The community-wide and guild-specific effects of pubescence on the folivorous insects of manzanitas Arctostaphylos spp.

1. Insect communities on 26 species of manzanita Arctostaphylos spp. (Ericaceae) were sampled in order to examine the effects of variation in foliar pubescence traits on a community of folivorous insects. Manzanitas vary widely in pubescence density, length, and glandularity both within and between species. 2. Linear models were fitted and evaluated to determine whether pubescence traits are associated with the species richness and abundance of folivorous insects after accounting for the effects of other relevant habitat and host-plant related characteristics. 3. Pubescence traits were clearly associated with both community-wide and guild-specific variation in the structure of the folivorous insect community of manzanitas, however the effects of pubescence were manifested primarily as effects on the abundance of folivores not on species richness. The species richness of folivorous insects on manzanitas was not associated with pubescence density or length but was associated positively with glandularity. 4. The abundance of all guilds except leaf-mining insects was lower on manzanitas having longer pubescence. In contrast, the abundance of external-chewing insects was higher on plants having denser pubescence and on plants having glandular pubescence. 5. Overall, the results suggest that both longer pubescence and the amount of contact between an insect and pubescence act quantitatively to decrease the abundance of external-feeding guilds of folivorous insects. The abundance of species in internal-feeding guilds that oviposit directly on leaves is unrelated to foliar pubescence traits in the host plant.