Evolution Of Pesticide Resistance Research Articles

Discovering new mode-of-action pesticide leads inhibiting protein-protein interactions: example targeting plant O-acetylserine sulfhydrylase.

The widespread evolution of pesticide resistance poses a significant challenge to current agriculture, necessitating the discovery of molecules with new modes of action. Despite extensive efforts, no major molecules with new modes of action have been commercialized for decades. Most pesticides function by binding to specific pockets on target enzymes, enabling a single target site mutation to confer resistance. An alternative approach is the disruption of protein-protein interactions (PPI), which require complementary mutations on both interacting partners for resistance to occur. Thus, our aim is the discovery and design of small-molecule inhibitors that target the interface of the PPI complex of O-acetylserine sulfhydrylase (OASS) and serine acetyltransferase (SAT), key obligatory interacting plant enzymes involved in the biosynthesis of the amino acid cysteine. By employing in silico filtering techniques on a virtual library of 30 million small molecules, we identified initial hits capable of binding OASS and interfering with its interaction with a peptide derived from SAT with a half-maximal inhibitory concentration (IC50) of 34 μm. Subsequently, we conducted molecular chemical optimizations, generating an early lead molecule (PJ4) with an IC50 value of 4 μm. PJ4 successfully inhibited the germination of Arabidopsis thaliana seedlings and inhibited clover growth in a pre-emergence application at an effective concentration of 4.6 kg ha-1. These new compounds described herein can serve as promising leads for further optimization as herbicides with a new mode-of-action. This technology can be used for discovering new modes of action chemicals inhibiting all pest groups. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Quantifying farm sustainability through the lens of ecological theory.

The achievements of the Green Revolution in meeting the nutritional needs of a growing global population have been won at the expense of unintended consequences for the environment. Some of these negative impacts are now threatening the sustainability of food production through the loss of pollinators and natural enemies of crop pests, the evolution of pesticide resistance, declining soil health and vulnerability to climate change. In the search for farming systems that are sustainable both agronomically and environmentally, alternative approaches have been proposed variously called 'agroecological', 'conservation agriculture', 'regenerative' and 'sustainable intensification'. While the widespread recognition of the need for more sustainable farming is to be welcomed, this has created etymological confusion that has the potential to become a barrier to transformation. There is a need, therefore, for objective criteria to evaluate alternative farming systems and to quantify farm sustainability against multiple outcomes. To help meet this challenge, we reviewed the ecological theories that explain variance in regulating and supporting ecosystem services delivered by biological communities in farmland to identify guiding principles for management change. For each theory, we identified associated system metrics that could be used as proxies for agroecosystem function. We identified five principles derived from ecological theory: (i) provide key habitats for ecosystem service providers; (ii) increase crop and non-crop habitat diversity; (iii) increase edge density: (iv) increase nutrient-use efficiency; and (v) avoid extremes of disturbance. By making published knowledge the foundation of the choice of associated metrics, our aim was to establish a broad consensus for their use in sustainability assessment frameworks. Further analysis of their association with farm-scale data on biological communities and/or ecosystem service delivery would provide additional validation for their selection and support for the underpinning theories.

Resevol: An R package for spatially explicit models of pesticide resistance given evolving pest genomes.

The evolution of pesticide resistance is a widespread problem with potentially severe consequences for global food security. We introduce the resevol R package, which simulates individual-based models of pests with evolving genomes that produce complex, polygenic, and covarying traits affecting pest life history and pesticide resistance. Simulations are modelled on a spatially-explicit and highly customisable landscape in which crop and pesticide application and rotation can vary, making the package a highly flexible tool for both general and tactical models of pest management and resistance evolution. We present the key features of the resevol package and demonstrate its use for a simple example simulating pests with two covarying traits. The resevol R package is open source under GNU Public License. All source code and documentation are available on GitHub.

The dynamic changes of genes revealed that persistently overexpressed genes drive the evolution of cyflumetofen resistance in Tetranychus cinnabarinus.

