Abstract

The efficacies of two isolates of M. anisopliae were evaluated against black maize beetle Heteronychus licas in the laboratory at 15 and 28^oC and relative humidity of 55 - 70% at the University of Zimbabwe in 2000. The beetles were exposed to the fungus that was suspended either in oil and in water at concentrations ranging from 1.4x10⁴ - 1.4x10⁸ conidia/ml. Mortality was observed in all concentrations and mortality increased with increase in conidia concentration. Fungal infection reduced feeding activity in beetles with most deaths occurring on the soil surface. Conidia concentration, isolate, type of medium, the interaction between temperature and medium and the interaction between isolate and medium had marked effects on beetle mortality (p < 0.05). The oil formulations were in general more effective than the water formulations. The most potent treatment at 15^oC was the oil suspension of isolate IMI098376 (LC₅₀ = 4.47x10⁴ conidia/ml) with an LT₅₀ at the lowest concentration (1.4x10⁴conidia/ml) of 13.3 weeks and earliest mortality at highest and lowest concentration occurring in 3 and 4 weeks, respectively.  At 28^oC the most potent treatment was the oil formulation of IMI098376 (LC₅₀ = 3.10x10⁴conidia/ml) with an LT₅₀ at the lowest concentration of 13.3 weeks and the earliest mortality at highest and lowest concentration occurring in 4 and 5 weeks, respectively. Field trails using the oil formulations are recommended.

Key words: Formulation, media, mortality, potent, efficacy, lethal concentration, biocontrol.