Resistance Management for Asian Citrus Psyllid, Diaphorina citri Kuwayama, in Florida

The Asian citrus psyllid, Diaphorina citri Kuwayma, is one of the most important pests in citrus production. The objective of this study was to evaluate D. citri resistance management with three insecticide rotations and compare them with no rotation and an untreated check. The different insecticides (modes of action) tested were: dimethoate, imidacloprid, diflubenzuron, abamectin 3% + thiamethoxam 13.9%, and fenpropathrin. Eggs, nymph, and adult psyllids were counted weekly. Five insecticide applications were made in 2016. Insecticide susceptibility was determined by direct comparison with a laboratory susceptible population and field populations before and after all treatments were applied. Rankings of eggs, nymphs, and adults counted in treated plots were significantly lower than in the untreated control plots after each application. Initially, the resistance ratio (RR₅₀) for each rotation model, as compared with laboratory susceptible strain and the field population before application, was less than 5.76 and 4.31, respectively. However, after five applications with dimethoate, the RR₅₀ using the laboratory and pre-treatment field populations was 42.34 and 34.74, respectively. Our results indicate that effectively rotating modes of action can delay and/or prevent development of insecticide resistance in populations of D. citri.

Evolution of imidacloprid resistance in Myzus persicae in Greece and susceptibility data for spirotetramat

BACKGROUND

Myzus persicae s.l. is a major crop pest globally and has evolved resistance to a range of insecticide classes making it increasingly difficult to control in some areas. Here we compare bioassay monitoring data for two important compounds, imidacloprid and spirotetramat, on field samples/clones collected in Greece.

RESULTS

A total of 122 aphid samples/clones from central and northern Greece were examined in dose-response bioassays with imidacloprid. There was an overall increase in the level of resistance (resistance factor = 15-40) within tobacco-collected samples from 78.7% in 2007 to 86.7% in 2015. The corresponding frequencies for peach samples were 13.3% and 6.7%. These results were confounded however by the first identification of the R81T target mutation in Greece during 2015 (4.3% as heterozygotes in peach) and 2016 (21.3% as heterozygotes in peach). No resistance to spirotetramat was found at the 60 clones collected in 2015.

CONCLUSION

Resistance to imidacloprid is continuing to increase within Greek M. persicae s.l. populations and the situation is likely to deteriorate further with the recent identification of the R81T resistance mutation. Resistance to spirotetramat has not been found and is therefore a good alternative to neonicotinoids for resistance management. © 2017 Society of Chemical Industry.

Mosquito Vector Biology and Control in Latin America-A 27th Symposium

The 27th Annual Latin American Symposium presented by the American Mosquito Control Association (AMCA) was held as part of the 83rd Annual Meeting of the AMCA in San Diego, CA, in February 2017. The Latin American Symposia promote the participation of vector control specialists, public health workers, and academicians from Latin America and the sharing of data between continents. Generally, presentations are in Spanish and simultaneously translated in English, although the majority of PowerPoint slides are in English so all meeting attendees can understand the content. This publication includes summaries of 23 oral presentations by participants from Brazil, Colombia, Mexico, Puerto Rico, and the USA. Topics addressed in the symposium included surveillance, operations and response thresholds/planning, mosquito ecology, insecticide resistance, and population control via chemicals, natural products, and biological control. Sterile insect technique protocols were explored regarding larval rearing diets and the use of microRNAs. Presentations were related to vectors including Aedes, Culex, and Anopheles mosquitoes, which can transmit malaria, dengue, chikungunya, and Zika, and Lutzomyia phlebotomine sand flies, the key vectors of leishmaniasis.

Fitness costs and life table parameters of highly insecticide-resistant strains of Plutella xylostella (L.) (Lepidoptera: Plutellidae) at different temperatures

BACKGROUND

In many cases, resistance alleles have been associated with fitness costs and are often dependent on environmental factors such as temperature. Here, we studied the effects of temperature on the overall fitness, including development, survival and reproduction, of three insecticide-resistant and one susceptible strain of diamondback moth (DBM), Plutella xylostella (L.).

RESULTS

The broader cross-resistance profile of the resistant strains previously selected by diamide and benzoylurea insecticides was tested. Cohort studies were conducted in the laboratory at three different temperatures (20 ± 1 °C, 25 ± 1 °C and 30 ± 1 °C), and involved fitness costs were estimated. We observed significant differences in the development time, with the susceptible strain showing a shorter developmental period from egg stage to adult stage compared with the resistant strains. Moreover, the resistant strains differed significantly between one another. Additionally, the population growth parameters varied among the strains, with the benzoylurea-resistant strain showing the highest costs affecting the overall fitness of this strain. A temperature of 30 °C was unfavourable for DBM development, resulting in a reduced fitness in all strains.

CONCLUSION

Benzoylurea selection pressure on a diamide-resistant P. xylostella strain resulted in lowest reproduction parameters and the longest generation time, as well as doubling the time among all strains tested. This suggests significant effects on the overall fitness and population growth parameters for diamide-resistant populations pressured by benzoylureas under applied conditions. © 2017 Society of Chemical Industry.

Evaluation of the toxic effects of doramectin, ivermectin and eprinomectin against Triatoma infestans using a rat model

INTRODUCTION

Pyrethroids have been frequently and intensively used for controlling the triatomine vectors of Trypanosoma cruzi. The emergence of resistance to these insecticides has resulted in an urgent need to identify novel, alternative and complementary control strategies.

OBJECTIVE

To evaluate the toxic effects of ivermectin, doramectin and eprinomectin on the bloodfeeding behaviour of Triatoma infestans using a rodent model.

MATERIALS AND METHODS

Fifth instar nymphs of T. infestans were fed at different times on Wistar rats pretreated with doramectin, ivermectin, eprinomectin or dimethylsulfoxide (excipient control) topically or orally administered. We determined the effects of each insecticide and of dimethyl sulfoxide on the amount of ingested blood, the volume of faecal discharge, and the mortality rates in triatomines.

RESULTS

Only the rate of triatomine mortality was associated with the antiparasitic compounds administered and the route of administration utilized. Doramectin administration was associated with a higher mortality rate (21.5%) than ivermectin, eprinomectin and dimethylsulfoxide (16, 11 and 2.5%, respectively), and topical administration was found to be most effective for inducing mortality (23 vs. 9.3 %).

CONCLUSION

These results demonstrate the toxic effects of the three assessed insecticides on T. infestans. The administration of ecto/endoparasiticides to domiciliary or peridomiciliary animals may serve as an interesting complementary strategy to the use of pyrethroids for the control of T. infestans.

Seasonal proportion change of ryanodine receptor mutation (G4946E) in diamondback moth populations

This study examined the seasonal proportion change of ryanodine receptor mutation (G4946E) for Plutella xylostella populations using quantitative sequencing. Results showed that the proportions of G4946E generally increased from spring through summer, but then decreased in autumn. Furthermore, the proportions in late autumn were similar to those in early spring of the subsequent year. These results suggest that diamide effectiveness for P. xylostella control in the reference year can be evaluated based on a proportion survey in the prior year.

Studies on Aphis gossypii cytochrome P450s CYP6CY22 and CYP6CY13 using an in vitro system

A field-collected Aphis gossypii clone [Kushima resistant (KR) clone] was resistant to neonicotinoid insecticides (23.8- to 394-fold). RNA-seq and next-generation sequence analyses were conducted to identify nine cytochrome P450 (CYP) genes that were significantly upregulated in the KR clone as compared with those in the insecticide-susceptible clone. A. gossypii P450s were transiently and efficiently expressed in S2 cell to show that CYP6CY22 (c21228) and CYP6CY13 (c21368), which were the most upregulated of the nine P450s in the KR clone, did not degrade sulfoxaflor, a new class of insecticides acting on insect nAChRs, but markedly metabolized all of the neonicotinoids tested. Hence, P450s are likely to underpin neonicotinoid resistance in other aphids as well in the future, and the P450 expression protocol established here will prompt studies on P450-medidated insecticide resistance and structural analyses of relevant metabolites.

