Efectos letales y subletales de acaricidas sintéticos en ácaros depredadores de la familia Phytoseiidae

El objetivo de esta investigación fue evaluar en laboratorio la toxicidad de acaricidas sintéticos en los ácaros Phytoseiidae Amblyseius swirskii y Neoseiulus californicus, y determinar mediante meta-análisis de estudios publicados los efectos subletales de acaricidas en especies de la familia Phytoseiidae. En las evaluaciones de laboratorio se observó que spirodiclofen, fenpiroximato y acequinocyl mostraron los valores más bajos de CL50 y CL90. Al comparar las concentraciones recomendadas en campo, spirodiclofen tendría mayor efecto tóxico sobre los ácaros depredadores evaluados, que sobre ácaros fitófagos. Por su parte, el meta-análisis mostró que todos los acaricidas, tienen efectos negativos en la supervivencia, fecundidad y periodo de oviposición. Los acaricidas inhibidores de respiración mitocondrial denominados METI I, presentaron mayores efectos negativos en estas variables, en especial en los géneros Neoseiulus y Phytoseius. Los acaricidas sintéticos de nueva generación tienen efectos tóxicos letales y efectos subletales en ácaros depredadores de la familia Phytoseiidae.

Sublethal Effects of Essential Plant Oils on Biochemical and Ecological Parameters of the Predatory Mite Amblyseius Swirskii

The predatory mite Amblyseius swirskii is widely used natural enemy of phytophagous pests. Due to negative effects of conventional pesticides on non-target organism, the development of selective natural and eco-friendly pesticides such as essential plant oils are a useful pest control tool to use in synergy with biological control agents. Essential oils of Nepeta crispa, Satureja hortensis and Anethum graveolens showed promising results to control Tetranychus urticae. Hence an experiment was carried out to evaluate the effects of these essential oils on biochemical and demographic parameters of A. swirskii. Significant reduction of carbohydrate, lipid and protein contents of oil-treated predatory mites was observed. However oils of S. hortensis and A. graveolens had no negative impact on lipid reserve. Glutathione-S-transferase activity of A. swirskii was influenced by A. graveolens. In addition, the enzyme activity of the α-esterases was elevated by all treatments. The essential oils showed no effect on β-esterases activity compared to the control treatment. None of the concentrations of the different tested oils affected the population growth parameters of A. swirskii. However, a significant reduction was observed in oviposition time and total fecundity of predatory mites. Our observations show that the tested essential plant oils need some caution when applied as alternatives to synthetic pesticides in combination with A. swirskii and may have critical implications for Integrated Pest Management (IPM) programs. However, semi-field and field studies are required to evaluate the effects of these products on T. urticae and A. swirskii for developing IPM strategies.

Functional and numerical responses of the predator Amblyseius swirskii to its prey Tetranychus turkestani in the laboratory

The tetranychid Tetranychus turkestani Ugarov and Nikolskii is a serious pest of many important crops around the world. Management of T. turkestani by augmentative biological control using predators such as the phytoseiid Amblyseius swirskii (Athias-Henriot) is envisioned as an environmentally safe alternative to acaricides. Foundational knowledge on T. turkestani – A. swirskii interactions in the laboratory are necessary to predict the outcome of A. swirskii augmentative releases in the field. In this study, the functional and numerical responses of adult A. swirskii females feeding on immature stages of T. turkestani were determined in the laboratory. Prey densities were 2, 4, 8, 16, 32, 64, or 128 individuals per Petri dish arena. The functional response of A. swirskii to prey showed a Holling's type II response. The attack rate and handling time estimates from the random predator equation were 0.1148/h and 0.3146 h, respectively, indicating that A. swirskii consumed 76.28 individuals per day at the maximum level. The number of eggs laid by the predator, i.e., the numerical response, increased as host density increased up to a maximum of 33.10 eggs per female; then oviposition rate leveled-off. This study suggests that A. swirskii is a suitable candidate for augmentative biological control of T. turkestani but follow-up experiments in greenhouses or open fields are necessary.

Compatibility of the fungus Lecanicillium muscarium and the predatory mite Amblyseius swirskii for their combined application against the greenhouse whitefly Trialeurodes vaporariorum

The present study evaluated effects of the fungus Lecanicillium muscarium (Ascomycota: Hypocreales) and an organic extract from its mycelium on the greenhouse whitefly Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) and its predator, mite Amblyseius swirskii (Acari: Phytoseiidae). Mites were exposed to fungal spores or organic extract prepared from L. muscarium mycelium. No negative effect was shown on the predator feeding on T. vaporariorum nymphs treated with fungal conidia at a concentration of 5 × 107 spores/ml; by day six the number of mite eggs and nymphs was 18.7 % higher than on leaves treated with Tween 80. In contrast, treatment of leaves with a 0.5 % alcohol extract derived from L. muscarium mycelium caused 35 % mortality of A. swirskii adults by day two. In a trial conducted in a commercial greenhouse on rose plants, the application of L. muscarium conidia followed by the release of A. swirskii suppressed T. vaporariorum more effectively than each of the control agents applied separately.

Use of Functional Response Modeling to Evaluate the Effect of Temperature on Predation of Amblyseius swirskii (Acari: Phytoseiidae) Adults Preying on Tetranychus urticae (Acari: Tetranychidae) Nymphs

In this research, functional responses of Amblyseius swirskii Athias-Henriot preying on different Tetranychus urticae Koch nymphal densities (2, 4, 8, 16, 32, 64, and 128) were studied at eight constant temperatures (15, 20, 25, 27.5, 30, 32.5, 35 and 37.5°C) in a circular Petri dish (3-cm diameter × 1-cm height) under lab conditions. At all temperatures, the logistic regression showed a type II functional response. A nonlinear relationship was found between temperature and attack rate and the reciprocal of handling time. The reciprocal of handling time decreased exponentially with increasing temperature. In contrast, the attack rate grew rapidly with increasing temperatures up to an optimum, showing a decreasing trend at higher temperatures. In order to quantify the functional response of A. swirskii over a broad range of temperatures and to gain a better estimation of attack rate and handling time, a temperature-settled functional response equation was suited to our data. Our model showed that the number of prey consumed increased with rising prey density. Also, the predation rates increased with increasing temperatures but decreased at extremely high temperatures. Based on our model, the predation rate begins at the lower temperature threshold (11.73°C) and reaches its peak at upper temperature threshold (29.43°C). The coefficient of determination (R2) of the random predator model was 0.99 for all temperatures. The capability of A. swirskii to search and consume T. urticae over a wide range of temperatures makes it a good agent for natural control of T. urticae in greenhouses.