Thermal Performance of Two Indigenous Pupal Parasitoids Attacking the Invasive Drosophila suzukii (Diptera: Drosophilidae).

Pachycrepoideus vindemiae (Rondani) and Trichopria drosophilae (Perkins) are among a few indigenous parasitoids attacking the invasive Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) in North America. Both parasitoid species occur in California, whereas only P. vindemiae has been reported from Oregon. We compared the thermal performance of the California populations of P. vindemiae and T. drosophilae, and the Oregon population of P. vindemiae at eight constant temperatures (12.6-32.8°C). Both P. vindemiae populations could develop at all tested temperatures. T. drosophilae failed to develop at or above 29.6°C. This species was, however, able to develop at a diurnal temperature regime of 15-32°C, and survival was higher in older developmental stages. T. drosophilae was less tolerant to both low and high temperatures than P. vindemiae, whereas the Oregon P. vindemiae population was more cold-tolerant but less heat-tolerant than the California population in terms of offspring survival, development, and reproduction. To develop storage strategies for mass-cultured parasitoids, we compared the cold tolerance of immature P. vindemiae and T. drosophilae of the California populations at 12°C for 1, 2, or 3 mo, followed by a 23°C holding period. Successful development to the adult stage decreased as cold storage duration increased. Successful development, however, increased when cold storage was initiated during the older developmental stages for 1-mo exposure for both parasitoid species. The results are discussed with regards to parasitoid thermal adaptation and the potential use of P. vindemiae and T. drosophilae for biological control of spotted-wing drosophila.

Effects of Temperature on Development and Voltinism of Chaetodactylus krombeini (Acari: Chaetodactylidae): Implications for Climate Change Impacts.

Temperature plays an important role in the growth and development of arthropods, and thus the current trend of climate change will alter their biology and species distribution. We used Chaetodactylus krombeini (Acari: Chaetodactylidae), a cleptoparasitic mite associated with Osmia bees (Hymenoptera: Megachilidae), as a model organism to investigate how temperature affects the development and voltinism of C. krombeini in the eastern United States. The effects of temperature on the stage-specific development of C. krombeini were determined at seven constant temperatures (16.1, 20.2, 24.1, 27.5, 30.0, 32.4 and 37.8°C). Parameters for stage-specific development, such as threshold temperatures and thermal constant, were determined by using empirical models. Results of this study showed that C. krombeini eggs developed successfully to adult at all temperatures tested except 37.8°C. The nonlinear and linear empirical models were applied to describe quantitatively the relationship between temperature and development of each C. krombeini stage. The nonlinear Lactin model estimated optimal temperatures as 31.4, 32.9, 32.6 and 32.5°C for egg, larva, nymph, and egg to adult, respectively. In the linear model, the lower threshold temperatures were estimated to be 9.9, 14.7, 13.0 and 12.4°C for egg, larva, nymph, and egg to adult, respectively. The thermal constant for each stage completion were 61.5, 28.1, 64.8 and 171.1 degree days for egg, larva, nymph, and egg to adult, respectively. Under the future climate scenarios, the number of generations (i.e., voltinism) would increase more likely by 1.5 to 2.0 times by the year of 2100 according to simulation. The findings herein firstly provided comprehensive data on thermal development of C. krombeini and implications for the management of C. krombeini populations under global warming were discussed. *Scientific Article No. 3278 of the West Virginia Agricultural and Forestry Experiment Station, Morgantown, West Virginia.

Biology of Habrobracon gelechiae (Hymenoptera: Braconidae), as a parasitoid of the obliquebanded leafroller (Lepidoptera: Tortricidae).

Habrobracon gelechiae Ashmead (Hymenoptera: Braconidae) was studied as a parasitoid of the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae) in California pistachio (Pistacia vera L.) orchards. Ovipositional behavior, adult longevity and fecundity, and the effects of temperature on developmental time and survival were determined. Habrobracon gelechiae develops as a gregarious, ectoparasitic idiobiont on late-instar C. rosaceana larvae. At 25°C, adult female wasps survived longer when provided honey and water (35.4 ± 4.9 d) or honey, water, and host larvae (34.4 ± 2.4 d) than when provided water (8.9 ± 1.1 d) or no food (5.9 ± 0.8 d). Over the adult lifespan, females parasitized 20.6 ± 2.1 hosts and deposited 228.8 ± 24.6 eggs. The intrinsic rate of increase was 0.24, the mean generation time was 18.15 d, and the double time 2.88 d. At constant temperatures, H. gelechiae successfully developed (egg to adult) from 15 to 35 °C. The developmental rate was fit to a nonlinear model, providing estimates of the parasitoid's lower (10.5 °C), upper (36.0 °C), and optimal (33.3 °C) development temperatures. Based on a linear model, 155 degree days were estimated for egg to adult eclosion. Temperature-dependent nonlinear model of survival showed similar shape with the model of development rate. The wasp developed under two diurnal temperature regimes, with 31.0 ± 13.3% survival at low (4-15 °C) and 63.0 ± 11.4% survival at high (15-35 °C) temperature regimes. The results are discussed with respect to H. gelechiae potential as a parasitoid of C. rosaceana in California's San Joaquin Valley.

