Preventive releases of phytoseiid and anthocorid predators provided with supplemental food successfully control Scirtothrips in strawberry
Description
Thrips of the subtropical genus Scirtothrips are emerging as important pests in several crops. Scirtothrips dorsalis has been increasingly invading new areas outside of its native region of South and East Asia causing economic damage to several crops. Scirtothrips inermis is another polyphagous species with worldwide distribution. Both species are polyphagous, and in recent years have emerged as key pests in strawberry. In this study, we first evaluated the predation and oviposition rate of commercially available phytoseiid predatory mites Amblyseius swirskii, Amblydromalus limonicus, Transeius montdorensis, and Neoseiulus cucumeris on larval stages of both Scirtothrips species, and oviposition rates of predatory mites on the supplementary food source Artemia franciscana cysts were also assessed. Predatory mites equally accepted both thrips species as prey and showed stable oviposition rates on these diets. Amblyseius swirskii and A. limonicus were the most voracious, also exhibiting the highest oviposition rate of the predators tested. We further evaluated the biological control potential of predatory mites and anthocorid predators Orius laevigatus and Orius limbatus in a greenhouse experiment. Predators were released preventively and supported with Artemia cysts before the introduction of S. inermis . Both Orius predators achieved good control of the pest, with O. limbatus developing higher numbers than O. laevigatus . Regarding phytoseiids, A. swirskii and A. limonicus both controlled the pest and built higher populations than T. montdorensis and N. cucumeris . Our results show that a preventive strategy based on phytoseiid or anthocorid predators in strawberry can be effective in suppressing S. inermis .
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Statistical analysis Differences in predation and oviposition rates of predatory mites among the different treatments were analysed with linear mixed effect models (LME) with log(x+1) transformed data to meet the assumptions of homoscedasticity and normality, as none of the available error distribution of generalized linear mixed models provided a good fit (assessed through residual plot diagnostics). LME models included predator and prey species and their interaction as fixed effects, and experiment individual and observation day as random effects. The analysis excluded natural thrips mortality, as it was negligible (less than 5%, data not shown). Generalized linear mixed models (GLMM) were fitted for the greenhouse experiment, with predator treatment as the fixed factor, and replicate (cage) and time added as random factors to the model to account for temporal pseudoreplication. Data were analysed with a negative binomial distribution and a log link function, as it provided the best fit based on visual diagnostic plots (Hartig 2022). The total number of Orius predators found at the end of the greenhouse experiment were compared with a Generalized Linear Model (GLM) with a Poisson error distribution and a log link function, accounting for overdispersion by including a dispersion parameter equal to Pearson’s χ2-based dispersion divided by the residual degrees of freedom (Hardin and Hilbe 2018). Data on leaf damage ratings were analysed with an ANOVA after the data were checked for normality and homoscedasticity through diagnostic plots. Contrasts among significant fixed factors for GLMM and LME were assessed through Tukey’s HSD with estimated marginal means (Lenth 2021). All analyses were performed using the statistical software R 4.2.2 (R Core Team 2021).