The role of ABC transporters in arthropod pesticide toxicity and resistance.

Pesticide resistance in arthropods threatens agricultural productivity and the control of vector-borne diseases. The ATP binding cassette (ABC) transporters have emerged as important factors in the toxicity of synthetic pesticides, as well as for Bacillus thuringiensis (Bt) insecticidal Cry protein binding. Depending on the localization of expression, both higher and lower expression of ABCs has been linked with pesticide resistance. The recent development of genetic-based approaches such as RNAi and CRISPR/Cas9 gene editing in non-model species, has greatly contributed to unveil their functional importance in pesticide toxicity and resistance. Using these tools, we are now poised to further unravel the molecular genetic mechanisms of gene regulation uncovering more elusive regulatory resistance genes.

A novel target-site mutation (H146Q) outside the ubiquinone binding site of succinate dehydrogenase confers high levels of resistance to cyflumetofen and pyflubumide in Tetranychus urticae.

Mitochondrial electron transfer inhibitors at complex II (METI-II), also referred to as succinate dehydrogenase inhibitors (SDHI), represent a recently developed class of acaricides encompassing cyflumetofen, cyenopyrafen, pyflubumide and cyetpyrafen. Despite their novelty, resistance has already developed in the target pest, Tetranychus urticae. In this study a new mutation, H146Q in a highly conserved region of subunit B of complex II, was identified in a T. urticae population resistant to all METI-IIs. In contrast to previously described mutations, H146Q is located outside the ubiquinone binding site of complex II. Marker-assisted backcrossing of this mutation in a susceptible genetic background validated its association with resistance to cyflumetofen and pyflubumide, but not cyenopyrafen or cyetpyrafen. Biochemical assays and the construction of inhibition curves with isolated mitochondria corroborated this selectivity. In addition, phenotypic effects of H146Q, together with the previously described H258L, were further examined via CRISPR/Cas9 gene editing. Although both mutations were successfully introduced into a susceptible T. urticae population, the H146Q gene editing event was only recovered in individuals already harboring the I260V mutation, known to confer resistance towards cyflumetofen. The combination of H146Q+I260V conferred high resistance levels to all METI-II acaricides with LC50 values over 5000 mg a.i./L for cyflumetofen and pyflubumide. Similarly, the introduction of H258L via gene editing resulted in high resistance levels to all tested acaricides, with extreme LC50 values (>5000 mg a.i./L) for cyenopyrafen and cyetpyrafen, but lower resistance levels for pyflubumide and cyflumetofen. Together, these findings indicate that different mutations result in a different cross-resistance spectrum, probably also reflecting subtle differences in the binding mode of complex II acaricides.

SYNCAS: Efficient CRISPR/Cas9 gene-editing in difficult to transform arthropods.

The genome editing technique CRISPR/Cas9 has led to major advancements in many research fields and this state-of-the-art tool has proven its use in genetic studies for various arthropods. However, most transformation protocols rely on microinjection of CRISPR/Cas9 components into embryos, a method which is challenging for many species. Alternatively, injections can be performed on adult females, but transformation efficiencies can be very low as was shown for the two-spotted spider mite, Tetranychus urticae, a minute but important chelicerate pest on many crops. In this study, we explored different CRISPR/Cas9 formulations to optimize a maternal injection protocol for T. urticae. We observed a strong synergy between branched amphipathic peptide capsules and saponins, resulting in a significant increase of CRISPR/Cas9 knock-out efficiency, exceeding 20%. This CRISPR/Cas9 formulation, termed SYNCAS, was used to knock-out different T. urticae genes - phytoene desaturase, CYP384A1 and Antennapedia - but also allowed to develop a co-CRISPR strategy and facilitated the generation of T. urticae knock-in mutants. In addition, SYNCAS was successfully applied to knock-out white and white-like genes in the western flower thrips, Frankliniella occidentalis. The SYNCAS method allows routine genome editing in these species and can be a game changer for genetic research in other hard to transform arthropods.

