Abstract
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.
Highlights
Cucurbits are widely cultivated around the world and are among the most important fruits and vegetables consumed in Africa [1]
Conidia of the three selected isolates of M. anisopliae germinated at all the temperatures tested with mean percentage germination ranging from 2.90% to 98.96% (Table 1)
The conidial percentage germination for all the three isolates was significantly affected by the various temperature regimes but was not affected by isolate (Table 1)
Summary
Cucurbits are widely cultivated around the world and are among the most important fruits and vegetables consumed in Africa [1]. They are a key source of income for small scale farmers [2] and very rich in several vitamins and minerals [1]. In Kenya, cucurbits are widely cultivated and among the most consumed commodities [3] Their production has declined over the years owing to several constraints, especially insect pests and diseases [2]. Among the major insect pests of cucurbits are fruit flies (Diptera: Tephritidae), aphids (Hemiptera: Aphididae), greenhouse whitefly. The diseases of economic importance include watermelon mosaic virus (WMV, potyvirus), angular leaf spot Xanthomonas fragariae (Xanthomonadales: Xanthomonadaceae) and damping off Pythium spp (Peronosporales: Pythiaceae) [6,7,8]
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