Are larger phytoseiids better biocontrol agents?

Abstract: In the present study, we tested whether the body size of phytoseiid predators can be increased by exploiting the temperature-size rule for ectothermic organisms. This rule states that ectotherms will develop slower at lower temperatures, but will mature at larger body size. Therefore, we reared four phytoseiids, namely Phytoseiulus persimilis, Neoseiulus californicus, Amblyseius swirskii and Amblydromalus limonicus, at 15 °C and 25 °C, measured the body sizes of females and assessed their predation capacity. For the predation experiments, P. persimilis and N. californicus were provided with 40 T. urticae eggs and A. swirskii and A. limonicus were provided with 15 first instars (< 6 h old) of the western flower thrips, Frankliniella occidentalis. When reared at 15 °C, all phytoseiid females had a larger body size than those reared at 25 °C. For P. persimilis and A. limonicus, the increased body size was accompanied with an increased predation capacity, whereas for N. californicus no differences were observed. For A. swirskii, larger females consumed less prey, which can be attributed to negative effects of rearing at 15 °C. In a second experiment, we found female A. limonicus that were reared at 15 °C, to possess higher lifetime fecundity than the smaller-sized females reared at 25 °C. Finally, we assessed whether larger-sized females have a higher predation capacity against second instars of F. occidentalis. Larger-sized females did not kill more second instar larvae but were able to lay more eggs when provided with second instars than the standard-sized females reared at 25 °C. Results obtained in this study demonstrate a potential to provide certain phytoseiid predators with a body size benefit, which may result in improved pest control.