Effects of fluctuating moisture and temperature regimes on sporulation of Beauveria bassiana on cadavers of Rhodnius prolixus

The effects of both moisture and temperature on the sporulation of an isolate of Beauveria bassiana, highly virulent to the Chagas' disease vector, Rhodnius prolixus, were studied in the laboratory under fluctuating regimes. Quantitative assays for conidial production from fungus-killed cadavers from 10-day-old tests showed that recycling was highly dependent on the duration of exposure to high relative humidity (RH). On first-instar larval cadavers, sporulation reached more than 10(5) conidia/nymph under most regimes with a favourable phase combining high humidity (97% RH) and temperatures of 20 or 25 degrees C for at least 12 h/day. Sporulation on third- and fifth-instar nymphs required a longer period (16 h/day or more) of favourable conditions (97% RH and 25 degrees C) per day The intensity of the conidial production from Rhodnius cadavers was enhanced when diurnal temperatures were high (28 and 35 degrees C). From a vector control standpoint, daily high humidity requirements appear to be a crucial constraint. The recycling ability of B. bassiana on fungus-killed R. prolixus is most likely to contribute to the regulation of this triatomine vector if applications are made during the rainy seasons and in the most favourable habitats.