Diapause, pupation sites and parasitism of the horn fly, Haematobia irritans, in south-eastern Brazil

In order to verify the occurrence of diapause, preference for pupation site s and hymenopteran parasitism, the pupae of the horn fly, Haematobia irrita ns (Diptera: Muscidae), were collected from undisturbed cattle dung pats in pastures, and adults of the fly were sampled from cattle in Sao Paulo Stat e, south-eastern Brazil, from April 1993 to July 1994. Diapause was verifie d in 7.7% of pupae sampled from pastures in June and July of 1993 and in 9. 9% of those sampled in May, June and July of 1994 (overall rate of 9.1%). A pproximately 8.3% of the pupae were parasitized by microhymenopterans, most ly Spalangia nigroaenea and S. cameroni (Hymenoptera: Pteromalidae). Horn f ly pupae were found almost exclusively inside the pat or in the soil immedi ately beneath and adjacent to it, and very few were collected elsewhere. Pu pa mortality was 54.4% and did not change significantly during the year, bu t mortality was greater among pupae collected in pastures when compared to those obtained from experimental pats, lacking natural enemies.