Climate and seasonal effects on phenology and biological control of giant whitefly Aleurodicus dugesii (Hemiptera: Aleyrodidae) with parasitoids in southern California, USA

The invasive giant whitefly Aleurodicus dugesii Cockerell (Hemiptera: Aleyrodidae), a pest of many important crops and ornamentals, has established throughout southern California, USA. The parasitoids Encarsia noyesi Hayat (Hymenoptera: Aphelinidae), Idioporous affinis LaSalle and Polaszek (Hymenoptera: Pteromalidae), and Entedononecremnus krauteri Zolnerowich and Rose (Hymenoptera: Eulophidae) were introduced as part of a classical biological control program against giant whitefly. Populations of giant whitefly can still reach high numbers, however, despite biological control efforts. Seasonal variation in giant whitefly population densities and parasitoids' species-specific parasitism rates across three climates types in southern California were examined by repeated censuses during 2015–2016 in order to identify potential underlying factors influencing giant whitefly population dynamics. Giant whitefly population densities did not vary between southern California climate types, but varied seasonally, with the highest observed population densities in the spring. Parasitism rates of all three parasitoids also varied seasonally, with total parasitism reaching a peak in late summer and declining until the start of spring. Only I. affinis parasitism rates varied between climate types. Parasitism rates of I. affinis were the highest of the three parasitoid species observed, followed by E. noyesi and E. krauteri. Potential explanations for these findings and their impact on giant whitefly control are discussed.