Thermotolerance, oxidative stress, apoptosis, heat-shock proteins and damages to reproductive cells of insecticide-susceptible and -resistant strains of the diamondback moth Plutella xylostella

In this study, we investigated thermotolerance, several physiological responses and damage to reproductive cells in chlorpyrifos-resistant (Rc) and -susceptible (Sm) strains of the diamondback moth, Plutella xylostella subjected to heat stress. The chlorpyrifos resistance of these strains was mediated by a modified acetylcholinesterase encoded by an allele, ace1R, of the ace1 gene. Adults of the Rc strain were less heat resistant than those of the Sm strain; they also had lower levels of enzymatic activity against oxidative damage, higher reactive oxygen species contents, weaker upregulation of two heat shock protein (hsp) genes (hsp69s and hsp20), and stronger upregulation of two apoptotic genes (caspase-7 and -9). The damage to sperm and ovary cells was greater in Rc adults than in Sm adults and was temperature sensitive. The lower fitness of the resistant strain, compared with the susceptible strain, is probably due to higher levels of oxidative stress and apoptosis, which also have deleterious effects on several life history traits. The greater injury observed in conditions of heat stress may be due to both the stronger upregulation of caspase genes and weaker upregulation of hsp genes in resistant than in susceptible individuals.

Heterogeneous gene duplications can be adaptive because they permanently associate overdominant alleles

Gene duplications are widespread in genomes, but their role in contemporary adaptation is not fully understood. Although mostly deleterious, homogeneous duplications that associate identical repeats of a locus often increase the quantity of protein produced, which can be selected in certain environments. However, another type exists: heterogeneous gene duplications, which permanently associate two (or more) alleles of a single locus on the same chromosome. They are far less studied, as only few examples of contemporary heterogeneous duplications are known. Haldane proposed in 1954 that they could be adaptive in situations of heterozygote advantage, or overdominance, but this hypothesis was never tested. To assess its validity, we took advantage of the well-known model of insecticide resistance in mosquitoes. We used experimental evolution to estimate the fitnesses associated with homozygous and heterozygous genotypes in different selection regimes. It first showed that balanced antagonist selective pressures frequently induce overdominance, generating stable polymorphic equilibriums. The frequency of equilibrium moreover depends on the magnitude of two antagonistic selective pressures, the survival advantage conferred by the resistant allele versus the selective costs it induces. We then showed that heterogeneous duplications are selected over single-copy alleles in such contexts. They allow the fixation of the heterozygote phenotype, providing an alternative and stable intermediate fitness trade-off. By allowing the rapid fixation of divergent alleles, this immediate advantage could contribute to the rarity of overdominance. More importantly, it also creates new material for long-term genetic innovation, making a crucial but underestimated contribution to the evolution of new genes and gene families.

Susceptibility of insecticide-resistant bed bugs (Cimex lectularius) to infection by fungal biopesticide

BACKGROUND

Bed bugs are a public health concern, and their incidence is increasing worldwide. Bed bug infestations are notoriously difficult to eradicate, further exacerbated by widespread resistance to pyrethroid and neonicotinoid insecticides. This study evaluated the efficacy of the newly developed fungal biopesticide Aprehend™, containing Beauveria bassiana, against insecticide-resistant bed bugs.

RESULTS

Overall mortality for the Harold Harlan (insecticide-susceptible) strain was high (98-100%) following exposure to Aprehend™ or Suspend SC (deltamethrin). The mean survival times (MSTs) for Harold Harlan bed bugs were 5.1 days for Aprehend™ and 4.8 and 3.0 days for the low and high concentrations of Suspend SC respectively. All three strains of pyrethroid-resistant bed bugs were susceptible to infection by B. bassiana, resulting in MSTs of <6 days (median = 4 days) and >94% overall mortality. Conversely, mortality of the three insecticide-resistant strains after exposure to Suspend SC was only 16-40%.

CONCLUSION

These results demonstrate that Aprehend™ is equally effective against insecticide-susceptible and insecticide-resistant bed bugs and could provide pest control operators with a promising new tool for control of bed bugs and insecticide resistance management. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Point mutations in acetylcholinesterase 1 associated with chlorpyrifos resistance in the brown planthopper, Nilaparvata lugens Stål

Insecticide resistance frequently results from target-site insensitivity, such as point mutations in acetylcholinesterases (AChEs) for resistance to organophosphates and carbamates. From a field-originated population of Nilaparvata lugens, a major rice pest, a resistant population (R9) was obtained by nine-generation continuous selection with chlorpyrifos. From the same field population, a relatively susceptible population (S9) was also constructed through rearing without any insecticides. Compared to the susceptible strain, Sus [medium lethal dose (LC₅₀ ) = 0.012 mg/l], R9 had a resistance ratio (RR) of 253.08-fold, whereas the RR of S9 was only 2.25-fold. Piperonyl butoxide and triphenyl phosphate synergized chlorpyrifos in R9 less than three-fold, indicating other important mechanisms for high resistance. The target-site insensitivity was supported by the key property differences of crude AChEs between R9 and S9. Compared to S9, three mutations (G119S, F331C and I332L) were detected in NlAChE1 from individuals of the R9 and field populations, but no mutation was detected in NlAChE2. G119S and F331C could decreased insecticide sensitivities in recombinant NlAChE1, whereas I332L took effect through increasing the influence of F331C on target insensitivity. F331C might be deleterious because of its influence on the catalytic efficiency of NlAChE1, whereas I332L would decrease these adverse effects and maintain the normal functions of AChEs.

Discovery of metabolic resistance to neonicotinoids in green peach aphids (Myzus persicae) in Australia

BACKGROUND

Myzus persicae is a serious pest that attacks a broad range of agricultural crops. This species has developed chemical resistance to many insecticides globally, and within Australia resistance to multiple chemical groups has been identified. Resistance to neonicotinoid insecticides has been discovered in several countries, but has not previously been confirmed in Australia. We use biomolecular assays and bioassays on field-collected populations to investigate neonicotinoid resistance in M. persicae within Australia.

RESULTS

Several geographically and genetically distinct populations showed evidence for resistance in bioassays. Genetic markers identified that the mechanism of neonicotinoid resistance in Australia is metabolic resistance through the enhanced expression of a cytochrome P450 gene, CYP6CY3.

CONCLUSION

M. persicae populations in parts of Australia are now resistant to four different insecticide chemical groups, raising concerns about the long-term management of this pest. While higher copy numbers of CYP6CY3 were seen in all resistant populations, the number of gene copies was not strongly correlated with the level of resistance as determined by LD₅₀ values generated through bioassays. This finding sheds further light on the complexity of the P450 genes in regulating neonicotinoid resistance. © 2016 Society of Chemical Industry.

Chlorfenapyr, a Potent Alternative Insecticide of Phoxim To Control Bradysia odoriphaga (Diptera: Sciaridae)

Bradysia odoriphaga is the major pest affecting Chinese chive production, and in China, it has developed widespread resistance to organophosphorus insecticides. Chlorfenapyr is a promising pyrrole insecticide with a unique mechanism of action that does not confer cross-resistance to neurotoxic insecticides. However, the effect of chlorfenapyr on organophosphate-resistant B. odoriphaga is not well understood. The present study evaluated the potential of chlorfenapyr for the control of phoxim-resistant B. odoriphaga. The results showed that chlorfenapyr had significant insecticidal activity to B. odoriphaga in multiple developmental stages, and there were no significant differences in susceptibility between the field (phoxim-resistant) and laboratory (phoxim-susceptible) populations. The pot experiment and field trials confirmed the results of our laboratory bioassays. In the field trial, chlorfenapyr applied at 3.0, 6.0, or 12.0 kg of active ingredient (a.i.)/ha significantly decreased the number of B. odoriphaga and improved the yield compared to phoxim at 6.0 kg of a.i./ha and the control conditions. Moreover, the final residues of chlorfenapyr on plants were below the maximum residue limits (MRLs) as a result of its non-systemic activity. These results demonstrate that chlorfenapyr has potential as a potent alternative to phoxim for controlling B. odoriphaga.

Use of an individual-based simulation model to explore and evaluate potential insecticide resistance management strategies

BACKGROUND

Tools with the potential to predict risks of insecticide resistance and aid the evaluation and design of resistance management tactics are of value to all sectors of the pest management community. Here we describe use of a versatile individual-based model of resistance evolution to simulate how strategies employing single and multiple insecticides influence resistance development in the pollen beetle, Meligethes aeneus.

