Bioefficacy of Isolates of Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metschnikoff) (Ascomycota: Hypocreales) as field Protectants of Citrullus lanatus (Thunb.) Matsum. and Nakai against Fruit Flies

The efficacy of field application of two isolates of Metarhizium anisopliae (MaD and ICIPE-69) and two isolates of Beauveria bassiana (Bb337, Bb338) was compared to that of synthetic insecticide, K-Optimal (Lambda-Cyhalothrin and Acetamiprid), for the control of major pests infesting watermelon (Citrullus lanatus), Zeugodacus cucurbitae and Dacus vertebratus. Both biopesticides and chemicals were applied twice a week from 3 weeks after sowing to 2 weeks before harvest. Experiments were conducted during the dry and rainy seasons at the garden of the International Institute of Tropical Agriculture (IITA) in Benin Republic. Significant damage was caused to watermelon, primarily in young and immature stages. During the dry season, the highest infestation rate (63.62 pupae/kg) was recorded in the control, with the lowest on plots treated with MaD (11.88 pupae/kg). However, infestation rate was not significantly different among treatments. The tendency of infestation load (number of pupae per kilogram of fruit) significantly varied during the rainy season. Thus, plots treated with ICIPE-69 had the highest number of pupae per kilogram (120.20 pupae/kg), and the lowest was on plots treated with Bb337 (44.48 pupae/kg). Marketable yields were 148.75 t/ha (MaD), 145.83 t/ha (K-optimal), 136.67 t/ha (Bb337), and 119.17 t/ha (Bb338). Beauveria bassiana (Bb337) and M. anisopliae (ICIPE-69) applied at 0.012 × 108 CFU/mL have a great potential to be used against both Z. cucurbitae and D. vertebratus infesting watermelon and have a little effect on nontarget organisms such as spiders, lady beetles, and ants.