Use of Pathogen Combinations to Overcome the Constraints of Temperature on Entomopathogenic Hyphomycetes against Grasshoppers

The influences of temperature on the mortality of grasshoppers (Melanoplus sanguinipes) inoculated with the entomopathogenic fungi,Beauveria bassianaandMetarhizium flavoviride,alone and in combination was investigated. Basking by grasshoppers had less influence on the prevalence and timing of mortality in nymphs treated withM. flavoviridethan withB. bassiana.InB. bassiana-treated nymphs allowed to bask for only 1 h/day, 44% less mortality was observed, decreasing to 98% less death in nymphs basking for ≥4 h/day. In contrast, only a slight decrease in mortality (13 to 23%) was observed inM. flavoviride-treated nymphs permitted to bask for 4 to 6 h/day. 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 onB. bassianathanM. 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 grasshopper thermoregulation during daylight periods (0600 to 2200 h). At 25°C, there was no difference between treatments in the prevalence of mortality. In the hot temperature environment, less mortality was observed forB. bassiana(3%) than forM. flavoviride(52%). Conversely, in the cool temperature environment, less mortality was observed forM. flavoviride(46%) than forB. bassiana(100%). Application of both pathogens simultaneously resulted in a final prevalence of mortality that was greater than that forM. flavoviridein the hot temperature environment and equal to that forB. bassianain the cool temperature environment. The application ofB. bassianaandM. flavoviridein 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.