EFFECTS OF RELATIVE-HUMIDITY ON THE HEMATOPHAGOUS BUG TRIATOMA-INFESTANS - HYGROPREFERENCE AND ECLOSION SUCCESS

The hygropreference of larvae and adults of the reduviid bug Triatoma infestans (Klug) was investigated along relative humidity (RH) gradients established by means of different salt solutions, as well as by H2SO4 dilutions. Both larvae and adults preferred to remain at or near 0% RH. This preference,vas similar for bugs reared in the laboratory under different conditions, and for those collected in the field. Several assays to control for both experimental asymmetries along the gradient and the effects of thigmotactic behavior permit exclusion of these factors as responsible for the behaviour of the insects. The preferred RH did not vary with the time of the day or fasting. Larval insects exhibited a significant tendency to remain close to 0% RH at the time of ecdysis. The same preference was exhibited to ovipositing females. The success of ecdysis and egg hatching were measured at different RH values ranging from 0 to 75%. No differences were found between groups; eclosion success ranged from 86 to 94% for egg-hatching and from 89.5 to 95% for ecdysis, at all RHs tested. Results agree with high saturation deficits found along the geographical areas exhibiting the highest prevalence of T. infestans. However, they are in contradiction with values usually recommended to rear this species in the laboratory. The adaptive value of the hygropreference is discussed.