Efficacy of Metarhizium anisopliae (Mechnikov) Sorokin ICIPE 69 against the melon fly Zeugodacus cucurbitae (Coquillett) infesting courgette (Cucurbita pepo L.) in field cages

Abstract

Effective integrated pest management (IPM) of the melon fly Zeugodacus cucurbitae (Coquillett), a devastating pest threatening horticultural production in Africa, is urgently needed. In this study, a caged field experiment was implemented in Thika, Kenya to test the efficacy of Metarhizium anisopliae (Mechnikov) Sorokin ICIPE 69 for Z. cucurbitae control in courgette Cucurbita pepo L. Treatments included: (1) dry conidia of M. anisopliae ICIPE 69 applied in an autodissemination device (fungus); (2) dry conidia of M. anisopliae ICIPE 69 in an autodissemination device combined with cuelure, a male attractant (fungus + cuelure); (3) a commercial insecticide (profenofos + cypermethrin) (insecticide); and (4) an untreated control (control). Each treatment was replicated thrice and the experiment was conducted twice during two seasons. Flies (300/tunnel) and treatments were introduced at flowering. One day later, 25 flies/tunnel were randomly collected from each cage to assess conidial acquisition (for fungus and fungus + cuelure treatments only) and mortality during a 10‐day interval in the laboratory. Flies in the fungus + cuelure treatment acquired more conidia (18.02 ± 0.48 conidia/fly) than those in the fungus treatment (11.93 ± 0.40 conidia/fly). Flies in the fungus + cuelure treatment experienced the highest mortality (95.31% ± 1.69%), while those in the insecticide treatment experienced the lowest (38.70% ± 4.32%). Dry conidia were collected from the autodissemination devices (in the fungus and fungus + cuelure treatment) daily for 7 days after flowering to check for compatibility through germination tests. Percentage germination reduced over time from 86.45% ± 1.77% and 87.72% ± 1.71% on day 1 to 16.39% ± 2.11% and 42.76% ± 1.74% on day 7 (seasons 1 and 2, respectively). The yield was significantly different among treatments and was, across seasons, highest in the fungus + cuelure (6961 ± 550 kg/ha) and insecticide (7267 ± 352 kg/ha) treatments and lowest in the control treatment (2089 ± 155 kg/ha).