Activity of flonicamid on the sweet potato whitely Bemisia tabaci (Homoptera: Aleyrodidae) and its natural enemies

Sublethal effects of flonicamid on the population growth of the grain aphid Rhopalosiphum padi (L.) (Hemiptera: Aphididae)

Rhopalosiphum padi is an important grain pest, causing severe losses during crop production. As a systemic insecticide, flonicamid can control piercing-sucking pests efficiently. In our study, the lethal effects of flonicamid on the biological traits of R. padi were investigated via a life table approach. Flonicamid is highly efficiently toxic to R. padi, with an LC50 of 9.068 mg L-1. The adult longevity and fecundity of the R. padi F0 generation were markedly reduced under the LC25 and LC50 concentrations of flonicamid exposure. In addition, negative transgenerational effects on R. padi were observed under exposure to lethal concentrations of flonicamid, with noticeable decreases in the reproductive period, adult longevity, total longevity, and total fecundity of the F1 generation under the LC25 concentration of flonicamid. Furthermore, the third nymph stage (N3), preadult stage, duration of the adult pre-reproductive period, duration of the total pre-reproductive period, reproductive period, adult longevity, total longevity, and total fecundity of the F1 generation were significantly lower under treatment with the LC50 concentration of flonicamid. The life table parameters were subsequently analysed, revealing that the intrinsic rate of increase (rm) and the net reproductive rate (R0) were significantly lower but that the finite rate of increase (λ) and the mean generation time (T) were not significantly different under the LC25 and LC50 concentrations of flonicamid. These data are beneficial for grain aphid control and are critical for exploring the role of flonicamid in the integrated management of this key pest.

Involvement of Inwardly Rectifying Potassium (Kir) Channels in the Toxicity of Flonicamid to Drosophila melanogaster

Inwardly rectifying potassium (Kir) channels regulate essential physiological processes in insects and have been identified as potential targets for developing new insecticides. Flonicamid has been reported to inhibit Kir channels, disrupting the functions of salivary glands and renal tubules. However, the precise molecular target of flonicamid remains debated. It is unclear whether flonicamid directly targets Kir channels or acts on other sites involved in the activation of transient receptor potential vanilloid (TRPV) channels. In this study, we observed that flonicamid is more toxic to flies than its metabolite, flumetnicam. This higher toxicity is difficult to reconcile if nicotinamidase is the active target, as flonicamid does not inhibit nicotinamidase. An alternative explanation is that flonicamid and flumetnicam may have distinct targets or act on multiple targets. Furthermore, reducing the expression of three individual Kir genes in the salivary glands of D. melanogaster significantly decreased the flies' susceptibility to both flonicamid and flumetnicam. The double knockdown of Kir1 with Kir3 or Kir2 with Kir3 further reduced the flies' sensitivity to both compounds. These findings confirm the involvement of Kir channels in mediating the toxic effects of flonicamid on flies. Overall, this study offers new insights into the physiological roles of insect Kir channels and flonicamid toxicity.

Toxicity of Flonicamid to Diaphorina citri (Hemiptera: Liviidae) and Its Identification and Expression of Kir Channel Genes

Flonicamid is a selective insecticide effective against piercing-sucking insects. Although its molecular target has been identified in other species, the specific effects and detailed mechanism of action in Diaphorina citri Kuwayama remain poorly understood. In this study, we determined that the LC50 of flonicamid for D. citri adults was 16.6 mg AI L-1 after 4 days of exposure. To explore the relevant mechanisms, the treatments with acetone and with 20 mg AI L-1 flonicamid for 96 h were collected as samples for RNA-Seq. The analysis of the transcriptomes revealed 345 differentially expressed genes (DEGs) in D. citri adults subjected to different treatments. Among these DEGs, we focused on the inward-rectifying potassium (Kir) channel genes, which have been extensively studied as potential targets of flonicamid. Three Kir subunit genes (Dckir1, Dckir2, Dckir3) in D. citri were successfully cloned and identified. Furthermore, the expression profiles of these DcKirs were investigated using RT-qPCR and showed that their expression significantly increased after D. citri eclosion to adulthood, particularly for DcKir3. The DcKirs were predominantly expressed in gut tissues, with DcKir1 and DcKir2 exhibiting high expression levels in the hindgut and midgut, respectively, while DcKir3 showing high expression in the midgut and Malpighian tubules. This study provides insights into the potential roles of Kir subunits in D. citri and enhances our understanding of the physiological effects of flonicamid in this pest.

