Friday, September 19, 2014

Scelionidae Wasp Hatching

Mark Bower sent me these pictures last month, a good example of what you can find with curiosity.....and a good photographer.  These eggs are 1mm in diameter (1/25 of an inch), hard to see with a magnifier and impossible to photograph.  I asked him to describe his find.
"These eggs were deposited on a wooden post on our front porch. When the first one emerged, it stayed with the eggs constantly. When others hatched, the first one watched intently, and immediately either attacked or mated with them. I say two "hatchlings" get attacked and expelled from the egg cluster, one gets mated with, and several others die (why?) before they could get out (after opening their eggs). Not sure what all was going on there; it all seemed sort of odd."
We sent this to Chris Barnhart who explained that "these are parasitoid wasps, emerging from eggs of hemiptera. The wasp is likely in the Scelionidae family."  Hemiptera are the order of "true bugs", the order that contains aphids, planthoppers, leafhoppers, shield bugs, and stink bugs that often plague your garden.  In this closeup Youtube video by Mark, at 1:03 you can see a wasp emerging from a hemipteran egg and an immediate attempted mating by a newly emerged male who was waiting for her to come out.

Not all species are black
The scelionidae family contains over 3000 species of parasitoid wasps.  They all lay their eggs on the eggs of insects or spiders where their young grow by using their host  as food.  Generally they are careful to eat only nonessential parts at first, prolonging the life of the host to obtain maximal nutrition.

These wasps and the eggs they attack are tiny!
Antennae with 9 visible segments
A typical scelionid wasp is black and slender although some are various colors and shapes.  In general they have long elbowed antennae with 9 or 10 segments.  These are tiny creatures, ant sized, and could be mistaken for them without magnification.  Most are winged except for some species that parasitize wingless beetles.

A miniscule wasp measuring 3mm in length would have a difficult time fly all over looking for insect eggs to parasitize but they have developed a strategy to find a host for their young- hitchhiking.  They get on the back of a female insect and hang on until she starts laying her eggs.  Then the wasp gets off and starts laying her eggs inside her hosts fresh laid eggs.  Finally, she adds a strong odor, warning away any other parasitic wasp that these are taken.*

Winged scelionid wasp
We tend to be judgmental about plants and animals, classifying them as "good" or  "bad" by our personal criteria.  In ecological terms, many "bad" bugs and plants are just misplaced, located where it is inconvenient or problematic for us.   Eating our garden or the caterpillars of butterflies we treasure labels them "bad".   Meanwhile they are, to paraphrase Arthur Dent in Hitchhikers Guide to the Galaxy, "just these bugs, you know", making babies the best they can.  And if you look closely, they can even be a little cute.
Cute? -  Compound eyes, "The better to see many of you with."
 *  More details at this page.

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