Changes in gene expression are associated with the evolution of pesticide resistance in arthropods. In this study, transcriptome sequencing was performed in 3 different resistance levels (low, L; medium, M; and high, H) of cyflumetofen-resistant strain (YN-CyR). A total of 1685 genes, including 97 detoxification enzyme genes, were upregulated in all 3 stages, of which 192 genes, including 11 detoxification enzyme genes, showed a continuous increase in expression level with resistance development (L to H). RNA interference experiments showed that overexpression of 7 genes (CYP392A1, TcGSTd05, CCE06, CYP389A1, TcGSTz01, CCE59, and CYP389C2) is involved in the development of cyflumetofen resistance in Tetranychus cinnabarinus. The recombinant CYP392A1 can effectively metabolize cyflumetofen, while CCE06 can bind and sequester cyflumetofen in vitro. We compared 2 methods for rapid screening of resistance molecular markers, including short-term induction and 1-time high-dose selection. Two detoxification enzyme genes were upregulated in the field susceptible strain (YN-S) by induction with 20% lethal concentration (LC20 ) of cyflumetofen. However, 16 detoxification enzyme genes were upregulated by 1-time selection with LC80 of cyflumetofen. Interestingly, the 16 genes were overexpressed in all 3 resistance stages. These results indicated that 1685 genes that were upregulated at the L stage constituted the basis of cyflumetofen resistance, of which 192 genes in which upregulation continued to increase were the main driving force for the development of resistance. Moreover, the 1-time high-dose selection is an efficient way to rapidly obtain the resistance-related genes that can aid in the development of resistance markers and resistance management in mites.

A metapopulation model reveals connectivity-driven hotspots in treatment resistance evolution in a marine parasite

Abstract In salmon aquaculture, the sustainable management of salmon lice (Lepeophtheirus salmonis) is limited by the adaptive capacity of the parasite. This is evident in the repeated evolution of pesticide resistance in the salmon louse population. To better prepare for resistance, we constructed a numerical metapopulation model that predicts the evolutionary dynamics of lice across an interconnected farm network. This model integrates within-farm population dynamics and between-farm louse dispersal, the latter using outputs from a state-of-the-art particle-tracking model. Distinct from previous metapopulation models, it also simulates spatial and temporal genetic variation arising from selection. The model was parameterized to simulate the evolution of resistance to the pesticide azamethiphos on farms in southern Norway. It successfully reproduced the rapid (within 10 years) evolution of azamethiphos resistance following extensive delousing treatments. It also identified strong spatial patterns in resistance, with regions of high farm connectivity being potential hotspots of louse adaptation. Rates of infestation and evolution were significantly reduced when highly connected farms were excluded from the simulation, compared to when low-connectivity or random sites were excluded. This model can be a valuable tool for coordinating pest management at a regional scale, in a way that slows or prevents the spread of resistance.

Predicting Resistance: Quantifying the Relationship between Urban Development, Agricultural Pesticide Use, and Pesticide Resistance in a Nontarget Amphipod.

Resistance alleles within the voltage-gated sodium channel (vgsc) have been correlated with pyrethroid resistance in wild populations of the nontarget amphipod, Hyalella azteca from California (CA), U.S.A. In the present study, we expand upon the relationship between land use and the evolution of pesticide resistance in H. azteca to develop a quantitative methodology to target and screen novel populations for resistance allele genotypes in a previously uninvestigated region of the U.S. (New England: NE). By incorporating urban land development and toxicity-normalized agricultural pesticide use indices into our site selection, we successfully identified three amino acid substitutions associated with pyrethroid resistance. One of the resistance mutations has been described in H. azteca from CA (L925I). We present the remaining two (vgsc I936F and I936V) as novel pyrethroid-resistance alleles in H. azteca based on previous work in insects and elevated cyfluthrin resistance in one NE population. Our results suggest that urban pesticide use is a strong driver in the evolution of resistance alleles in H. azteca. Furthermore, our method for resistance allele screening provides an applied framework for detecting ecosystem impairment on a nationwide scale that can be incorporated into ecological risk assessment decisions.

Dominance shifts increase the likelihood of soft selective sweeps.

