Comparative toxicity of pesticides in three phytoseiid mites with different life-style occurring in citrus: Euseius stipulatus, Neoseiulus californicus and Phytoseiulus persimilis

Impacts of cultivar and management practices on the diversity and population dynamics of mites in soybean crops

The objective of this study was to evaluate the diversity and population dynamics of mites in soybean crops with different cultivars and management practices. The study was conducted in two soybean production fields in the municipalities of Mato Queimado (L1) and Três de Maio (L2), Rio Grande do Sul state, Brazil. Two transgenic cultivars were used, and insecticide applications varied among treatments. Sampling began at the V2 stage, with 60 leaves/area/collection that were sorted, mites were collected and identified using dichotomous keys. A total of 18,100 mites belonging to 12 species were found. Among the species, Tetranychus urticae Koch, Mononychellus planki (McGregor), and Tetranychus ludeni Zacher (Tetranychidae) were the most abundant, whereas the most abundant predatory mites were the phytoseiids Neoseiulus californicus McGregor and Neoseiulus idaeus Denmark and Muma, with N. idaeus being more abundant and present in all areas. The acarofauna was influenced by environmental conditions and management practices. Neoseiulus idaeus was commonly associated with populations of M. planki, T. ludeni, and T. urticae. Neoseiulus californicus tolerated pesticide use but was affected by severe water stress, whereas N. idaeus tolerated periods of low relative humidity and high temperatures.

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.

Mutations in the voltage-gated sodium channel gene associated with deltamethrin resistance in commercially sourced Phytoseiulus persimilis

The implementation of Integrated Pest Management in current agricultural practice is a convenient and very effective strategy to keep pest populations under control. The use of biological control agents, such as Phytoseiulus persimilis, is key for the success of such an approach. This predatory mite is widely used as it is very effective for controlling Tetranychus urticae, one of the most devastating crop pests. Here, we identify several mutations located in the voltage-gated sodium channel (VGSC) of commercially sourced P. persimilis that correlate with a reduced susceptibility to the pyrethroid deltamethrin. We found that the mites sourced from two different biocontrol product companies have intrinsic genotypic differences that correlate with their phenotype when tested with different concentrations of deltamethrin. Mites from Syngenta Bioline, carrying the mutations M918L and A1536T, were able to survive deltamethrin concentrations of up to 10 ppm, while the mites from Koppert Biological Systems, with the combination M918L, L925V and S1539T, survived treatment with 40 ppm. All of the point mutations identified in the predatory mite samples are located in a particular region of the VGSC, previously proposed as the binding site for this family of pesticides and identified as a 'hot spot' for resistance.

Not all predators are equal: miticide non-target effects and differential selectivity

BACKGROUND

Biological control in conventional agroecosystems involves the integration of chemical and conservation tactics, requiring knowledge of pesticide non-target effects on key natural enemies. Even for natural enemy groups such as predatory mites (Acari: Phytoseiidae), where pesticide non-target effects have been thoroughly examined, there may be significant differences in species susceptibility to specific active ingredients, including newer selective products. Using bioassays, we examined lethal (female mortality) and sublethal (fecundity, egg hatch, larval survival) effects of ten miticides on a spider mite pest (Tetranychus urticae) and three insectary-purchased predatory mites (Phytoseiulus persimilis, Neoseiulus californicus, and N. fallacis) commonly used for its management. Susceptibility of field-collected and insectary-reared populations of P. persimilis was also compared. Cumulative impacts on production of larvae by treated female spider mites and predators were compared to create a metric that simultaneously accounted for miticide efficacy and selectivity.

RESULTS

Bifenthrin was the least selective, as it caused acute toxicity to all predators and had little efficacy against T. urticae. Hexythiazox and cyflumetofen were the most selectively favorable. Phytoseiulus persimilis populations were similar in which miticides they were sensitive to, although the insectary-purchased population was generally more sensitive.

CONCLUSIONS

All products, including those considered selective (cyflumetofen, bifenazate, acequinocyl) had non-target effects on at least one species of predator tested. This work emphasizes that there is high variability in selectivity among species, highlighting the need to examine key natural enemies individually when creating management programs. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

Effects of spirodiclofen on life history traits and population growth of a spider mite predator Oligota flavicornis (Coleoptera: Staphyllinidae) based on the age-stage two-sex life table theory

BACKGROUND

Knowledge of the compatibility between spirodiclofen and the predator Oligota flavicornis is an important aspect for the management of spider mites.