RESULTS

Under repeated exposure to a single insecticide, resistance evolved faster to a pyrethroid (lambda-cyhalothrin) than to a pyridine azomethane (pymetrozine), due to difference in initial efficacy. A mixture of these compounds delayed resistance compared to use of single products. The effectiveness of rotations depended on the sequence in which compounds were applied in response to pest density thresholds. Effectiveness of a mixture strategy declined with reductions in grower compliance. At least 50% compliance was needed to cause some delay in resistance development.

CONCLUSION

No single strategy meets all requirements for managing resistance. It is important to evaluate factors that prevail under particular pest management scenarios. The model used here provides operators with a valuable means for evaluating and extending sound resistance management advice, as well as understanding needs and opportunities offered by new control techniques. © 2016 Society of Chemical Industry.

Over-expression of UDP-glycosyltransferase gene UGT2B17 is involved in chlorantraniliprole resistance in Plutella xylostella (L.)

BACKGROUND

UDP-glycosyltransferases (UGTs) are phase II detoxification enzymes widely distributed within living organisms. Their involvement in the biotransformation of various lipophilic endogenous compounds and phytoalexins in insects has been documented. However, the roles of this enzyme family in insecticide resistance have rarely been reported. Here, the functions of UGTs in chlorantraniliprole resistance in Plutella xylostella were investigated.

RESULTS

Treatment with sulfinpyrazone and 5-nitrouracil (both inhibitors of UGT enzymes) significantly increased the toxicity of chlorantraniliprole against the third instar larvae of P. xylostella. Among the 23 UGT transcripts examined, only UGT2B17 was found to be over-expressed (with a range from 30.7- to 77.3-fold) in all four chlorantraniliprole-resistant populations compared to the susceptible one (CHS). The knock-down of UGT2B17 by RNA interference (RNAi) dramatically increased the toxicity of chlorantraniliprole by 27.4% and 29.8% in the CHS and CHR (resistant) populations, respectively. In contrast, exposure to phenobarbital significantly increased the relative expression of UGT2B17 while decreasing the toxicity of chlorantraniliprole to the larvae by 14.0%.

CONCLUSION

UGT2B17 is involved in the detoxification of chlorantraniliprole, and its over-expression may play an important role in chlorantraniliprole resistance in P. xylostella. These results shed some light upon and further our understanding of the mechanisms of diamide insecticide resistance in insects. © 2016 Society of Chemical Industry.

Resistance irrelevant CYP417A2v2 was found degrading insecticide in Laodelphax striatellus

Cytochrome P450 monooxygenases (CYPs) usually overexpressed in resistant strain were found involved in oxidative detoxification of insecticides. In this study, an investigation was conducted to confirm if resistance irrelevant CYPs which were not overexpressed in resistant strain before, were capable of degrading insecticides. Three resistance irrelevant CYPs viz. CYP417A2v2, CYP425A1v2, and CYP4DJ1 from CYP4 family of Laodelphax striatellus were randomly selected for experiments. CYP417A2v2 and CYP425A1v2 were found expressed successfully in Sf9 cell line while CYP4DJ1 was not expressed successfully and out of two expressed CYPs, only CYP417A2v2 showed its efficient catalytic activity. For catalytic activity, three traditional model probe substrates and five insecticides were assayed. For the probe substrates screened, p-nitroanisole and ethoxycoumarin were preferentially metabolized by CYP417A2v2 (specific activity 3.76 ± 1.22 and 1.63 ± 0.37 nmol min-1 mg protein-1, respectively) and they may be potential diagnostic probes for this enzyme. Among insecticides, only imidacloprid was efficiently degraded by CYP417A2v2. Incubation of imidacloprid with CYP417A2v2 of L. striatellus and subsequent HPLC, LC-MS, and MS/MS analysis revealed the formation of imidacloprid metabolites, that is, 4' or 5'hydroxy-imidacloprid by hydroxylation. This result implies the exemption of CYPs character that it is not always, all the CYPs degrading insecticides being selected and overexpressed in resistant strains and the degrading CYPs without mutations to upregulate could be candidates during insecticide resistance evolution. This characterization of individual insect CYPs in insecticide degradation can provide insight for better understand of insecticide resistance development.

Insights from agriculture for the management of insecticide resistance in disease vectors

Key to contemporary management of diseases such as malaria, dengue, and filariasis is control of the insect vectors responsible for transmission. Insecticide‐based interventions have contributed to declines in disease burdens in many areas, but this progress could be threatened by the emergence of insecticide resistance in vector populations. Insecticide resistance is likewise a major concern in agriculture, where insect pests can cause substantial yield losses. Here, we explore overlaps between understanding and managing insecticide resistance in agriculture and in public health. We have used the Global Plan for Insecticide Resistance Management in malaria vectors, developed under the auspices of the World Health Organization Global Malaria Program, as a framework for this exploration because it serves as one of the few cohesive documents for managing a global insecticide resistance crisis. Generally, this comparison highlights some fundamental differences between insect control in agriculture and in public health. Moreover, we emphasize that the success of insecticide resistance management strategies is strongly dependent on the biological specifics of each system. We suggest that the biological, operational, and regulatory differences between agriculture and public health limit the wholesale transfer of knowledge and practices from one system to the other. Nonetheless, there are some valuable insights from agriculture that could assist in advancing the existing Global Plan for Insecticide Resistance Management framework.

Priorities for Broadening the Malaria Vector Control Tool Kit

Long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) have contributed substantially to reductions in the burden of malaria in the past 15 years. Building on this foundation, the goal is now to drive malaria towards elimination. Vector control remains central to this goal, but there are limitations to what is achievable with the current tools. Here we highlight how a broader appreciation of adult mosquito behavior is yielding a number of supplementary approaches to bolster the vector-control tool kit. We emphasize tools that offer new modes of control and could realistically contribute to operational control in the next 5 years. Promoting complementary tools that are close to field-ready is a priority for achieving the global malaria-control targets.

Insecticide-Treated Nets and Protection against Insecticide-Resistant Malaria Vectors in Western Kenya

Insecticide resistance might reduce the efficacy of malaria vector control. In 2013 and 2014, malaria vectors from 50 villages, of varying pyrethroid resistance, in western Kenya were assayed for resistance to deltamethrin. Long-lasting insecticide-treated nets (LLIN) were distributed to households at universal coverage. Children were recruited into 2 cohorts, cleared of malaria-causing parasites, and tested every 2 weeks for reinfection. Infection incidence rates for the 2 cohorts were 2.2 (95% CI 1.9–2.5) infections/person-year and 2.8 (95% CI 2.5–3.0) infections/person-year. LLIN users had lower infection rates than non-LLIN users in both low-resistance (rate ratio 0.61, 95% CI 0.42–0.88) and high-resistance (rate ratio 0.55, 95% CI 0.35–0.87) villages (p = 0.63). The association between insecticide resistance and infection incidence was not significant (p = 0.99). Although the incidence of infection was high among net users, LLINs provided significant protection (p = 0.01) against infection with malaria parasite regardless of vector insecticide resistance.

Control of Malaria Vector Mosquitoes by Insecticide-Treated Combinations of Window Screens and Eave Baffles

We assessed window screens and eave baffles (WSEBs), which enable mosquitoes to enter but not exit houses, as an alternative to indoor residual spraying (IRS) for malaria vector control. WSEBs treated with water, the pyrethroid lambda-cyhalothrin, or the organophosphate pirimiphos-methyl, with and without a binding agent for increasing insecticide persistence on netting, were compared with IRS in experimental huts. Compared with IRS containing the same insecticide, WSEBs killed similar proportions of Anopheles funestus mosquitoes that were resistant to pyrethroids, carbamates and organochlorines and greater proportions of pyrethroid-resistant, early exiting An. arabiensis mosquitoes. WSEBs with pirimiphos-methyl killed greater proportions of both vectors than lambda-cyhalothrin or lambda-cyhalothrin plus pirimiphos-methyl and were equally efficacious when combined with binding agent. WSEBs required far less insecticide than IRS, and binding agents might enhance durability. WSEBs might enable affordable deployment of insecticide combinations to mitigate against physiologic insecticide resistance and improve control of behaviorally resistant, early exiting vectors.

