Seasonal variations in the abundance of Gasterophilus spp. larvae in donkeys in northern Jordan.

One hundred and five donkeys were examined over a 12-month period for the presence of Gasterophilus spp. larvae in their stomachs. G. intestinalis and G. nasalis were found, but there was a distinct seasonal variation in their abundance. The numbers of second-stage larvae (L2) peaked during the early winter and early summer, but they were absent or at low levels during the early spring and early autumn. This suggests that there are two periods of adult fly activity (late autumn and late spring) for both G. nasalis and G. intestinalis. Third-stage larvae (L3) were found throughout the year, but the lowest levels were seen in the late summer and autumn. The parasites also had an aggregated distribution, which may be due to host selection by the fly. The numbers of larvae did not vary significantly with age, which may be due to a lack of acquired protective immunity or to tolerance after repeated exposure.