EFFECT OF HOST PLANT FERTILIZATION ON THE DEVELOPMENTAL BIOLOGY AND FEEDING PREFERENCE OF THE GLASSY-WINGED SHARPSHOOTER Project Leader:

The main objective of this research was to evaluate the effect of host plant fertilization on the survival, immature development, adult fecundity, and the feeding of the glassy-winged sharpshooter (GWSS), a primary vector of Xylella fastidiosa (Xf). The development biology of GWSS was studied on cowpea plants, Vigna unguiculata treated with three fertilization regimes (NPK alone, urea alone, and a combination of NPK and urea) along with a non-fertilized control. Fertilization affected cowpea plant growth, the total protein content and the profile of free amino-acids in the xylem sap. The ultimate nymphal survivorship was significantly higher on fertilized plants than on control plants. In addition, newly emerged adult weight significantly increased with fertilization; specifically, GWSS nymphs reared on plants fertilized with urea yielded adults with the highest weight. NPK fertilization significantly reduced the nymphal development period for females but not for males. Females maintained on fertilized plants showed higher oviposition frequency and number of egg masses laid compared to unfertilized plants with highest oviposition potential recorded on urea treated plants. In addition, significantly bigger egg mass sizes were obtained from fertilized plants. Consequently, GWSS populations that developed on fertilized plants and more so on urea treated plants had a higher intrinsic rate of increase compared to those developing on unfertilized control plants. In choice tests, adult GWSS showed a preference for fertilized cowpea plants. The number of GWSS adults per plant and the proportion of plants infested were significantly higher for plants that received fertilization compared to the non-fertilized control plants. However, no feeding preference was recorded for nymphs. INTRODUCTION The pest status of glassy-winged sharpshooter (GWSS), Homalodisca coagulata (Say), has been exacerbated since its introduction, establishment, and continued spread in California. GWSS is a highly polyphagous xylem-feeder indigenous to the southern United States and to the northern Mexico (Turner and Pollard 1959). It effectively transmits the bacterium Xylella fastidiosa, a causal agent of economically important diseases of several agronomic, horticultural and landscape ornamental crops. The development of efficient rearing methods will greatly improve our knowledge of the pest biology and enhance implementation of adequate control programs. A simple method for rearing GWSS on cowpea plants has been developed (Sétamou and Jones 2005), but a rapid deployment of novel control methods required increased accessibility of GWSS to researchers. So far, no artificial diet for rearing GWSS has been commercialized and most diets are at either at the development or formulation stages. Thus, rearing methods of GWSS rely heavily on the use of plants. Although nymphs and adults have different nutritional requirements and often required different host plants for their successful development (Brodbeck et al. 1996), Sétamou and Jones (2005) showed that cowpea or black-eyed pea (Vigna unguiculata) is a suitable host plant that supports the development of both immature and adults stages. But development of GWSS populations in laboratory colonies depends on many factors such as host plant quality. Plant nitrogen content has been identified as an indication of host plant quality for herbivorous insects (Mattson 1980). It is widely reported in the literature that nitrogen content of host plants influences the survival, development and reproduction of insects, particularly homopteran and also other insects orders (van Emden 1966). Nitrogen content of plants is directly related to the level of fertilization (Jauset et al. 1998). In this project we are testing the effects of host plant fertilization on the bionomics of GWSS in order to find the most suitable host plant fertilization regimes for maximizing the production of GWSS. Two types of fertilizers, i.e., water soluble NPK (20-20-20) from Peter Professional® and agrillane urea (46-0-0) from Magic CarpetTM were used individually or in combination at the recommended doses for cowpea production to fertilize potted plants used in the experiments. OBJECTIVES 1. Evaluate the effects of nitrogen fertilization on plant growth and on N content and free amino-acid composition of xylem exudates. 2. Determine the influence that fertilization of cowpea plants has on the survival, growth and development of both immature and adult GWSS. 3. Test whether GWSS exhibit any feeding and oviposition preferences for fertilized plants.