Progression of phosphine resistance in susceptible Tribolium castaneum (Herbst) populations under different immigration regimes and selection pressures

Insecticide resistance is an escalating global issue for a wide variety of agriculturally important pests. The genetic basis and biochemical mechanisms of resistance are well characterized in some systems, but little is known about the ecological aspects of insecticide resistance. We therefore designed a laboratory experiment to quantify the progression of phosphine resistance in Tribolium castaneum populations subject to different immigration regimes and selection pressures. Mated resistant females were added to originally susceptible populations under two distinct migration rates, and in addition, half of the populations in each migration treatment were exposed to selection pressures from phosphine fumigation. The progression of phosphine resistance was assessed by screening beetles for the resistance allele at rph2. Phosphine resistance increased slowly in the low migration treatment and in the absence of selection, as expected. But at the higher migration rate, the increase in frequency of the resistance allele was lower than predicted. These outcomes result from the high levels of polyandry known in T. castaneum females in the laboratory, because most of the Generation 1 offspring (86%) were heterozygous for the rph2 allele, probably because resistant immigrant females mated again on arrival. Phosphine resistance was not fixed by fumigation as predicted, perhaps because susceptible gametes and eggs survived fumigation within resistant females. In terms of phosphine resistance progression in populations exposed to selection, the effect of fumigation negated the difference in migration rates. These results demonstrate how species‐specific traits relating to the mating system may shape the progression of insecticide resistance within populations, and they have broad implications for the management of phosphine resistance in T. castaneum in the field. ​We specify and discuss how these mating system attributes need to be accounted for when developing guidelines for resistance management.

Genome-Wide Transcription and Functional Analyses Reveal Heterogeneous Molecular Mechanisms Driving Pyrethroids Resistance in the Major Malaria Vector Anopheles funestus Across Africa

Pyrethroid resistance in malaria vector, An. funestus is increasingly reported across Africa, threatening the sustainability of pyrethroid-based control interventions, including long lasting insecticidal nets (LLINs). Managing this problem requires understanding of the molecular basis of the resistance from different regions of the continent, to establish whether it is being driven by a single or independent selective events. Here, using a genome-wide transcription profiling of pyrethroid resistant populations from southern (Malawi), East (Uganda), and West Africa (Benin), we investigated the molecular basis of resistance, revealing strong differences between the different African regions. The duplicated cytochrome P450 genes (CYP6P9a and CYP6P9b) which were highly overexpressed in southern Africa are not the most upregulated in other regions, where other genes are more overexpressed, including GSTe2 in West (Benin) and CYP9K1 in East (Uganda). The lack of directional selection on both CYP6P9a and CYP6P9b in Uganda in contrast to southern Africa further supports the limited role of these genes outside southern Africa. However, other genes such as the P450 CYP9J11 are commonly overexpressed in all countries across Africa. Here, CYP9J11 is functionally characterized and shown to confer resistance to pyrethroids and moderate cross-resistance to carbamates (bendiocarb). The consistent overexpression of GSTe2 in Benin is coupled with a role of allelic variation at this gene as GAL4-UAS transgenic expression in Drosophila flies showed that the resistant 119F allele is highly efficient in conferring both DDT and permethrin resistance than the L119. The heterogeneity in the molecular basis of resistance and cross-resistance to insecticides in An. funestus populations throughout sub-Saharan African should be taken into account in designing resistance management strategies.

Insecticide Resistance of Several Field-Collected German Cockroach (Dictyoptera: Blattellidae) Strains

German cockroaches, Blattella germanica (L.), remain one of the most difficult indoor insect species to control because of its ability to develop resistance to insecticides. The toxicity and resistance levels of five technical-grade insecticides (permethrin, chlorpyrifos, propoxur, imidacloprid, and fipronil) were determined for adult males of seven strains of the German cockroach, a laboratory-reared susceptible strain (S) and six field-collected strains (B, D, E, G, H, and I). Using topical application methods, fipronil was the most toxic insecticide to all seven strains. The LD50 values of fipronil in the susceptible strain (S) and the field-collected strains B, D, E, G, H, and I were 1.33, 2.62, 11.53, 5.07, 7.66, 5.15, and 10.15 ng/insect, respectively. The field-collected strains were most resistant to permethrin among the five insecticides, except for strain H. The resistance ratios of strains B, D, E, G, and I to permethrin were 31.8, 37.3, 51.9, 34.9, and 37.5, respectively. With a resistance ratio of 6.4, the field-collected strain H was most resistant to chlorpyrifos. The field-collected strains were not significantly resistant to propoxur. Strains B, H, and I were not significantly resistant to imidacloprid when compared with the susceptible strain. Based on the different resistance ratios for each insecticide, we conclude that there are high rates of insecticide resistance in German cockroaches from Franklin County, NC, and that the field-collected strains most likely had different treatment histories.

Susceptibility of MED-Q1 and MED-Q3 Biotypes of Bemisia tabaci (Hemiptera: Aleyrodidae) Populations to Essential and Seed Oils

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a major pest of many agricultural and ornamental crops in tropical and subtropical regions causing damages that result in important economic losses. Insecticides are commonly used in greenhouses or fields to control B. tabaci populations leading to rapid evolution of resistance that render treatments inefficient. Therefore, and for environmental and human health concerns, other approaches must be developed for this pest management. In the present study, we compare, using the leaf dip method, the toxicity of three essential oils (Cymbopogon citratus, Ocimum americanum, and Hyptis spicigera) and three seed oils (Lannea microcarpa, Lannea acida, and Carapa procera) with three chemical insecticides (acetamiprid, deltamethrin, and chlorpyrifos-ethyl) on adults. Two B. tabaci biotypes (MED-Q1 and MED-Q3) belonging to the Mediterranean species and collected in Burkina Faso were used. Essential oils were analyzed by gas chromatography-mass spectrometry and gas chromatography-flame ionization detector. We showed that these two biotypes have different levels of resistance to the three insecticides, MED-Q3 being more sensitive than MED-Q1. Moreover, they differ in the frequency of resistance alleles to insecticides, especially for organophosphates, as these alleles are almost fixed in MED-Q1. On the other hand, the two biotypes prove to be more susceptible to the plant extracts than to insecticides except for chlorpyrifos-ethyl, with essential oils that showed the highest insecticidal activities. Monoterpenes content were the most abundant and showed the highest insecticidal activities. Our results indicated that essential oils, but also seed oils, have the potential to constitute an alternative strategy of pest management.

Diagnostic Doses of Insecticides for Adult Aedes aegypti to Assess Insecticide Resistance in Cuba

The objective of this study was to determine diagnostic doses (DDs) of 5 insecticides for the Rockefeller susceptible strain of Aedes aegypti , using the Centers for Disease Control and Prevention (CDC) bottle bioassay as a tool for monitoring insecticide resistance in the Cuban vector control program. The 30-min DD values determined in this study were 13.5 μg/ml, 6.5 μg/ml, 6 μg/ml, 90.0 μg/ml, and 15.0 μg/ml for cypermethrin, deltamethrin, lambda-cyhalothrin, chlorpyrifos, and propoxur, respectively. To compare the reliability of CDC bottle bioassay with the World Health Organization susceptible test, 3 insecticide-resistant strains were evaluated for deltamethrin and lambda-cyhalothrin. Results showed that the bottles can be used effectively from 21 to 25 days after treatment and reused up to 4 times, depending on the storage time. The CDC bottle bioassay is an effective tool to assess insecticide resistance in field populations of Ae. aegypti in Cuba and can be incorporated into vector management programs using the diagnostic doses determined in this study.

Field-Evolved Resistance of Bemisia tabaci (Hemiptera: Aleyrodidae) to Carbodiimide and Neonicotinoids in Pakistan

The evolution of resistance to carbodiimide (a toxic metabolite of diafenthiuron) and four neonicotinoids imidacloprid, acetamiprid, thiamethoxam, and thiacloprid in the Pakistani populations of sweetpotato whitefly (Bemisia tabaci Gennadius) was monitored from 1996 to 2015 using a leaf-dip bioassay. Diafenthiuron, imidacloprid, and acetamiprid were introduced into Pakistani agriculture in mid-1990s and heavily used since then, because B. tabaci resistance and consequently control failures to conventional insecticides such as organophosphates, carbamates, and pyrethroids were widespread during the 1990s. According to the current studies, resistance to carbodiimide, imidacloprid, and acetamiprid during 1996-2010 and to thiamethoxam during 1999-2007 remained very low, but then it rose sharply, and by the year 2015, the B. tabaci resistance increased to very high levels. Among neonicotinoids, thiacloprid was the latest introduction in Pakistan in 2002. There was no thiacloprid resistance in 2002 and 2003, a low to moderate resistance during 2004-2006, and a very high resistance during 2007-2010 that even exceeded resistance to previous neonicotinoids. We may conclude that diafenthiuron and neonicotinoids remained effective against B. tabaci for 15 yr following their intensive use under field conditions, before a significant resistance, leading to their field failures, occurred in Pakistan.

