The performance of entomopathogenic fungi in pest control is usually affected by both biotic and abiotic factors. This study aimed to determine the effects of various temperatures (15, 20, 25 and 30 °C) on conidial germination, mycelial growth and conidial density and virulence to the melon fly Zeugodacus cucurbitae of three selected isolates of Metarhizium anisopliae. The three isolates, ICIPE 18, ICIPE 30 and ICIPE 69, had previously been selected in laboratory bioassays. Percentage mortality by the three isolates ranged between 16.25% and 100.0% across the different temperatures. The isolates ICIPE 69 and ICIPE 18 recorded the highest percentage mortality of 96.25% and 100% and the shortest LT50 values of 2.61 and 2.63 days, respectively, at 30 °C. However, at 30 °C, ICIPE 69 produced the highest number of conidia of 90.5 × 107 /mL and was therefore selected for global mapping to predict its efficacy against Z. cucurbitae using the geospatial temperature data layer and the best fitted quadratic model. The map showed that the isolate would be more effective in the tropics than in temperate climates.

In the laboratory, the pathogenicity of thirteen isolates of Metarhizium anisopliae (Metschnikoff) Sorokin and two isolates of Beauveria bassiana (Balsamo) Vuillemin against the melon fly Zeugodacus cucurbitae (Coquillett) were assessed by exposing adults to 0.3 g of dry conidia (~3 × 109 conidia) of each isolate for 5 min and monitoring mortality for up to 5 days. Compatibility with a male pheromone, cuelure, (4-(p-acetoxyphenyl)-2-butanone), was determined by testing conidial germination and germ tube growth of the most promising isolate, M. anisopliae ICIPE 69, in the presence of cuelure at different temperatures. For horizontal transmission, the flies were separated by sex, separately exposed to M. anisopliae ICIPE 69, and subsequently mixed with non-exposed flies from the other sex. The most pathogenic isolates were M. anisopliae ICIPE 69, 18, and 30, causing mortalities of 94, 87, and 81%, with 5 days post-exposure, respectively. Metarhizium anisopliae ICIPE 69 caused the highest pupal mortality of 74%, with 15 days post-exposure. Horizontal transmission of M. anisopliae ICIPE 69 among male and female Z. cucurbitae was confirmed by 59 and 67% mortality after exposure to infected donor males and females, respectively. Metarhizium anisopliae ICIPE 69 affected the oviposition, but not hatchability, of infected Z. cucurbitae females. Metarhizium anisopliae ICIPE 69 is, therefore, a potential isolate for biopesticide development for Z. cucurbitae management in cucurbit production systems.

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).