Long term dynamics of aphelinid parasitoids attacking Bemisia tabaci

Aphelinid parasitoids are widely known natural enemies of Bemisia tabaci (Gennadius), a serious pest of agriculture globally. Here we examine pest-parasitoid interactions and dynamics in Arizona cotton from 1996 to 2010, during which a classical biological control program was implemented. Two native species, Eretmocerus eremicus Rose and Zolnerowich and Encarsia meritoria (Gahan) were either largely or completely displaced by exotic Eretmocerus sp. (Ethiopia) and Encarsia sophia (Gahan) in the early 2000s. Further, E. sophia became the dominant parasitoid of B. tabaci in cotton after many years of predominance by native and exotic Eretmocerus. Apparent rates of parasitism were highly variable within and between years and averaged ≈17% overall. In some years there was evidence that B. tabaci populations declined as apparent parasitism increased. Lower pest abundance was associated with higher rates of apparent parasitism over the entire 15-year period but this pattern was not supported by long term life-table based measurements of parasitism. Detailed life table studies within the entire agro-ecosystem will be needed to fully assess the impact of the classical biological control program.