Monday, 13 October 2014

Conopid flies

The morning mail made a heavy thump as it landed on the front door mat and I was pleased to see that the latest issue (No 78) of Bulletin of the Dipterists Forum had arrived. It brightened the day, compensating for the rain which was falling unremittingly outside. 

On the front cover was an fine photograph, by Darwyn Sumner, of Conops flavipes. I record a few conopid flies most years but on checking my records I was surprised to realise that I have not recorded this species, despite it being widespread throughout England and Wales. I frequently record a close relative, Conops quadrifasciatus.

There are 23 members of the Conopidae found in Britain and I'm afraid all, dear Reader, have a rather ghoulish lifestyle. All are solitary internal parasites, mainly of wasps and bees, although a few are parasitic on grasshoppers and their relatives.

A conopid fly will seize a bee and lay 2-3 eggs on the victim's abdomen. When the eggs have hatched the larvae make their way to the abdomen of the unwilling host and proceed to eat the internal organs, usually with only one larva surviving. Apparently the remaining larva then make its way to the abdomen where pupation takes place. Conopid flies are themselves often victims of Chalcids, tiny insects related to bees - a curious sort of familial revenge. I dug out my copy of K.G.V. Smith's monograph on the family, where I read, "...females wait on nearby vegetation and attack foraging bees with a very quick strike, when both bee and fly may roll on the ground together in a violent struggle."

Bee with almost completely hollow thorax, probably the victim of
a conopid fly. Byfield Pocket Park. Northants. June, 2014

Earlier this year, in Byfield Pocket Park. I netted a bee (which I failed to identify) with the thorax almost completely hollow. It was almost certainly a victim of a conopid fly. But, quite extraordinarily, the creature was still alive and was able to crawl feebly around my net. Had I thought to open up the abdomen I may have found the larva there. Occasionally a wet, bedraggled-looking bee may be seen on the ground. It may be worth taking the bee and keeping it in order to check for the presence of a conopid larva - but you would need to be prepared for a long wait until the adult fly emerges.

In theory conopid flies could be a problem for keepers of honeybees but, although some minor difficulties have been reported from central U.S.A. their depredations seem not to be a serious concern.

With bumble bees the problem is far more serious. Research in the U.S.A. shows that a bumble bee, after spending 20 hours of foraging has a 50% chance of conopid "infection", and after 40 hours this figure rises to almost 100%! For more about this read, "Meet the Conopid Fly; a bumblebee horror story", by Carolyn Beans. This can be easily found by googling "Conopid flies".

Comments? Tony White, e-mail:

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