Bio-control potential of the Fungus Beauverja Bassiana (balsamo) against the Desert locust, schistocerca gregaria (forskal)

Abstract

Pathological potential of the fungus Beauveria bassiana Balsamo on the desert locust Schistocerca gregaria Forsk was evaluated with an aim to develop a mycoinsecticide as a supplement to the persistent chemical insecticides used for desert locust control in order to min imize the pollution in agroecosystems. Conidial suspension of B. bassiana when topically applied to locusts was found to be effoctive under 27.5 ± 2.50°C and 90% RH. Comparative stage susceptibility studies showed instars I and II as the most susceptible followed by Ill and IV. Adults showed the lowest mortality. Bioassays to establish the critical pathogenicity indices showed the lethal dose (LD50) to be 5xl07 conidia/ml at 8 days post-innoculation. Mortality was found to be directly proportional to conidial concentration with the highest cumulative mortality at 5xl012 conidia/ml. However sub-lethal doses could be improved through serial in vivo passage of fungi through the host.Dose-mortality relationship studies to determine optimum environmental requirements of B. bassiana when conducted under laboratory conditions showed that a temperature of 27.5 ± 2.5°C and 90.0% ± 10% RH produced maximum mortality while the optimum RH range was 90% ± 10%.Conidial activity was suppressed by prolonged periods of irradiation.Conidial efficacy oulside the optimum conditions was enhanced in oil formulations and addition of UV-proteclants. Oi l formulated conic.Ha showed improved mortalities even at higher temperatures and low relative humidity compared to non-formulated coni<lial suspensions. UV-protectants improved conidial stability even after prolonged UV exposures. A combination of oil and molasses formulation proved to be the most stable at different environmental conditions. Screening tests against beneficial insects to determine toxicity to bees and rats respectively showed B. bassiana was safe against both organisms.The biocontrol potential of B. bassiana to S. gregaria under field cage conditions showed mortality to be higher in formulated than non-formulated Pathogen. This indicated that B. bassiana has a potential for controlling S. gregaria in the field.