid resistance exhibited by this strain in the field. Since the dispersal of aphid vectors is key to the transmission of viruses across crop fields this has implications for current crop protection practice.

Imidacloprid induces changes in the structure, genetic diversity and catabolic activity of soil microbial communities

This is the first report describing the effect of imidacloprid applied at field rate (FR, 1 mg/kg of soil) and 10 times the FR (10*FR, 10 mg/kg of soil) on the structural, genetic and physiological diversity of soil bacterial community as determined by the phospholipid fatty acid (PLFA), the denaturing gradient gel electrophoresis (DGGE), and the community level physiological profile (CLPP) approaches. PLFA profiles showed that imidacloprid significantly shifted the microbial community structure and decreased the biomass of the total, bacterial and fungal PLFAs, however, this effect was transient at the FR dosage. The alterations in DGGE patterns caused by imidacloprid application, confirmed considerable changes in the overall richness and diversity of dominant bacteria. Although, as a result of imidacloprid application, the metabolic activity of microbial communities was generally lower, the richness and functional biodiversity of the soil microbial community were not negatively affected. In general, the analysis of the variance indicated that the measured parameters were significantly affected by treatment and the incubation time, however, the incubation time effect explained most of the observed variance. Imidacloprid degradation and the appearance of some new bands in DGGE profiles suggest the evolution of bacteria capable of degrading imidacloprid among indigenous microflora.

Laboratory assessment of Beauveria bassiana (Hypocreales: Clavicipitaceae) strain GHA for control of Listronotus maculicollis (Coleoptera: Curculionidae) adults

Bioassays were designed to evaluate Beauveria bassiana (Balsamo) Vuillemin strain GHA against Listronotus maculicollis (Kirby) adults. B. bassiana and its "inert" carrier oil in the product BotaniGard and the inert carrier oil alone provided 99 and 96% mortality, respectively, in petri dish assays 1 d after treatment when applied in 1 ml water. When the same treatments were applied in 0.5 ml of carrier water, mortality was only 1.4 and 0.7%, respectively, 1 d after treatment. After 10 d in petri dishes, B. bassiana and its inert carrier oil and the inert carrier oil alone applied in 0.5 ml water showed 77 and 9% mortality, respectively. When one-tenth the label dosage of B. bassiana and inert carrier oil was combined with neonicotinoids applied in 1 ml water, there were significant increases in weevil mortality over the neonicotinoids alone 1 d after treatment. When 88.7% of one-tenth the label dosage of inert carrier oil alone was combined with neonicotinoids clothianidin, imidacloprid, and dinotefuran applied in 1 ml water, there was also a significant increases (38%) with clothianidin in weevil mortality over clothianidin alone 1 d after treatment. B. bassiana and its inert carrier oil provided 28, 50, and 78% mortality at the highest label dosage and 47, 76, and 89% mortality at 4x the highest label dosage in turf plug assays at 7, 10, and 14 d after treatment. Addition of 5 or 20% MycoMax (a nutrient source for B. bassiana) did not significantly increase mortality.

Two cytochrome P450 genes are involved in imidacloprid resistance in field populations of the whitefly, Bemisia tabaci, in China

The sweet potato whitefly, Bemisia tabaci (Gennadius) (Hemiptera:Aleyrodidae), is an invasive and damaging pest of field crops worldwide. The neonicotinoid insecticide imidacloprid has been widely used to control this pest. We assessed the species composition (B vs. Q), imidacloprid resistance, and association between imidacloprid resistance and the expression of five P450 genes for 14-17 B. tabaci populations in 12 provinces in China. Fifteen of 17 populations contained only B. tabaci Q, and two populations contained both B and Q. Seven of 17 populations exhibited moderate to high resistance to imidacloprid, and eight populations exhibited low resistance to imidacloprid, compared with the most susceptible field WHHB population. In a study of 14 of the populations, resistance level was correlated with the expression of the P450 genes CYP6CM1 and CYP4C64 but not with the expression of CYP6CX1, CYP6CX4, or CYP6DZ7. This study indicates that B. tabaci Q has a wider distribution in China than previously reported. Resistance to imidacloprid in field populations of B. tabaci is associated with the increased expression of two cytochrome P450 genes (CYP6CM1 and CYP4C64).

