UC Riverside

Whether interactions among biocontrol agents limits their ability to control shared prey has been one of the most important and controversial questions surrounding biological control. In California multiple parasitoid wasp species have been introduced to control the invasive giant whitefly Aleurodicus dugesii Cockerell (Hemiptera: Aleyrodidae). The overall goal of this dissertation was to determine aspects of these species’ basic biologies and investigate factors contributing to the efficacy of these parasitoids. Findings of these studies will provide a better understanding of how parasitoid community complexity affects biological control and may enhance biological control of A. dugesii in California and elsewhere.

First the effects of temperature on survival and development of A. dugesii were assessed. Starting at 10°C development rate of A. dugesii increased until an optimum of 29°C was reached, then development ceased at 30°C. Using these data developmental degree days were calculated for A. dugesii.

Second, host stage preferences of the three parasitoids were determined. All host nymphal stages were accepted by I. affinis for oviposition, while only the 2nd–4th and 3rd–4th instars were accepted by E. noyesi and E. krauteri respectively. Host stage preferences overlapped considerably between species.

Third, the effects of A. dugesii nymphal wax production on I. affinis and E. noyesi efficacy was determined. Wax production decreased parasitoid effectiveness, with I. affinis being more negatively impacted by wax than E. noyesi. Wax was found to serve as an effective defense against parasitism.

Finally, the effects of climate and season on population dynamics of species in this system were assessed. Population densities of A. dugesii were found to not differ across climate types in southern California. Total and E. noyesi parasitism rates also did not differ across climate types. Parasitism rates of I. affinis were highest in inland climate sites. Parasitism by E. noyesi and I. affinis was high throughout the year, except during the early spring. The contribution of E. krauteri to A. dugesii biological control appears to be negligible.