Susceptibility of Tuta absoluta (Lepidoptera: Gelechiidae) Pupae to Soil Applied Entomopathogenic Fungal Biopesticides

SIMPLE SUMMARY: The invasive tomato pinworm is one of the most destructive insect pests of tomato in Africa. The majority of farmers respond to infestations by applying chemical insecticides. However, the overreliance on this control method has deemed several insecticides ineffective due to resistance evolution. It is therefore crucial that integrated approaches are put in place, of which biopesticides play an important role, to mitigate this problem. Amongst the biopesticides, entomopathogenic fungi (EPF) are promising options. EPF applications aimed to control this pest have been highly effective, although the majority are applied against the larval and egg stages. This study investigated the susceptibility of pupae of the tomato pinworm against EPF products (Beauveria bassiana and Metarhizium anisopliae) when applied as a soil drench. High pupal mortality rates were recorded for all EPF products tested in bioassays and growth tunnel experiments. A significant reduction in fecundity was observed in moths that survived the pupal EPF applications, with no effects on moth fertility. Overall, our findings provide evidence of the suppressive potential when administering EPF conidia as a soil drench to disrupt the life cycle of Tuta absoluta for use in integrated pest management programs. ABSTRACT: Management of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in greenhouses and under open-field tomato cultivation relies on an integrated approach, largely targeting the egg and larval stages of the pest. However, little to no research has been done on the efficacy of EPFs for control of the pupal stage. The aims of this study were to determine the susceptibility of T. absoluta pupae to Beauveria bassiana and Metarhizium anisopliae spores applied as soil drench treatments, and the possible effects of these treatments on fecundity and fertility of moths. The lethal concentrations (LC(50) and LC(80)) of the respective products were estimated in dose-response bioassays by exposing pupae in a soil substrate to different concentrations of EPF products. Emerging moths were paired in different combinations, according to EPF exposure treatments after which fecundity and fertility of females were recorded. Pupae in the soil were effectively controlled by all EPF products in both bioassays as well as in a growth tunnel experiment. The LC(50) value of the B. bassiana oil formulation was significantly lower than that of other treatments. The fecundity of females that were subjected to the B. bassiana oil formulation was significantly lower than that of the control treatment. This study showed the potential of soil drench applications of both B. bassiana and M. anisopliae for control of T. absoluta pupae.