Intergenerational Sublethal Effects of Flonicamid on Cotton Aphid, Aphis gossypii: An Age-Stage, Two-Sex Life Table Study

Flonicamid is a novel systemic insecticide widely used against aphids. However, the intergenerational sublethal effects of flonicamid on cotton aphid, Aphis gossypii, have not been fully studied. This study aimed to evaluate the sublethal effects of flonicamid on the biological parameters of adult A. gossypii (F0) and its subsequent intergenerational effects on the offspring (F1 generation) through age-stage, two-sex life table analysis. The results of the bioassays indicate that flonicamid exhibits significant toxicity toward adult A. gossypii, as evidenced by an LC50 value of 0.372 mg L-1 after a 48-h exposure period. The longevity, fecundity, and reproductive days of adult cotton aphids (F0) were significantly decreased when treated with the sublethal concentrations of flonicamid. The pre-adult stage exhibited an increase, whereas the adult longevity, total longevity, and fecundity experienced a notable decrease in F1 aphids after the exposure of F0 aphids to sublethal concentrations of flonicamid. Furthermore, the key demographic parameters, including r, λ, R0, and RPd, showed a significant decrease, while the total pre-reproductive period (TPRP) experienced a significant increase in the F1 generation. Collectively, our findings indicate that sublethal concentrations of flonicamid impact the demographic parameters of A. gossypii, resulting in suppression of population growth. This study presents comprehensive information on the overall impact of flonicamid on A. gossypii, which could potentially aid in managing this major pest.

Pollen provisioning attenuates pesticide side-effects on a phytoseiid predator

BACKGROUND

Biological control with predatory mites is applied against pests in greenhouse crops. Chemical control with the use of selective, reduced-risk pesticides, is an important component of Integrated Pest Management (IPM) programs, that often needs to be combined with biological control. Here, we evaluated the effect of plant pollen when used as supplementary food on the survival, reproduction and predation of the predatory mite Amblydromalus limonicus (Acari: Phytoseiidae) after exposing young larvae and adults to flonicamid, an insecticide of moderate toxicity to phytoseiids. Pollen is an important alternative food for generalist phytoseiids ensuring survival and supporting populations build-up during periods of prey scarcity. Two regimes of cattail (Typha angustifolia L.) pollen differing in application frequency were used. In the first, the total amount of pollen was supplied once, within 30 min after insecticide application, whereas in the second regime, the same amount of pollen was supplied gradually, i.e., every 48 h.

RESULTS

Regardless of the frequency of application, pollen provisioning results in a reduction in prey (thrips) consumption relative to the control (no pollen provisioning). Nevertheless, when adult mites were directly exposed to flonicamid residues, pollen provisioning attenuated the reduction in prey consumption as compared to the control. In addition, the gradual (every 48 h) provisioning of pollen to adult predators exposed to flonicamid residues impacted positively the intrinsic rate of population increase (rm) of A. limonicus as compared to when feeding on prey.

CONCLUSION

Our results reveal an unexpected role of pollen provisioning in alleviating pesticides side-effects on phytoseiids. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Impact of sublethal concentrations of flonicamid on key demographic parameters and feeding behavior of Schizaphis graminum

