Dependence of the entomopathogenic fungus, Beauveria bassiana, on high humidity for infection of Rhodnius prolixus.

The impact of relative humidity (RH) on the infective potential of the isolate Bb INRA 297 of Beauveria bassiana (Bals.) Vuillemin (Deuteromycotina: Hyphomycetes) against first instar nymphs of Rhodnius prolixus Stål. (Hemiptera: Reduviidae) was determined. Fungus-treated insects were exposed to RHs ranged from 75 to 100% at 25 degrees C. Results clearly showed a threshold of humidity at ca. 96% for high and rapid mortality. After initial exposure to increasing periods of 97% (4, 8, 16, 24, 36 and 48 h) and subsequent transfer to constant lower RHs (43, 53, 75 and 86%) at a constant 25 degrees C, an incubation of at least 48 h at 97% RH was necessary to kill all insects. On changing RHs of 97/75% and different regimes of temperature (15/28 degrees C, 20/25 degrees C, 25/28 degrees C, and 25/35 degrees C), at least 72 h of initial exposure at 97% RH for the 15/28 degrees C regime, 48 h for the 20 degrees/25 degrees C and 25/28 degrees C regimes and 36 h for 25/35 degrees C were needed to kill all insects over a 6-day incubation time. Delayed exposure to favorable moisture condition (97% RH), significantly affected infection for up to a 3-day delay within the various temperature-humidity regimes tested.