Improving the compatibility of pesticides and predatory mites: recent findings on physiological and ecological selectivity

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.

Acute toxicity effects of pesticides on beneficial organisms - Dispelling myths for a more sustainable use of chemicals in agricultural environments

Agricultural practitioners, researchers and policymakers are increasingly advocating for integrated pest management (IPM) to reduce pesticide use while preserving crop productivity and profitability. Using selective pesticides, putatively designed to act on pests while minimising impacts on off-target organisms, is one such option - yet evidence of whether these chemicals control pests without adversely affecting natural enemies and other beneficial species (henceforth beneficials) remains scarce. At present, the selection of pesticides compatible with IPM often considers a single (or a limited number of) widely distributed beneficial species, without considering undesired effects on co-occurring beneficials. In this study, we conducted standardised laboratory bioassays to assess the acute toxicity effects of 20 chemicals on 15 beneficial species at multiple exposure timepoints, with the specific aims to: (1) identify common and diverging patterns in acute toxicity responses of tested beneficials; (2) determine if the effect of pesticides on beetles, wasps and mites is consistent across species within these groups; and (3) assess the impact of mortality assessment timepoints on International Organisation for Biological Control (IOBC) toxicity classifications. Our work demonstrates that in most cases, chemical toxicities cannot be generalised across a range of beneficial insects and mites providing biological control, a finding that was found even when comparing impacts among closely related species of beetles, wasps and mites. Additionally, we show that toxicity impacts increase with exposure length, pointing to limitations of IOBC protocols. This work challenges the notion that chemical toxicities can be adequately tested on a limited number of 'representative' species; instead, it highlights the need for careful consideration and testing on a range of regionally and seasonally relevant beneficial species.

Compatibility of synthetic and biological pesticides with a biocontrol agent Phytoseiulus longipes (Acari: Phytoseiidae)

Phytoseiulus longipes is a predatory mite of Tetranychus evansi, which is an invasive pest in Africa and elsewhere. The introduction of this predator in Africa has considerable potential, but little is known about the compatibility of P. longipes with commonly used pesticides. Here, we examined lethal and sublethal effects of two pyrethroids (cypermethrin and deltamethrin), two organophosphates (dimethoate and chlorpyrifos), one nicotinoid (imidacloprid), two acaricides (propargite and abamectin), two naturally derived pesticides (oxymatrine and azadirachtin), and one entomopathogenic fungal-based formulation (Hirsutella thompsonii) on P. longipes eggs and adults. The pesticides were sprayed at their maximum recommended concentrations. Topical exposures to azadirachtin, imidacloprid, propargite, abamectin, oxymatrine, and H. thompsonii significantly reduced the net reproductive rate (R0), intrinsic rate of increase (r) and finite rate of increase (λ)of P. longipes. Pesticide lethal and sublethal effects on the predator were summarized in a reduction coefficient (Ex) for the classification based on IOBC toxicity categories. Results revealed that Azadirachtin and H. thompsonii were slightly harmful effects to adults. Imidacloprid, propargite, abamectin, and oxymatrine were moderately harmful to both eggs and adults. Residual persistence bioassays revealed that 4-day-old residue of azadirachtin had no harmful effect on the predator. Abamectin, oxymatrine, and H. thompsonii became harmless to it 10 days post-spraying, and propargite and imidacloprid were considered harmless after 20 days. Cypermethrin, deltamethrin, dimethoate, and chlorpyrifos were highly harmful to both eggs and adults, persistence remaining high even after 31 days of application. These findings provide valuable insights into decision-making when considering P. longipes for use in IPM programs.

Residual effect of commonly used fungicides in strawberries on Amblyseius swirskii, Neoseiulus cucumeris, and Neoseiulus californicus (Mesostigmata: Phytoseiidae)

Florida's strawberry industry is currently valued at $511 million annually but faces challenges from pathogens and arthropod pests especially Tetranychus urticae Koch (twospotted spider mite) and Scirtothrips dorsalis Hood (chilli thrips). Predatory mites, particularly Neoseiulus cucumeris Oudemans, Neoseiulus californicus McGregor, and Amblyseius swirskii Athias-Henriot, play a crucial role in pest management. However, there are concerns regarding how these biological control agents are affected by fungicides used in current pathogen management strategies. This study assessed the residual effects of commonly used fungicides in strawberries on the survival, feeding, and oviposition of these predatory mites. Commercially sourced predatory mites were reared on S. dorsalis larvae, and gravid female predators placed on fungicide treated strawberry leaf discs in a Munger cell for 120 h. Fungicides tested included two formulations of Captan, hydrogen peroxide + peroxyacetic acid, cyprodinil + fludioxonil, tetramethylthiuram disulfide, cyflufenamid and a control. All fungicides tested had an impact on the survival, feeding, and oviposition of the predators. Among the fungicide treatments, the lowest predator survival was observed in the cyprodinil + fludioxonil treatment, while the highest was observed in the hydrogen peroxide + peroxyacetic acid and tetramethylthiuram disulfide treatments. In all treatments, feeding and oviposition greatly varied among predators; specifically, N. cucumeris and A. swirskii had the lowest prey consumption, while N. californicus had the highest. These findings highlight the potential incompatibility between fungicides and predatory mites and demonstrate the need for the development of a fungicide rotation program tailored to the different susceptibilities of predators to fungicides.

