Gd. Inglis et al., EFFECTS OF TEMPERATURE AND SUNLIGHT ON MYCOSIS (BEAUVERIA-BASSIANA) (HYPHOMYCETES, SYMPODULOSPORAE) OF GRASSHOPPERS UNDER FIELD CONDITIONS, Environmental entomology, 26(2), 1997, pp. 400-409
The influence of environmental conditions on mycosis of grasshoppers c
aused by Beauveria bassiana (Balsamo) Vuillemin, was investigated. Des
pite the deposition of considerable quantities of conidia onto grassho
ppers (6.7 x 10(3) colony-forming units [CFU] per nymph), B. bassiana
did not significantly reduce held populations nor did it affect specif
ic grasshopper taxa. Conditions were warm and sunny during the trial,
and slopes of conidial persistence were equally poor on both grasshopp
ers and grass leaves. Small numbers of conidia (<2 CFU per grasshopper
) were recovered from surface-sterilized grasshoppers 5-15 d after app
lication indicating that if infection occurred, B. bassiana did not pr
oliferate in the hemocoel. Considerable mycosis was observed in grassh
oppers placed in cages in the greenhouse, but not in grasshoppers conf
ined in cages adjacent to the field plots. Furthermore, the prevalence
of disease in the greenhouse cages decreased with the sampling date b
ut the onset of mycosis always occurred 3-4 d after collection, sugges
ting that environmental conditions in the greenhouse were responsible
for the increased susceptibility of grasshoppers. Higher prevalence an
d more rapid development of disease were observed in grasshoppers plac
ed in shaded cages (83-89%) than in cages exposed to full sunlight (0-
15%) or protected from UVB radiation (1-43%); conidial survival was eq
ually enhanced in the shaded and UVB-protected environments. Our resul
ts indicate that the poor efficacy of B. bassiana against rangeland gr
asshoppers was a result of conditions of temperature and light exposur
e (reduced grasshopper thermoregulation), and not the result of inadeq
uate host targeting or pathogen virulence.