Genetic models of adaptation to a new environment have typically assumed that the alleles involved maintain a constant fitness dominance across the old and new environments. However, theories of dominance suggest that this should often not be the case. Instead, the alleles involved should frequently shift from recessive deleterious in the old environment to dominant beneficial in the new environment. Here, we study the consequences of these expected dominance shifts for the genetics of adaptation to a new environment. We find that dominance shifts increase the likelihood that adaptation occurs from standing variation, and that multiple alleles from the standing variation are involved (a soft selective sweep). Furthermore, we find that expected dominance shifts increase the haplotypic diversity of selective sweeps, rendering soft sweeps more detectable in small genomic samples. In cases where an environmental change threatens the viability of the population, we show that expected dominance shifts of newly beneficial alleles increase the likelihood of evolutionary rescue and the number of alleles involved. Finally, we apply our results to a well-studied case of adaptation to a new environment: the evolution of pesticide resistance at the Ace locus in Drosophila melanogaster. We show that, under reasonable demographic assumptions, the expected dominance shift of resistant alleles causes soft sweeps to be the most frequent outcome in this case, with the primary source of these soft sweeps being the standing variation at the onset of pesticide use, rather than recurrent mutationthereafter.

Increasing Frequency of G275E Mutation in the Nicotinic Acetylcholine Receptor α6 Subunit Conferring Spinetoram Resistance in Invading Populations of Western Flower Thrips in China.

Simple SummaryThe western flower thrips (WFT) Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is an important invasive pest in agriculture and forestry. It has developed resistance to a frequently used pesticide spinetoram world widely, including the invading area of China. However, the mechanism of resistance to spinetoram is unclear in China. In this study, we found the presence of the G275E mutation in the nicotinic acetylcholine receptor Foα6 in the early invading populations, which has now increased to a high frequency in China. There was a correlation between the frequency of the G275E mutation and resistance to spinetoram as characterized by median lethal concentration. Our results showed that G275E mutation is one of the mechanisms conferring spinetoram resistance in invading populations in China, as in many other countries. Our study highlights the rapid spread of the G275E mutation in China in the 2009–2021 period.The western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is an important invasive pest worldwide. Field-evolved resistance to the pesticide spinetoram is an increasing problem in the chemical control of this pest. Here, we examined changes in the frequency of a genetic mutation associated with spinetoram resistance, the G275E mutation in the acetylcholine receptor Foα6, in 62 field populations collected from 2009 to 2021 across areas of China invaded by this pest. We found a low frequency of the G275E mutation in populations collected at the early invasion stage, in contrast to a high frequency in native USA populations. However, the frequency of the G275E mutation has increased to a high level in recently collected populations, with the mutation becoming fixed in some populations. There was a correlation between the frequency of the G275E mutation and resistance to spinetoram as characterized by median lethal concentration, although two populations were outliers. These results showed that G275E mutation is one of the mechanisms conferring spinetoram resistance in many invading populations in China. Ongoing dispersal of the WFT may have facilitated a rapid increase in the G275E mutation across China. Our study highlights the rapid evolution of pesticide resistance in an invasive species and points to a useful marker for molecular diagnostics of spinetoram resistance.

Circular RNA, circ1-3p, is Involved in Cyflumetofen Resistance by Acting as a Competitive RNA against miR-1-3p in Tetranychus cinnabarinus.

As a newly recognized type of noncoding RNA, circular RNA can mediate a variety of physiological changes in mammals by regulating the post-transcriptional expression level of genes. However, the function of circRNA in the evolution of pesticide resistance in arthropods is still unknown. In this study, 2546 circRNAs were identified in Tetranychus cinnabarinus by transcriptome sequencing. The differentially expressed gene analysis indicated that 44 circRNAs were overexpressed in a cyflumetofen-resistant strain, of which a circRNA (named circ1-3p) was found to contain the response elements of miR-1-3p, an miRNA that is involved in cyflumetofen resistance by targeting TcGSTm04. The circular structure of circ1-3p was further determined using a divergent primer. The results of different molecular assays in vitro and in vivo showed that circ1-3p can compete with TcGSTm04 in miR-1-3p binding. The colocalization of circ1-3p and miR-1-3p was found using fluorescence in situ hybridization, suggesting that circ1-3p can directly sponge miR-1-3p in T. cinnabarinus. In addition, silencing the expression of circ1-3p resulted in the upregulation of miR-1-3p and the downregulation of TcGSTm04 as well as a significant increase in the sensitivity of T. cinnabarinus to cyflumetofen. All these pieces of evidence indicates that overexpressed circ1-3p promotes the expression of TcGSTm04 through sponging miR-1-3p, thereby involving in the evolution of cyflumetofen resistance in T. cinnabarinus.

Differential local genetic adaptation to pesticide use in organic and conventional agriculture in an aquatic non-target species.

