Role of vegetable oil as UV light protector for Beauveria bassiana and Metarhizium anisopliae in management of Bactrocera zonata

Abstract

Entomopathogenic fungi (EPF), Metarhizium anisopliae and Beauveria bassiana, are used in the field against different insect pests because they are best candidates to include in integrated pest management. But the efficacy of these EPF is limited in the field conditions because different environmental conditions like; sunlight, UV light, visible light, temperature and humidity affects the conidial viability, shelf life and pathogenicity of EPF. The solution to this problem is the use of vegetable oils as liquid carriers to coat and shield the conidia. In the present study three different oils were used like, Sesame oil, sunflower oil and corn oil. The conidia of M. anisopliae and B. bassiana were exposed to three different intervals of UV light 15, 30 and 45 minutes. Conidia exposed to UV light after the addition of oil and making oil water emulsion with fungus. The germination percentage and pathogenicity of M. anisopliae and B. bassiana against adult and pupae (through immersion method) of Bactrocera zonata were recorded after exposure to UV light. Sesame oil showed highest conidia germination, adult mortality for M. anisopliae and B. bassiana after UV light exposure. In case of M. anisopliae germination rate reached up to 79.5% (48–51 h) and mortality 84.4% (7th day), lower rates in aqueous suspensions (germination: 43.3%; mortality: 35.6%).  In case of B. bassiana germination rate reached up to 69.17% (48–51 h) and mortality 64.4% (7th day), lower rates in aqueous suspensions (germination: 33.3%; mortality: 35.6%).  Adult emergence was highest in the aqueous suspensions and lowest in the sesame oil based formulation. Overall, M. anisopliae performed better than B. bassiana with sesame oil recommended to protect conidia from UV radiation.