RESULTS

We used the age-stage, two-sex life table to assess the effects of spirodiclofen on the life history traits and population growth of O. flavicornis. At the maximum recommended concentration (60 mg a.i. L^-1 ) and also at twice the maximum recommended dosage (120 mg a.i. L^-1 ), the preadult stages of O. flavicornis were significantly lengthened, while the adult longevity and fecundity decreased significantly. The finite rate (λ), intrinsic rate of increase (r), and net reproduction rate (R₀ ) decreased, while the mean generation time (T) was longer after both the 60 and 120 mg a.i. L^-1 treatments than it was in the control and 30 mg a.i. L^-1 treatments. Life expectancy and reproductive value were higher in the control and 30 mg a.i. L^-1 treatment than in the 60 and 120 mg a.i. L^-1 treatments; the two higher concentrations were detrimental to the development of O. flavicornis.

CONCLUSION

A proper combination of the O. flavicornis and spirodiclofen to control the spider mite, while avoiding the side effect of spirodiclofen, could be achieved based on the knowledge of life tables. © 2018 Society of Chemical Industry.

The effects of a windborne pollen-provisioning cover crop on the phytoseiid community in citrus orchards in Israel

BACKGROUND

Several phytoseiid species can potentially control the citrus rust mite (CRM). Their effectiveness varies, however, as do their intraguild interactions. Under laboratory conditions, Euseius stipulatus, E. scutalis and Iphiseius degenerans preyed effectively on CRM, whereas Amblyseius swirskii and Typhlodromus athiasae had no effect on CRM. In combination with A. swirskii, Euseius numbers were reduced due to intraguild predation, and consequently CRM suppression was less effective. In the field, predatory mite species can be variably provisioned by windborne pollen released from cover crops such as Rhodes grass (RG). We aimed to determine the effects of RG on the phytoseiid community in two field experiments, on different cultivars (pomelo and Shamouti orange). We also tested these communities for negative interspecific abundance relationships that are expected if their respective laboratory-observed intraguild interactions are manifested in the field.

RESULTS

Overall, on pomelo, we observed a dominance of A. swirskii, relatively low E. stipulatus and high CRM abundances. Amblyseius swirskii and E. stipulatus abundances were both elevated near RG, despite apparent intraguild predation by A. swirskii. Conversely, T. athiasae abundances were lower near RG, likely due to predation by A. swirskii. On Shamouti, E. stipulatus abundances were much higher than on pomelo and were not negatively related to A. swirskii abundances. There, RG increased E. stipulatus abundance, and CRM was reduced.

CONCLUSION

RG cover cropping can enhance CRM control, depending on variation in intraguild interactions among phytoseiids, particularly between A. swirskii and E. stipulatus. These may be modulated by climatic and/or cultivar effects. © 2018 Society of Chemical Industry.

Persimmon orchards harbor an abundant and well-established predatory mite fauna

Traditionally persimmon cultivation has been considered a minor crop in Spain, but in recent years this crop has experienced an important increase in both cultivated area and production. This increase has been mainly attributed to the widespread adoption of a new postharvest treatment which considerably extends the fruit commercialization period. The sudden expansion of this crop has not allowed time to correctly develop an integrated pest management (IPM) program. Consequently, chemical treatments have become the main strategy to lessen the impact of pests. Given the importance of phytoseiids in other Mediterranean fruit crops, where they are the basis of IPM, we sought to determine whether they could be similarly employed in persimmon crops. For this, we studied the predatory mite complex, the phytoseiid population dynamics and the potential prey for them during three consecutive seasons in four persimmon orchards, two of which managed conventionally, and two organically. Phytoseiids were abundant throughout the season, found on average at a density of more than 1 predatory mite per leaf. The most abundant species was Euseius stipulatus (57.3%) followed by Typhlodromus phialatus (24.8%), Amblyseius andersoni (17.1%) and Paraseiulus talbii (0.8%). Persimmon leaves provided a diversity of prey for predatory mites throughout the year, the most abundant being mealybugs, coccids, whiteflies and thrips. The abundance of predatory mites was significantly correlated to the abundance of potential prey available. From our results we anticipate that phytoseiids will be key actors in the development of persimmon IPM. Their role in this crop is discussed, as well as how to conserve their populations.

