Monday, January 28, 2013

More on parasitoid nuptial gifts

I did a bit more poking around the literature (there is, fortunately, quite a lot on parasitoids) and found many other examples where some comparison was made between mated and virgin females. Every paper seemed to have different methodology and different measured metrics (related to whatever the paper was about).

A bad picture of a beautiful wasp, Mesostenus thoracicus, female, Walpole, Maine, 2009

The results of all these studies were not at all in agreemend. Some agreed with the findings in Bracon hancocki and found that virgins lived significantly shorter lives than mated females. Others found the exact opposite. Many showed that virgins lay fewer eggs or parasitize fewer hosts (independent of eggs, as in many cases more males can develop in a host than females), but others found the opposite result. Some showed that virgin females spent less time moving and ovipositing than mated females, which suggests they wait for mates. Others found no difference in similar metrics.

An unidentified Ichneumonid (Pimplinae?) ovipositing into a Herpetogramma thesausalis pupa, Maine, 2009

Perhaps the most interesting result was that of Sagarra et al (2002) who found that female Anagyrus kamali did not differ in longevity based on mating status, but males did. Unmated males lived 40% longer than mated males and females required more than one mating to get sufficient sperm to fertilize all their eggs (some scientists believe this is rare in parasitoids, others don't - I don't have an opinion). This does suggest that males put some serious investment into their sperm, as all other conditions were equal for these males.

Bob Carlson, one of the most knowledgeable Ichneumonid specialists around, said: "There are so many kinds of parasitoid Hymenoptera, that I expect it certain that some of them have evolved such that females get sustenance from male seminal fluid. "

That seems pretty reasonable to me, though it might be a needle in a haystack search for it. Anyone interested in the references I have compiled on this or a longer summary of each paper's finding, let me know. 

This Ichneumon (Ichneumoninae, I believe) is a rare parasitoid of  Herpetogramma thesausalis. This male was
buzzing around a patch of sensitive fern with lots of host shelters, likely mate-searching.

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