Pesticide application is an important stressor to non-target species and can profoundly affect ecosystem functioning. Debates continue on the choice of agricultural practices regarding their environmental impact, and organic farming is considered less detrimental compared to conventional practices. Nevertheless, comparative studies on the impacts of both agricultural approaches on the genetic adaptation of non-target species are lacking. We assessed to what extent organic and conventional agriculture elicit local genetic adaptation of populations of a non-target aquatic species, Daphnia magna. We tested for genetic differences in sensitivity of different D. magna populations (n = 7), originating from ponds surrounded by conventional and organic agriculture as well as nature reserves, to pesticides used either in conventional (chlorpyrifos) or organic agriculture (deltamethrin and copper sulfate). The results indicate that D. magna populations differentially adapt to local pesticide use. Populations show increased resistance to chlorpyrifos as the percentage of conventional agriculture in the surrounding landscape increases, whereas populations from organic agriculture sites are more resistant to deltamethrin. While organic agriculture is considered less harmful for non-target species than conventional, both types of agriculture shape the evolution of pesticide resistance in non-target species in a specific manner, reflecting the differences in selection pressure.

Spatial Variation in Australian Neonicotinoid Usage and Priorities for Resistance Monitoring.

Australia is the third largest exporting country of cereals and a leader in other major commodity crops, yet little data exist on pesticide usage patterns in agriculture. This knowledge gap limits the management of off-target chemical impacts, such as the evolution of pesticide resistance. Here, for the first time, we quantify spatial patterns in neonicotinoid applications in Australia by coalescing land use data with sales and market research data contributed by agrichemical and agribusiness companies. An example application to resistance management is explored through the development of recommendations for the cosmopolitan crop pest, Myzus persicae (Sulzer) (Hemiptera: Aphididae), utilizing spatial statistical models. This novel dataset identified Australian neonicotinoid usage patterns, with most neonicotinoid products in Australia applied as cereal, canola, cotton and legume seed treatments and soil applications in sugarcane. Importantly, there were strong regional differences in pesticide applications, which will require regionally specific strategies to manage off-target impacts. Indeed, the estimated spatial grid of neonicotinoid usage demonstrated a statistically significant influence on the distribution of M. persicae neonicotinoid resistance, indicating off-target impacts are unevenly distributed in space. Future research on neonicotinoid usage will be supported by the spatial grids generated and made available through this study. Overall, neonicotinoid pesticides are widely relied upon throughout Australia's plant production systems but will face increasing pressure from resistance evolution, emerging research on off-target impacts, and stricter regulatory pressures.

Genetic differentiation in pesticide resistance between urban and rural populations of a nontarget freshwater keystone interactor, Daphnia magna.

There is growing evidence that urbanization drives adaptive evolution in response to thermal gradients. One such example is documented in the water flea Daphnia magna. However, organisms residing in urban lentic ecosystems are increasingly exposed to chemical pollutants such as pesticides through run‐off and aerial transportation. The extent to which urbanization drives the evolution of pesticide resistance in aquatic organisms and whether this is impacted by warming and thermal adaptation remains limitedly studied. We performed a common garden rearing experiment using multiple clonal lineages originating from five replicated urban and rural D. magna populations, in which we implemented an acute toxicity test exposing neonates (<24h) to either a solvent control or the organophosphate pesticide chlorpyrifos. Pesticide exposures were performed at two temperatures (20°C vs. 24°C) to test for temperature‐associated differences in urbanization‐driven evolved pesticide resistance. We identified a strong overall effect of pesticide exposure on Daphnia survival probability (−72.8 percentage points). However, urban Daphnia genotypes showed higher survival probabilities compared to rural ones in the presence of chlorpyrifos (+29.7 percentage points). Our experiment did not reveal strong temperature x pesticide or temperature x pesticide x urbanization background effects on survival probability. The here observed evolution of resistance to an organophosphate pesticide is a first indication Daphnia likely also adapts to pesticide pollution in urban areas. Increased pesticide resistance could facilitate their population persistence in urban ponds, and feed back to ecosystem functions, such as top‐down control of algae. In addition, adaptive evolution of nontarget organisms to pest control strategies and occupational pesticide use may modulate how pesticide applications affect genetic and species diversity in urban areas.

High-resolution genetic mapping reveals cis-regulatory and copy number variation in loci associated with cytochrome P450-mediated detoxification in a generalist arthropod pest.

