Abstract
ABSTRACTThe glassy-winged sharpshooter, Homalodisca vitripennis (Germar), is an invasive pest which presents a major economic threat to grape industries in California, because it spreads a disease-causing bacterium, Xylella fastidiosa. In this note we develop a time and temperature dependent mathematical model to analyze aggregate population data for H. vitripennis from a 10-year study consisting of biweekly monitoring of H. vitripennis populations on unsprayed citrus, during which H. vitripennis decreased significantly. This model was fitted to the aggregate H. vitripennis time series data using iterative reweighted weighted least squares (IRWLS) with assumed probability distributions for certain parameter values. Results indicate that the H. vitripennis model fits the phenological and temperature data reasonably well, but the observed population decrease may possibly be attributed to factors other than the abiotic effect of temperature. A key factor responsible for this decline but not analyzed here could be biotic, for example, potentially parasitism of H. vitripennis eggs by Cosmocomoidea ashmeadi. A biological control program targeting H. vitripennis utilizing the mymarid egg parasitoid Cosmocomoidea (formerly Gonatocerus) ashmeadi (Girault) is described.
Highlights
The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), is a xylem-feeding leafhopper native to the Southeastern United States and Northeastern Mexico [17]
In the present initial investigation we develop a mathematical model to investigate whether abiotic density independent factors, such as climate, could be the primary cause of the observed decrease in H. vitripennis populations over time
This study takes a rst look at aggregate population phenology data for H. vitripennis collected over the course of 10 years at the Agricultural Operations Facility at the University of California Riverside
Summary
The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), is a xylem-feeding leafhopper native to the Southeastern United States and Northeastern Mexico [17]. H. vitripennis has exhibited high invasion potential and has become a signicant pest outside of its native range. Around 1990, GWSS invaded California and represented a major economic threat to the wine, table, and raisin grape industries, because it was implicated in a signicant increase of the lethal and incurable grape malady, Pierce's disease [17, 19]. This disease cost approximately $104 million per year in crop damage and resources devoted to mitigating this threat [20]. There are a number of abiotic and biotic factors that can be implicated in regulating GWSS population numbers, including temperature, rainfall, parasitism, etc. - with, for example, Cosmocomoidea ashmeadi known to be a primary parasitoid
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