NEMATODE HETEROTYLENCHUS-AUTUMNALIS AND FACE FLY MUSCA-AUTUMNALIS - FIELD-STUDY IN NORTHERN CALIFORNIA

Abstract

H. autumnalis was found in 6 northern California [USA] counties surveyed, and the incidence of nematode infection of face flies ranged from 4.7-43.8%. Intensive studies at a cattle ranch in Yuba County showed that population densities of the host and nematode infections were highest in flies from cow pats receiving full sun. Average host population density was 105.7 puparia/pat and nematode infection averaged 38.6%. Pats in partial sun averaged 13.5 puparia and 13.1% nematode infection. No face fly was recovered from shaded pats. When data from pats first exposed during day or night were compared, no significant differences in host population density or nematode infection rates were apparent. Uninfected and superinfected flies were more frequent than predicted by a Poisson distribution. Infected and uninfected female flies of all ages captured on white sticky traps appeared to feed with similar frequency on a creamy substance which was probably acquired from cattle. However, older infected females fed less on blood and more on dung than older uninfected females. Percent nematode infection and host population densities were highest in spring and early summer, declined to a midsummer low and then increased slightly. Both dung-reared flies and captured females showed similar trends in abundance and infection rates. Regression analysis indicated that H. autumnalis may not be regulating face fly population density.