Temperature-dependent modelling and spatial prediction reveal suitable geographical areas for deployment of two Metarhizium anisopliae isolates for Tuta absoluta management

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.

Efficacy of Metarhizium anisopliae and (E)–2–hexenal combination using autodissemination technology for the management of the adult greenhouse whitefly, Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae)

“…Temperature affects the germination and growth of the fungus, humidity is important for the germination rate of the fungus on the insect's body and subsequent infection, while direct sunlight exposes the fungus to ultra-violet (UV) radicals that cause alteration in its DNA structure (29, 69). Different fungal species and isolates of the same species have been shown to have variable UV tolerance and thermotolerance levels (70), and this has also been reported for different M. anisopliae isolates (71)(72)(73). Metarhizium anisopliae ICIPE 18 and M. anisopliae ICIPE 69 exhibited better and similar environmental fitness with respect to fungal viability and persistence than M. anisopliae ICIPE 62.…”

Performance of Metarhizium rileyi Nm017: nutritional supplementation to improve production and quality conidia

“…Moreover, M. anisopliae isolates and Nm017 had similar substrate consumption patterns, e.g. , Tumuhaise et al ( 2018 ) reported a consumption percentage of 32.8%, and Agbessenou et al ( 2021 ) reached values close to 25%.…”

Immunological responses and gut microbial shifts in Phthorimaea absoluta exposed to Metarhizium anisopliae isolates under different temperature regimes

“…During our trials, temperatures above 30°C were fatal to the insects, given that all insects, including control groups, died during the first 2 days after their introduction into the incubator. The bioassays were therefore conducted at 15, 20, 25, and 30°C, representing the temperature range in which P. absoluta thrives in the field (Agbessenou et al, 2021). A total of 25 P. absoluta adults that were 1-3 days old were exposed to dry conidia of M. anisopliae strains using velvet-coated plastic jars (measuring 150 mm × 80 mm) as contamination devices.…”

“…The devices were contaminated with 1 g (equivalent to 0.15 × 10 9 conidia/g) of dry conidia for each fungal isolate. This dosage was chosen based on previous studies by Akutse et al (2020a,b) and Agbessenou et al (2021). The moths were introduced into the contamination device for 3 min to pick up the spores.…”

“…Due to their negligible effect on non-target organisms and easy mass production, EPF are considered the next-generation control agent for insect pests (Jiang et al, 2020). M. anisopliae isolates (ICIPE 665, ICIPE 18, ICIPE 20) (Agbessenou et al, 2021) have recently been identified as potential control agents for the sustainable management of P. absoluta adults (Akutse et al, 2020a,b). However, their efficacy against insect pests is affected by abiotic factors such as temperature, humidity, light, and pH (Dimbi et al, 2009;Silva et al, 2020).…”