Squash trichome traits are associated with Bemisia tabaci abundance and treatment efficacy across cultivars

Two entomopathogenic fungal strains, Beauveria bassiana (Bals. -Criv.) Vuill. GHA and Cordyceps javanica (Bally) Kepler, B. Shrestha & Spatafora wfGA17 (Hypocreales: Cordycipitaceae), are biological control agents of the sweetpotato whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), a major pest causing substantial yield losses in squash ( Cucurbita pepo L.). Previous research has shown that the efficacy of these entomopathogenic fungi (EPF) and chemical insecticides varies across squash cultivars. This study examined interactions among trichome traits of squash cultivars, B. tabaci populations, and treatments, including Entomopathogenic Fungus (EPFs), insecticides, and their combinations, at 7 days post-treatment to identify cultivar-specific patterns. The results showed that trichome density, length, and diameter varied among squash cultivars, with B. tabaci nymph abundance decreasing as non-glandular trichome density increased in a cultivar-dependent manner. Trichome density was negatively associated with B. tabaci nymph abundance. Early Summer, Fortune, Respect, and Gentry cultivars aligned with higher trichome density and lower nymph abundance, while Green Eclipse, Golden Glory, Lioness, and Gray Summer had lower trichome densities, and consistently associated with higher nymph densities. Trichome density contributed substantially to variation in nymph mortality with cyantraniliprole-based applications, whereas imidacloprid-based treatments were dominated by mortality effects largely independent of trichome traits. Overall, imidacloprid-based treatments resulted in the highest nymph mortality across cultivars. Fortune, Green Eclipse, Golden Glory, Respect, and Lioness cultivars responded similarly, regardless of treatment type (EPF species alone, chemical insecticide alone, and EPF-insecticide combinations). In contrast, Early Summer, Gray Summer, and Gentry changed their responses depending on the treatment, especially under fungal and insecticide–fungal combinations. This study provides a model for understanding plant–insect–fungus interactions and offers tools to design pest management strategies that mitigate pesticide resistance.