EFFECT OF FORMULATION AND APPLICATION METHOD ON THE EFFICACY OF AERIAL AND SUBMERGED CONIDIA OF METARHIZIUM FLAVOVIRIDE FOR LOCUST AND GRASSHOPPER CONTROL
Ne. Jenkins et Mb. Thomas, EFFECT OF FORMULATION AND APPLICATION METHOD ON THE EFFICACY OF AERIAL AND SUBMERGED CONIDIA OF METARHIZIUM FLAVOVIRIDE FOR LOCUST AND GRASSHOPPER CONTROL, Pesticide science, 46(4), 1996, pp. 299-306
A study was carried out to investigate the relative infectivity of aer
ial and submerged conidia of Metarhizium flavoviride to Schistocerca g
regaria and Zonocerus variegatus. The effect of formulation and applic
ation method on initial infectivity and field persistence of these con
idia was investigated. Strain IMI 330189 was highly virulent to S. gre
garia but showed relatively low virulence to Z. variegatus. Direct con
tact with conidia from the initial spray application resulted in 100%
mortality of S. gregaria for all formulation and application combinati
ons. The mean survival time of infected locusts was significantly shor
ter for treatments using a knapsack sprayer containing submerged conid
ia in water plus 10 ml litre(-1) 'Codacide'(R) (seven days), than trea
tments with aerial conidia in oil using ULV techniques (8.9 days) or s
ubmerged conidia in modified (water plus adjuvants) ULV (MULV) (nine d
ays) or in water-based (VLV) applications (9.3 days). Both aerial and
submerged conidia persisted long enough in the environment to effect s
ignificant mortality via secondary pick-up of spray residue from veget
ation. Persistence was greatest in the ULV and MULV treatments, where
the oil component of the formulations provided greater protection of t
he conidia from environmental stresses. The consequences of secondary
pick-up of conidia from the different treatments on total mortality fr
om a single application were examined using a simple host-pathogen mod
el. This predicted that the ULV treatment would be much more effective
than the other treatments under conditions where direct contact with
the spray was limited. The results of these investigations are discuss
ed in the context of development of optimum spray strategies for contr
ol of locusts and grasshoppers, and other pests, under different envir
onmental conditions.