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.

Compatibility of pesticides with the predatory mite Neoseiulus barkeri

Multiple arthropod pests can affect the same crop in agricultural systems, requiring the integration of control methods. In the present study, the effects of residual exposure to four broad-spectrum insecticides/acaricides (azadiractin, abamectin, chlorfenapyr, and fenpyroximate) on immature (development and survival time) and adult females (longevity, fecundity, and fertility life table parameters) of the predatory mite Neoseiulus barkeri were evaluated. Additionally, the insecticides/acaricides were categorized according to their selectivity based on the classification proposed by the International Organization for Biological Control (IOBC) for assessing the susceptibility of arthropods in laboratory experiments. Method 004, proposed by the Insecticide Resistance Action Committee (IRAC), was adopted for the bioassays with predators exposed to insecticide-acaricide residues. Among the insecticides/acaricides studied, azadirachtin had minimal effects on immature and adult N. barkeri (all non-significant) and was considered harmless based on the classification of toxicity according to the standards/categories proposed by the IOBC. All other insecticides/acaricides affected immature and adult N. barkeri and were considered slightly harmful in terms of toxicity, according to the IOBC.

Toxicity risk assessment of flupyradifurone for the predatory pirate bug, Orius strigicollis (Poppius) (Heteroptera: Anthocoridae), a biological control agent of Diaphorina citri Kuwayama (Hemiptera: Liviidae)

Diaphorina citri Kuwayama (Hemiptera: Liviidae), commonly known as the Asian citrus psyllid, is a prominent citrus tree pest that serves as a vector for Asian huanglongbing (HLB). The substantial costs incurred by the citrus industry as a consequence of this disease have spurred considerable interest in the combined control of D. citri using insecticides and natural enemies. However, the successful implementation of such integrated pest management strategies is dependent on ensuring the compatibility of using natural enemies in the presence of insecticides. In this regard, we evaluated the lethal and sublethal effects of flupyradifurone on Orius strigicollis (Poppius) (Heteroptera: Anthocoridae), an important predatory biological control agent, in which we assessed the risk of exposure to flupyradifurone under both in- and off-field scenario. The median lethal rate (LR50) value of flupyradifurone against O. strigicollis (9.089 g a.i. ha-1), was found to be significantly lower than the maximum field recommended rate (MFRR, 170 g a.i. ha-1). Additionally, at 0.254 g a.i. ha-1, flupyradifurone was established to significantly prolong the developmental duration of O. strigicollis from the first to third instar nymphs. Although we detected no significant difference in the survival of immature O. strigicollis subjected to 0.064 g a.i. ha-1 and control treatments, survival was significantly lower in 0.127 and 0.254 g a.i. ha-1 treatments. Moreover, whereas there were no significant differences in adult longevity between the 0.127 g a.i. ha-1 and control treatments, we recorded a significant reduction in fecundity. Furthermore, there were reductions in peak life expectancy, reproductive value, finite rate of increase, intrinsic rate of increase, and net reproduction rate in response to exposure to increasing flupyradifurone rate. Additionally, at 0.127 g a.i. ha-1, the mean generation time was significantly longer than that under control conditions. Following simulated exposure to flupyradifurone for 100 days, population of O. strigicollis in the 0.064 g a.i. ha-1 and control treatments were found to be significantly larger than those exposed to 0.127 g a.i. ha-1. On the basis on LR50 evaluations, whereas the risk of exposure risk was unacceptable for O. strigicollis under in-field scenario, it remained acceptable off-field. Nonetheless, the sublethal effect of prolonged exposure to residual flupyradifurone could pose an unacceptable off-field risk to O. strigicollis (e.g., in adjacent habitats). Consequently, the effects of different flupyradifurone exposure scenarios on O. strigicollis should be thoroughly assessed, and reducing the dosage of flupyradifurone could be advantageous for the control of D. citri when combine with augmentative release of O. strigicollis.