Biochemical mechanisms of imidacloprid resistance in Nilaparvata lugens: over-expression of cytochrome P450 CYP6AY1

Imidacloprid is a key insecticide extensively used for control of Nilaparvata lugens, and its resistance had been reported both in the laboratory selected strains and field populations. A target site mutation Y151S in two nicotinic acetylcholine receptor subunits and enhanced oxidative detoxification have been identified in the laboratory resistant strain, contributing importantly to imidacloprid resistance in N. lugens. To date, however, imidacloprid resistance in field population is primarily attributable to enhanced oxidative detoxification by over-expressed P450 monooxygenases. A resistant strain (Res), originally collected from a field population and continuously selected in laboratory with imidacloprid for more than 40 generations, had 180.8-fold resistance to imidacloprid, compared to a susceptible strain (Sus). Expression of different putative P450 genes at mRNA levels was detected and compared between Res and Sus strains, and six genes were found expressed significantly higher in Res strain than in Sus strain. CYP6AY1 was found to be the most different expressed P450 gene and its mRNA level in Res strain was 17.9 times of that in Sus strain. By expressing in E. coli cells, CYP6AY1 was found to metabolize imidacloprid efficiently with initial velocity calculated of 0.851 ± 0.073 pmol/min/pmol P450. When CYP6AY1 mRNA levels in Res strain was reduced by RNA interference, imidacloprid susceptibility was recovered. In four field populations with different resistance levels, high levels of CYP6AY1 transcript were also found. In vitro and in vivo studies provided evidences that the over-expression of CYP6AY1 was one of the key factors contributing to imidacloprid resistance in the laboratory selected strain Res, which might also be the important mechanism for imidacloprid resistance in field populations, when the target site mutation was not prevalent at present.

Attractive toxic sugar baits: control of mosquitoes with the low-risk active ingredient dinotefuran and potential impacts on nontarget organisms in Morocco

We evaluated the efficacy of attractive toxic sugar baits (ATSB) in the laboratory and field with the low-risk active ingredient dinotefuran against mosquito populations. Preliminary laboratory assays indicated that dinotefuran in solution with the sugar baits was ingested and resulted in high mortality of female Culex quinquefasciatus Say and Aedes aegypti Linnaeus. Field studies demonstrated >70% reduction of mosquito populations at 3 wk post-ATSB application. Nontarget feeding of seven insect orders-Hymenoptera, Lepidoptera, Coleoptera, Diptera, Hemiptera, Orthoptera, and Neuroptera-was evaluated in the field after application of attractive sugar baits (ASB) on vegetation by dissecting the guts and searching for food dye with a dissecting microscope. Nontargets were found stained with ASB 0.9% of the time when the application was applied on green nonflowering vegetation. Only two families were significantly impacted by the ASB application: Culicidae (mosquitoes) and Chironomidae (nonbiting midges) of the order Diptera. Pollinators of the other insect orders were not significantly impacted. No mortality was observed in the laboratory studies with predatory nontargets, wolf spiders or ground beetles, after feeding for 3 d on mosquitoes engorged on ATSB applied to vegetation. Overall, this novel control strategy had little impact on nontarget organisms, including pollinators and beneficial insects, and was effective at controlling mosquito populations, further supporting the development of ATSB for commercial use.

Transgenerational shifts in reproduction hormesis in green peach aphid exposed to low concentrations of imidacloprid

Hormesis is a biphasic phenomenon that in toxicology is characterized by low-dose stimulation and high-dose inhibition. It has been observed in a wide range of organisms in response to many chemical stressors, including insects exposed to pesticides, with potential repercussions for agriculture and pest management. To address questions related to the nature of the dose-response and potential consequences on biological fitness, we examined transgenerational hormesis in the green peach aphid, Myzus persicae, when exposed to sublethal concentrations of the insecticide imidacloprid. A hormetic response in the form of increased reproduction was consistently observed and a model previously developed to test for hormesis adequately fit some of our data. However, the nature of the dose-response differed within and across generations depending upon the duration and mode of exposure. Decreased reproduction in intermediate generations confirmed that fitness tradeoffs were a consequence of the hormetic response. However, recovery to levels of reproduction equal to that of controls in subsequent generations and significantly greater total reproduction after four generations suggested that biological fitness was increased by exposure to low concentrations of the insecticide, even when insects were continuously exposed to the stressor. This was especially evident in a greenhouse experiment where the instantaneous rate of population increase almost doubled and total aphid production more than quadrupled when aphids were exposed to potato plants systemically treated with low amounts of imidacloprid. Our results show that although fitness tradeoffs do occur with hormetic responses, this does not necessarily compromise overall biological fitness.

Translation of viral mRNAs that do not require eIF4E is blocked by the inhibitor 4EGI-1

High throughput screening has rendered new inhibitors of eukaryotic protein synthesis. One such molecule, 4EGI-1 has been reported to selectively block the initiation factor eIF4E. We have investigated the action of this inhibitor on translation directed by several viral mRNAs which, in principle, do not utilize eIF4E. We found that 4EGI-1 inhibits translation directed by poliovirus IRES, in rabbit reticulocyte lysates, to a similar extent as capped mRNA. Moreover, 4EGI-1 inhibits translation driven by poliovirus IRES, both in vitro and in cultured cells, despite cleavage of eIF4G by picornavirus proteases. Finally, translation of vesicular stomatitis virus mRNAs and Sindbis virus subgenomic mRNA is blocked by 4EGI-1 in infected cells to a similar extent as cellular mRNAs. These findings cast doubt on the selective action of this inhibitor, and suggest that this molecule may affect other steps in protein synthesis unrelated to cap recognition by eIF4E.