Conidia of two entomogenous fungi, Beauveria bassiana (Balsamo) and Metarhizium anisopliae (Metschnikoff) Sorokin, were applied to chrysomelid beetle-attracting tubers, Ceratosanthes hilariana Cogniaux, cowpea foliage, and cover slips and held outdoors under three exposure conditions of sunlight, or in the laboratory at 27 and 4°C, to determine the stability of conidia for potential use as microbial control agents of chrysomelid pests of grain legumes in Brazil. Under each exposure condition of sunlight (i.e., full, partial, or no protection from sunlight) conidia of B. bassiana survived best on the cucurbitaceous tubers, but the persistence of M. anisopliae conidia was more variable. In all cases for both fungi, exposure of conidia to full sunlight on all substrates was most detrimental to conidial stability; the half-life was generally 1–2 days and conidia were inviable within 1 week of exposure to sunlight. In contrast, conidia protected from sunlight survived much longer, in some cases remaining highly viable for ≥3 weeks. Results indicate that B. bassiana conidia retain high stability on beetle-attracting tubers if protected from sunlight. Use of fungal-treated tubers as a bait for control of chrysomelid beetles in cowpea-growing regions of Brazil or other countries is of potential importance.
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Daoust et al. (1986) studied this question.