Development of Diagnostic Insecticide Concentrations and Assessment of Insecticide Susceptibility in German Cockroach (Dictyoptera: Blattellidae) Field Strains Collected From Public Housing

Insecticide resistance in German cockroaches (Blattella germanica (L.)) has been a barrier to effective control since its first documentation in the 1950s. A necessary first step toward managing resistance is to understand insecticide susceptibility profiles in field-collected strains so that active ingredients (AIs) with lowest resistance levels can be identified. As a first step in this study, diagnostic concentrations (DCs) were determined for 14 insecticide AIs based on lethal concentrations that killed 99% or 90% of the individuals from a susceptible lab strain (JWax-S). Next, cockroaches were collected from two low-income multifamily housing complexes in Danville, IL, and Indianapolis, IN, and used to establish laboratory strains. These strains were screened against the 14 AI-DCs in vial bioassays, and susceptibility profiles were determined by comparing percent mortalities between the field strains relative to the JWax-S strain. Results revealed lowest resistance of field strains to boric acid, abamectin, dinotefuran, clothianidin, thiamethoxam, and chlorfenapyr. For the AIs hydramethylnon and imidacloprid, field strains did not display survivorship different than the lab strain, but >90% mortality was never achieved. Lastly, both field strains displayed resistance to indoxacarb, fipronil, acetamiprid, beta-cyfluthrin, bifenthrin, and lambda-cyhalothrin, but at varying levels. These results satisfy two objectives. First, baseline monitoring DCs were established for 14 insecticides presently registered for use against cockroaches, which represents a useful resource. Second, our findings reveal insecticide AIs with lowest resistance levels for use in forthcoming field studies that will investigate impacts of different insecticide deployment strategies on resistance management and evolution in cockroach field populations.

Multiple ATP-binding cassette transporters are involved in insecticide resistance in the small brown planthopper, Laodelphax striatellus

ATP-binding cassette (ABC) transporters are membrane-bound proteins involved in the movement of various substrates, including drugs and insecticides, across the lipid membrane. Demonstration of the role of human ABC transporters in multidrug resistance has led to speculation that they might be an important mechanism controlling the fate of insecticides in insects. However, the role of ABC transporters in insects remains largely unknown. The small brown planthopper, Laodelphax striatellus Fallén, has developed resistance to most of the insecticides used for its control. Our goals were to identify the ABC transporters in La. striatellus and to examine their involvement in resistance mechanisms, using related strains resistant to chlorpyrifos, deltamethrin and imidacloprid, compared with the susceptible strain. Based on the transcriptome of La. striatellus, 40 full-length ABC transporters belonging to the ABCA-ABCH subfamilies were identified. Quantitative PCR revealed that over 20% of genes were significantly up-regulated in different resistant strains, and eight genes from the ABCB/C/D/G subfamilies were up-regulated in all three resistant strains, compared with the susceptible strain. Furthermore, synergism studies showed verapamil significantly enhanced insecticide toxicity in various resistant strains but not in the susceptible strain. These results suggest that ABC transporters might be involved in resistance to multiple insecticides in La. striatellus.

Detection of Reduced Susceptibility to Chlorfenapyr- and Bifenthrin-Containing Products in Field Populations of the Bed Bug (Hemiptera: Cimicidae)

Insecticide resistance is a major impediment for effective control of Cimex lectularius L. Previous resistance detection studies with bed bugs have focused on certain pyrethroid, neonicotinoid, organochlorine, organophosphate, and carbamate insecticides. Within the pyrethroid class, resistance studies have mostly been limited to deltamethrin, lambda-cyhalothrin, and alpha- and beta-cyfluthrin. The goal of this study was to develop diagnostic concentration bioassays for assessing bed bug susceptibility levels to chlorfenapyr- and bifenthrin-containing products. First, glass vial and filter paper bioassay methods were compared for their utility in susceptibility monitoring. Statistical comparison of toxicity data between bioassays indicated that the vial assay was less confounded by assay susbtrate effects, required less insecticide, and was faster, especially for chlorfenapyr. Next, using vial diagnostic concentrations (LC99) for each insecticide, 10 laboratory-adapted field strains and the Harlan lab-susceptible strain were screened for susceptibility to chlorfenapyr and bifenthrin. The results of this study reveal recent bed bug susceptibility levels to certain chlorfenapyr- and bifenthrin-containing products. Reduced susceptibility was detected in three and five field strains to chlorfenapyr and bifenthrin, respectively. Detection of reduced susceptibility suggests that certain strains may be segregating toward greater chlorfenapyr and bifenthrin resistance. These results merit continuous resistance monitoring efforts to detect chlorfenapyr and bifenthrin susceptibility shifts. Additionally, to reduce insecticide selection pressures and delay resistance development, adoption of integrated bed bug control strategies that combine chemical and nonchemical methods is recommended.

APPEARANCE AND SWEEP OF A GENE DUPLICATION: ADAPTIVE RESPONSE AND POTENTIAL FOR NEW FUNCTIONS IN THE MOSQUITO CULEX PIPIENS

Evolution of a new gene function is a fundamental process of adaptation. Gene duplication followed by divergence due to relaxed selection on redundant copies has been viewed as the predominant mechanism involved in this process. At a macroevolutionary scale, evidence for this scenario came from the analysis of sequences of genes families. However, even if several genetic models have described the different potential microevolutionary scenario for a new function to evolve, little is really known about the initial evolutionary dynamics of such processes. We analyze such early dynamics in natural populations of the mosquito Culex pipiens polymorphic for a duplication at Ace.1, a locus involved in insecticide resistance. The date of occurrence and the selective advantages of the duplication were estimated using frequency data. We propose a scenario where the spread of a duplication is driven, from the very beginning, by selection due to insecticide treatment.

Malaria Vector Control Still Matters despite Insecticide Resistance

Mosquito vectors' resistance to insecticides is usually considered a major threat to the recent progresses in malaria control. However, studies measuring the impact of interventions and insecticide resistance reveal inconsistencies when using entomological versus epidemiological indices. First, evaluation tests that do not reflect the susceptibility of mosquitoes when they are infectious may underestimate insecticide efficacy. Moreover, interactions between insecticide resistance and vectorial capacity reveal nonintuitive outcomes of interventions. Therefore, considering ecological interactions between vector, parasite, and environment highlights that the impact of insecticide resistance on the malaria burden is not straightforward and we suggest that vector control still matters despite insecticide resistance.

Baseline Insecticide Susceptibility Screening Against Six Active Ingredients for Culex and Aedes (Diptera: Culicidae) Mosquitoes in the United States

Mosquitoes may develop resistance to insecticide active ingredients (AI). Thus, mosquitoes should be tested for resistance to confirm efficacy of insecticide-based control, inform management decisions, and protect public and environmental health. Our objectives were to determine a baseline of resistance for six AIs used in mosquito control in the United States to assess how resistance differs between mosquito collection location, AI, and mosquito species (container-ovipositing Aedes and Culex that may oviposit in containers or other sources). Field-collected eggs from 26 mosquito populations of five different species or hybrid species (Aedes albopictus Say, Aedes triseriatus Say, Culex pipiens L., Culex quinquefasciatus Say, Culex pipiens/quinquefasciatus) were obtained from four regions across the United States. Centers for Disease Control and Prevention bottle bioassays were used to determine baseline resistance and susceptibility status for six AIs (bifenthrin, deltamethrin, etofenprox, malathion, permethrin, and phenothrin). World Health Organization guidelines were used to classify mosquitoes as susceptible (98-100% mortality at diagnostic time [DT]), possibly resistant (80-97% mortality at DT), or resistant (< 80% mortality at DT). Aedes spp. mosquitoes were less likely to exhibit resistance, compared with Culex spp. mosquitoes. A high degree of resistance to etofenprox and malathion was observed (4-26-fold greater resistance to these two AIs compared with the other examined AIs). Baseline data on resistance and susceptibility for mosquitoes exposed to commonly used insecticides may help us evaluate resistance trends and highlight the importance of assessing local resistance trends before insecticide-based control measures are implemented.