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.

Non-target pesticide impacts on pest natural enemies: Progress and gaps in current knowledge

Avoiding pesticide non-target effects on natural enemies is a cornerstone of conservation biological control. Recent advances in this field have included increased examination of nuanced sublethal effects, including microbiome changes. There is an interest in lifetable-based approaches, while also simplifying results to reduce the amount of information a grower needs to interpret to make a judicious application decision. Newer pesticides are showing promise for selectivity to both natural enemies and humans. Major research gaps still remain, with few published studies on ground-dwelling natural enemies, herbicides, adjuvants, or pesticide mixes. Translating the results of laboratory assays to field-level effects remains a major challenge. Field studies examining entire management programs and meta-analyses of laboratory studies may begin to address this issue.

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.

Selectivity and molecular stress responses to classical and botanical acaricides in the predatory mite Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae)

BACKGROUND

Acaricide application remains an integral component of integrated pest management (IPM) for the two-spotted spider mite Tetranychus urticae. Species and strains of phytoseiid predatory mites vary significantly in their response to acaricides. For the success of IPM, it is imperative to identify the determinants of selectivity and molecular stress responses of acaricides in predatory mites.

RESULTS

The three classical acaricides bifenazate, cyflumetofen, and fenbutatin oxide did not affect the survival and fecundity of Phytoseiulus persimilis regardless of the route of exposure. Selectivity of the orange oil and terpenoid blend-based botanical acaricides was low via a combination of direct exposure, acaricide-laced diet, and residual exposure but improved when limiting exposure only to diet. To gain insights into the molecular stress responses, the transcriptome of P. persimilis was assembled. Subsequent gene expression analysis of predatory mites orally exposed to fenbutatin oxide and orange oil yielded only a limited xenobiotic stress response. In contrast, P. persimilis exhibited target-site resistance mutations, including I260M in SdhB, I1017M in CHS1, and kdr and super-kdr in VGSC. Extending the screen using available Phytoseiidae sequences uncovered I136T, S141F in cytb, G119S in AChE, and A2083V in ACC, well-known target-sites of acaricides.

CONCLUSION

Selectivity of the tested botanical acaricides to P. persimilis was low but could be enhanced by restricting exposure to a single route. Differential gene expression analysis did not show a robust induced stress response after sublethal exposure. In contrast, this study uncovered target-site mutations that may help to explain the physiological selectivity of several classical acaricides to phytoseiid predators.

Pirimicarb resistance and associated mechanisms in field-collected and selected populations of Neoseiulus californicus

The predatory mite Neoseiulus californicus McGregor (Acari: Phytoseiidae) is an important natural enemy of phytophagous mites, and naturally established populations are often found in apple orchards. However, insecticide applications to control pests cause side effects to non-target organisms such as N. californicus. Pirimicarb, a widely used carbamate insecticide in apple orchards, is generally considered a selective aphidicide, however, toxicity to beneficial insects and predatory mites has been reported. Furthermore, the molecular basis for this selectivity, if present in N. californicus, is still largely unknown. In this study, 8 field-collected N. californicus populations were investigated and showed up to 27-fold resistance compared to a susceptible laboratory population. Selection in the laboratory for 5 consecutive generations resulted in a 69-fold pirimicarb resistance. Although there were no significant difference in terms of the acetlycholinesterase (AChE) activity between susceptible and field-collected populations, the selected population exhibited a significantly higher AChE activity. In addition, gene copy number variation of acetylcholinesterase (ace) gene among populations was detected and ranged from 1.6 to 2.1-fold relative to the susceptible population. All field-collected populations, but not the selected population, had a significantly higher ace copy number compared to the susceptible population (t-test, p < 0.05). Molecular analysis of the target-site (AChE) revealed, for the first time, a phenylalanine to tryptophan substition at position 331 in AChE (Torpedo californica numbering), both in field-collected and the selected population, but not in the susceptible population. Last, the selected F5 population consumed significantly more Tetranychusurticae adults than the parental population. Together, the results of this study shed light on the molecular determinants of acaricide selectivity in predatory mites, and will contribute to a better design of an integrated mite management program, including the use of pesticide resistant N. californicus in apple orchards.

