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.
