Effect of constant and cyclical temperatures on the mortality of Triatoma infestans (Klug) (Hemiptera: Reduviidae) treated with Beauvaria bassiana (Bals.) Vuill. (Hyphomycetes)

Abstract

The mortality of Triatoma infestans (Klug) treated with Beauvaria bassiana (Bals.) Vuill. under several temperature regimes was analyzed. Mortality rates were highest at 26°C and 22°C and lowest at constant 34°C. The combinations 26/34°C or 34/26°C (12:12h cycles) were significantly different from the combinations 18/26°C and 26/18°C, showing that high temperatures (34°C) affect mortality most significantly. The combinations also indicate that when an extreme high temperature is associated with an optimal temperature of 26°C, the susceptibility of T. infestans to B. bassiana infection decreases. Exposure to extreme temperature (18°C or 34°C) associated with an optimal temperature of 26°C in 8:8:8h cycles, reduces the mortality of T. infestans. In cycles of 6:6:6:6h, only the mortality associated with the 34/30/26/22°C combination was similar to the combinations at constant 22°C and 26°C. Extreme temperatures during the first stage affect mortality less than when this period is not longer than 6h. Mortality decreases significantly when an extreme high initial temperature is followed by an abrupt fall (34/22/26/30°C). Our results indicate that Beauvaria bassiana should be applied to the field in the late afternoon to avoid the negative impact of abrupt changes in temperature, or of high temperatures during the critical first stages of the infectious cycle of this entomopathogenic fungi.