| Abstrakt: |
A study was conducted to determine the effects of temperature on the competitive infection and colonization of grasshoppers (Melanoplus sanguinipes) byBeauveria bassianaandMetarhizium flavovirideapplied alone and in combination. Nymphal mortality and proliferation of the fungi in the hemocoel were measured in four environments with the same mean daily temperature (25°C) but differing in the degree to which they oscillated daily (constant 25°C, 20 to 30°C, 15 to 35°C, or 10 to 40°C). For nymphs inoculated withB. bassianaand to a lesser extentM. flavoviride,mortality decreased as the amplitude of temperature increased. Fungal populations in the hemocoel of nymphs increased over time in all environments, but fewer colony-forming units (CFU) were recovered from nymphs as the degree of temperature oscillation increased. Densities of CFU were significantly correlated with mortality. BothB. bassianaandM. flavoviridewere isolated from the hemocoel of nymphs that were coinoculated, but coapplication of the two fungi did not significantly affect the prevalence of mortality. In some instances total fungal populations in the hemocoel of nymphs coinoculated withB. bassianaandM. flavoviridewere smaller than those in nymphs treated with each fungus alone, indicating a degree of interspecies antagonism. Furthermore, moreB. bassianathanM. flavovirideCFU were recovered from coinoculated nymphs at constant 25°C, but as the amplitude of temperature increased, populations ofM. flavovirideincreased relative toB. bassiana,suggesting that temperature influenced their competitiveness. The results of this study indicate thatM. flavovirideis superior toB. bassianaagainst grasshoppers under conditions of oscillating temperature and that the advantage of applyingB. bassianain combination withM. flavoviridewill primarily be when daytime conditions are overcast and/or cool. |
Full Text from ScienceDirect