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Chapter 18
Musca domestica L., House Fly (Diptera:
Muscidae)
R.A. COSTELLO
Aies, particularly Musea domes/iea L., associated with egg producing operations have
become an increasing problem in British Columbia's Fraser Valley in recent years.
Conflicts between farmers and their nonfarming neighbours have intensified with the
encroachment of urban development on agricultural areas. Flies can also be a considerable
annoyance to farm operators and their families and employees.
Certain parasitoid wasps have been found effective in suppressing nuisance fly populations
in egg producing operations in California (Legner & Dietrick 1972, Legner e/ al.
1975). A commercial insectary in that state provided the parasitoids for this study. The
pupal parasitoid Spa/angia endius Walker (Hymenoptera: Pteromalidae) was selected
for this trial because of its tendency to burrow deeper into manure than other available
parasitoids in search of pupae (Legner 1977). Pre-release sampling indicated that more
than 90% of the pupae were further than 3 cm below the surface.
In 1978, a total of 400000 Spa/angia endius, in the form of parasitized house fly pupae,
were released into a deep pit layer barn in Aldergrove, British Columbia. The barn,
measuring 91 m by 12 m, contained 27 000 layers. The pit contained a 9 month accumulation
of manure at the start of the trial. Four releases of 100 000 parasitoids each were
made at 3 week intervals commencing 20 April. No other control methods were applied
in this barn. Fly numbers, as indicated by "spot cards" (Rutz & Axtell 1979). were
compared to those in a bam 30 m away where fly control consisted of chemical insecticides
applied as space sprays. residual surface sprays, and floor baits. The spot cards
consisted of white 7.6 x 12.7 cm unlined file cards. These were pinned to posts in the
barns, collected weekly. and the fecal and regurgitation marks counted.
Levels of parasitism were measured by collecting manure samples once a week.
floating out fly pupae, and holding them at 30"C until either flies or parasitoids emerged.
This also provided an indication of the fly species involved and all pupae collected were
Musca domes/iea.
Ay numbers were monitored in both barns from 25 April to 13 June. The spot card
counts were similar for the first weeks, averaging 45.3 per card in the bam using
chemical control methods and 35.7 in the barn where parasitoids were released. By the
end of the third week, mean spot card counts rose to 390.2 in the chemical control barn
and fell to 26.9 in the barn containing Spa/angia endius. Repeated applications of
pyrethrum as a thermal fog resulted in a reduction of the mean spot card count to 213.2
by the end of the 6th week when the manure was removed and spot card counts were
discontinued. Spot counts in the barn using parasitoids averaged 20 to 25 during the 4th,
5th and 6th weeks of the trial.
Six weeks after the initial introduction of parasitoids 63% of the fly pupae separated
from manure samples contained Spa/angia endius larvae and pupae. This was the highest
level of parasitism found during the sampling period.
House fly numbers in the barn containing parasitoids rcmnincd nt acceptnble levels
throughout the trial and the remainder of the fly senson, while flies in the bam employing
chemical control methods were intolerably abundant and eventually necessitated
removing the manure to relieve the problem. The commercial value of the parasitoids
used in this study was approximately $800, about the same as the operator spent on
chemicals the previous year.
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