The effect of temperature and relative humidity on survival of unfed hyalomma impeltatum (acarina: ixodidae)

Abstract

This work investigates survival of unfed Hyalomma impeltatum in which 8089 larvae, 3946 nymphs, 2058 males and 2304 females held at different combinations of temperature (21, 25, 29 and 34°C) and relative humidity (RH) (32, 52, 75 and 97%) levels. Survival was significantly improved with rise in RH and fall in temperature in all stages. The magnitude of the effect of RH and temperature on survival varied significantly between stages. Changes in RH and temperature had a stronger impact on survival in larvae than in nymphs and adults; and nymphs were the most tolerant to changes in temperature. Using 97% RH as a base-line level, the temperature-adjusted relative death rate (RDR) at 32% RH levels was 417.0 in larvae, 13.9 in nymphs and 8.1 in adults. The RH-adjusted RDR at 34°C relative to 21°C in these stages was 13.3, 4.6 and 7.3, respectively. Males fared significantly better than females, with age-, RH- and temperature-adjusted RDR for females relative to males being 1.7. The survival difference between males and females was largely post-median. No significant interaction was found between the effects on adult survival of (a) RH and temperature and (b) RH and sex. The difference in tolerance to RH and temperature changes were discussed in relation to differences in the cuticle properties and adaptability of the difference stages.