House Reinfestation With Triatoma infestans (Hemiptera: Reduviidae) After Community-Wide Spraying With Insecticides in the Argentine Chaco: A Multifactorial Process

We investigated the dynamics and underlying causes of house (re)infestation with Triatoma infestans (Klug 1834) after a community-wide residual spraying with pyrethroids in a well-defined rural section of Pampa del Indio municipality (northeastern Argentina) over a 4-yr period. House infestation was assessed by timed manual searches, during insecticide applications, and by opportunistic householders' bug collections. All reinfested houses were selectively re-sprayed with insecticides. The resident population comprised Qom (66.6%) and Creole (33.4%) households, whose sociodemographic profiles differed substantially. The prevalence of house infestation dropped, less than expected, from 20.5% at baseline to 5.0% at 14 months postspraying (MPS), and then fluctuated between 0.8 and 4.2% over 21-51 MPS. Postspraying house infestation was positively and highly significantly associated with prespraying infestation. Most of the foci detected over 14-21 MPS were considered persistent (residual), some of which were moderately resistant to pyrethroids and were suppressed with malathion. Infestation patterns over 27-51 MPS suggested bug invasion from internal or external foci, but the sources of most findings were unaccounted for. Local spatial analysis identified two hotspots of postspraying house infestation. Using multimodel inference with model averaging, we corroborated that baseline domestic infestation was closely related to refuge availability, housing quality, and occurrence of peridomestic infestation. The diminished effectiveness of single pyrethroid treatments, partly attributable to moderate resistance compounded with rather insensitive vector detection methods and poor housing conditions, contributed to vector persistence. Improved control strategies combined with broad social participation are needed for the sustainable elimination of vector-borne human Chagas disease from the Gran Chaco.

Evolution of resistance to pyrethroid insecticides in Musca domestica

Houseflies, Musca domestica L., are a significant pest because of the numerous diseases they transmit. Control of housefly populations, particularly at animal production facilities, is frequently done using pyrethroid insecticides which kill insects by prolonging the open time of the voltage-sensitive sodium channel (VSSC). Houseflies have evolved resistance to pyrethroids owing to mutations in Vssc and by cytochrome-P450-mediated detoxification. Three Vssc mutations are known: kdr (L1014F), kdr-his (L1014H) and super-kdr (M918T + L1014F). Generally, the levels of resistance conferred by these mutations are kdr-his < kdr < super-kdr, but this pattern does not hold for multihalogenated benzyl pyrethroids, for which super-kdr confers less resistance than kdr. P450-mediated resistance can result from overexpression of CYP6D1 or another P450 (unidentified) whose overexpression is linked to autosomes II or V. The initial use of field-stable pyrethroids resulted in different patterns of evolution across the globe, but with time these mutations have become more widespread in their distribution. What is known about the fitness costs of the resistance alleles in the absence of insecticide is discussed, particularly with respect to the current and future utility of pyrethroid insecticides. © 2016 Society of Chemical Industry.

Effects of Different Surfaces and Insecticide Carriers on Residual Insecticide Bioassays Against Bed Bugs, Cimex spp. (Hemiptera: Cimicidae)

The performance of five insecticides (bendiocarb, deltamethrin, DDT, malathion, and imidacloprid) using three application methods (oil-based insecticide films on filter paper, and acetone-based insecticide deposits on two substrates: filter paper and glass) was assessed against a susceptible strain of Cimex lectularius (L.) and two resistant strains of Cimex hemipterus (F.). Substrate type significantly affected (P < 0.05) the insecticide knockdown response of the susceptible strain in acetone-based insecticide bioassays, with longer survival time on filter paper than on the glass surface. With the exception of deltamethrin, the different diluents (oil and acetone) also significantly affected (P < 0.05) the insecticide knockdown response of the susceptible strain in the filter paper-based insecticide bioassays, with longer survival time with acetone as the diluent. For both strains of C. hemipterus, there were no significant effects with the different surfaces and diluents for all insecticides except for malathion and imidacloprid, which was largely due to high levels of resistance. The lower effectiveness for the insecticide acetone-based treatment on filter paper may be due to crystal bloom. This occurs when an insecticide, dissolved in a volatile solvent, is applied onto absorptive surfaces. The effect is reduced on nonabsorptive surfaces and slowed down with oil-based insecticides, whereby the oil forms a film on absorptive surfaces. These findings suggest that nonabsorptive surfaces should be used in bioassays to monitor insecticide resistance. If absorptive surfaces are used in bioassays for testing active ingredients, then oil-based insecticides should be preferably used.

Identification of a novel cytochrome P450 CYP321B1 gene from tobacco cutworm (Spodoptera litura) and RNA interference to evaluate its role in commonly used insecticides

Insect cytochrome P450 monooxygenases (CYPs or P450s) play an important role in detoxifying insecticides leading to resistance in insect populations. A polyphagous pest, Spodoptera litura, has developed resistance to a wide range of insecticides. In the present study, a novel P450 gene, CYP321B1, was cloned from S. litura. The function of CYP321B1 was assessed using RNA interference (RNAi) and monitoring resistance levels for three commonly used insecticides, including chlorpyrifos, β-cypermethrin and methomyl. The full-length complementary DNA sequence of CYP321B1 is 1814 bp long with an open reading frame of 1 488 bp encoding 495 amino acid residues. Quantitative reverse-transcriptase polymerase chain reaction analyses during larval and pupal development indicated that CYP321B1 expression was highest in the midgut of fifth-instar larvae, followed by fat body and cuticle. The expression of CYP321B1 in the midgut was up-regulated by chlorpyrifos, β-cypermethrin and methomyl with both lethal concentration at 15% (LC₁₅ ) (50, 100 and 150 μg/mL, respectively) and 50%(LC₅₀ ) dosages (100, 200 and 300 μg/mL, respectively). Addition of piperonyl butoxide (PBO) significantly increased the toxicity of chlorpyrifos, β-cypermethrin and methomyl to S. litura, suggesting a marked synergism of the three insecticides with PBO and P450-mediated detoxification. RNAi-mediated silencing of CYP321B1 further increased mortality by 25.6% and 38.9% when the fifth-instar larvae were exposed to chlorpyrifos and β-cypermethrin, respectively, at the LC₅₀ dose levels. The results demonstrate that CYP321B1 might play an important role in chlorpyrifos and β-cypermethrin detoxification in S. litura.

Resistance Monitoring for Eight Insecticides on the Sweetpotato Whitefly (Hemiptera: Aleyrodidae) in China

The sweetpotato whitefly, Bemisia tabaci (Gennadius), is an important pest of many crops worldwide. Because control of B. tabaci still depends on the application of insecticides in China, monitoring the insecticide resistance of B. tabaci populations is essential for achieving control and for managing resistance. In this study, field populations of B. tabaci on vegetables were collected in three regions of China in 2011, 2012, and 2013. The resistance of these populations (all of which were determined to belong to biotype Q) to eight insecticides (abamectin, spinetoram, imidacloprid, thiamethoxam, acetamiprid, nitenpyram, chlorpyrifos, and bifenthrin) was assessed by the leaf-dip method. No resistance to abamectin and spinetoram was detected. All of the B. tabaci populations exhibited resistance to neonicotinoid insecticides; the resistance was 3.6- to 125.0-fold greater than that of a susceptible reference strain. The traditional insecticides chlorpyrifos and bifenthrin had very low toxicity. Bemisia tabaci specimens in some regions exhibited annual differences in resistance to some of the insecticides. The data presented will be helpful for making decisions on the proper insecticide usage in the field.

