But the cocoones were quite thin, like unfinished, and inside was a rather repulsive looking, thick sausage with no recognizable organisation.
|Cocoons of noctuid moth caterpillars on basil. The caterpillars were killed by parasites|
Under magnification, little eyes became visible on those white grains. So probably really parasites. Larval (or pupal) wasps rather than flies, because those eyed creatures did not look like headless maggots.
|Copidosoma spp, Pupae|
Charles Melton and Dennis Haines had the answer quickly:
|Copidosoma spp, adult female|
The tiny, 1.5mm long wasp female produced just a few eggs, and probably even spread those among the three affected caterpillars that I found. But she did not actually attack the caterpillar, she had laid her eggs early, right when a moth female deposited her eggs on my basil plant.
The wasp eggs multiplied then by cloning into as many as a few thousand (polyembryony). The larvae didn't begin growing until the caterpillar has reached a certain size. So they all uniformly ended up killing their caterpillar just as it was about to spin a cocoon and pupate.
I collected two of the cocoons to see what will emerge. Dennis Haines remarked that these wasps are obviously interesting for researchers working on biological control, but they are difficult to raise in captivity.
The sex of the larvae seems to be determined by temperature ... just one more fascinating aspect.