Gd. Inglis et al., EFFECTS OF TEMPERATURE AND THERMOREGULATION ON MYCOSIS BY BEAUVERIA-BASSIANA IN GRASSHOPPERS, Biological control, 7(2), 1996, pp. 131-139
The influence of behavioral thermoregulation by grasshoppers (Melanopl
us sanguinipes) on mycosis caused by Beauveria bassiana was investigat
ed in controlled environments. The cardinal temperature for B. bassian
a conidial germination and hyphal development was approximately 35 deg
rees C. A low prevalence of mycosis (less than or equal to 7%) was obs
erved in inoculated nymphs exposed to a continuous temperature of 35 a
nd 40 degrees C, whereas continuous exposure to 30 degrees C did not h
ave a significant effect on disease development. Daily exposures to 35
and 40 degrees C for 1 and 6 h, respectively, decreased mycosis in ny
mphs. In both environments, a strong correlation (r greater than or eq
ual to 0.95) was observed between hyphal growth on potato dextrose aga
r and final mycosis, Although high temperatures delayed conidial germi
nation, only conidia exposed to continuous 35 or to 40 degrees C for m
ore than 8 h exhibited reduced germination after 24 h, The effects of
temperature on conidial germination were poorly correlated with diseas
e, and when nymphs were exposed to 35 degrees C for 24 h, less mycosis
was observed only in grasshoppers exposed between 1 and 2 days postin
oculation. The thoracic temperature of nymphs permitted to bask adjace
nt to a heat source ranged from 38 to 42 degrees C, In nymphs basking
for 1 h per day, 46% less mycosis was observed, decreasing to 98% less
disease in nymphs allowed to bask for 6 h or greater per day. On a he
at gradient, a higher prevalence of B. bassiana-infected nymphs select
ed hotter positions than noninfected nymphs, suggesting a ''behavioral
fever'' response to infection. This study indicates that high tempera
ture and thermoregulation can adversely affect B. bassiana mycosis of
grasshoppers and may explain the poor efficacy of this entomopathogen
observed in some held experiments. (C) 1996 Academic Press, Inc.