Whitefly suppression by multiple natural enemies challenges with whitefly immigration or delayed natural enemy releases

Augmentative biological control, the regular release of natural enemies to suppress a target pest population, is a promising management strategy for sweetpotato whiteflies, Bemisia tabaci Gennadius (Hemiptera: Aleyroididae), in poinsettia production. The viability of biological control can be compromised by immigration of whiteflies and unanticipated delays in natural enemy releases. In this study, we investigate whether adding a predatory mite, Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae), to the regular release of a parasitic wasp, Eretmocerus eremicus Rose & Zolnerowich (Hymenoptera: Aphelinidae), can increase B. tabaci suppression on color poinsettias when challenged with delayed natural enemy releases or whitefly immigration. Natural enemy releases resulted in significant B. tabaci suppression compared to the untreated control. The combination treatment (E. eremicus + A. swirskii) consistently provided equivalent or improved suppression of B. tabaci compared to either E. eremicus or A. swirskii treatments alone. Delayed natural enemy releases increased mean and variation in B. tabaci nymph populations by week 10 for single natural enemy treatments (E. eremicus alone), but not the combination treatment (E. eremicus + A. swirskii) for the duration of the trial (16 weeks). Both early (week 4) and late (week 8) B. tabaci immigration resulted in increased variation in B. tabaci nymph populations in single (E. eremicus), but not combination (E. eremicus + A. swirskii), treatments. Our results support that adding A. swirskii to E. eremicus can increase effective suppression of B. tabaci when challenged with delayed natural enemy releases and whitefly immigration.