Interaction of Whitefly Effector G4 with Tomato Proteins Impacts Whitefly Performance.

The phloem-feeding insect Bemisia tabaci is an important pest, responsible for the transmission of several crop-threatening virus species. While feeding, the insect secretes a cocktail of effectors to modulate plant defense responses. Here, we present a set of proteins identified in an artificial diet on which B. tabaci was salivating. We subsequently studied whether these candidate effectors can play a role in plant immune suppression. Effector G4 was the most robust suppressor of an induced- reactive oxygen species (ROS) response in Nicotiana benthamiana. In addition, G4 was able to suppress ROS production in Solanum lycopersicum (tomato) and Capsicum annuum (pepper). G4 localized predominantly in the endoplasmic reticulum in N. benthamiana leaves and colocalized with two identified target proteins in tomato: REF-like stress related protein 1 (RSP1) and meloidogyne-induced giant cell protein DB141 (MIPDB141). Silencing of MIPDB141 in tomato reduced whitefly fecundity up to 40%, demonstrating that the protein is involved in susceptibility to B. tabaci. Together, our data demonstrate that effector G4 impairs tomato immunity to whiteflies by interfering with ROS production and via an interaction with tomato susceptibility protein MIPDB141. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Contrasting roles of cytochrome P450s in amitraz and chlorfenapyr resistance in the crop pest Tetranychus urticae.

The molecular mechanisms of amitraz and chlorfenapyr resistance remain only poorly understood for major agricultural pests and vectors of human diseases. This study focusses on a multi-resistant field strain of the crop pest Tetranychus urticae, which could be readily selected in the laboratory to high levels of amitraz and chlorfenapyr resistance. Toxicity experiments using tralopyril, the active toxophore of chlorfenapyr, suggested decreased activation as a likely mechanism underlying resistance. Starting from the same parental strain, transcriptome profiling revealed that a cluster of detoxifying genes was upregulated after amitraz selection, but unexpectedly downregulated after chlorfenapyr selection. Further functional validation associated the upregulation of CYP392A16 with amitraz metabolism and the downregulation of CYP392D8 with reduced activation of chlorfenapyr to tralopyril. Genetic mapping (QTL analysis by BSA) was conducted in an attempt to unravel the genetic mechanisms of expression variation and resistance. This revealed that chlorfenapyr resistance was associated with a single QTL, while 3 QTLs were uncovered for amitraz resistance. Together with the observed contrasting gene expression patterns, we argue that transcriptional regulators most likely underly the distinct expression profiles associated with resistance, but these await further functional validation.

Adaptation of an arthropod predator to a challenging environment is associated with a loss of a genome-wide plastic transcriptional response.

BACKGROUND: Structural and chemical plant defence traits may reduce the efficacy of biological control agents in integrated pest management. Breeding programmes have shown arthropod predators' potential to acclimate to challenging host plants. However, whether and how these predators adapt to novel plant environments remain unclear. Using the predatory mite Phytoseiulus persimilis - herbivorous mite Tetranychus urticae system in an experimental evolution setup, we studied the adaptation mechanisms to tomato and cucumber, plants that possess a distinct repertoire of defensive traits. RESULTS: Experimental evolution experiments on whole plants revealed that allowing P. persimilis to adapt to tomatoes led to an ~100% larger population size. Independent feeding assays showed that tomato- and cucumber-adapted prey reduced predator fecundity. The deleterious effect of ingesting low-quality prey persisted after adaptation of the predator to both cucumber and tomato. We demonstrated that jasmonic acid (JA)-dependent defences reduce prey quality by evaluating predator performance on prey fed on JA defence-deficient tomato plants. Transcriptomic profiling of the replicated P. persimilis lines showed that long-term propagation on tomato and cucumber plants produces distinctive gene-expression levels. Predator adaptation to tomatoes results in the loss of a large transcriptional response, in which predicted cuticle-building rather than detoxification pathways are affected. CONCLUSION: We showed that the adaptation of predatory arthropods to a novel, challenging plant does not necessarily occur via the prey, but rather through the physical environment of the plant. We provided first insights into the underlying molecular mechanisms. © 2023 Society of Chemical Industry.

