PARENT SESSION
Oral Session #38: Herbivory: Herbivore Response to Plants. Presiding: P. Kleintjes.
Tuesday, August 7, 2001. 1:00 PM to 4:30 PM. Hall of Ideas J.
Effect of N additions and host tree phenology on population dynamics of fruit-tree leafroller on oak during outbreak conditions.
Eatough, Michele1, Paine, Timothy1, 1
ABSTRACT- During spring 2000, there was an outbreak of fruit-tree leafroller (Archips argyrospilus Walker) on California black oak (Quercus kellogii Newb.). Many trees in the San Bernardino mountains were heavily damaged. This outbreak area is impacted by anthropogenic N deposition from the LA basin. To examine the effects of N additions on leafroller dynamics we assayed leafroller abundance and foliage variables. Treatments consisted of ambient N control (40 kg/ha/yr) and N fertilizer additions (150 kg/ha/yr). In May, as the leafrollers completed development, control oak were significantly more damaged than fertilized oak. This was surprising since N fertilization has been shown to enhance performance and increase abundance of arthropods. Further investigation showed that in April, newly opened, expanding buds of fertilized oaks had significantly longer leaves and significantly fewer leaves/g foliage, indicating that leaves of fertilized trees had developed faster than leaves on control trees. Leafroller abundance was significantly correlated with number of leaves sampled (r2 = 0.56, p = 0.001) and negatively correlated with leaf length (r2 = -0.39, p = 0.032), but not correlated with foliage mass sampled (r2 = 0.23, p = 0.21). We hypothesize that rather than being influenced primarily by plant chemistry which would predict better leafroller performance on fertilized trees, leafroller performance was effected by plant phenology, and early instar leafrollers performed better on the more closed and protected buds of the unfertilized oak.
KEY WORDS: N deposition, Archips argyrospilus, Quercus kellogii