Effects of four potent entomopathogenic fungal isolates on the survival and performance of Telenomus remus, an egg parasitoid of fall armyworm

Fall armyworm (FAW), <i>Spodoptera frugiperda</i> is a generalist pest known to feed on more than 300 plant species, including major staple crops such as rice, maize and sorghum. Biological control of FAW using a combination of a major indigenous egg parasitoid <i>Telenomus remus</i> and entomopathogenic fungi was explored in this study. <i>Metarhizium anisopliae</i> strains (ICIPE 7, ICIPE 41, and ICIPE 78) and <i>Beauveria bassiana</i> ICIPE 621 which demonstrated effectiveness to combat the pest, were evaluated through direct and indirect fungal infection to assess their pathogenicity and virulence against <i>T. remus</i> adults, <i>S. frugiperda</i> eggs and their effects on <i>T. remus</i> parasitism rates. <i>Metarhizium anisopliae</i> ICIPE 7 and ICIPE 78 exhibited the highest virulence against <i>T. remus</i> adults with LT₅₀ values >2 days. ICIPE 7 induced the highest <i>T. remus</i> mortality rate (81.40 ± 4.17%) following direct infection with dry conidia. Direct fungal infection also had a significant impact on parasitoid emergence, with the highest emergence rate recorded in the <i>M. anisopliae</i> ICIPE 7 treatment (42.50 ± 5.55%), compared to the control ± (83.25 ± 5.94%). In the indirect infection, the highest concentration of 1 x 10⁹ conidia ml^-1 of ICIPE 78 induced the highest mortality (100 ± 0.00%) of <i>T. remus</i> adults, and the highest mortality (51.25%) of FAW eggs, whereas the least FAW egg mortality (15.25%) was recorded in the lowest concentration 1 x 10⁵ conidia ml^-1 of ICIPE 41. The number of parasitoids that emerged and their sex ratios were not affected by the different fungal strain concentrations except in ICIPE 7 at high dose. This study showed that potential combination of both <i>M. anisopliae</i> and <i>B. bassiana</i> with <i>T. remus</i> parasitoid can effectively suppress FAW populations.