Risk Assessment of Insecticides Used in Tomato to Control Whitefly on the Predator Macrolophus basicornis (Hemiptera: Miridae)

Simple Summary

The whitefly Bemisia tabaci is a problem in tomato crops worldwide. The use of chemicals is one method to control this pest. Predators from the family Miridae have been used in Europe as biological control agents. We tested the insecticides most often used to control B. tabaci in tomato fields in Brazil for compatibility with the native Brazilian mirid Macrolophus basicornis. The results showed that regarding lethality, buprofezin, cyantraniliprole and spiromesifen were reduced-risk insecticides. Acetamiprid, bifenthrin, etofenprox + acetamiprid and pyriproxyfen + acetamiprid were considered broad-spectrum insecticides. The insecticides were also tested to be classified ecologically and were found to be safe, except for acetamiprid that was moderately toxic. Overall, our findings indicated that it is possible to use M. basicornis as a biological agent to control B. tabaci in tomato crops by means of pest management strategies that are compatible with agrochemicals in current use.

Abstract

The generalist mirid predator Macrolophus basicornis may contribute to Integrated Pest Management (IPM) of Bemisia tabaci in tomato crops. It is important to know the compatibility of the chemicals used to control this pest with this promising biological control agent. Seven insecticides were tested to investigate their toxicity to the predator. For four of the products, the LC₅₀ for adults were determined. Buprofezin, cyantraniliprole and spiromesifen did not cause lethality and were classified as harmless. Acetamiprid, bifenthrin, etofenprox + acetamiprid and pyriproxyfen + acetamiprid caused acute toxicity and were classified as harmful. LT₅₀ for all harmful insecticides were relatively low, ranging from 1.8 to 3.2 days. Moreover, these four insecticides have low LC₅₀, with acetamiprid (0.26 mg a.i. L⁻¹) as the lowest, followed by bifenthrin (0.38 mg a.i. L⁻¹), etofenprox + acetamiprid (4.80 mg a.i. L⁻¹) and pyriproxyfen + acetamiprid (8.71 mg a.i. L⁻¹). However, the calculated risk quotient (RQ) values demonstrated that these insecticides were mostly ecologically safe for this predator, except for acetamiprid, classified as slightly to moderately toxic. The present study can contribute to the use of M. basicornis as a biological control agent on tomato crops and to compatible use with the insecticides tested, according to IPM strategies.

Meta-analysis and review of pesticide non-target effects on phytoseiids, key biological control agents

Understanding pesticide non-target effects on natural enemies is a key element of successful conservation biological control. Due to their importance in agroecosystems worldwide, the phytoseiid mites are the most well-studied natural enemies in pesticide selectivity research. The wealth of literature associated with this topic allows for a thorough meta-analysis of pesticide non-target effects and may also indicate general trends relevant to many cropping systems. We conducted a meta-analysis using 2386 observations from 154 published papers examining the impact of pesticides on lethal (adult and juvenile mortality) and sublethal (fecundity, egg hatch) effects. Insecticides and herbicides did not statistically differ in toxicity to phytoseiids, but research on herbicide non-target effects is scarce. Specific insecticides, fungicides, and miticides were sorted into least and most harmful categories. Phytoseiid species also differed in sensitivity, with Galendromus occidentalis (Nesbitt), Neoseiulus californicus (McGregor), and Typhlodromus pyri Scheuten among the least sensitive species. Sensitivity variation may be partly due to pesticide resistance; the greatest differences between species were within older mode of action (MOA) groups, where resistance development has been documented. It has been speculated that specialist phytoseiids, which closely associate with Tetranychus spp. spider mites, have more opportunities for resistance development due to their necessary proximity to a pest that rapidly develops resistance. Effect sizes were higher for generalist phytoseiid species, supporting this hypothesis. This meta-analysis highlights pesticide types (herbicides) and MOA groups where more research is clearly needed. Our analysis also allows for more robust generalizations regarding which pesticides are harmful or selective to phytoseiids. © 2021 Society of Chemical Industry. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Biological control of the Japanese pear rust mite, Eriophyes chibaensis (Acari: Eriophyidae) and the Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae) with Euseius sojaensis (Acari: Phytoseiidae)

Euseius sojaensis (Ehara) is an effective indigenous natural enemy of some eriophyid mites and spider mites in Japan. However, pesticides that are toxic to it are frequently applied in commercial Japanese pear orchards until early summer, when the predator densities are at their peak. Here, we examined the suppressive effect of inoculative release of E. sojaensis on Eriophyes chibaensis Kadono and Tetranychus kanzawai Kishida under conservation control using selective pesticides from late April to late June. The densities of E. sojaensis peaked in early June. In E. sojaensis-release plots, phytoseiid populations were larger, E. chibaensis and T. kanzawai populations were smaller, and rates of leaf mosaic and russeting caused by E. chibaensis were significantly lower than in control plots. These results suggest that E. sojaensis can control E. chibaensis and T. kanzawai populations simultaneously. As it may be difficult to suppress E. chibaensis densities below the control threshold of 50 mites per leaf only by conservation using selective pesticides, enhancement and augmentation of E. sojaensis for sustainable control of mites should be considered as an option in commercial Japanese pear orchards.

