Document: DIR-3-48-27

Plant-insect interactions between bear oak and some of its insect pests.

VANDERKLEIN, D.* ¹, R.WILKENS ², T.CERRA ¹ and R.LEMKE ²

Montclair State University, Montclair, NJ 07043, USA ¹
Dowling College, Oakdale, NY, USA ²

Abstract:
In this poster we discuss a pilot study concerning the ecological and physiological relationship between insect herbivores and bear oak (Quercus ilicifolia). In the study we compared insect caused herbivory patterns within shrubs and measured the effects of herbivory and rolling on leaf water status. Bear oak shrubs were sampled in the dwarf pine region of the West Hampton Beach Pine Plains (Long Island, NY) where they were directly exposed to the sun. The sampled bear oaks had a three dimensional structure that resulted in an outside layer of leaves that formed a dome and an inside set of leaves within the dome. Microhabitat differences and insect damage between these two structures were assessed by measuring leaf surface temperature and light intensity and measuring leaf area of damaged and undamaged leaves in randomly selected shrubs. Undamaged leaves on the inside were significantly larger and had significantly lower light intensities and surface temperatures than those on the outside. Insect damage was significantly greater for the outside leaves. The effect of insect damage on leaf water potential of the outside leaves was assessed using a pressure chamber. Three treatment categories were assessed: undamaged controls, chewed leaves and rolled leaves. Leaf rolling was induced by lepidopterans (species unknown). Additionally, leaves were rolled by hand to assess the effect of rolling by itself. All treatments were measured on the same shrubs and shrubs were randomly chosen for measurement. On average, partial defoliation had no effect on mid-morning leaf water potential. In contrast, leaf rolling, natural or artificial, resulted in significantly higher leaf water potentials than controls. When rolled and chewed leaves were combined there was a significant relationship between the amount of leaf area reduced and leaf water potential, but not between leaf area exposed and leaf water potential. We also found that differently treated leaves within the same shrub responded independently of each other suggesting a degree of hydraulic autonomy. Our data suggest that bear oak shrubs create an insect reduced space and that insects may have a neutral or "positive" effect on leaf water status depending on the amount of leaf area changed.

Keywords: Insect reduced space, defoliation, leaf rolling, water potential

This abstract is being presented at: 3:30 PM in session:
HERBIVORE EFFECTS ON PLANTS