Use of the synergist piperonyl butoxide can slow the development of alpha-cypermethrin resistance in the whitefly Bemisia tabaci

The development of insecticide resistance in insect pests of crops is a growing threat to sustainable food production, and strategies that slow the development of resistance are therefore urgently required. The insecticide synergist piperonyl butoxide (PBO) inhibits certain insect detoxification systems and so may delay the evolution of metabolic resistance. In the current study we characterized resistance development in the silverleaf whitefly, Bemisia tabaci, after selection with either a neonicotinoid (thiacloprid) or pyrethroid (alpha-cypermethrin) insecticide alone or in combination with PBO. Resistance development was significantly suppressed (> 60%) in the line selected with alpha-cypermethrin + PBO compared to the line selected with alpha-cypermethrin alone. RNA sequencing (RNAseq) analyses revealed an increase in frequency of a knock-down resistance mutation but no differentially expressed genes were identified that could explain the sensitivity shift. No significant difference was observed in the level of resistance between the thiacloprid and thiacloprid + PBO selected lines, and RNA sequencing (RNAseq) analyses revealed that the cytochrome P450 monooxygenase CYP6CM1, known to metabolize neonicotinoids, was significantly upregulated (>10-fold) in both lines. The findings of this study demonstrate that PBO used in combination with certain insecticides can suppress the development of resistance in a laboratory setting; however, the mechanism by which PBO supresses resistance development remains unclear.

Development of Near-Isogenic Lines in a Parthenogenetically Reproduced Thrips Species, Frankliniella occidentalis

Although near-isogenic lines (NILs) can standardize genetic backgrounds among individuals, it has never been applied in parthenogenetically reproduced animals. Here, through multiple rounds of backcrossing and spinosad screening, we generated spinosad resistant NILs in the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), with a haplo-diploid reproduction system. The resultant F. occidentalis NIL-R strain maintained a resistance ratio over 30,000-fold, which was comparable to its parental resistant strain, Spin-R. More importantly, F. occidentalis NIL-R shared 98.90% genetic similarity with its susceptible parental strain Ivf03. By developing this toolset, we are able to segregate individual resistance and facilitate the mechanistic study of insecticide resistances in phloem-feeding arthropods, a group of devastating pest species reproducing sexually as well as asexually.

Resistance evolution in Drosophila: the case of CYP6G1

The massive use of DDT as an insecticide between 1940 and 1970 has resulted in the emergence of a resistant population of insects. One of the main metabolic mechanisms developed by resistant insects involves detoxification enzymes such as cytochrome P450s. These enzymes can metabolise the insecticide to render it less toxic and facilitate its elimination from the organism. The P450 Cyp6g1 was identified as the major factor responsible for DDT resistance in Drosophila melanogaster field populations. In this article, we review the data available for this gene since it was associated with resistance in 2002. The knowledge gained on Cyp6g1 allows a better understanding of the evolution of insecticide resistance mechanisms and highlights the major role of transposable elements in evolutionary processes. © 2016 Society of Chemical Industry.

Efficacy of Deltagard®, Fyfanon®, and Evoluer™ 31-66 Against Culex quinquefasciatus In Harris County, Texas

The comparative efficacy of ultra-low volume applications of deltamethrin, permethrin, and malathion against specific adult populations of Culex quinquefasciatus , a primary regional vector of Saint Louis encephalitis and West Nile virus, using field cage tests is described. At labeled application rates, the estimated mass median diameters for Fyfanon^®, Evoluer™, and DeltaGard^® were 18.32, 19.24, and 17.44 μm, respectively. No significant differences (P ≥ 0.01) in mean percent control were observed across all 3 wild populations and a susceptible Sebring strain tested with Fyfanon, DeltaGard, and Evoluer, providing 98.25%, 98.20%, and 97.24% mean percent control. Mean percent control for Sebring and 3 wild populations was 99.38%, 97.79%, 97.26%, and 97.15%, respectively, which were not significantly different from one another (P ≥ 0.01). Across all tests, highly significant differences (P ≤ 0.01) in mean percent control were obtained at 30.48, 60.96, and 91.44 m distances downwind, with mean percent control at 91.44 m being significantly less than that observed at 30.48 m, but not at 60.96 m. Individually, tests for DeltaGard, Fyfanon, and Evoluer resulted in no significant differences (P ≥ 0.01) in mean percent control between all mosquito populations tested, ranging from 96.47 to 100. However, Evoluer obtained significantly less (P ≤ 0.01) mean percent control at 91.44 m compared to DeltaGard and Fyfanon. Data suggest that the wild Cx. quinquefasciatus specimens collected were as susceptible as the laboratory Sebring strain. The use of Sebring as positive controls downwind strongly supported determination of the efficacy of all adulticides and susceptibility of wild populations tested.

Temporal patterns of imidacloprid resistance throughout a growing season in Leptinotarsa decemlineata populations

BACKGROUND

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is a major agricultural pest of commercial potatoes. Pest managers use a combination of control tactics to limit populations, including multiple insecticides. Finding a window of insecticide susceptibility and understanding genetic responses to insecticide exposure during a growing season may provide novel management recommendations for L. decemlineata.

RESULTS

We examined temporal changes (during one growing season) in phenotypic response between a susceptible population and an imidacloprid-resistant population. Beetles remained more susceptible to imidacloprid in the susceptible population throughout the growing season. Estimated mean LC₅₀ values varied throughout the growing season in the resistant population, with increased susceptibility among overwintered and recently emerged adult beetles compared with a heightened level of resistance in the second generation. RNA transcript abundance was compared among multiple time points through the growing season, showing that cuticular proteins and cytochrome p450s were highly upregulated during peaks of measured resistance.

CONCLUSION

Temporal variation in imidacloprid susceptibility of L. decemlineata was observed, which included early time points of susceptibility and later peaks in resistance. Heightened resistance occurred during the second generation and correlated to increased transcript abundance of multiple mechanisms of resistance, including multiple cuticular protein and cytochrome p450 transcripts. © 2016 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A perspective on management of Helicoverpa armigera: transgenic Bt cotton, IPM, and landscapes

Helicoverpa armigera is a major pest of agriculture, horticulture and floriculture throughout the Old World and recently invaded parts of the New World. We overview of the evolution in thinking about the application of area-wide approaches to assist with its control by the Australian Cotton Industry to highlight important lessons and future challenges to achieving the same in the New World. An over-reliance of broad-spectrum insecticides led to Helicoverpa spp. in Australian cotton rapidly became resistant to DDT, synthetic pyrethroids, organophosphates, carbamates and endosulfan. Voluntary strategies were developed to slow the development of insecticide resistance, which included rotating chemistries and basing spray decisions on thresholds. Despite adoption of these practices, insecticide resistance continued to develop until the introduction of genetically modified cotton provided a platform for augmenting Integrated Pest Management in the Australian cotton industry. Compliance with mandatory resistance management plans for Bt cotton necessitated a shift from pest control at the level of individual fields or farms towards a coordinated area-wide landscape approach. Our take-home message for control of H. armigera is that resistance management is essential in genetically modified crops and must be season long and area-wide to be effective. © 2016 Society of Chemical Industry.

Evolution of Stored-Product Entomology: Protecting the World Food Supply

Traditional methods of stored-product pest control were initially passed from generation to generation. Ancient literature and archaeology reveal hermetic sealing, burning sulfur, desiccant dusts, and toxic botanicals as early control methods. Whereas traditional nonchemical methods were subsequently replaced by synthetic chemicals, other traditional methods were improved and integrated with key modern pesticides. Modern stored-product integrated pest management (IPM) makes decisions using knowledge of population dynamics and threshold insect densities. IPM programs are now being fine-tuned to meet regulatory and market standards. Better sampling methods and insights from life histories and ecological studies have been used to optimize the timing of pest management. Over the past 100 years, research on stored-product insects has shifted from being largely concentrated within 10 countries to being distributed across 65 countries. Although the components of IPM programs have been well researched, more research is needed on how these components can be combined to improve effectiveness and assure the security of postharvest food as the human population increases.

An Operational Framework for Insecticide Resistance Management Planning

Arthropod vectors transmit organisms that cause many emerging and reemerging diseases, and their control is reliant mainly on the use of chemical insecticides. Only a few classes of insecticides are available for public health use, and the increased spread of insecticide resistance is a major threat to sustainable disease control. The primary strategy for mitigating the detrimental effects of insecticide resistance is the development of an insecticide resistance management plan. However, few examples exist to show how to implement such plans programmatically. We describe the formulation and implementation of a resistance management plan for mosquito vectors of human disease in Zambia. We also discuss challenges, steps taken to address the challenges, and directions for the future.

