Efficacy of Entomopathogenic Fungi Against <i>Bruchus rufimanus</i> (Coleoptera: Chrysomelidae) in Laboratory and Field Trials Using Dropleg Spraying Technique

Entomopathogenic fungi (EPF)-based biopesticides have attracted growing interest in pest management as alternatives to neurotoxic insecticides. Their potential was evaluated against various pests, including the broad bean weevil (<i>Bruchus rufimanus Boheman 1833</i>), a significant threat to faba bean (<i>Vicia faba</i> L.) crops. This study examined the entomotoxic effects and sublethal impacts (on oviposition) of three fungal strains under laboratory conditions: <i>Beauveria bassiana</i> (GHA), <i>Metarhizium brunneum</i> (USDA 4556), and <i>M. brunneum</i> (V275) on <i>B. rufimanus</i> adults. Subsequently, a large-scale field trial assessed the efficacy of <i>B. bassiana</i> (GHA) against <i>B. rufimanus</i> infestations using conventional anti-drift and dropleg spraying methods. The laboratory LT₅₀ values ranged from four days for <i>B. bassiana</i> to eight days for <i>M. brunneum</i> (V275). The mortality rates recorded after ten days ranged from 86.6% for <i>M. brunneum</i> (V275) to 96.6% for <i>B. bassiana</i> (GHA). The inhibition of oviposition rates ranged from 12% for <i>M. brunneum</i> (USDA 4556) to 36% for <i>B. bassiana</i> (GHA). Field trials showed that the dropleg nozzles targeted faba bean pods, the oviposition sites of <i>B. rufimanus</i>, more effectively than the anti-drift nozzles. However, both fungal and chemical treatments applied via dropleg nozzles offered limited protection, reducing the infestation rates by 7% and 14%, respectively, with only a 3% improvement over anti-drift nozzles. This suggests that the large-scale spraying of chemical or fungal agents, including <i>B. bassiana</i> GHA, is not an optimal IPM strategy for managing <i>B. rufimanus</i> in faba beans. These laboratory and field results highlight the potential of EPF for managing <i>B. rufimanus</i>. However, the limitations of spray-applied plant protection methods underscore the need to redirect research toward more targeted strategies, such as attract-and-infect or endophytic EPF approaches.