The Control of the American Leafhopper Erasmoneura vulnerata (Fitch) in European Vineyards: Impact of Synthetic and Natural Insecticides

The American leafhopper Erasmoneura vulnerata, detected in Europe in the early 2000s, has recently become a pest in North-Italian vineyards. Infestations were recorded in organic and conventional vineyards despite the application of insecticides targeting other pests. Erasmoneura vulnerata completes three generations per year, and the second generation is frequently associated with large populations. The selection of appropriate active ingredients and the timing of their application is crucial for effective pest control. Field trials were carried out in Northeastern Italy, using a randomized design, to evaluate the impact of insecticides applied against other grapevine leafhoppers on E. vulnerata populations. The beginning of the second generation was selected as the best time for insecticide application. For natural products, two applications were planned. Among the selected insecticides, the most effective were acetamiprid, flupyradifurone and lambda-cyhalothrin. Regarding natural products, the most effective was kaolin which could represent an alternative to pyrethrins in organic vineyards. The identification of pest threshold levels and the evaluation of side effects of the most effective insecticides on key natural enemies occurring in vineyards are required.

Residual action of five insecticides on larvae and adults of the neotropical predators Chrysoperla externa (Neuroptera: Chrysopidae) and Eriopis connexa (Coleoptera: Coccinellidae)

This work aimed to evaluate the residual action of five insecticides on larvae and adults of the predators Chrysoperla externa (Hagen) and Eriopis connexa (Germar). The insecticides gamma-cyhalothrin, imidacloprid+beta-cyfluthrin, methomyl, thiamethoxam, and thiamethoxam+lambda-cyhalothrin were sprayed in pod bean plants until the point of runoff. Weekly, at 3, 10, 17, 24, and 31 days, first instar larvae and adults of both predators were exposed to leaves containing dry residues of the insecticides. Based on the mortality observed throughout the bioassays, the insecticides were classified according to the scale of the residual effects proposed by the International Organization for Biological and Integrated Control (IOBC). Except for thiamethoxam+lambda-cyhalothrin, which was moderately persistent (class 3) to larvae of C. externa and E. connexa, all other tested insecticides were persistent (class 4) to larvae of both species. Gamma-cyhalothrin, imidacloprid + beta-cyfluthrin, and methomyl were persistent (class 4) to C. externa adults, while thiamethoxam was moderately persistent (class 3) and thiamethoxam + lambda-cyhalothrin was slightly persistent (class 2) to the adult stage. As for E. connexa adults, imidacloprid + beta-cyfluthrin and methomyl were persistent (class 4) and gamma-cyhalothrin, thiamethoxam, and thiamethoxam + lambda-cyhalothrin were moderately persistent (class 3). Thus, due to extended residual effect, these insecticides must be avoided when larvae and adults of both predators are active in the crop.

Toxicity and risk assessment of acaricides on the predatory mite, Euseius scutalis (Athias-Henriot) (Acari: Phytoseiidae) under laboratory conditions

Predatory mites belonging to family Phytoseiidae (Acari: Mesostigmata) have long been considered as the most promising candidates for biological control of some economically important plant feeding mites and insects. Among them, Euseius scutalis (Athias-Henriot) is one of the most abundant predators and can be considered as an important component for integrated pest management (IPM) programs in Mediterranean citrus orchards. Evaluation of non-target and toxic effects of pesticides is crucial to measure their threats to E. scutalis. In this study, the effects of some selected acaricides (abamectin, etoxazole, spirodiclofen, spirotetramat and pyridaben), that were widely used in citrus orchards, on eggs, larvae, and adult females of E. scutalis were determined under laboratory conditions. In order to observe some possible results at "worst-case scenario", the test units were sprayed at maximum recommended doses. According to the results, abamectin and pyridaben respectively caused 18.00% and 33.50% mortality on eggs, 57.33% and 65.33% on larvae, 23.33% and 44.00% on adult females. While etoxazole was only toxic to the larvae with mortality rates reaching 55.33%, spirodiclofen and spirotetramat were harmless to all developmental stages of the predatory mite. In addition, abamectin, etoxazole and pyridaben caused a significant reduction in the egg production of E. scutalis when compared to the control. Accordingly, spirodiclofen and spirotetramat may be compatible with E. scutalis in IPM programs where it is implemented as a predator. However, further semi-field and/or field experiments are essential in order to draw a final conclusion on compatibility of the other three acaricides.