The host plant strongly modulates acaricide resistance levels to mitochondrial complex II inhibitors in a multi-resistant field population of Tetranychus urticae.

The two-spotted spider mite Tetranychus urticae is a polyphagous pest with an extraordinary ability to develop acaricide resistance. Here, we characterize the resistance mechanisms in a T. urticae population (VR-BE) collected from a Belgian tomato greenhouse, where the grower was unsuccessful in chemically controlling the mite population resulting in crop loss. Upon arrival in the laboratory, the VR-BE population was established both on bean and tomato plants as hosts. Toxicity bioassays on both populations confirmed that the population was highly multi-resistant, recording resistance to 12 out of 13 compounds tested from various mode of action groups. DNA sequencing revealed the presence of multiple target-site resistance mutations, but these could not explain resistance to all compounds. In addition, striking differences in toxicity for six acaricides were observed between the populations on bean and tomato. The highest difference was recorded for the complex II inhibitors cyenopyrafen and cyflumetofen, which were 4.4 and 3.3-fold less toxic for VR-BE mites on tomato versus bean. PBO synergism bioassays suggested increased P450 based detoxification contribute to the host-dependent toxicity. Given the involvement of increased detoxification, we subsequently determined genome-wide gene expression levels of VR-BE on both hosts, in comparison to a reference susceptible population, revealing overexpression of a large set of detoxification genes in VR-BE on both hosts compared to the reference. In addition, a number of mainly detoxification genes with higher expression in VR-BE on tomato compared to bean was identified, including several cytochrome P450s. Together, our work suggests that multi-resistant field populations can accumulate a striking number of target-site resistance mutations. We also show that the host plant can have a profound effect on the P450-associated resistance levels to cyenopyrafen and cyflumetofen.

Structural and functional studies reveal the molecular basis of substrate promiscuity of a glycosyltransferase originating from a major agricultural pest.

The two-spotted spider mite, Tetranychus urticae, is a major cosmopolitan pest that feeds on more than 1100 plant species. Its genome contains an unprecedentedly large number of genes involved in detoxifying and transporting xenobiotics, including 80 genes that code for UDP glycosyltransferases (UGTs). These enzymes were acquired via horizontal gene transfer from bacteria after loss in the Chelicerata lineage. UGTs are well-known for their role in phase II metabolism; however, their contribution to host adaptation and acaricide resistance in arthropods, such as T. urticae, is not yet resolved. TuUGT202A2 (Tetur22g00270) has been linked to the ability of this pest to adapt to tomato plants. Moreover, it was shown that this enzyme can glycosylate a wide range of flavonoids. To understand this relationship at the molecular level, structural, functional, and computational studies were performed. Structural studies provided specific snapshots of the enzyme in different catalytically relevant stages. The crystal structure of TuUGT202A2 in complex with UDP-glucose was obtained and site-directed mutagenesis paired with molecular dynamic simulations revealed a novel lid-like mechanism involved in the binding of the activated sugar donor. Two additional TuUGT202A2 crystal complexes, UDP-(S)-naringenin and UDP-naringin, demonstrated that this enzyme has a highly plastic and open-ended acceptor-binding site. Overall, this work reveals the molecular basis of substrate promiscuity of TuUGT202A2 and provides novel insights into the structural mechanism of UGTs catalysis.

A glutamate-gated chloride channel as the mite-specific target-site of dicofol and other diphenylcarbinol acaricides.