Lethal and Sub-Lethal Effects of Insecticides on the Pink Hibiscus Mealybug, Maconellicoccus hirsutus (Hemiptera: Pseudococcidae)

The pink hibiscus mealybug, Maconellicoccus hirsutus (Green) (Hemiptera: Pseudococcidae) is a pest of many plants, and a new problem on dates in California. The effects of seven insecticides and water on different life stages of this mealybug were studied to identify the best material for control. Water did not have any significant effect on mealybugs, but the insecticide treatments significantly affected all life stages tested. The egg hatch rate ranged from 28.5% to 17.2% for spirotetramat, bifenthrin, flupyradifurone, fenpropathrin, and buprofezin treatments, and was lower for sulfoxaflor (2.8%) and acetamiprid (0.1%). Despite high survival of neonate crawlers in the non-treated control and water treatments, 53.1% and 34.6% survived in the spirotetramat and buprofezin treatments, respectively; survival was zero in the other treatments. Spirotetramat and buprofezin caused very low mortality of nymphs in the first day post-treatment, but mortality significantly increased over time and reached 42.8% and 50.6% by day 6, respectively. The other treatments were highly toxic to the nymphs (79.4⁻99.4% on day 6). Insecticides also had a significant effect on the feeding ability of nymphs. By day 6 after treatment, 73.9% to 100% of nymphs treated with different insecticides stopped feeding although they were still alive. Insecticides showed no effect on the mortality of adult females, but the percentages of ovipositing females were significantly reduced (51.1% to 10.6%) in all insecticide treatments, except buprofezin, which was not statistically different from water and the non-treated control. In the process of our studies, we identified abnormalities in the appearance of eggs from females treated with various insecticides, and these aberrant eggs are described.

Toxicity of six insecticides to predatory mite Amblyseius cucumeris (Oudemans) (Acari: Phytoseiidae) in- and off-field

Amblyseius cucumeris (Oudemans) is a beneficial non-target arthropod (NTA) and a key predator of tetranychid mites in integrated pest management (IPM) programs across China. Evaluating the toxic effects of insecticides on such predatory mites is essential for the success and development of IPM. We tested six insecticides to determine the risk of neonicotinoid insecticide toxicity to predatory mites, using the 'open glass plate method' and adult female A. cucumeris in a "worst case laboratory exposure" scenario. A 48-h toxicity test was performed using the hazard quotient (HQ) approach to evaluate the risk of each insecticide. The LR₅₀ values (application rate that caused 50% mortality) of acetamiprid, thiamethoxam, imidacloprid, and dinotefuran were 76.4, 104.5, 84.9, and 224.6 g active ingredient (a.i.) ha^-1, respectively, with in-field HQ values of 0.40, 1.28, 0.49, and 0.82, respectively. The HQ values were lower than the trigger value of 2, and were consistent with off-field values. The risks of the four neonicotinoid insecticides to adult female A. cucumeris were acceptable in two exposure scenarios in field and off field. The 48-h LR₅₀ values for bifenthrin and malathion were 0.008 and 0.062 g. a.i. ha^-1, respectively, which were much lower than the recommended field application rates. The HQ values were much higher than the trigger values for both in- and off-field, indicating that the risks of these two insecticides were unacceptable. Bifenthrin and malathion posed an extremely high risk to the test species, and their use should be restricted to reduce risks to the field with augmentative releases of A. cucumeris.

Non-target effects of commonly used plant protection products in roses on the predatory mite Euseius gallicus Kreiter & Tixier (Acari: Phytoseidae)

BACKGROUND

Euseius gallicus Kreiter & Tixier (Acari: Phytoseidae) is a predatory mite recently available for use against various pests in roses. We tested in greenhouse trials the impact on the numbers of eggs and motiles of E. gallicus of the most commonly used plant protection products in roses in northern Europe: the acaricides acequinocyl and etoxazole, the insecticides azadirachtin-A, acetamiprid, flonicamid, imidacloprid, indoxacarb, thiacloprid and thiamethoxam and the fungicides boscalid and kresoxim-methyl, cyprodinil + fludioxonil, dodemorph and fluopyram + tebuconazole.

RESULTS

The neonicotinoids thiacloprid, thiamethoxam, acetamiprid and imidacloprid had a negative impact on the number of eggs (47, 62, 81 and 76% reduction, respectively, compared with a water treatment) and number of motiles of E. gallicus (42.2, 42.9, 59.9 and 60.6% reduction) and were classified as slightly to moderately toxic. Also, the number of motiles was reduced after treatment with acequinocyl (47%) and etoxazole (43.9%) and after two treatments with flonicamid (41%) with a 1 week interval between treatments.

CONCLUSION

Azadirachtin-A, acetamiprid, flonicamid, boscalid and kresoxim-methyl, cyprodinil + fludioxonil, dodemorph and fluopyram + tebuconazole were harmless for E. gallicus. Special attention should be paid to the impact of neonicotinoids and of acequinocyl and etoxazole, and to the application frequency with flonicamid on E. gallicus. © 2015 Society of Chemical Industry.