EFFECT OF FORMULATION AND APPLICATION METHOD ON THE EFFICACY OF AERIAL AND SUBMERGED CONIDIA OF METARHIZIUM FLAVOVIRIDE FOR LOCUST AND GRASSHOPPER CONTROL

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.