The biology of two Eretmocerus spp. (Haldeman) and three Encarsia spp. Forster and their potential as biological control agents of Bemisia tabaci biotype B in Australia

The performance, as measured by daily rate of parasitism and total parasiti sm, of five aphelinid species found in Australia parasitising Bemisia tabac i were compared on cotton, hibiscus, rockmelon, soybean and tomato. Two Ere tmocerus spp., both indigenous to Australia, gave the highest levels of par asitism on each of the plant host species tested. The tritrophic interactio ns between B. tabaci, host plant species and Eret. mundus (Australian parth enogenetic form) (APF) were also examined. In general, more whiteflies were parasitised when cotton was the source host or rockmelon the test host. Pa rasitism was always low when tomato was either the source or test host. Whe n parasitoids were transferred from rockmelon to cotton, parasitism decline d. In contrast, parasitism increased when parasitoids were transferred from cotton to rockmelon. Parasitism also increased when parasitoids were trans ferred from soybean to rockmelon, yet failed to do so when shifted from soy bean to cotton despite cotton normally being a better host. However, when p arasitoids were transferred from cotton to soybean there was a marked incre ase in parasitism. Possible causes are discussed. The field cage trial demo nstrated that parasitism by both Eretmocerus spp. increased with increasing whitefly density. Further, the increase in parasitism was not due to the p resence of more parasitoids as neither the parasitoid-whitefly ratio nor th e total number of parasitoids present had a significant effect on parasitis m. The combination of the two species, gave similar levels of parasitism to that achieved by Eret. mundus (APF) alone. Subsequent identification of th e emerged individuals indicated that over 50% of the parasitism was due to this species suggesting that it out-competed Eret. queenslandensis. Despite this competition, there was no evidence that overall control was compromis ed.