PKStic. SCi. 1996, 46, 299-306 Effect of Formulation and Application Method on the Efficacy of Aerial and-Submerged Conidia of Metarhizium flavoviride for Locust and Grasshopper Control Nina E. Jenkins"* & Matthew B. Thomasb International Institute of Tropical Agriculture (IITA), Biological Control Centre for Africa, BPOS-0932 Cotonou, Republic of Benin Leverhulme Unit for Population Biology and Biological Control, Natural Environmental Research Council Centre for Population Biology, Imperial College, Silwood Park, Ascot, Berks SL5 7PY, UK (Received 20 June 1995; accepted 19 October 1995) Abstract: A study was carried out to investigate the relative infectivity of aerial and submerged conidia of Metarhizium Javouiride to Schistocerca gregaria and Zonocerus uariegatus. The effect of formulation and application method on initial infectivity and field persistence of these conidia was investigated. Strain IMI 330189 was highly virulent to S. gregaria but showed relatively low virulence to Z . uariegatus. Direct contact with conidia from the initial spray application resulted in 100% mortality of S. gregaria for all formulation and application combinations. The mean survival time of infected locusts was signifi- cantly shorter for treatments using a knapsack sprayer containing submerged conidia in water plus 10 ml litre-' 'Codacide'@ (seven days), than treatments with aerial conidia in oil using ULV techniques (8.9 days) or submerged conidia in modified (water plus adjuvants) ULV (MULV) (nine days) or in water-based (VLV) applications (9.3 days). Both aerial and submerged conidia persisted long enough in the environment to effect significant mortality via secondary pick-up of spray residue from vegeta- tion. Persistence was greatest in the ULV and MULV treatments, where the oil component of the formulations provided greater protection of the conidia from environmental stresses. The consequences of secondary pick-up of conidia from the different treatments on total mortality from a single application were exam- ined using a simple host-pathogen model. This predicted that the ULV treat- ment 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 discussed in the context of development of optimum spray strategies for control of locusts and grasshoppers, and other pests, under different environmental conditions. Key words : Schistocerca gregaria, Zonocerus variegatus, Metarhizium jlauo- uiride, formulation, persistence, infectivity. * To whom correspondence should be addressed at: International Institute of Biological Control, Silwood Park, Buckhurst Road, Ascot, Berks SL5 7TA, UK 299 Pestic. Sci. 0031-613X/96/$09.00 1996 SCI. Printed in Great Britain