Is parasitoid host specificity dynamic?

Choice of host individuals by parasitoids is dynamic, varying with physiological state and experience.  In particular, female parasitoids with high egg loads and low life expectancy are more willing to accept low quality hosts than females with low egg loads and high life expectancy.  However, studies of dynamic acceptance behavior in parasitoids have only considered high versus low quality hosts within the same host species. Here, we report the first results on whether acceptance of host species that vary in quality is also dynamic, using aphid parasitoids in the genus Aphelinus (Hymenoptera: Aphelinidae). Stresses (starvation and age) and experience that should increase the perception of time limitation did not affect acceptance of low quality host species by one Aphelinus species, and had a weak effect on another species. Oviposition in a high quality host species increased with egg load (as expected), but did not vary with egg load for females exposed to low quality host species.  This is an unexpected pattern since the proportional acceptance of low quality hosts decreases with increasing egg load.  Three hypotheses may explain the lack of a shift to less specificity in these parasitoids: (1) frequent transient egg limitation, (2) higher fitness from egg resorption than oviposition, and (3) neural contraints on host recognition. Rejection of hosts both for host feeding and oviposition, and variation among females in acceptance of low quality host species suggests that the latter hypothesis may hold.