Flonicamid is a novel systemic insecticide that efficiently controls sap-sucking insect pests. However, the impact of sublethal concentrations of flonicamid on key demographic parameters and the feeding behavior of greenbug, Schizaphis graminum has not yet been studied. In this study, we used the age stage, two-sex life table approach, and electrical penetration graphs (EPGs) to investigate the sublethal effects of flonicamid on the biological traits and feeding behavior of S. graminum. Bioassays showed that flonicamid possesses high toxicity to adult S. graminum with LC50 of 5.111 mg L-1 following 48 h exposure. Sublethal concentrations of flonicamid (LC5 and LC10) significantly decreased the longevity and fecundity of directly exposed parental aphids (F0), while the reproductive days were reduced only at LC10. The pre-adult stage and total pre-reproductive period (TPRP) increased in F1 individuals after exposure of F0 aphids to the sublethal concentrations of flonicamid. Furthermore, the adult longevity, fecundity and key demographic parameters (R0, r, and λ) were significantly reduced in progeny generation (F1). EPG recordings showed that the total duration of phloem sap ingestion and concurrent salivation (E2) decreased substantially in F0 and F1 aphids after exposure to LC5 and LC10 of flonicamid. Taken together, our results showed that the sublethal concentrations of flonicamid affect the demographic parameters and feeding behavior that ultimately suppress the population growth of S. graminum. This study provides in-depth information about the overall effects of flonicamid on S. graminum that might help to manage this key pest.

Reducing Expression of Salivary Protein Genes by Flonicamid Partially Contributed to Its Feeding Inhibition of the Brown Planthopper on Rice

Flonicamid inhibits the feeding of piercing-sucking pests as a selective systemic insecticide. The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most serious pests on rice. During feeding, it uses its stylet to collect sap by penetrating the phloem, and at the same time, it delivers saliva into the rice plant. Insect salivary proteins play important roles in feeding and interacting with plants. Whether flonicamid affects the expression of salivary protein genes and then inhibits the feeding of BPH is not clear. Here, from 20 functionally characterized salivary proteins, we screened five salivary proteins (NlShp, NlAnnix5, Nl16, Nl32, and NlSP7) whose gene expressions were significantly inhibited by flonicamid. We performed experimental analysis on two of them (Nl16 and Nl32). RNA interference of Nl32 significantly reduced the survival rate of BPH. Electrical penetration graph (EPG) experiments showed that both flonicamid treatment and knockdown of Nl16 and Nl32 genes significantly reduced the feeding activity of N. lugens in the phloem and also reduced the honeydew excretion and fecundity. These results suggested that the inhibition of flonicamid on the feeding behavior in N. lugens might be partially attributed to its effect on the expression of salivary protein genes. This study provides a new insight into the mechanism of action of flonicamid on insect pests.

An insecticide target in mechanoreceptor neurons

Hundreds of neurotoxic insecticides are currently in use. However, only a few direct targets have been identified. Here, using Drosophila and the insecticide flonicamid, we identified nicotinamidase (Naam) as a previous unidentified molecular target for an insecticide. Naam is expressed in chordotonal stretch-receptor neurons, and inhibition of Naam by a metabolite of flonicamid, TFNA-AM (4-trifluoromethylnicotinamide), induces accumulation of substrate nicotinamide and greatly inhibits negative geotaxis. Engineered flies harboring a point mutation in the active site show insecticide resistance and defects in gravity sensing. Bees are resistant to flonicamid because of a gene duplication, resulting in the generation of a TFNA-AM-insensitive Naam. Our results, in combination with the absence of genes encoding Naam in vertebrate genomes, suggest that TFNA-AM and potential species-specific Naam inhibitors could be developed as novel insecticides, anthelmintics, and antimicrobials for agriculture and human health.

An impact assessment of insecticides application on the non-targeted mosquito Aedes albopictus (Skuse) in Punjab rice fields, Pakistan

