EFFECTS OF IMMERSION IN WATER ON SURVIVAL OF PREIMAGINAL STAGES OF HAEMATOBIA-IRRITANS (DIPTERA, MUSCIDAE)

Laboratory studies on effects of immersion and immersion duration on a ll Haematobia irritans (L.) preimaginal stages revealed a significant disparity in tolerance limits among different developmental stages and in tolerance to different immersion durations (0, 1, 6, 18, and 30 h) . Of the 4 preimaginal stages, 2nd instars were most susceptible to im mersion of any duration, whereas eggs and pupae were most resistant. A ll instars were intolerant of immersion durations >6 h, with <10% surv ival at 6-, 18-, and 30-h immersion durations. Survival of 2nd instars was reduced to 38% by 0-h immersion, when compared with the control g roup. Adult eclosion was reduced by immersion durations of 18 and 30 h during the pupal stage. Life stage survival was dependent upon immers ion duration, with survival generally decreasing as a negative linear function of increasing immersion duration. Immersion durations of 0, 1 , 6, 18, and 30 h resulted in overall mortality rates of approximate t o 30, 37, 53, 61, and 82%, respectively. In wet regions with low eleva tions, water accumulation may significantly affect horn fly distributi on and abundance. In drier regions, where flooding events are sporadic and water accumulation variable, the effect on horn fly populations i s uncertain.