Influences of Temperature onHomalodisca vitripennis(Hemiptera: Cicadellidae) Survival Under Various Feeding Conditions

Abstract

Survival of the glassy-winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), was studied under various constant temperatures and feeding conditions. When provided a host plant (Citrus limon L. Burm. f.) to feed on during a 21-d trial, 100% mortality occurred at 0.1, 3.2, and 40.1 degrees C, whereas an average of 74-76% of adults survived in the 13.2-24.5 degrees C range. When individually confined with moist cotton, adult longevity was greatest (16.3 d) at 13.3 degrees C, but it was <3 d at -2.4 and 36.2 degrees C. In a companion study comparing the presence versus absence of a host plant, the presence of a host plant was not a significant factor influencing survival at temperatures < or =7.8 degrees C but was at temperatures > or =18.9 degrees C. The relationship between temperature and survival was described by a nonlinear function that estimated the optimum temperature in each feeding regimen: no host plant or moist cotton (5.5 degrees C), moist cotton (9.9 degrees C), and accessible host plant (25.1 degrees C). The model quantitatively predicted that H. vitripennis would survive longer periods at a wider temperature regimen when provided with a host plant than when provided with water alone (moist cotton) or when provided with neither plant host nor water. Our results suggest that continuous exposure to either low (<5 degrees C) or high (>30 degrees C) temperatures are detrimental for adult survival. Specifically, low temperatures caused early mortality because of inhibition of feeding activity and presumably this threshold lies between 7.8 and 13.2 degrees C. Furthermore, this study clearly shows that temperature may influence the survival of H. vitripennis adults regardless of feeding regimens, and its implications for population dynamics are discussed.

Estimation of Feeding Threshold for <I>Homalodisca vitripennis</I> (Hemiptera: Cicadellidae) and Its Application to Prediction of Overwintering Mortality

“…In fact, no adults tested in our study survived the 48-h trial at 40.8ЊC. Similarly, we have ob- served that H. vitripennis adult longevity was negatively inßuenced by continuous exposure to high temperatures (Son et al 2009). However, unlike the adults we conÞned in the sachet, adults in the Þeld might be capable of actively avoiding unfavorable microclimates upon exposure to the extreme conditions, as a result of thermoregulatory behavior.…”

“…However, we know of no published reports that describe the inßuences of temperature on H. vitripennis feeding, other than our previous study (Son et al 2009). This information is needed to fully understand this pestÕs feeding behavior in relation to pathogen transmission, predict its seasonal population dynamics, and delimitate its potential geographic distribution.…”

“…The Þndings in this study imply that effects of these plant variables on the insectÕs feeding could be more evident when the insects are able to feed under conditions where the ambient temperature stays near optimal or at least above the threshold. At low temperatures (Յ7.8ЊC) below the threshold, independent of host plant availability, the insects were physiologically inactive without any feeding or movement (Son et al 2009). Under Þeld situations, if temperature stays above the threshold long enough to trigger activity of this insect, plant characteristics can be more inßuential on host selection behavior, particularly host acceptance and use , Nadel et al 2008, Krugner et al 2009).…”

“…In the laboratory, Son et al (2009) showed that adult H. vitripennis survival was negatively inßuenced by prolonged exposure to temperatures Յ7.8ЊC, independent of the availability of suitable host plants. They hypothesized that long-term exposure to low temperatures would impede H. vitripennis feeding and, as the insect starves, it would suffer dehydration, depletion of energy reserves, and ultimately death.…”

“…, and individually transplanted into pots (3.78 liter), which were then maintained in a greenhouse at the University of California Kearney Agricultural Research and Extension Center (Parlier, CA). Lemon trees were used as a feeding host because they were a common year-round host for H. vitripennis in southern California (Perring et al 2001) and did not show visible stress symptoms caused by low or high temperatures in a previous study (Son et al 2009). …”