Insecticidal control of insect pests of rice crop may influence the environment and nontarget species in rice fields. Aedes albopictus, one of the most common nontarget species present in rice fields, received lethal and sublethal exposures to insecticides used in rice cultivated fields. The present work explores the effects of insecticides in six non-targeted Ae. albopictus strains collected from rice fields with a history of insecticidal usage in comparison with a laboratory susceptible reference strain (REF) and a strain (LHR) collected from a rice field with no, or minimal, history of insecticidal usage. Two types of effects, the resistance development and performance of biological traits, were studied by selecting seven commonly used insecticides in rice fields in Punjab, Pakistan. The results revealed that the strains collected from the rice fields with histories of insecticidal usage exhibited significant levels of resistance to flonicamid, chlorantraniliprole, gamma-cyhalothrin, fipronil, monomehypo, triazophos, and carbofuran, when compared with REF and LHR strains. In addition, Ae. albopictus strains revealed a significantly weaker performance of biological traits (rate of pupae formation, survival of male and female adults (except females of OKR and MTN strains), and ovipositing females) than those of the REF and LHR strains. However, the fecundity of all field strains was only significantly different with that of the REF strain. In conclusion, the results highlight the problem of the negative effects of insecticidal usage in rice fields on nontarget species present in the same environment, and emphasize the need to adopt pest management activities that are safe for the environment.

Evaluation of the Effect of Fungatol and Gamma-T-ol on the Emergence and Adult Parasitoid Survival of Mummies of Cotton Aphids Parasitized by Aphidius colemani

Simple Summary

Biological control can be used as an alternative control measure to reduce pesticide resistance. Unfortunately, many biological control agents, such as natural enemies of pests, are susceptible to a broad spectrum of pesticides. This creates a potential problem when these two components are utilized together. Therefore, it is necessary to find alternatives that are not harmful to natural enemies but also have the potential to replace synthetic pesticides. Essential oils (EOs) are widely used in crop protection and organic agriculture. The EO formulations evaluated in this study are new botanical pesticides that play an important role in agriculture. EOs are available as an alternative to synthetic pesticides. Two blends (Fungatol and Gamma-T-ol) are mostly composed of Alpha Tops, and Gamma Tops were assessed for their effects on the aphid parasitoid Aphidius colemani in laboratory and glasshouse trials. According to the International Organization for Biological Control (IOBC) classification, they were found to be safe or only slightly toxic, making them potential candidates for introduction into an integrated pest control program for aphids.

Abstract

Beneficial insects play a major role in controlling pest populations. In sustainable agricultural production systems, control methods compatible with integrated pest management (IPM) are preferred over broad-spectrum pesticides. EOs from aromatic plants may provide a new and safe alternative to synthetic chemicals. In this research, the efficacy of Fungatol, Gamma-T-ol, Fungatol plus neem, and Gamma-T-ol plus neem was evaluated against Aphidius colemani Viereck (Hymenoptera: Braconidae; Aphidiidae), the parasitoid of the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae). Under laboratory and greenhouse conditions, five different concentrations of each formulation were applied to parasitized mummies and adult parasitoids. Results for parasitoid emergence from aphid mummies sprayed with different concentrations of Fungatol, Gamma-T-ol, Fungatol plus neem, and Gamma-T-ol plus neem in the laboratory and glasshouse showed that the formulations did not adversely affect adult emergence as rates above 60% were observed. For residual toxicity tests done by exposing adult parasitoids to a fresh, dry biopesticide film sprayed on glass plates, less than 20% mortality was observed after 48 h of exposure. Adult longevity tests revealed that the highest concentrations of some of the formulations evaluated were slightly toxic to A. colemani. According to the IOBC rating, our results indicated that most of the tested concentrations for each formulation were harmless to A. colemani. Based on the above results, it may be proposed that the formulations evaluated in this study are potential botanical pesticide candidates for incorporation into an IPM program.

Risk Assessment of Flonicamid Resistance in Musca domestica (Diptera: Muscidae): Resistance Monitoring, Inheritance, and Cross-Resistance Potential