Chemical control strategies are driving the evolution of pesticide resistance in pest populations. Understanding the genetic mechanisms of these evolutionary processes is of crucial importance to develop sustainable resistance management strategies. The acaricide pyflubumide is one of the most recently developed mitochondrial complex II inhibitors with a new mode of action that specifically targets spider mite pests. In this study, we characterize the molecular basis of pyflubumide resistance in a highly resistant population of the spider mite Tetranychus urticae. Classical genetic crosses indicated that pyflubumide resistance was incompletely recessive and controlled by more than one gene. To identify resistance loci, we crossed the resistant population to a highly susceptible T. urticae inbred strain and propagated resulting populations with and without pyflubumide exposure for multiple generations in an experimental evolution set-up. High-resolution genetic mapping by a bulked segregant analysis approach led to the identification of three quantitative trait loci (QTL) linked to pyflubumide resistance. Two QTLs were found on the first chromosome and centered on the cytochrome P450 CYP392A16 and a cluster of CYP392E6-8 genes. Comparative transcriptomics revealed a consistent overexpression of CYP392A16 and CYP392E8 in the experimental populations that were selected for pyflubumide resistance. We further corroborated the involvement of CYP392A16 in resistance by in vitro functional expression and metabolism studies. Collectively, these experiments uncovered that CYP392A16 N-demethylates the toxic carboxamide form of pyflubumide to a non-toxic compound. A third QTL coincided with cytochrome P450 reductase (CPR), a vital component of cytochrome P450 metabolism. We show here that the resistant population harbors three gene copies of CPR and that this copy number variation is associated with higher mRNA abundance. Together, we provide evidence for detoxification of pyflubumide by cytochrome P450s that is likely synergized by gene amplification of CPR.

Design, Synthesis, and Pesticidal Activities of Pyrimidin-4-amine Derivatives Bearing a 5-(Trifluoromethyl)-1,2,4-oxadiazole Moiety.

It is important to discover new pesticides with new modes of action because of the increasing evolution of pesticide resistance. In this study, a series of novel pyrimidin-4-amine derivatives containing a 5-(trifluoromethyl)-1,2,4-oxadiazole moiety were designed and synthesized. Their structures were confirmed by 1H NMR, 13C NMR, and HRMS. Bioassays indicated that the 29 compounds synthesized possessed excellent insecticidal activity against Mythimna separata, Aphis medicagini, and Tetranychus cinnabarinus and fungicidal activity against Pseudoperonospora cubensis. Among these pyrimidin-4-amine compounds, 5-chloro-N-(2-fluoro-4-(5-(trifluoromethyl)-1,2,4-oxadiazol-3-yl)benzyl)-6-(1-fluoroethyl)pyrimidin-4-amine (U7) and 5-bromo-N-(2-fluoro-4-(5-(trifluoromethyl)-1,2,4-oxadiazol-3-yl)benzyl)-6-(1-fluoroethyl) pyrimidin-4-amine(U8) had broad-spectrum insecticidal and fungicidal activity. The LC50 values were 3.57 ± 0.42, 4.22 ± 0.47, and 3.14 ± 0.73 mg/L for U7, U8, and flufenerim against M. separata, respectively. The EC50 values were 24.94 ± 2.13, 30.79 ± 2.21, and 3.18 ± 0.21 mg/L for U7, U8, and azoxystrobin against P. cubensis, respectively. The AChE enzymatic activity testing revealed that the enzyme activities of compounds U7, U8, and flufenerim are 0.215, 0.184, and 0.184 U/mg prot, respectively. The molecular docking results of compounds U7, U8, and flufenerim with the AChE model demonstrated the opposite docking mode between compound U7 or U8 and positive control flufenerim in the active site of AChE. The structure-activity relationships are also discussed. This work provided excellent pesticide for further optimization. Density functional theory analysis can potentially be used to design more active compounds.

Increasing temperature elevates the variation and spatial differentiation of pesticide tolerance in a plant pathogen.

