St. Jaronski et Ms. Goettel, DEVELOPMENT OF BEAUVERIA-BASSIANA FOR CONTROL OF GRASSHOPPERS AND LOCUSTS, Memoirs of the Entomological Society of Canada, (171), 1997, pp. 225-237
Recognition of the potential of Beauveria bassiana (Balsamo) Vuillemin
as a control agent of grasshoppers and locusts occurred as early as 1
936, in South Africa. Field testing of B. bassiana as an inundative co
ntrol agent of grasshoppers and locusts has been facilitated by develo
pment of a solid substrate method for mass-production of the fungus an
d has resulted in the registration of a strain against grasshoppers in
the United States. In some, but not all field trials, application has
resulted in substantial reductions in grasshopper populations. Numero
us environmental constraints, including temperature and ultraviolet (U
V) radiation, may limit field efficacy of the fungus. Laboratory studi
es suggest that low humidity does not limit the ability of the fungus
to initiate disease. Sunlight is the major cause of mortality of conid
ia on leaf surfaces. The incorporation of UVB protectants in formulati
ons can increase conidial survival; however, these have not yet been e
valuated for their effects on field efficacy of B. bassiana against in
sects. Thermoregulation by grasshoppers has been implicated in resista
nce to mycosis. Results of laboratory studies indicate that grasshoppe
rs infected with B. bassiana preferentially seek temperatures between
40 and 42 degrees C and these temperatures are inhibitory to disease d
evelopment. In field-cage trials, a higher prevalence and more rapid d
evelopment of disease were observed in grasshoppers placed in shaded c
ages than in grasshoppers placed in cages exposed to full sunlight. In
laboratory experiments simulating grasshopper thermoregulation during
daylight periods, application of both Metarhizium flavoviride Gams an
d Rozsypal and B. bassiana simultaneously resulted in a final prevalen
ce of disease that was greater than M. flavoviride alone in the hot te
mperature environment, and equal to B. bassiana alone in the cool temp
erature environment. Incorporation of sublethal levels of Dimilin with
conidia of B. bassiana increased efficacy of the fungus against grass
hoppers in laboratory and field trials. Once environmental constraints
are better quantified, it may be possible to overcome them through im
proved formulation, strain selection, genetic or phenotypic manipulati
on, and inoculum targeting. Ultimately, success of B. bassiana as a mi
crobial control agent will depend on our ability to overcome environme
ntal and other constraints and/or to predict its efficacy under variou
s environmental conditions.