Upper thermal limits for Hypoderma lineatum (Diptera: Oestridae) egg hatching and development.

During periods of Hypoderma lineatum (De Villers) oviposition activity, ambient temperatures reached 28 degrees C and dorsal bovine dermal temperatures exceeded 45 degrees C. Egg hatch decreased linearly with increased constant temperatures from 79% at 35 degrees C to 0% at 39 degrees C. Egg hatch varied from 58 to 80% after 1-, 3-, or 5-h exposures to 40 or 45 degrees C. Exposures of 3 h or more at 50 degrees C were lethal, whereas 66% of all eggs survived 1-h exposures to 50 degrees C. The upper thermal limit for survival at constant temperatures lies between 38 and 39 degrees C, with approximately 53% survival at 37 degrees C. H. lineatum eggs are well adapted to typical temperatures occurring in their natural habitat; however, these temperatures can at times exceed the eggs' upper developmental threshold. This limitation of the host environment may have led to the evolution of adult oviposition preferences for the lower parts of the host animal, shielded from incident solar radiation.