Resistance mutation conserved between insects and mites unravels the benzoylurea insecticide mode of action on chitin biosynthesis

Despite the major role of chitin biosynthesis inhibitors such as benzoylureas (BPUs) in the control of pests in agricultural and public health for almost four decades, their molecular mode of action (MoA) has in most cases remained elusive. BPUs interfere with chitin biosynthesis and were thought to interact with sulfonylurea receptors that mediate chitin vesicle transport. Here, we uncover a mutation (I1042M) in the chitin synthase 1 (CHS1) gene of BPU-resistant Plutella xylostella at the same position as the I1017F mutation reported in spider mites that confers etoxazole resistance. Using a genome-editing CRISPR/Cas9 approach coupled with homology-directed repair (HDR) in Drosophila melanogaster, we introduced both substitutions (I1056M/F) in the corresponding fly CHS1 gene (kkv). Homozygous lines bearing either of these mutations were highly resistant to etoxazole and all tested BPUs, as well as buprofezin-an important hemipteran chitin biosynthesis inhibitor. This provides compelling evidence that BPUs, etoxazole, and buprofezin share in fact the same molecular MoA and directly interact with CHS. This finding has immediate effects on resistance management strategies of major agricultural pests but also on mosquito vectors of serious human diseases such as Dengue and Zika, as diflubenzuron, the standard BPU, is one of the few effective larvicides in use. The study elaborates on how genome editing can directly, rapidly, and convincingly elucidate the MoA of bioactive molecules, especially when target sites are complex and hard to reconstitute in vitro.

Mapping the distribution of Anopheles funestus across Benin highlights a sharp contrast of susceptibility to insecticides and infection rate to Plasmodium between southern and northern populations

Background. Malaria remains an important public health issue in Benin, with Anopheles gambiae s.l. and Anopheles funestus s.s being the predominant vectors. This study was designed to generate information on An. funestus distribution, molecular speciation, Plasmodium infection rate and insecticide susceptibility status across Benin. Methods. Mosquito samples were collected from December 2014 to January 2016 in 46 localities in Benin. These samples were mapped and An. funestus collected were speciated to the molecular level. Plasmodium infection rate was determined using a Taqman assay and susceptibility to insecticides was assessed using the WHO guidelines. The genotyping of the L119F- Gste2 mutation was also carried out.  Results.  An. funestus was found in 8 out of the 46 localities surveyed with a high presence in Tanongou (wet Sudanese ecological zone), Kpome, Doukonta and Pahou (sub-equatorial ecological zone). Molecular identifications revealed that only An. funestuss.s was present in southern Benin, whereas in Tanongou (northern Benin) An. funestus s.s. and An. leesoni were found in sympatry at proportions of 77.7% and 22.3% respectively. Plasmodium infection rate of An. funestus was higher in southern Benin at a range of 13 to 18% compared to 5.6% recorded in Tanongou. High DDT (8±0.5%) and permethrin (11±0.5%) resistance were observed in Doukonta, Kpome and Pahou, contrasting with relatively low resistance profiles: mortality-DDT=90±3.18% and mortality-permethrin=100% in Tanongou. Genotyping analysis revealed  high frequency  of the resistant 119F allele in the South (Kpome and Doukonta) compared to the North (Tanongou).  Discussion and Conclusion. The high presence of   An. funestus in the South compared to the North  could be due to favorable environmental and climatic conditions found in both regions. A significant Plasmodium infection rate was recorded across the country. A high resistance profile was recorded in the southern Benin; this raises the need for further investigations on resistance selection factors.

Mapping the distribution of Anopheles funestus across Benin highlights a sharp contrast of susceptibility to insecticides and infection rate to Plasmodium between southern and northern populations

Background. Malaria remains an important public health issue in Benin, with Anopheles gambiae s.l. and Anopheles funestus s.s being the predominant vectors. This study was designed to generate information on An. funestus distribution, molecular speciation, Plasmodium infection rate and insecticide susceptibility status across Benin. Methods. Mosquito samples were collected from December 2014 to January 2016 in 46 localities in Benin. These samples were mapped and An. funestus collected were speciated to the molecular level. Plasmodium infection rate was determined using a Taqman assay and susceptibility to insecticides was assessed using the WHO guidelines. The genotyping of the L119F- Gste2 mutation was also carried out.  Results.  An. funestus was found in 8 out of the 46 localities surveyed with a high presence in Tanongou (wet Sudanese ecological zone), Kpome, Doukonta and Pahou (sub-equatorial ecological zone). Molecular identifications revealed that only An. funestuss.s was present in southern Benin, whereas in Tanongou (northern Benin) An. funestus s.s. and An. leesoni were found in sympatry at proportions of 77.7% and 22.3% respectively. Plasmodium infection rate of An. funestus was higher in southern Benin at a range of 13 to 18% compared to 5.6% recorded in Tanongou. High DDT (8±0.5%) and permethrin (11±0.5%) resistance were observed in Doukonta, Kpome and Pahou, contrasting with relatively low resistance profiles: mortality-DDT=90±3.18% and mortality-permethrin=100% in Tanongou. Genotyping analysis revealed  high frequency  of the resistant 119F allele in the South (Kpome and Doukonta) compared to the North (Tanongou).  Discussion and Conclusion. The high presence of   An. funestus in the South compared to the North  could be due to favorable environmental and climatic conditions found in both regions. A significant Plasmodium infection rate was recorded across the country. A high resistance profile was recorded in the southern Benin; this raises the need for further investigations on resistance selection factors.

Evidence of Tolerance to Silica-Based Desiccant Dusts in a Pyrethroid-Resistant Strain of Cimex lectularius (Hemiptera: Cimicidae)

Insecticide resistance in bed bugs (Cimex lectularius and Cimex hemipterus) has become widespread, which has necessitated the development of new IPM (Integrated Pest Management) strategies and products for the eradication of infestations. Two promising options are the diatomaceous earth and silica gel-based desiccant dusts, both of which induce dehydration and eventual death upon bed bugs exposed to these products. However, the impact of underlying mechanisms that confer resistance to insecticides, such as cuticle thickening, on the performance of these dusts has yet to be determined. In the present study, two desiccant dusts, CimeXa Insecticide Dust (silica gel) and Bed Bug Killer Powder (diatomaceous earth) were evaluated against two strains of C. lectularius; one highly pyrethroid-resistant and one insecticide-susceptible. Label-rate doses of both products produced 100% mortality in both strains, albeit over dissimilar time-frames (3–4 days with CimeXa vs. 14 days with Bed Bug Killer). Sub-label rate exposure to CimeXa indicated that the pyrethroid-resistant strain possessed a degree of tolerance to this product, surviving 50% longer than the susceptible strain. This is the first study to suggest that mechanisms conferring resistance to pyrethroids, such as cuticular thickening, may have potential secondary impacts on non-synthetic insecticides, including desiccant dusts, which target the bed bug’s cuticle.

Genetic variation in target-site resistance to pyrethroids and pirimicarb in Tunisian populations of the peach potato aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae)

BACKGROUND

We used molecular assays to diagnose resistance to pyrethroids and pirimicarb in samples of Myzus persicae from field crops or an insect suction trap in Tunisia. Genotypes for resistance loci were related to ones for polymorphic microsatellite loci in order to investigate breeding systems and patterns of genetic diversity, and to inform resistance management tactics.

RESULTS

The kdr mutation L1014F conferring pyrethroid resistance was found in all samples. The M918T s-kdr mutation also occurred in most samples, but only in conjunction with kdr. We discovered a previously unreported genotype heterozygous for L1014F but homozygous for M918T. Samples with modified acetylcholinesterase (MACE) conferring resistance to pirimicarb were less common but widespread. 16% of samples contained both the kdr and MACE mutations. Many unique microsatellite genotypes were found, suggesting that M. persicae is holocyclic in Tunisia. There were no consistent associations between resistance and microsatellite markers.

CONCLUSION

This first study of insecticide resistance in M. persicae in North Africa showed genetic variation in insecticide resistance within microsatellite multilocus genotypes (MLG_M s) and the same resistance mechanisms to be present in different MLG_M s. This contrasts with variation in northern Europe where M. persicae is fully anholocyclic. Implications for selection and control strategies are discussed. © 2016 Society of Chemical Industry.