Mb. Thomas et al., PERSISTENCE OF METARHIZIUM-FLAVOVIRIDE AND CONSEQUENCES FOR BIOLOGICAL-CONTROL OF GRASSHOPPERS AND LOCUSTS, Pesticide science, 49(1), 1997, pp. 47-55
The residual infectivity of an oil formulation of the fungal entomopat
hogen Metarhizium flavoviride was measured during a field trial agains
t the rice grasshopper, Hieroglyphus daganensis, in north Benin. The p
attern of infectivity was shown to decline exponentially following app
lication, with a half-life of 6.8 days. In this environment, infection
s due to residual spores from the spray were identified as a key route
of infection and accounted for 40-50% of the total infection measured
12 days after application.To examine the within- and between-season c
onsequences of such residual infection, a simple host-pathogen model w
as developed. The model revealed that even very small increases in res
idual activity could provide large increases in total mortality and th
at under certain conditions, residual infection was essential for effe
ctive pest control. This aspect of the activity of mycopesticides is r
arely considered. The implications of these results are discussed in t
he context of developing optimum spray strategies for locust and grass
hopper control under different ecological conditions.