Climate change and pesticide resistance are two of the most imminent challenges human society is facing today. Knowledge of how the evolution of pesticide resistance may be affected by climate change such as increasing air temperature on the planet is important for agricultural production and ecological sustainability in the future but is lack in scientific literatures reported from empirical research. Here, we used the azoxystrobin‐Phytophthora infestans interaction in agricultural systems to investigate the contributions of environmental temperature to the evolution of pesticide resistance and infer the impacts of global warming on pesticide efficacy and future agricultural production and ecological sustainability. We achieved this by comparing azoxystrobin sensitivity of 180 P. infestans isolates sampled from nine geographic locations in China under five temperature schemes ranging from 13 to 25°C. We found that local air temperature contributed greatly to the difference of azoxystrobin tolerance among geographic populations of the pathogen. Both among‐population and within‐population variations in azoxystrobin tolerance increased as experimental temperatures increased. We also found that isolates with higher azoxystrobin tolerance adapted to a broader thermal niche. These results suggest that global warming may enhance the risk of developing pesticide resistance in plant pathogens and highlight the increased challenges of administering pesticides for effective management of plant diseases to support agricultural production and ecological sustainability under future thermal conditions.

Parasites under pressure: salmon lice have the capacity to adapt to depth-based preventions in aquaculture

The evolution of pesticide resistance has driven renewed interest in non-chemical pest controls in agriculture. Spatial manipulations (physical barriers and fallowing, for example) can be an effective method of prevention, but these too might impose selection and cause rapid adaptation in pests. In salmon aquaculture, various non-chemical approaches have emerged to combat parasitic salmon lice (Lepeophtheirus salmonis) – a major pest with clear signs of evolved chemical resistance. ‘Depth-based’ preventions, now widely implemented, reduce infestation rates by physically segregating salmon from lice in their infective copepodid stage occurring in surface waters. Copepodids distributed deeper in the water column, however, can bypass these barriers and infest farms. If swimming depth is a heritable trait, we may see rapid evolutionary shifts in response to widespread depth-based prevention. We collected lice from Norwegian salmon farms and assayed more than 11,250 of their laboratory-reared offspring across 37 families. The vertical distributions of copepodids were measured using experimental water columns pressurised to simulate conditions at 0, 5 and 10 m depths. We demonstrated that lice respond strongly to hydrostatic pressure: an increase in pressure doubled the number of lice that migrated to the top of columns. There was also a large effect of family on this response, with the percentage of lice ascending to the top of pressurised columns ranging from 17 to 79% across families. Families with a weak swimming response to pressure are expected to occur deeper in the water column and so be more likely to infest farms employing depth-based preventions. If this between-family variation reflects genetic variation, then the parasite population may have the capacity to adapt to preventative measures. Such adaptation would have important commercial and ecological implications.

Dietary antioxidant vitamin C influences the evolutionary path of insecticide resistance in Drosophila melanogaster

Herbivorous insects encounter a variety of toxic environmental substances ranging from ingested plant defensive compounds to human-introduced insecticidal agents. Dietary antioxidants are known to reduce the negative physiological impacts of toxins in mammalian systems through amelioration of reactive oxygen-related cellular damage. The analogous impacts to insects caused by multigenerational exposure to pesticides and the effects on adaptive responses within insect populations, however, are currently unknown. To address these research gaps, we used Drosophila as a model system to explore adaptive phenotypic responses to acute dichlorodiphenyltrichloroethane (DDT) exposure in the presence of the dietary antioxidant vitamin C and to examine the structural genomic consequences of this exposure. DDT resistance increased significantly among four replicates exposed to a low concentration of DDT for 10 generations. In contrast, dietary intake of vitamin C significantly reduced DDT resistance after mutigenerational exposure to the same concentration of DDT. As to the genomic consequences, no significant differences were predicted in overall nucleotide substitution rates across the genome between any of the treatments. Despite this, replicates exposed to a low concentration of DDT without vitamin C showed the highest number of synonymous and non-synonymous variants (3196 in total), followed by the DDT plus vitamin C (1174 in total), and vitamin C alone (728 in total) treatments. This study demonstrates the potential role of diet (specifically, antioxidant intake) on adaptive genome responses, and thus on the evolution of pesticide resistance within insect populations.

Population-specific effect of Wolbachia on the cost of fungal infection in spider mites.