Flonicamid is a chordotonal modulator and novel systemic insecticide that has been used frequently for controlling a broad range of insect pests. The risk of flonicamid resistance was assessed through laboratory selection and determining inheritance pattern and cross-resistance potential to five insecticides in house fly, Musca domestica L. Very low to high flonicamid resistance in M. domestica populations was found compared with the susceptible strain (SS). A flonicamid-selected (Flonica-RS) M. domestica strain developed 57.73-fold resistance to flonicamid screened for 20 generations compared with the SS. Overlapping 95% fiducial limits of LC50 of the F1 and F1ǂ, and dominance values (0.87 for F1 and 0.92 for F1ǂ) revealed an autosomal and incomplete dominant flonicamid resistance. The monogenic model of resistance inheritance suggested a polygenic flonicamid resistance. The Flonica-RS strain displayed negative cross-resistance between flonicamid and sulfoxaflor (0.10-fold) or clothianidin (0.50-fold), and very low cross-resistance between flonicamid and flubendiamide (4.71-fold), spinetoram (4.68-fold), or thiamethoxam (2.02-fold) in comparison with the field population. The estimated realized heritability (h2) value of flonicamid resistance was 0.02. With selection mortality 40-90%, the generations required for a 10-fold increase in LC50 of flonicamid were 94-258 at h2 (0.02) and slope (3.29). Flonicamid resistance was inherited as autosomal, incomplete dominant, and polygenic in the Flonica-RS. Negative or very low cross-resistance between flonicamid and sulfoxaflor, clothianidin, flubendiamide, spinetoram, and thiamethoxam means that these insecticides can be used as alternatives for controlling M. domestica. These data can be useful in devising the management for M. domestica.

Flonicamid and knockdown of inward rectifier potassium channel gene CsKir2B adversely affect the feeding and development of Chilo suppressalis

BACKGROUND

The selective insecticide flonicamid shows highly insecticidal activities against piercing-sucking insects and has been widely used for the control of Hemipteran insect pests, whereas its effects on Lepidopteran insect pests remain largely unknown. Recently, inward rectifier potassium (Kir) channel has been verified to be a target of flonicamid, however, functional characterization of Lepidopteran Kir genes is still lacking.

RESULTS

Flonicamid shows no insecticidal toxicity against Chilo suppressalis larvae. However, the feeding and growth of larvae were reversibly inhibited by flonicamid (50-1200 mg L^-1 ). Flonicamid treatment also remarkably reduced and delayed the pupation and eclosion of Chilo suppressalis. Additionally, five distinct Kir channel genes (CsKir1, CsKir2A, CsKir2B, CsKir3A and CsKir3B) were cloned from Chilo suppressalis. Expression profiles analysis revealed that CsKir2A was predominately expressed in the hindgut of larvae, whereas CsKir2B had high expressions in the Malpighian tubules and hindgut. RNA interference (RNAi)-mediated knockdown of CsKir2B significantly reduced the growth and increased the mortalities of larvae, whereas silencing of CsKir2A had no obvious effects on Chilo suppressalis.

CONCLUSION

Flonicamid exhibits adverse effects on the growth and development of Chilo suppressalis. CsKir2B might be involved in the feeding behavior of Chilo suppressalis. These results provide valuable information on the effects of flonicamid on non-target insects as well as the function of insect Kir channels, and are helpful in developing new insecticide targeting insect Kir channels. © 2020 Society of Chemical Industry.

Augmentation and compatibility of Beauveria bassiana with pesticides against different growth stages of Bemisia tabaci (Gennadius); an in vitro and field approach

BACKGROUND

Bemisia tabaci is a notorious agricultural pest that causes serious damage to many crops via herbivory and spread of viral diseases. Effective control measures are, therefore, required. Integrating entomopathogenic fungi into the chemical control system offers promise for B. tabaci management.

RESULTS

In-vitro assays on the augmentative effect of Beauveria bassiana GHA strain with insecticides, and its compatibility with fungicides were tested. Varying egg mortality was observed for most insecticides except for milbemectin. Pyrifluquinazon was less effective against the nymphs. Flonicamid showed no insecticidal effect on either nymphs or adults. However, increased mortality in nymphs and adults was observed when flonicamid was mixed with Beauveria bassiana GHA strain. Furthermore, no significant synergistic effect of mixing pesticides with B. bassiana GHA strain was observed. Most insecticides (when not mixed with B. bassiana) showed high (>80%) mortality against B. tabaci nymphs and adults. Most fungicides tested showed no inhibitory effects on B. bassiana GHA strain against B. tabaci nymphs and adults. Fungistatic effect was observed in the mycelial and spore germination inhibition studies. Weekly rotation of some pesticides with B. bassiana GHA strain in greenhouse conditions yielded significant reduction in different growth stages of B. tabaci. However, no significant difference in viral incidence was observed.