Pattern of stylet penetration activity by Homalodisca vitripennis (Hemiptera: Cicadellidae) adults in relation to environmental temperature and light conditions.

Effects of ambient spring air temperature and light intensity on stylet penetration activities of the glassy-winged sharpshooter, Homalodisca vitripennis (Germar), were studied under field conditions by using an electrical penetration graph. Electrical penetration graph waveforms representing salivary sheath formation and searching (pathway phase), xylem contact (X waves), and ingestion of xylem fluid (waveform C) were analyzed. Previous research supported the concept that acquisition of Xylella fastidiosa, the Pierce's disease bacterium, occurs during ingestion, whereas inoculation occurs during xylem contact periods (X waves). 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 time. 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 of the nonlinear models indicated that they well predicted the WDIs for both ingestion and combined stylet activities, using temperature only as a single input. Overall, findings clearly demonstrate that temperature is an important factor that influences the H. vitripennis feeding behaviors responsible for transmission (acquisition and inoculation) of the Pierce's disease bacterium, with implications for vector ecology and management, as well as disease epidemiology.

Estimation of feeding threshold for Homalodisca vitripennis (Hemiptera: Cicadellidae) and its application to prediction of overwintering mortality.

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar), vectors the bacterium Xylella fastidiosa that induces Pierce's disease of grape. This study determined the effect of temperature on the feeding activity of H. vitripennis adults and the resulting production of excreta. The Logan type I model described a nonlinear pattern that showed excreta production increased up to an optimal temperature (33.1°C), followed by an abrupt decline near an estimated upper threshold (36.4°C). A temperature threshold for feeding, at or below which adults cease feeding, was estimated to be 10°C using a linear regression model based on the percentage of adults producing excreta over a range of constant temperatures. A simulated winter-temperature experiment using fluctuating thermal cycles confirmed that a time period above the temperature threshold for feeding was a critical factor in determining adult survival. Using data from the simulated temperature study, a predictive model was constructed by quantifying the relationship between cumulative mortality and cooling degree-hours. In field validation experiments, the model accurately predicted the temporal pattern of overwintering mortality of H. vitripennis adults held under winter temperatures simulating conditions in Bakersfield and Riverside, California, in 2006-2007. Model prediction using winter temperature data from a Riverside weather station indicated that H. vitripennis adults would experience an average of 92% overwintering mortality before reproduction in the spring, but levels of mortality varied depending on winter temperatures. The potential for temperature-based indices to predict temporal and spatial dynamics of H. vitripennis overwintering is discussed.

Influences of temperature on Homalodisca vitripennis (Hemiptera: Cicadellidae) survival under various feeding conditions.

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.

Temperature-dependent emergence of Osmia cornifrons (Hymenoptera: Megachilidae) adults.

Japanese hornfaced bees Osmia cornifrons (Radoszkowski) (Hymenoptera: Megachilidae) are used for pollination of spring blooming fruit crops such as apple, pear, and blueberry. Because O. cornifrons has a short adult life span, synchronization of bee emergence with bloom is critical to maximize crop pollination. This study was conducted to determine lower temperature thresholds (LTDs), optimum temperatures, and required degree-day accumulation for emergence of O. cornifrons adults. Patterns of temperature-dependent emergence of O. cornifrons adults at seven temperatures (3.9, 12.0, 18.6, 26.6, 30.3, 35.6, and 42.5 degrees C) were modeled and simulated with linear and nonlinear regression analyses. Results of this study showed that required degree-days (DD) for emergence of male and female O. cornifrons adults were 125.2 DD, with LTD of 8.9 degrees C and 179.8 DD, with LTD of 8.6 degrees C, respectively. The optimum temperatures for emergence were 36.5, 30.2, and 35.7 degrees C for male, female, and both sexes combined, respectively. This study indicated that emergence of O. cornifrons adults could be manipulated to synchronize with pollination periods of target fruit crops.