Spatial dispersion patterns of house fly larvae, Musca domestica L., and associated predatory mites (Acari : macrochelidae) in poultry manure

Abstract

Third-instar house fly larvae and both sexes of Macrocheles muscaedomesticae exhibit an aggregated spatial dispersion in poultry manure. Populations of both species were sampled by random quadrats of three sizes at a narrow, caged-layer poultry house. House fly larval clusters were also transected by a series of contiguous samples. The values for the index of dispersion (ID) and Lloyd's index of patchiness (IL) were significantly greater than one for all samples indicating an aggregated population for both larvae and mites. The negative binomial did not differ significantly from the observed frequency distribution at α = 0.05 for either species except for the large sample larval counts and the small sample female mite counts and provided the best fit among eight tested distributions. A decrease in IL with increasing sample size with a relatively fixed ID suggested a negative binomial compound Poisson (λ) V LSD (θ) clustering model for the dispersion of house fly larvae. A social mechanism was supported by a sharp density gradient across larval clusters and the high intensity of the cluster pattern. An increase in ID with sample size and a relatively fixed IL suggested a negative binomial compound Poisson (θ) Λ gamma (α, β) heterogeneity model for the dispersion of both sexes of Macrocheles muscaedomesticae. Manure accumulation and manure moisture content appeared to have the greatest influence on the dispersion of the larvae and the mites. Few of the sampled larvae (5-7%) were found in areas of distinct cone formation while a majority of the mites were recovered from the manure cone. Larvae were recovered from a moisture range of 40-80%. The mites were recovered in manure ranging up to 80% and more mites than larvae were associated with dryer portions of the manure. The dispersions of the larvae and the mites were independent according to a x^2 test for independence and Lloyd's index of interspecific patchiness (IP[XY]) for measuring spatial overlap. The mite sexes were positively associated and IP[XY] indicated a 671%, 237% and 253% higher probability of encounter than would be the case if both sexes were randomly distributed in the habitat. The apparent response by the house fly to environmental patchiness indicates elements of both heterogeneity and social clustering are involved with the evidence supporting the strength of larval interactions in the dispersion. The lack of larvae in the manure cone may be due to predation by the mite on egg clusters in this area. The mites lack any gregarious behavior and environmental heterogeneity determines their dispersion in poultry manure.