CONCLUSION

Laboratory and field tests showed positive effects of augmenting pesticides and B. bassiana GHA strain against B. tabaci nymphs and adults. Therefore, augmentation of pesticides and B. bassiana GHA strain is one prospect towards developing an effective B. tabaci IPM system. © 2020 Society of Chemical Industry.

Lethal and Sublethal Effects of Methyl Benzoate on the Predatory Bug Nesidiocoris tenuis

Benzoates (naturally occurring plant toxins) produce pesticidal effects on various pest insects and mites, but their effects on non-target insects are poorly understood. In this study, we evaluate the lethal and sublethal toxicity of methyl benzoate (MB) to adults of the generalist predatory bug Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae). To assess lethal effects, N. tenuis was exposed to plant surfaces treated with 0.25%, 0.5% and 1% MB, as well as negative and positive controls (water and the neonicotinoid acetamiprid, respectively). Exposure to 1% MB resulted in the highest corrected mortality of 17.8% and 13.3% under laboratory and greenhouse conditions, respectively. Thus, 1% MB can be classified as harmless to N. tenuis according to the International Organization for Biological Control rating scheme. At the sublethal level, MB exposure did not significantly affect the consumption of eggs of the whitefly Bemisia tabaci by N. tenuis relative to negative control feeding rates. In contrast, acetamiprid at the manufacturer's recommended concentration reduced N. tenuis feeding activity by 45.4%. Furthermore, in a Y-tube olfactometer assay, there were no significant differences between the olfactory responses of N. tenuis to MB concentrations and the negative control (water). This study therefore suggests that MB could be used safely for pest control in combination with N. tenuis.

Selectivity of novel and traditional insecticides used for management of whiteflies on the parasitoid Encarsia formosa

BACKGROUND

Encarsia formosa Gahan is the most important parasitoid exploited for the control of whitefly pests of vegetable crops. However, the non-target effects of recently developed insecticides for controlling whiteflies toward this biocontrol agent is little documented. Here we evaluated the susceptibility of E. formosa adults and juveniles to eight commonly used insecticides against whiteflies.

RESULTS

Residual toxicity tests on glass showed that E. formosa adults were susceptible (over 98% mortality after 6 h treated) to field concentrations of the tested neonicotinoids (imidacloprid, acetamiprid, nitenpyram and thiamethoxam), abamectin, cyantraniliprole, and sulfoxaflor at their field concentrations. Pyriproxyfen was harmless to both adult and pupae of E. formosa. A risk quotient analysis showed that toxicity of pyriproxyfen to E. formosa adults was the lowest, followed by acetamiprid and cyantraniliprole. In the leaf residues test, mortality of E. formosa adults under all insecticides decreased when the residue age increased. Interestingly, E. formosa experiencing contact with the residues of most insecticides, except pyriproxyfen and abamectin, parasitized significantly more hosts 5-days after treatment, suggesting a hormetic effect on parasitism.

CONCLUSION

The risk assessment of insecticides indicated that pyriproxyfen and cyantraniliprole were the least toxic to E. formosa. Our results suggest that the inclusion of the insecticides in sustainable integrated pest management programs of whiteflies should be carefully evaluated on a case-by-case basis. © 2019 Society of Chemical Industry.

