Evaluation of the biocontrol potential of native Metarhizium (Hypocreales: Clavicipitaceae) species against the false codling moth (Thaumatotibia leucotreta Meyrick) on chilli peppers in Ghana

The false codling moth (FCM, Thaumatotibia leucotreta Meyrick) is a major constraint on chilli pepper production and export in Ghana. Although chemical pesticides remain the main control strategy, their effectiveness is limited and export restrictions on synthetic residues highlight the need for sustainable alternatives. To address this challenge, the virulence of seven native Metarhizium isolates (UGKAP1, UGJKCS9, UGJKCS10, UGNAKC1, UGAFMF20, UGAFMF8 and UGSUHC1) obtained from agricultural fields in Ghana against final instar FCMs at 1 x 10⁸ conidia/mL was evaluated via conidial-sand assays, and compared with that of two USDA ARSEF isolates (Beauveria bassiana ARSEF 252 and Metarhizium anisopliae sensu lato ARSEF 4570). As abiotic environmental factors can affect fungal efficacy, the influence of humidity on the infectivity of four selected isolates (UGJKCS9, UGJKCS10, UGSUHC1 and UGAFMF20) was assessed. All seven native isolates caused > 80% pupal mortality within 21 days. The pupal mortality rates of ARSEF 252 and ARSEF 4570 were 49% and 57%, respectively. The most virulent isolate, UGJKCS9, exhibited an LC50 of 2.7 x 106 conidia/mL and an LT50 of 3 days. High pupal mortality (82-100% at 105 and 10⁷ conidia/mL) occurred across all tested humidity levels (43%, 75% and 98% RH) for all four isolates. These results indicate that the tested isolates, particularly UGJKCS9, exhibit strong potential as sustainable alternative control agents for FCMs in Ghana, warranting further evaluation under field conditions for integration into chilli pepper pest management programmes.