Abstract
Tuta absoluta is one of the most devastating pests of Solanaceae crops in Africa. We previously demonstrated the efficacy of Metarhizium anisopliae isolates ICIPE 18, ICIPE 20 and ICIPE 665 against adult T. absoluta. However, adequate strain selection and accurate spatial prediction are fundamental to optimize their efficacy and formulations before field deployment. This study therefore assessed the thermotolerance, conidial yield and virulence (between 15 and 35 °C) of these potent isolates. Over 90% of conidia germinated at 20, 25 and 30 °C while no germination occurred at 15 °C. Growth of the three isolates occurred at all temperatures, but was slower at 15, 33 and 35 °C as compared to 20, 25 and 30 °C. Optimum temperatures for mycelial growth and spore production were 30 and 25 °C, respectively. Furthermore, ICIPE 18 produced higher amount of spores than ICIPE 20 and ICIPE 665. The highest mortality occurred at 30 °C for all the three isolates, while the LT50 values of ICIPE 18 and ICIPE 20 were significantly lower at 25 and 30 °C compared to those of ICIPE 665. Subsequently, several nonlinear equations were fitted to the mortality data to model the virulence of ICIPE 18 and ICIPE 20 against adult T. absoluta using the Entomopathogenic Fungi Application (EPFA) software. Spatial prediction revealed suitable locations for ICIPE 18 and ICIPE 20 deployment against T. absoluta in Kenya, Tanzania and Uganda. Our findings suggest that ICIPE 18 and ICIPE 20 could be considered as effective candidate biopesticides for an improved T. absoluta management based on temperature and location-specific approach.
Highlights
Tuta absoluta is one of the most devastating pests of Solanaceae crops in Africa
Our findings suggest that ICIPE 18 and ICIPE 20 could be considered as effective candidate biopesticides for an improved T. absoluta management based on temperature and location-specific approach
All the three M. anisopliae isolates (ICIPE 18, ICIPE 20 and ICIPE 665) tested in this study showed significant variation in germination, radial growth, conidial production and virulence against adult T. absoluta across the various temperature regimes with ICIPE 18 and ICIPE 20 showing their superiority as the best candidate biopesticides for sustainable management of the pest
Summary
Tuta absoluta is one of the most devastating pests of Solanaceae crops in Africa. We previously demonstrated the efficacy of Metarhizium anisopliae isolates ICIPE 18, ICIPE 20 and ICIPE 665 against adult T. absoluta. The extent of damage and the associated alarming level of economic losses (estimated at US$ 1.1 billion) being reported annually due to T. absoluta are enormous and are likely to increase significantly if left uncontrolled, leading to additional production costs to manage the p est[3] In response to this challenging situation, smallholder vegetable farmers have been desperately applying cocktails of synthetic p esticides[11], largely driven by government-subsidized agrochemical input schemes, aggressive marketing by pesticide company representatives and out of desperation to reduce the pest infestation. Among the microbials being explored, entomopathogenic fungi (EPF) offer effective and viable alternative to control insect pests of economic importance, as they cause epizootics in the target host population while minimizing impacts on beneficial and other non-target organisms as well as increasing the quality of agricultural p roducts[20,21] These make them potential option as biopesticides for controlling the tomato leafminer, T. absoluta[18]. Accurate prediction of the potential ecological fitness of these virulent fungal isolates is fundamental to optimize their efficacy in field application against the tomato leafminer
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