Block of Kir channels by flonicamid disrupts salivary and renal excretion of insect pests

Flonicamid is a selective insecticide for the control of sap-sucking insects; it exerts toxic effects by inhibiting insect feeding. However, its molecular target remains elusive. In this study, we functionally characterized NlKir1 channels of the brown planthopper (Nilaparvata lugens) in HEK293 cells. Homomeric NlKir1 channels generated inward-rectifying K⁺ currents. Flonicamid inhibited NlKir1 channels at nanomolar concentrations. Furthermore, flonicamid inhibited honeydew and salivary secretions of planthoppers, and reduced the renal excretion of female mosquitoes in a dose-dependent manner. The inhibitory effect of flonicamid on fluid secretion of isolated Malpighian tubules from Culex pipiens pullens was comparable to that of the selective Kir1 inhibitor. The observed physiological alterations by flonicamid are likely mediated by Kir1 channels and could lead to the disruption of feeding behaviors and eventually lethality. Our study establishes the Kir1 channel as the target of flonicamid and provided new insights into the mode of action of flonicamid.

Toxicity of seven insecticides to different developmental stages of the whitefly Bemisia tabaci MED (Hemiptera: Aleyrodidae) in multiple field populations of China

Chemical control is important in the management of the tobacco whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Susceptibility of B. tabaci to insecticides may vary among different developmental stages and geographical populations. In this study, we examined toxicity of seven commonly-used insecticides to B. tabaci MED in four field populations from China. Avermectin has high level of toxicity to all stages of B. tabaci MED in all four populations. Cyantraniliprole and sulfoxaflor have high toxicity to adults. Spirotetramat, cyantraniliprole and flonicamid have high toxicity to nymphs but not adults. Acetamiprid, cyantraniliprole and sulfoxaflor have high toxicity to eggs. However, the relative toxicity of B. tabaci MED to these chemicals varied across different populations, with little consistency in population differences across developmental stages. Our findings together with some instances where LC₉₅ values were higher than field recommended dosages indicate field-evolved resistance to insecticides (such as thiamethoxam and sulfoxaflor) and stage-specific mechanisms that will influence effective control of B. tabaci MED by insecticides.

Quantifying Conservation Biological Control for Management of Bemisia tabaci (Hemiptera: Aleyrodidae) in Cotton

Conservation biological control can be an effective tactic for minimizing insect-induced damage to agricultural production. In the Arizona cotton system, a suite of generalist arthropod predators provides critical regulation of Bemisia tabaci Gennadius (MEAM1) (Hemiptera: Aleyrodidae) and other pests. Arthropod predator and B. tabaci populations were manipulated with a range of broad-spectrum and selective insecticide exclusions to vary predator to prey interactions in a 2-yr field study. Predator to prey ratios associated with B. tabaci densities near the existing action threshold were estimated for six predator species found to be negatively associated with either adult and/or large nymphs of B. tabaci [Misumenops celer (Hentz) (Araneae: Thomisidae), Drapetis nr divergens (Diptera: Empididae), Geocoris pallens Stäl (Hemiptera: Geocoridae), Orius tristicolor (White) (Hemiptera: Anthocoridae), Chrysoperla carnea s.l. (Neuroptera: Chrysopidae), and Collops spp. (Coleoptera: Melyridae)] with the first three most consistently associated with declining B. tabaci densities. Ratios ranged from 1 M. celer per 100 sweeps to 1 B. tabaci adult per leaf to 44 D. nr. divergens per 100 sweeps to 1 large nymph per leaf disk. These ratios represent biological control informed thresholds that might serve as simple-to-use decision tool for reducing risk in the current B. tabaci integrated pest management strategy. The identification of key predators within the large, flexible food web of the cotton agro-ecosystem and estimation of predator to B. tabaci ratios clarifies the role of key predators in B. tabaci suppression, yielding potential decision-making advantages that could contribute to further improving economic and environmental sustainability of insect management in the cotton system.

