Trichome-density preferences of Galendromus occidentalis and implications for biological control

TRICHOME-DENSITY PREFERENCES OF GALENDROMUS OCCIDENTALIS AND IMPLICATIONS FOR BIOLOGICAL CONTROL

Rebecca A. Schmidt¹

¹Washington State University, Department of Entomology, Pullman, WA

It has long been established that many pests are host-specific or have preferences for certain crops. However, only somewhat recently has the relationship between predators and their host plants been explored.  In the phytoseiid mites, research has emphasized their use of leaf physical structures, like trichomes, as shelter from climate or predation. These structures have also been hypothesized to increase leaf retention of pollen, a secondary food source for many phytoseiids. Despite this interest, no studies have examined the use of trichomes by Galendromus occidentalis, a predatory mite commonly used in biological control of spider mites in apple orchards. Tests using dual-choice arenas indicate that G. occidentalis prefers to oviposit on the trichome-dense Red Delicious variety over the trichome-poor Golden Delicious variety. This preference is only exhibited if the leaf midrib is included as part of each side of the arena. Furthermore, the prey species studied, Tetranychus urticae, exhibits the opposite preference. Finally, despite its ovipostion preferences, the predator does not discriminate between apple varieties during foraging. These results may indicate that G. occidentalis uses the trichome-dense area near leaf midribs to provide shelter for eggs. A better understanding of the preferences of this predator could provide useful information for apple breeding programs desiring to create varieties more resistant to pest mites.