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.

Thursday, January 10, 2013

Parasitoid nuptial gifts?

A Braconid, Alabagrus texanus, a male. I doubt any nuptial gifts are given in this species scramble-mating system. 

I found something yesterday that I think is really-cool. While browsing old copies of the journal Bulletin of Entomological Research, I stumbled across this quote, in reference to Bracon sp. (probably hancocki).

"Average life-span for mated females was 13.6 days, whereas virgin females lived for an average of 5.6 days."

Here's the catch: parasitoids are unreported (at least that I could find) to give "nuptial gifts" i.e. a resource given by male to female during courtship or copulation. Charles Godfray, in his book (bible), Parasitoids: Behavioral and Evolutionary Ecology, says "I know of no evidence of nutrient transfer during mating in parasitoids". Many other insects are known to (katydids, certain flies, etc.). This quote makes it seem like there could be some transfer of nutrients in the sperm (as the authors made no mention of courtship behavior).

Making the story more interesting, and believable, the authors state that the females copulated many times with the same male upon emergence, then began egg-laying a few days later. Multiple matings are rare in parasitoids, another indication that the female is likely gaining something else besides just sperm from the male.

An interesting observation, and one that probably could be examined, as Bracon is a fairly common genus.

Reference: Olaifa, J. I., & Akingbohungbe, A. E. (1982). Bionomics of Bracon ?hancocki (Wilkinson)(Hymenoptera: Braconidae), a Larval Parasite of Cydia Ptychora (Meyrick)(Lepidoptera: Tortricidae) in Nigeria. Bulletin of Entomological Research, 72(04), 567-572.

Godfray, HC. (1994) Parasitoids: Behavioral and evolutionary ecology. Princeton University Press. 

This is the same species in the photo above emerging from a Herpetogramma caterpillar, prior
to spinning its cocoon.