Compatibility of insecticides and fungicides with the zoophytophagous mirid predator Nesidiocoris tenuis

Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) is an effective predator of multiple pests of vegetable crops, such as thrips, mites, aphids, whiteflies, leafminers. It is mass-reared and released for augmentative biocontrol programs mainly aimed at controlling whiteflies and Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in greenhouses and open field. We evaluated the lethal and sublethal toxicity upon N. tenuis adults of label doses of three insecticides (pyriproxyfen, spirotetramat, cypermethrin) and seven fungicides (benomyl, chlorothalonil, copper oxychloride, cyazofamid, fluopicolide + propamocarb hydrochloride (FPH), penconazol, trifloxystrobin) commonly used in various crops. Two exposure routes were tested: (i) contact with dry residues of insecticides or fungicides on tomato sprouts and (ii) multiple exposure to these chemicals via topical sprays on adults which foraged on treated sprouts; and fed on treated eggs of Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) simultaneously. Mortality and reproductive capacity were investigated as indicators of lethal and sublethal effects on N. tenius. The tested insecticides and fungicides were all classified as harmless when predator was exposed only to the dry residues of each. However, the multiple exposure to either cypermethrin, benomyl, chlorothalonil, copper oxychloride or trifloxystrobin caused significant mortality of N. tenuis adults. Cypermethrin also significantly reduced its reproductive capacity. Interestingly, N. tenuis produced a higher number of progeny when exposed to fungicides penconazol and FPH in both exposure scenarios. Overall, findings suggest that the two insecticides, pyriproxyfen and spirotetramat but not cypermethrin, and all tested fungicides can be considered compatible with N. tenuis.

The toxicity of flonicamid to cotton leafhopper, Amrasca biguttula (Ishida), is by disruption of ingestion: an electropenetrography study

BACKGROUND

The cotton leafhopper, Amrasca biguttula, is one of the most destructive pests of cotton in Asia. This species is thought to cause damage by injecting enzymatic saliva into various, presently unknown, cotton tissues and ingesting the resulting macerate. Flonicamid is a novel systemic insecticide used to control the cotton leafhopper; however, its mode of action is unknown.

RESULTS

The mechanism of action of flonicamid on cotton leafhopper was investigated using electropenetrography (EPG). EPG recordings revealed six waveforms, i.e. Np (non-probing), A1 (channel cutting), A2, A3, A4, A5 and A6. Waveforms A2 and A3 probably represent active ingestion with (A2) and without (A3) simultaneous watery salivation. The meanings of A4, A5 and A6 are presently unknown, but minor in duration. Flonicamid significantly increased the mean duration of non-probing events and strongly inhibited ingestion by treated insects, which resulted in the slow death of leafhoppers. Inhibition of ingestion was dose dependent, and near-complete suppression was observed when the flonicamid concentration was increased to 10 000 mg L^-1 .

CONCLUSIONS

We propose that starvation caused by inhibition of active ingestion is the mechanism of toxicity for flonicamid. This knowledge could aid in applicability and use of this new insecticide for field management of leafhopper populations. © 2016 Society of Chemical Industry.

Development of a lateral flow test to detect metabolic resistance in Bemisia tabaci mediated by CYP6CM1, a cytochrome P450 with broad spectrum catalytic efficiency

Cotton whitefly, Bemisia tabaci (Genn.) (Homoptera: Aleyrodidae) is a major sucking pest in many agricultural and horticultural cropping systems globally. The frequent use of insecticides of different mode of action classes resulted in populations resisting treatments used to keep numbers under economic damage thresholds. Recently it was shown that resistance to neonicotinoids such as imidacloprid is linked to the over-expression of CYP6CM1, a cytochrome P450 monooxygenase detoxifying imidacloprid and other neonicotinoid insecticides when recombinantly expressed in insect cells. However over-expression of CYP6CM1 is also known to confer cross-resistance to pymetrozine, an insecticide not belonging to the chemical class of neonicotinoids. In addition we were able to demonstrate by LC-MS/MS analysis the metabolisation of pyriproxyfen by recombinantly expressed CYP6CM1. Based on our results CYP6CM1 is one of the most versatile detoxification enzymes yet identified in a pest of agricultural importance, as it detoxifies a diverse range of chemical classes used to control whiteflies. Therefore we developed a field-diagnostic antibody-based lateral flow assay which detects CYP6CM1 protein at levels providing resistance to neonicotinoids and other insecticides. The ELISA based test kit can be used as a diagnostic tool to support resistance management strategies based on the alternation of different modes of action of insecticides.