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Objectives
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Determine moisture preferences of adult Fannia spp. for oviposition and document influence of moisture on development and survival of immature Fannia spp. in the laboratory. Document the field microdistribution of immature Fannia spp. in the manure, with particular reference to moisture, temperature, and depth. Test for competitive interactions between the two dominant Fannia spp. in the laboratory.
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End-year
progress
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Both Fannia species have the ability to develop successfully at surprisingly low manure moisture levels, much lower than those required for the common housefly. First instar larvae placed into manure as dry as 40% moisture can develop to the adult stage, although emergence is reduced, they take significantly longer to develop in drier manure, and emerging adults are smaller. The pest fly, F. canicularis, appeared to be more stressed by 40% moisture than did F. femoralis. First instar larvae could not develop in 32% moisture manure, but third instar F. canicularis larvae were more resistant and could develop to adult emergence even as low as 32% moisture. Adult female F. canicularis showed a marked preference for oviposition on manure > 55% moisture and laid almost no eggs on manure drier than 45%. Field sampling indicates that F. canicularis larvae remain closer to the manure surface (wetter manure) than do larvae of F. femoralis. Both flies are most common in spring, and larval survival and development are inhibited by temperatures >80-85oF. Manure in build-up systems in spring, in a dry year, might become dry enough to inhibit F. canicularis oviposition. In a normal or wet year, however, manure should remain acceptable for oviposition most of the time. Once larvae are in place, manure in a build-up system remains suitable for development of these species, since it is rare for piled manure under cages to reach moisture levels below 40%. Manure, which is spread for drying in winter or spring, would seldom become dry enough quickly enough to prevent larval development completely. The inhibition of Fannia spp. by spreading manure for drying thus is more likely to result from higher temperatures from solar radiation and/or predation by birds, etc. than from drying itself.
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