Whitefly control potential of Eretmocerus parasitoids with different reproductive modes

A major component of the evaluation of biological control agents is the study and comparison of their biology, including the reproductive mode. In hymenopteran parasitoids, reproductive modes include thelytoky and arrhenotoky. Since a thelytokous population produces only females, it is assumed that they may be better suited for biological control than an arrhenotokous population. Here we compare the effects of these two modes of reproduction on life-history parameters in the whitefly parasitoid Eretmocerus mundus. We also determined biological parameters of two populations of E. mundus on three host plants (tomato, poinsettia and gerbera) under laboratory conditions, to be able to evaluate the effect of the host plant on the parasitoid. In all situations the developmental times of nymphal stages were not significantly different. Females lived longer on tomato than on poinsettia and gerbera. The number of progeny of both parasitoid populations was highest on tomato, lowest on gerbera and intermediate on poinsettia. Reproduction is high during the first twodays of the female’s life for both populations on the different host plants; thereafter it decreases quickly. Arrhenotokous females had a higher fecundity than thelytokous ones. The sex ratio for the arrhenotokous population was 50/50 on the three host plants, while we could find only a few males for the thelytokous population. The intrinsic rate of population increase (rm) was highest on tomato, intermediate on poinsettia and lowest on gerbera, and similar for the arrhenotokous and the thelytokous populations. The results will be discussed in the framework of selecting the best Eretmocerus species/strain for biological control of whitefly. Introduction Whiteflies are a serious pest of vegetable, ornamental, and agronomic crops throughout the world. They have caused enormous damage to many crops during the past century (Gerling, 1990; Gerling and Mayer, 1996). Control of whiteflies with chemical pesticides is often problematic because of the wide occurrence of resistance (e.g. Palumbo et al., 2001). Therefore, during the past decades, much research was directed at finding efficient natural enemies of whiteflies (for overviews, see Gerling 1990; Gerling & Mayer, 1995; Gerling et al., 2001). Among different categories of natural enemies to control whiteflies (e.g. predators, parasitoids and microbial agents), parasitoids are the most successful (van Lenteren, 1990; Gerling et al., 2001). So far, several solitary parasitoids of the genera Encarsia, Amitus, and Eretmocerus have