Autoparasitism, interference, and parasitoid-pest population dynamics

Autoparasitoids ("heteronomous hyperparasitoids") are parasitoids that lay female eggs on homopteran hosts and male eggs on juvenile parasitoids of ei ther the same species or another species. Males develop as hyperparasitoids and eventually kill the juvenile parasitoid. We present a series of stage- structured models that investigate the effects of autoparasitism on populat ion dynamics. Autoparasitism causes density-dependent mortality on juvenile parasitoids and therefore has a stabilizing effect. This also leads to an increase in host population abundance. In most cases an autoparasitoid lead s to higher host equilibrium densities than a comparable primary parasitoid (except when the primary parasitoid is arrhenotokous (sexual) and the auto parasitoid has a low preference for attacking parasitized hosts or can atta ck the parasitized host for only a small portion of its development). When male autoparasitoids are followed explicitly in the models, mate limitation reduces the stabilizing effect of autoparasitism and leads to a further in crease in host abundance. Coexistence of an autoparasitoid with a nonprimar y parasitoid or second autoparasitoid is possible when the level of conspec ific autoparasitism is greater than the level of heterospecific autoparasit ism. When an autoparasitoid coexists with a primary parasitoid, the resulti ng host density is always greater than that with only the primary parasitoi d. Therefore, autoparasitoids have the potential to disrupt control achieve d by primary parasitoids. When two autoparasitoids coexist, the resulting h ost density is always lower than that attained by either autoparasitoid alo ne. The effects of autoparasitism are compared with those of other forms of interference competition. (C) 2001 Academic Press.