Dicofol has been widely used to control phytophagous mites. Although dicofol is chemically related to DDT, its mode of action has remained elusive. Here, we mapped dicofol resistance in the spider mite Tetranychus urticae to two genomic regions. Each region harbored a glutamate-gated chloride channel (GluCl) gene that contained a mutation-G314D or G326E-known to confer resistance against the unrelated acaricide abamectin. Using electrophysiology assays we showed that dicofol and other diphenylcarbinol acaricides-bromopropylate and chlorobenzilate-induce persistent currents in Xenopus oocytes expressing wild-type T. urticae GluCl3 receptors and potentiate glutamate responses. In contrast, the G326E substitution abolished the agonistic activity of all three compounds. Assays with the wild-type Drosophila GluClα revealed that this receptor was unresponsive to dicofol. Homology modeling combined with ligand-docking confirmed the specificity of electrophysiology assays. Altogether, this work elucidates the mode of action of diphenylcarbinols as mite-specific agonists of GluCl.

A nuclear receptor HR96-related gene underlies large trans-driven differences in detoxification gene expression in a generalist herbivore.

The role, magnitude, and molecular nature of trans-driven expression variation underlying the upregulation of detoxification genes in pesticide resistant arthropod populations has remained enigmatic. In this study, we performed expression quantitative trait locus (eQTL) mapping (n = 458) between a pesticide resistant and a susceptible strain of the generalist herbivore and crop pest Tetranychus urticae. We found that a single trans eQTL hotspot controlled large differences in the expression of a subset of genes in different detoxification gene families, as well as other genes associated with host plant use. As established by additional genetic approaches including RNAi gene knockdown, a duplicated gene with a nuclear hormone receptor HR96-related ligand-binding domain was identified as causal for the expression differences between strains. The presence of a large family of HR96-related genes in T. urticae may enable modular control of detoxification and host plant use genes, facilitating this species' known and rapid evolution to diverse pesticides and host plants.

The complex II resistance mutation H258Y in succinate dehydrogenase subunit B causes fitness penalties associated with mitochondrial respiratory deficiency.

BACKGROUND: The acaricides cyflumetofen, cyenopyrafen and pyflubumide inhibit the mitochondrial electron transport chain at complex II [succinate dehydrogenase (SDH) complex]. A target site mutation H258Y was recently discovered in a resistant strain of the spider mite pest Tetranychus urticae. H258Y causes strong cross-resistance between cyenopyrafen and pyflubumide, but not cyflumetofen. In fungal pests, fitness costs associated with substitutions at the corresponding H258 position that confer resistance to fungicidal SDH inhibitors have not been uncovered. Here, we used H258 and Y258 near-isogenic lines of T. urticae to quantify potential pleiotropic fitness effects on mite physiology. RESULTS: The H258Y mutation was not associated with consistent significant changes of single generation life history traits and fertility life table parameters. In contrast, proportional Sanger sequencing and droplet digital polymerase chain reaction showed that the frequency of the resistant Y258 allele decreased when replicated 50:50 Y258:H258 experimentally evolving populations were maintained in an acaricide-free environment for approximately 12 generations. Using in vitro assays with mitochondrial extracts from resistant (Y258) and susceptible (H258) lines, we identified a significantly reduced SDH activity (48% lower activity) and a slightly enhanced combined complex I and III activity (18% higher activity) in the Y258 lines. CONCLUSION: Our findings suggest that the H258Y mutation is associated with a high fitness cost in the spider mite T. urticae. Importantly, while it is the most common approach, it is clear that only comparing life history traits and life table fecundity does not allow to reliably estimate fitness costs of target site mutations in natural pest populations. © 2023 Society of Chemical Industry.

Host adaptation and specialization in Tetranychidae mites.

