Observations on the winter ecology of the bat fly Trichobius corynorhini Cockerell (Diptera: Streblidae).

Abstract

The frequency and levels of infestation of the bat fly Trichobius corynorhini Cockerell on its normal host Plecotus townsendii Cooper are examined. A direct relationship between winter host density and levels of bat fly infestation is demonstrated. Frequency and levels of infestation are greatest on females. No differences in frequency or levels of infestation are shown for solitary and clustered female hosts, although clustered males are more frequently and heavily parasitized than solitary males. It is hypothesized that higher frequencies and levels of bat fly infestation on males in winter are coincident with a shift from a solitary behavior of males in summer to an increase in cluster frequency and association with females in autumn and winter. Apparent movements of bat flies from more heavily infested females to male hosts may reduce intraspecific competition and thus permit optimal utilization of food resources (blood) when both sexes of the host are together in hibernation and blood from the host is potentially limiting due to a decrease in peripheral circulation. Evidence from the disproportionate frequencies and levels of infestation on males and females in clusters suggests the existence of a host factor produced by females which may attract flies and thus enhance their hostfinding success. This may be necessary to insure reproductive success of flies in the warm summer months owing to the propensity for males to roost singly at this time and for females to form nursery aggregations.