Impact of UV light exposure on the biocontrol efficacy of Beauveria bassiana and Metarhizium anisopliae against Bactrocera zonata

Abstract

Ultraviolet (UV) radiation and high temperatures have negative impact on persistence, pathogenicity and efficacy of entomopathogenic fungi in field conditions. This study evaluated effect of UV light, visible light and sunlight exposure on conidial viability of Metarhizium anisopliae and Beauveria bassiana at 3 intervals 15, 30 and 45 minutes. After exposure of these lights viability of conidia was evaluated through percentage germination of conidia, their pathogenicity against pupae and adult of Bactrocera zonata. In percentage germination data were collected at two time intervals of 24-27 hours and 48-51 hours after incubation. In pathogenicity test against B. zonata data of adult emergence from pupae and mortality of adult were recorded at 3, 5 and 7^th day of post-treatment application. For M. anisopliae untreated control had showed highest conidial germination (50.83% at 24–27 hours, 87.17% at 48–51 hours) while UV-45 exposure reduced it to 16.50 % and 35.50% respectively. For B. bassiana germination was highest in the untreated control (30.17% and 50.83%) and lowest in UV-45 (8.50% and 22.50%). In case of M. anisopliae untreated control provided highest mortality of adults 62.2% at 3^rd day, 80.00% at 5^th day and 91.1% at 7^th day. Lowest was in case of UV light treatment, 4.4% at 3^rd day, 11.1% at 5^th day and 13.3% at 7^th day. Adult emergence was highest from pupae after UV light treatment, 57.8% at 3^rd day, 68.9% at 5^th day and 80.00% at 7^th day. Lowest was in case of untreated control, 17.8% at 3^rd day, 28.9% at 5^th day and 37.8% at 7^th day. In case of B. bassiana untreated control provided highest mortality of adults 44.4% at 3^rd day, 57.8% at 5^th day and 71.1% at 7^th day. Lowest was in case of UV light treatment, 2.2% at 3^rd day, 6.7% at 5^th day and 11.1% at 7^th day. Adult emergence was highest from pupae after UV light treatment, 42.2%at 3^rd day, 57.8% at 5^th day and 62.2% at 7^th day. Lowest was in case of untreated control, 13.3% at 3^rd day, 22.2% at 5^th day and 26.7% at 7^th day. The untreated control without light exposure gives maximum control of B. zonata and has a maximum pathogenicity because conidia viability was not affected with exposure to any light stress. In the comparison UV light caused more damage to the fungal conidia following sunlight and visible light respectively. Moreover, 45 minutes’ exposures were most damaging than 30 and 15 minutes. This study highlighted the detrimental effect of UV light concluded that these EPF can be effective in shaded areas of orchard against B. zonata.