Composite generalist herbivores are comprised of host-adapted populations that retain the ability to shift hosts. The degree and overlap of mechanisms used by host-adapted generalist and specialist herbivores to overcome the same host plant defenses are largely unknown. Tetranychidae mites are exceptionally suited to address the relationship between host adaptation and specialization in herbivores as this group harbors closely related species with remarkably different host ranges-an extreme generalist the two-spotted spider mite (Tetranychus urticae Koch [Tu]) and the Solanaceous specialist Tetranychus evansi (Te). Here, we used tomato-adapted two-spotted spider mite (Tu-A) and Te populations to compare mechanisms underlying their host adaptation and specialization. We show that both mites attenuate induced tomato defenses, including protease inhibitors (PIs) that target mite cathepsin L digestive proteases. While Te solely relies on transcriptional attenuation of PI induction, Tu and Tu-A have elevated constitutive activity of cathepsin L proteases, making them less susceptible to plant anti-digestive proteins. Tu-A and Te also rely on detoxification of tomato constitutive defenses. Te uses esterase and P450 activities, while Tu-A depends on the activity of all major detoxification enzymatic classes to disarm tomato defensive compounds to a lesser extent. Thus, even though both Tu-A and Te use similar mechanisms to counteract tomato defenses, Te can better cope with them. This finding is congruent with the ecological and evolutionary times required to establish mite adaptation and specialization states, respectively.

A review of the molecular mechanisms of acaricide resistance in mites and ticks.

The Arachnida subclass of Acari comprises many harmful pests that threaten agriculture as well as animal health, including herbivorous spider mites, the bee parasite Varroa, the poultry mite Dermanyssus and several species of ticks. Especially in agriculture, acaricides are often used intensively to minimize the damage they inflict, promoting the development of resistance. Beneficial predatory mites used in biological control are also subjected to acaricide selection in the field. The development and use of new genetic and genomic tools such as genome and transcriptome sequencing, bulked segregant analysis (QTL mapping), and reverse genetics via RNAi or CRISPR/Cas9, have greatly increased our understanding of the molecular genetic mechanisms of resistance in Acari, especially in the spider mite Tetranychus urticae which emerged as a model species. These new techniques allowed to uncover and validate new resistance mutations in a larger range of species. In addition, they provided an impetus to start elucidating more challenging questions on mechanisms of gene regulation of detoxification associated with resistance.

Intraspecific diversity in the mechanisms underlying abamectin resistance in a cosmopolitan pest.

Pesticide resistance relies on a myriad of mechanisms, ranging from single mutations to a complex and polygenic architecture, and it involves mechanisms such as target-site insensitivity, metabolic detoxification, or a combination of these, with either additive or synergistic effects. Several resistance mechanisms against abamectin, a macrocyclic lactone widely used in crop protection, have been reported in the cosmopolitan pest Tetranychus urticae. However, it has been shown that a single mechanism cannot account for the high levels of abamectin resistance found across different mite populations. Here, we used experimental evolution combined with bulked segregant analyses to map quantitative trait loci (QTL) associated with abamectin resistance in two genetically unrelated populations of T. urticae. In these two independent QTL mapping experiments, three and four QTLs were identified, of which three were shared between experiments. Shared QTLs contained genes encoding subunits of the glutamate-gated chloride channel (GluCl) and harboured previously reported mutations, including G314D in GluCl1 and G326E in GluCl3, but also novel resistance candidate loci, including DNA helicases and chemosensory receptors. Surprisingly, the fourth QTL, present only in only one of the experiments and thus unique for one resistant parental line, revealed a non-functional variant of GluCl2, suggesting gene knock-out as resistance mechanism. Our study uncovers the complex basis of abamectin resistance, and it highlights the intraspecific diversity of genetic mechanisms underlying resistance in a cosmopolitan pest.

Incomplete reproductive barriers and genomic differentiation impact the spread of resistance mutations between green- and red-colour morphs of a cosmopolitan mite pest.

