PARENT SESSION
Poster Session 7: Invasive Species.
Monday, August 2 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.
Influences of the homopteran Opsius stactogalus on its host Tamarix ramosissima under varying edaphic factors.
MCCONNELL, PATRICK*,1, WILLIAMS, KATHY1, 1 San Diego State University, San Diego, CA
ABSTRACT- Opsius stactogalus is a host-specific phloem-feeding herbivore of Tamarix ramosissima, an invasive riparian weed of western U.S. Previous studies suggest that Opsius herbivory reduces growth of Tamarix. However, that conclusion is not supported by all studies. Thus, we examined whether water and nitrogen availability affected the degree to which Opsius reduces growth of Tamarix roots and shoots. In a random stratified design, Tamarix, grown from cuttings, were placed in treatment blocks representing 12 combinations of Opsius densities (none, moderate (50/plant), high (150/plant)), nitrogen availabilities (10ppmN, 100ppmN), and water stress (no water stress or drought conditions). Nitrogen was added at times of watering. Water stress was created by allowing plants to reach their wilting point prior to watering. Dry masses of all roots and shoot growth added from the start of treatments, were used as response variables. ANOVA revealed that Opsius herbivory reduced both root and shoot growth. Increased nitrogen and water reduced negative effects of herbivory on Tamarix shoot growth. However, neither ameliorated Opsius effects on root mass. Thus, increased nutrient loading into rivers and streams of western U.S. may be contributing to continued success of Tamarix. The feeding method of this insect apparently limits the allocation of carbohydrates to the roots, and increased nutrients do little to compensate for that. Opsius apparently has less effect on Tamarix shoot growth, but continuing decline in water tables in conjunction with Opsius attack may negatively influence the above-ground growth of Tamarix, particularly in areas where available nitrogen is not excessive.
Key words: Opsius, effects of homopteran herbivory, Tamarix, invasive riparian plants