Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2007
Publication Date: 2/1/2008
Citation: Castle, S.J., Naranjo, S.E. 2008. Comparison of sampling methods for determining relative densities of Homalodisca vitripennis (Hemiptera: Cicadellidae) on Citrus. Journal of Economic Entomology. 101(1):226-235.
Interpretive Summary: : Knowledge-based crop protection begins with an understanding of how different densities of a pest impact the growth and development of a crop. Development of sound sampling methodology is essential for the appraisal of pest densities and the informed implementation of control measures. In the case of the glassy-winged sharpshooter (Homalodisca vitripennis (Germar)) invasion of California, little information was available concerning what densities were important from a crop protection standpoint or what field sampling methods would most effectively evaluate relative densities. Four sampling methods that included A-Vac, D-Vac, pole-bucket, and beat-net devices were evaluated for estimating relative densities of glassy-winged sharpshooter nymphs and adults on citrus trees. A hand-held device, the pole-bucket, proved to be the most efficient method for sampling immature GWSS and equally efficient as the beat-net device in sampling adults.
Technical Abstract: : Four sampling methods that included A-Vac, D-Vac, pole-bucket, and beat-net devices were evaluated for estimating relative densities of glassy-winged sharpshooter (Homalodisca vitripennis (Germar)) nymphs and adults on citrus trees. All four methods produced similar temporal and spatial distribution profiles, although significant differences in quantities of H. vitripennis adults and nymphs caught by each device were observed. The four sampling methods also showed a consistent male bias in adult populations across a range of densities, suggesting that previously reported male-biased sex ratios in H. vitripennis adult populations are real and not a product of sampling bias. A strong relationship (R2 = 0.95) between the monitoring methods we evaluated and yellow sticky trap catches of female H. vitripennis adults suggest that yellow-sticky trap catches may provide a good relative index of infestation levels in citrus trees. Based on quantitative analyses examining precision and cost, the pole bucket was the most efficient method for sampling nymphs and was as efficient as the beat-net method for sampling adults and both stages combined. In addition to these analyses, consideration of other sampling characteristics such as added flexibility in sampling and higher sensitivity in detecting infestations within individual trees helped to fortify the conclusion that the pole bucket was the best overall sampling method of those tested.