Use of pathogen combinations to overcome the constraints of temperature on entomopathogenic hyphomycetes against grasshoppers.
The influence of temperature on the mortality of Melanoplus sanguinipes inoculated with Beauveria bassiana and Metarhizium flavoviride, alone and in combination, was investigated in the laboratory. Basking by Melanoplus sanguinipes had less influence on the prevalence and timing of mortality in nymphs treated with Metarhizium flavoviride than with B. bassiana. In B. bassiana-treated nymphs allowed to bask for only 1 h day-1, 44% less mortality was observed, falling to 98% less death in nymphs basking for ¬>4 h day-1. In contrast, only a slight decrease in mortality (from 13 to 23%) was observed in M. flavoviride-treated nymphs permitted to bask for 4-6 h day-1. For both fungi, more mortality was observed in nymphs exposed to 35 than to 40°C for various durations per day. However, exposure to high temperatures had a greater inhibitory effect on B. bassiana than M. flavoviride. The efficacy of both entomopathogens, alone and in combination, was determined in simulated cool and hot fluctuating temperature environments and at a constant 25°C. The former two environments were derived from weather data on two different days at Lethbridge in July and were adjusted to simulate thermoregulation by Melanoplus sanguinipes during daylight periods (06.00 to 22.00 h). At 25°C, there was no difference between treatments in the prevalence of mortality. In the hot temperature environment, less mortality was observed for B. bassiana (3%) than for Metarhizium flavoviride (52%). Conversely, in the cool temperature environment, less mortality was observed for M. flavoviride (46%) than for B. bassiana (100%). Application of both pathogens simultaneously resulted in a final prevalence of mortality that was greater than that for M. flavoviride in the hot temperature environment, and equal to that for B. bassiana in the cool temperature environment. It was concluded that the application of B. bassiana and M. flavoviride in combination may be a way to overcome some of the constraints of temperature on entomopathogenic Hyphomycetes against grasshoppers, especially where temperatures fluctuate or are high for a significant period of time.