Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/27/2012
Publication Date: 10/1/2012
Citation: Son, Y., Backus, E.A., Johnson, M., Groves, R. 2012. Pattern of stylet penetration activity by Homalodisca vitripennis (Hemiptera: Cicadellidae) adults in relation to environmental temperature and light conditions. Environmental Entomology. 41(5):1215-1230. Interpretive Summary: The glassy-winged sharpshooter, Homalodisca vitripennis is a serious pest of grape, stone fruit, nursery trees, and ornamental plants in California because it transmits the plant-pathogenic bacterium, Xylella fastidiosa. Previous research showed that cold ambient temperatures below 10°C cause significant mortality to the insect and pathogen, potentially limiting disease spread into and within California vineyards during winter and spring. The present study was undertaken to determine whether environmental conditions decrease sharpshooter feeding, in part explaining mortality and reduced bacterial transmission. Effects of air temperature and light intensity during spring on sharpshooter feeding were studied outdoors using an electrical penetration graph (EPG) monitor. EPG waveforms representing searching for xylem (pathway phase), xylem contact (X waves), and ingestion of xylem fluid (waveform C) were analyzed. Previous research supports that acquisition (uptake) of X. fastidiosa, occurs during ingestion, while inoculation (injection) occurs during xylem contact periods. Results showed that, regardless of light condition, xylem ingestion occurred for the longest duration when temperatures were warmer than 10°C, and only occurred at temperatures below 10°C when ingestion was continued from a preceding, warmer period. Number of X waves also was significantly higher at warm temperatures. Thus, both acquisition and inoculation behaviors are increased during warm temperatures compared with cold temperatures. Overall, findings demonstrated that temperature is an important factor that influences glassy-winged sharpshooter feeding behaviors responsible for transmission of X. fastidiosa.
Technical Abstract: Effects of ambient spring air temperature and light intensity on stylet penetration activities of the glassy-winged sharpshooter, Homalodisca vitripennis (Germar) were studied outdoors, at ambient light and temperatures, using an electrical penetration graph (EPG). EPG waveforms representing salivary sheath formation/searching (pathway phase), xylem contact (X waves), and ingestion of xylem fluid (waveform C) were analyzed. Previous research supports that acquisition of Xylella fastidiosa, the Pierce’s disease bacterium, occurs during ingestion, while inoculation occurs during xylem contact periods. Diel patterns of H. vitripennis stylet activity showed that, regardless of light condition, xylem ingestion occurred for the longest duration when temperature remained above the feeding threshold (10°C), and only occurred at temperatures below the threshold when ingestion was continued from a preceding, warmer period. Regression analysis indicated that mean waveform durations per insect (WDI) for combined stylet activities (pathway and ingestion) as well as X wave frequencies were significantly influenced by temperature, but there was no significant impact of light intensity or interaction between temperature and light intensity. The relationship between temperature and stylet activities in terms of WDI and X wave frequency was described using linear and nonlinear models. Validation indicated that the models well predicted the WDIs for both ingestion and combined stylet activities, using temperature only as the single input. Overall, findings clearly demonstrated that temperature is an important factor that influences H. vitripennis feeding behaviors responsible for transmission (acquisition and inoculation) of the Pierce’s disease bacterium.