Biological Control of House Flies
Effectiveness and temperature sensitivity of two beneficial wasp species compared on dairy farms
Dairy farmers have limited chemical options for house fly control in their barns and calf hutches due to increasing resistance on the part of the flies and to increasing regulation of pesticides. Previous IPM projects have shown that biological control is an effective means of managing house flies and stable flies in dairy barns and poultry houses.
In 1996 and 1997 the efficacy of two biological control agents, two tiny wasp species that consume immature flies ("pupae"), has been evaluated. This year's project focused on the wasps' abilities to find hidden flies, their rates of parasitism, and any temperature effects on these characteristics.
Results on searching ability indicate that both of the wasps (M. raptor and M. raptorellus) killed more of the fly pupae that were planted on the surface of straw bedding than those that were buried 2 cm beneath the straw. Neither wasp species found the buried pupae within a 24-hour period. Parasitism rates were equivalent for the two species.
M. raptorellus is considered the more promising of the two biological control agents because of its ability to lay six to eight eggs in each fly pupa and thus build its population more quickly than can M. raptor, which lays only one egg per pupa.
Temperature considerations may prove to be an equalizing factor in a choice between the two, however. M. raptorellus produced multiple progeny only when temperatures exceeded 18 deg. C (normal temperatures between June 15 and Sept. 1 ). Rates of fly consumption were significantly greater for both wasp species on unusually warm days (above 24 deg. C) than at lower temperatures.
As yet untried are controlled comparisons of sustained mass releases of the two species on dairy farms. This is the next logical step before a recommendation can be made to farmers regarding the two agents.