Laboratory and field evaluation of different formulations of Metarhizium anisopliae var. acridum submerged spores and aerial conidia for the control of locusts and grasshoppers

Two emulsions and two water-based-formulations of freeze dried submerged spores of Metarhizium anisopliae var. acridum (Metch.) Sorokin (isolate IMI 330189) were compared with aerial conidia (GREEN MUSCLE™) for their efficacy against Hieroglyphus daganensis (Krauss) and Locusta migratoria (R. & F.). The field experiments were conducted in East Niger on H. daganensis whereas the laboratory investigations were carried out in Germany using L. migratoria. In the fields, all formulations were applied on one hectare plots using ULV application techniques. Direct and residual spray effects were assessed. In all cases there were highly significant (p < 0.001) differences between formulations as regards to total mortalities and median survival times (MST). In both direct and spray residue effect assessments, aerial conidia formulated in diesel oil showed over 95% mortality with significantly shorter MST (3 to 8 days) under field conditions. These were followed by emulsions of submerged spores, which resulted in a mortality ranging from 56 to 92% (MST = 8 to 16 days) for the direct spray and 90 to 97% (MST = 7 to 12 days) for spray residue effect assessments. Experiments in the laboratory positively confirmed these results. There were no apparent differences between water-based formulations and the control with respect to mortality and MST. These results emphasize the importance of employing oil carriers to protect spores from environmental stress and thus enhance efficacy. The study also demonstrated the importance of secondary spore pick up from the spray residues. Spores in all formulations persisted over five days and caused mortalities ranging from 62 to 100% on healthy grasshoppers exposed to the spray residue from treated vegetation. The results of this research suggest that emulsions may be an effective option to improve efficacy of submerged spores for ultra low volume application under Sahelian conditions.