Interactions of some registered agrochemicals in Nigerian farming systems with entomopathogenic fungi, <i>Metarhizium anisopliae</i> and <i>Isaria farinose</i>

Abstract

Entomopathogenic fungi, Metarhizium anisopliae and Isaria farinosa are biocontrol agents (BCA) widely reported for the management of insect pests, and they are potential components of Integrated Pest Management (IPM) systems. Compatibility of their infective conidia with low rates of four agrochemicals; Champ-DP  (Fungicide), Uproot (Glycophosphate herbicide,), DP-Force (Organophosphate insecticide) and Sniper (Methylphosphate insecticide) were evaluated in vitro. The conidia were cultured on Sabouraud Dextrose Agar (SDA) containing 0, 10, 15, 25, 50 and 100 ppm of each agrochemical and incubated at ambient temperature (mean temperature=27 °C) for 12-14 days. Growth lag times, growth rates and conidia densities of the isolates were evaluated. All the agrochemicals significantly  (P<0.05) extended the lag time of M. anisopliae, but eventual rates of growth and conidiation increased significantly (P<0.05). Variabilities in the levels of  interactions of the agrochemicals with the fungi were concentration-dependent. DD-Force significantly (P<0.05) increased conidiation rates at the five concentrations and appeared to be the most compatible with M. anisopliae among the four agrochemicals. I. farinosa, on the other hand, was relatively incompatible with the agrochemicals and caused 'growth' or 'no growth' responses at different concentrations. The I. farinosa isolate could not grow at the lowest concentration (10 ppm) of the herbicide (Uproot) and 15 ppm of the insecticide (Sniper) but tolerated up to 25 ppm of Champ-DP (Fungicide) and DD-Force (Insecticide). Conidiation of the I. farinosa was null at all concentrations of the agrochemicals except Champ-DP treatments which allowed some conidia production at 10-25 ppm. However, 8-32% inhibition of conidiation occurred at these concentrations. The agrochemicals were compatible with M. anisopliae but relatively toxic to I .farinosa by inhibition of sporulation and growth at most concentrations.

Keywords: Agrochemicals, Entomopathogenic fungi, Compatibility, Growth, Lag time, Conidiation