EFFECT OF TEMPERATURE AND ULTRAVIOLET RADIATION ON GROWTH AND PATHOGENICITY OF Metarhizium anisopliae

The efficacy of entomopathogenic fungi in the field depends on the influence of various environmental factors, including temperature and level of exposure to UV light. It is hypothesized that temperature and level of UV light exposure of Metarhizium anisopliae (Hypocreales, Clavicipiceae) may affect its efficiency in controlling the sweetpotato weevil (Cylas formicarius, Fabricius; Coleoptera, Brentidae). The objective of this study was to evaluate the influence of temperature and ultraviolet light radiation on the growth and pathogenicity of different native strains of Cuban origin of the M. anisopliae Sorokin complex with biological activity against C. formicarius. Colony diameter was measured at 28, 30, 32 and 34 °C temperature and exposed to ultraviolet light (254 nm) for 10, 15, 20, 30, 30, 60 and 120 minutes. Under laboratory conditions, the percentage germination of conidia of strains LBMa-11, LBM-30, LBM-41 and LBM-146 was determined, as well as their pathogenic capacity by means of bioassays with adults of C. formicarius in terms of the percentage of cumulative mortality and the mean lethal time (TL50). Results proved that temperature and UV light affect the ability of M. anisopliae to control C. formicarius. A delay in cumulative mortality was detected for all strains exposed to UV light, with an increase in TL50. The optimum temperature range was between 28 and 30 °C. The strain LBM-127 showed the highest sensitivity to temperature, LBMa-11 the highest tolerance to UV light, and LBM-146 was the most virulent according to Probit regression analysis.