Many studies have revealed the ability of the endosymbiotic bacterium Wolbachia to protect its arthropod hosts against diverse pathogens. However, as Wolbachia may also increase the susceptibility of its host to infection, predicting the outcome of a particular Wolbachia‐host–pathogen interaction remains elusive. Yet, understanding such interactions and their eco‐evolutionary consequences is crucial for disease and pest control strategies. Moreover, how natural Wolbachia infections affect artificially introduced pathogens for biocontrol has never been studied. Tetranychus urticae spider mites are herbivorous crop pests, causing severe damage on numerous economically important crops. Due to the rapid evolution of pesticide resistance, biological control strategies using entomopathogenic fungi are being developed. However, although spider mites are infected with various Wolbachia strains worldwide, whether this endosymbiont protects them from fungi is as yet unknown. Here, we compared the survival of two populations, treated with antibiotics or naturally harboring different Wolbachia strains, after exposure to the fungal biocontrol agents Metarhizium brunneum and Beauveria bassiana. To control for potential effects of the bacterial community of spider mites, we also compared the susceptibility of two populations naturally uninfected by Wolbachia, treated with antibiotics or not. In one population, Wolbachia‐infected mites had a better survival than uninfected ones in absence of fungi but not in their presence, whereas in the other population Wolbachia increased the mortality induced by B. bassiana. In one naturally Wolbachia‐uninfected population, the antibiotic treatment increased the susceptibility of spider mites to M. brunneum, but it had no effect in the other treatments. These results suggest that natural Wolbachia infections may not hamper and may even improve the success of biological control using entomopathogenic fungi. However, they also draw caution on the generalization of such effects, given the complexity of within‐host–pathogens interaction and the potential eco‐evolutionary consequences of the use of biocontrol agents for Wolbachia‐host associations.

Inter- and intraspecific variation of spider mite susceptibility to fungal infections: Implications for the long-term success of biological control.

Spider mites are severe pests of several annual and perennial crops worldwide, often causing important economic damages. As rapid evolution of pesticide resistance in this group hampers the efficiency of chemical control, alternative control strategies, such as the use of entomopathogenic fungi, are being developed. However, while several studies have focused on the evaluation of the control potential of different fungal species and/or isolates as well as their compatibility with other control methods (e.g., predators or chemical pesticides), knowledge on the extent of inter‐ and intraspecific variation in spider mite susceptibility to fungal infection is as yet incipient. Here, we measured the mortality induced by two generalist fungi, Beauveria bassiana and Metarhizium brunneum, in 12 spider mite populations belonging to different Tetranychus species: T. evansi, T. ludeni, and T. urticae (green and red form), within a full factorial experiment. We found that spider mite species differed in their susceptibility to infection by both fungal species. Moreover, we also found important intraspecific variation for this trait. These results draw caution on the development of single strains as biocontrol agents. Indeed, the high level of intraspecific variation suggests that (a) the one‐size‐fits‐all strategy may fail to control spider mite populations and (b) hosts resistance to infection may evolve at a rapid pace. Finally, we propose future directions to better understand this system and improve the long‐term success of spider mite control strategies based on entomopathogenic fungi.

Reduced effectiveness of repellents in a pyrethroid‐resistant strain of Aedes aegypti (Diptera: culicidae) and its correlation with olfactory sensitivity

The mosquito, Aedes aegypti (Diptera: Culicidae), is a vector of dengue fever, zika, chikungunya, and yellow fever viruses, and in many areas possesses significant levels of resistance to pyrethroids. Behavioral performance was assessed in 15, 30, and 60 min exposures in a high throughput vapor phase spatial repellency assay to three contact repellent standards: N,N-diethyl-3-methylbenzamide (DEET), ethyl 3-[acetyl(butyl)amino] propanoate (IR3535), and 2-undecanone, as well as pyrethrum extract, transfluthrin, and metofluthrin in susceptible (Orlando) and a pyrethroid-resistant Puerto Rico strain of Aedes aegypti. Additionally, electroantennographic studies were used to investigate the antennal sensitivities to these compounds in both strains. Resistance was found to all tested insect repellents in the Puerto Rico strain of Ae. aegypti. Resistance ratios at the different time points were about 2 for DEET, 3 for 2-undecanone, and 12 for IR3535. Resistance was also observed to pyrethrum extract (∼9-fold), transfluthrin (∼5-fold), and metofluthrin (∼48-fold) in repellent behavioral response. Electrophysiological analysis found decreased antennal sensitivity to all repellents tested, consistent with their behavioral effects. The reduced sensitivity to these repellents may represent a fitness cost arising from the kdr mutation present in Puerto Rico Aedes aegypti. This work highlights the need for understanding collateral effects from the evolution of pesticide resistance in mosquitoes, and the importance of finding alternative strategies to control resistance development. © 2019 Society of Chemical Industry.