Pesticide resistance represents a clear and trackable case of adaptive evolution with a strong societal impact. Understanding the factors associated with the evolution and spread of resistance is imperative to develop sustainable crop management strategies. The two-spotted spider mite Tetranychus urticae, a major crop pest with worldwide distribution and a polyphagous lifestyle, has evolved resistance to most classes of pesticides. Tetranychus urticae exists as either a green- or a red-coloured morph. However, the extent of genetic divergence and reproductive compatibility vary across populations of these colour morphs, complicating their taxonomic resolution at the species level. Here, we studied patterns of genetic differentiation and barriers to gene flow within and between morphs of T. urticae in order to understand the factors that influence the spread of resistance mutations across its populations. We derived multiple iso-female lines from Tetranychus populations collected from agricultural crops. We generated genomic and morphological data, characterized their bacterial communities and performed controlled crosses. Despite morphological similarities, we found large genomic differentiation between the morphs. This pattern was reflected in the incomplete, but strong postzygotic incompatibility in crosses between colour morphs, while crosses within morphs from different geographical locations were largely compatible. In addition, our results suggest recent/on-going gene flow between green-coloured T. urticae and T. turkestani. By screening the sequences of 10 resistance genes, we found evidence for multiple independent origins and for single evolutionary origins of target-site resistance mutations. Our results indicate that target-site mutations mostly evolve independently in populations on different geographical locations, and that these mutations can spread due to incomplete barriers to gene flow within and between populations.

Recombinant expression and characterization of GSTd3 from a resistant population of Anopheles arabiensis and comparison of DDTase activity with GSTe2.

The development of insecticide resistance in malaria vectors is a challenge for the global effort to control and eradicate malaria. Glutathione S-transferases (GSTs) are multifunctional enzymes involved in the detoxification of many classes of insecticides. For mosquitoes, it is known that overexpression of an epsilon GST, GSTe2, confers resistance towards DDT and pyrethroids. In addition to GSTe2, consistent overexpression of a delta class GST, GSTd3, has been observed in insecticide resistant populations of different malaria vector species. However, the functional role of GSTd3 towards DDT resistance has not yet been investigated. Here, we recombinantly expressed both GSTe2 and GSTd3 from Anopheles arabiensis and compared their metabolic activities against DDT. Both AaGSTd3 and AaGSTe2 exhibited CDNB-conjugating and glutathione peroxidase activity and DDT metabolism was observed for both GSTs. However, the DDT dehydrochlorinase activity exhibited by AaGSTe2 was much higher than for AaGSTd3, and AaGSTe2 was also able to eliminate DDE although the metabolite could not be identified. Molecular modeling revealed subtle differences in the binding pocket of both enzymes and a better fit of DDT within the H-site of AaGSTe2. The overexpression but much lower DDT metabolic activity of AaGSTd3, might suggest that AaGSTd3 sequesters DDT. These findings highlight the complexity of insecticide resistance in the major malaria vectors and the difficulties associated with control of the vectors using DDT, which is still used for indoor residual spraying.

Hormetic effects of neonicotinoid insecticides on Rhizoglyphus robini (Acari: Acaridae).

The stimulation of biological processes by sublethal doses of insecticides or other stressors is known as hormesis. Here, we have evaluated whether exposure to field-relevant or low concentrations of neonicotinoids induce changes in the reproductive capacity of the bulb mite Rhizoglyphus robini (Acari: Acaridae). Among the tested neonicotinoids imidacloprid, thiamethoxam, and dinotefuran, the highest hormetic effect on the reproduction of R. robini occurred 24 h after the 48 h exposure period to imidacloprid at concentrations of 70 and 140 mg a.i./L. Despite the stimulating effects of imidacloprid on mite reproduction, no significant differences were observed in the offspring (F1) for biological aspects including egg hatch rate, embryonic period and sex ratio, while an increase was found in the duration of development time from egg to adult. Evaluation of the detoxification enzyme activities of treated adults showed that the highest activity of carboxyl/cholinesterases, cytochrome P450s, and glutathione S-transferases was obtained when exposed to 70, 140 and 70 mg a.i./L imidacloprid, immediately after the exposure period, respectively. Also, an increase in the activity of the antioxidant enzyme catalase was observed compared to that of the control. After imidacloprid pretreatment (140 mg a.i./L), the tolerance of adult mites to diazinon was increased about two-fold. This study shows that exposure to imidacloprid can induce hormetic effects on R. robini and could severely complicate its control due to a higher reproduction, enhanced detoxification enzyme activities, and increased tolerance against other pesticides.

