Effects of foliar apple trichomes on Galendromus occidentalis (Nesbitt) (Acari: Phytoseiidae): preferences, fecundity and prey consumption

Tritrophic interactions may alter the efficacy of biocontrol agents such as Galendromus occidentalis, the primary predator of tetranychids in Washington State apple. Apple cultivars vary in leaf pubescence, which may differentially affect the performance of G. occidentalis. The present study aimed to determine both preference and performance of G. occidentalis on pubescent and glabrous surfaces. Choice tests were conducted on two apple cultivars: 'Oregon Spur Delicious' - pubescent and 'Golden Delicious' - glabrous, as well as by adding simulated trichomes to a bean leaf disk. No-choice tests measured oviposition and prey consumption on the two apple cultivars. Galendromus occidentalis consumed more prey on the 'Oregon Spur Delicious' side of arenas, although only when arenas were constructed without including the leaf midrib. When the midrib was included, G. occidentalis preferred to oviposit on the 'Oregon Spur Delicious' side. The preference of G. occidentalis for simulated trichomes did not lead to a performance difference between cultivars. In the no-choice test, G. occidentalis did not differ in performance between cultivars. These studies indicate that G. occidentalis may have a slight preference for more pubescent surfaces, although this preference is not sufficiently strong to alter its biocontrol performance. As a specialist, G. occidentalis may be more adapted to tracking populations of its prey than locating 'ideal' host plants.