Seasonal abundance and reproductive output of the dung fliesNeomyia cornicinaandN. viridescens(Diptera: Muscidae)

Abstract

AbstractThe seasonal abundance and reproductive output of two common, but little studied, dung-breeding flies,Neomyia cornicinaandN. viridescens, were examined in artificial cow pats in pastures in southwest England in 2001 and 2004. In 2001, the numbers of bothNeomyiaspecies increased slowly over summer to show a sharp seasonal peak in late August and early September. There was no significant effect of mean temperature, mean relative humidity or dung water content on abundance or seasonally de-trended abundance. High levels of aggregation were seen between pats and, when present, greater numbers ofN. cornicinaemerged thanN. viridescens.Neomyia cornicinawas present in 13% of 240 artificial standardized pats put out in 2001, at a median of 19 adults per colonized pat;N.viridescenswas present in 8% of artificial pats at a median of three adults per colonized pat. In 2004,N. cornicinaemerged from 46% of the 94 artificial pats put out at a median of three adults per colonized pat, whileN. viridescensemerged from only 12% of pats at a median of one adult per colonized pat. Flies were also collected in 2004, using sticky-traps and hand nets. Again, free-flyingN. cornicinaappeared to be more abundant in the field thanN. viridescens; 162N. cornicinawere caught compared to 44N. viridescensover the same sampling period. The size of each adult female was recorded and ovarian dissection was used to determine the numbers of eggs matured. FemaleN. viridescenswere significantly larger than theN. cornicinaand matured significantly higher numbers of eggs. GravidN. viridescensmatured a mean of 37.1 (±16.9) eggs, whereas gravidN. cornicinamatured a mean of 28.8 (±13.2) eggs. The reasons why the larger, more fecund,N. viridescensadults are less abundant in the field or emerging from pats thanN. cornicinaare unknown. Further work is required to identify the nature and cause of the mortality experienced by the larvae of these species and the ecological differences and functional specialisation which allows co-existence to be maintained.