Increased metabolism in combination with the novel cytochrome b target-site mutation L258F confers cross-resistance between the Qo inhibitors acequinocyl and bifenazate in Tetranychus urticae.

Acequinocyl and bifenazate are potent acaricides acting at the Qo site of complex III of the electron transport chain, but frequent applications of these acaricides have led to the development of resistance in spider mites. Target-site resistance caused by mutations in the conserved cd1- and ef-helices of the Qo pocket of cytochrome b has been elucidated as the main resistance mechanism. We therefore monitored Qo pocket mutations in European field populations of Tetranychus urticae and uncovered a new mutation, L258F. The role of this mutation was validated by revealing patterns of maternal inheritance and by the independently replicated introgression in an unrelated susceptible genetic background. However, the parental strain exhibited higher resistance levels than conferred by the mutation alone in isogenic lines, especially for acequinocyl, implying the involvement of strong additional resistance mechanisms. This was confirmed by revealing a polygenic inheritance pattern with classical genetic crosses and via synergism experiments. Therefore, a genome-wide expression analysis was conducted that identified a number of highly overexpressed detoxification genes, including many P450s. Functional expression revealed that the P450 CYP392A11 can metabolize bifenazate by hydroxylation of the ring structure. In conclusion, the novel cytochrome b target-site mutation L258F was uncovered in a recently collected field strain and its role in acequinocyl and bifenazate resistance was validated. However, the high level of resistance in this strain is most likely caused by a combination of target-site resistance and P450-based increased detoxification, potentially acting in synergism.

Imperfect diet choice reduces the performance of a predatory mite.

Two mutually unexclusive hypotheses prevail in the theory of nutritional ecology: the balanced diet hypothesis states that consumers feed on different food items because they have complementary nutrient and energy compositions. The toxin-dilution hypothesis poses that consumers feed on different food items to dilute the toxins present in each. Both predict that consumers should not feed on low-quality food when ample high-quality food forming a complete diet is present. We investigated the diet choice of Phytoseiulus persimilis, a predatory mite of web-producing spider mites. It can develop and reproduce on single prey species, for example the spider mite Tetranychus urticae. A closely related prey, T. evansi, is of notorious bad quality for P. persimilis and other predator species. We show that juvenile predators feeding on this prey have low survival and do not develop into adults. Adults stop reproducing and have increased mortality when feeding on it. Feeding on a mixed diet of the two prey decreases predator performance, but short-term effects of feeding on the low-quality prey can be partially reversed by subsequently feeding on the high-quality prey. Yet, predators consume low-quality prey in the presence of high-quality prey, which is in disagreement with both hypotheses. We suggest that it is perhaps not the instantaneous reproduction on single prey or mixtures of prey that matters for the fitness of predators, but that it is the overall reproduction by a female and her offspring on an ephemeral prey patch, which may be increased by including inferior prey in their diet.

Molecular Basis for the Selectivity of the Succinate Dehydrogenase Inhibitor Cyflumetofen between Pest and Predatory Mites.

Acaricides that act as inhibitors of the mitochondrial succinate dehydrogenase (SDHIs) provide excellent control of phytophagous mites but display limited toxicity to predatory mites and other beneficial organisms. However, the molecular mechanism of selectivity is not fully understood. Here, we first confirm that SDHI acaricides are over 10,000-fold more toxic to spider mites than predatory mites. Next, we show that differential penetration, pro-acaricide activation, or metabolism are most likely not the main reason for this selectivity. In contrast, the inhibition of AB-1 on the SDH target is approximately 200-fold more potent in spider mites compared to predatory mites, revealing strong target-site selectivity. Strikingly, a key motif associated with differential binding was identified and validated by gene editing in Drosophila. Our findings contribute to understanding the selectivity of SDHIs, which can be used for the rational design of selective acaricides in support of an integrated pest management.