Virulence of the entomopathogenic fungus Lecanicillium longisporum against the greenhouse whitefly,Trialeurodes vaporariorum and its parasitoid Encarsia formosa

Understanding the interactions among biological control agents, such as competition for the same host in intraguild predation, is a key component for successful biological control strategies. The pathogenic ability of Lecanicillium longisporum (Petch) Zare and Gams (Ascomycota: Clavicipitaceae) against the greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) and its parasitoid, Encarsia formosa Gahan (Hymenoptera: Aphelinidae) was assessed. Treatment with six serial deposition rates of fungal conidia on cucumber leaf surface indicated that whitefly mean mortalities for isolates LRC190, LRC216 and LRC229 reached 61, 79 and 54% at 2.6 × 10⁷ conidia/mm², respectively. Median lethal time (LT₅₀) values for isolates LRC190, LRC216 and LRC229 were 6.2, 4.9 and 6.9 days, and median lethal dose (LD₅₀) values were 1.2 × 10⁶, 2.9 × 10⁵ and 6.9 × 10⁶ conidia/mm², respectively. The number of surviving parasitoid larvae, pupae and adults decreased with increasing concentrations of fungus, and earlier developmental stages of parasitoid were affected negatively by fungal treatment. Reproductive capacity and longevity of female parasitoid emerging from fungus-treated hosts were not affected by fungus treatment. These results indicate that correct timing of fungal and parasitoid application may mitigate the negative effects due to direct competition for the same host. In this regard, treatment with fungi in later immature stages of the parasitoid was generally positive with minimum risks of deleterious effects.