Abstract: Long-term separation of a host from its native parasitoids may result in divergent thermal adaptation between host and parasitoid. The olive fruit fly, Bactrocera oleae (Rossi), most likely originated from Sub-Saharan Africa, but has since had a long invasion history in cultivated olives that spans geographical barriers and continents. This study compared three major thermal performance profiles (development, survival, and reproduction) across a wide range of temperatures (10–34 °C) among a Californian population of the olive fruit fly and two African parasitoids, Psyttalia lounsburyi (Silvestri) and Psyttalia humilis (Silvestri), believed to have co-adapted with the fruit fly in its native range. Temperature ranges for the development and survival were 10–30 °C for the fly, 10–28 °C for P. lounsburyi, and 14–32 °C for P. humilis. There was no difference in any thermal performance measured between two P. humilis populations (Kenya and Namibia) tested. The most suitable temperature ranges for reproduction were 22–30 °C for the fly, 18–32 °C for P. humilis, and 18–26 °C for P. lounsburyi. The results showed slight differences in the thermal profiles among olive fruit fly and both parasitoids species, with P. humilis being more heat tolerant whereas P. lounsburyi was less heat tolerant than the fruit fly. The results are discussed with respect to thermal co-adaptation and classical biological control of the olive fruit fly.
Abstract: Two dominant parasitoids, <i>Platygaster matsutama</i> Yoshida and <i>Inostemma seoulis</i> Ko, often coexist in the host-parasitoid community of the pine needle gall midge, <i>Thecodiplosis japonensis</i> Uchida et Inouye. Subtle differences in parasitoid phenology appear to play a key role in reducing interspecific competition, but the specific thermal conditions for development of each species have not been defined. We examined the thermal biology of two sympatric parasitoids during postdiapause development at seven constant temperatures (12, 15, 18, 21, 24, 27, and 30 °C) to determine species-specific developmental parameters. The lower developmental threshold was estimated to be 4.2 °C and 8.4 °C, and the thermal constant was 741.2 and 946.1 degree days (DD) for <i>P. matsutama</i> and <i>I. seoulis</i>, respectively, using the linear model. The nonlinear model determined that the optimal temperature was 24.8 and 26.5 °C for P. matsutama and I. seoulis, respectively, but with an upper threshold temperature (30 °C) that was the same for both species. The development rate of P. matsutama was higher than that of I. seoulis over the entire thermal range, and the difference was highest at 21.5 °C. Despite the lower developmental rate, I. seoulis was more heat tolerant and its optimal temperature was closer to that of host insect than those of <i>P. matsutama</i>. The results showed clear differences in thermal biology between <i>P. matsutama</i> and <i>I. seoulis</i>. Potential implications are discussed with respect to coexistence of two parasitoids on a single host and biological control of <i>T. japonensis</i>.
Abstract: The effects of temperature on the development (egg–adult emergence) of <i>Gonatocerus morgani </i> Triapitsyn, a newly-described parasitoid of <i>Homalodisca vitripennis</i> (Germar), were determined at 14.8, 18.7, 23.5, 26.9, 28.7, 30.4, 32.8, and 33.8 °C in the laboratory. Survival rate (percent adult emergence from parasitized host eggs) varied significantly among the experimental temperatures, with the highest (59%) and lowest (0%) occurring at 30.4 and 33.8 °C, respectively. The survival rates (%) were fitted with a polynomial model to describe a temperature-dependent pattern. Developmental rates (1/d) across seven temperatures were fitted with the nonlinear Briere model, which estimated the lower threshold to be 8.06 °C, the optimal temperature to be 29.22 °C, and the upper threshold to be 33.49 °C. A linear model fitted to developmental rates at 14.8–28.7 °C indicated that 189.75 degree-days above the lower threshold of 9.71 °C were required to complete development. A simulation model of <i>G. morgani</i> adult emergence was constructed to predict daily counts over the entire range of constant temperatures by incorporating the survival rate model, the Briere model, and the Weibull model. In outdoor validation, a degree-day model for predicting adult emergence showed ~2 d differences between prediction and observation. Based on the observed temperature requirement, the insect could complete thirteen to sixteen generations per year in southern California, depending on weather and location.
Abstract: 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, CA, 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 prior to 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.
Abstract: 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°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°C and 179.8 DD, with LTD of 8.6°C, respectively. The optimum temperatures for emergence were 36.5, 30.2, and 35.7°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.
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°C, whereas an average of 74–76% of adults survived in the 13.2–24.5°C range. When individually confined with moist cotton, adult longevity was greatest (16.3 d) at 13.3°C, but it was <3 d at -2.4 and 36.2°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 ≤7.8°C but was at temperatures ≥18.9°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°C), moist cotton (9.9°C), and accessible host plant (25.1°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°C) or high (>30°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°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.
Abstract: 1 <i>Otiorhynchus sulcatus</i> was collected from five geographical locations in the U.S.A. All weevils from each location were infected by Wolbachia belonging to supergroup B.
2 We hypothesized that treatment with tetracycline, which has been used to clear Wolbachia infection, would influence the reproduction of Wolbachia-infected parthenogenetic O. sulcatus females. Tetracycline treatment of preovipositional O. sulcatus females specifically inhibited egg hatching but had no effect relative to controls on any other physiological trait.
3 Treatment with gentamicin, which reportedly has no effect on Wolbachia infection but is indistinguishable from tetracycline in inhibiting protein synthesis of other bacterial genera, did not influence egg hatching.
4 These findings strongly suggest that the inhibition of egg development results from the antibiotic effect on Wolbachia rather than by direct toxic effects on O. sulcatus physiology.
5 We speculate that Wolbachia may be necessary for normal development of O. sulcatus eggs and discuss the implications of these findings for O. sulcatus ecology.
Abstract: We determined the influence of temperature on post-diapause development of overwintered Thecodiplosis japonensis Uchida et Inouye (Dipt., Cecidomyiidae) under various treatments (12, 15, 18, 21, 24, 27 and 30°C) in an effort to predict its spring emergence. Survival and developmental period for the overwintered larvae and pupae were significantly influenced by temperature. Linear and nonlinear regression models quantitatively described temperature-dependent development and survival of T. japonensis. The survival models exhibited right-skewed bell shape patterns for all stages, indicating a more detrimental impact on survival at high temperatures. Theoretical optimum temperatures with highest survival were 22.3, 24.0 and 24.0°C for the overwintered larvae, pupae and total post-diapause development (the larvae to adults) respectively. Pupal mortality was higher at all temperatures than larval mortality and the suitable range of temperature for pupae was narrower than that of larvae. The nonlinear Briere model estimated that optimum temperatures with the fastest development were 29.1°C for larvae, 27.6°C for pupae and 27.0°C for larvae to adults. In a linear model, the lower threshold temperatures were 5.1, 7.1 and 5.9°C for larvae, pupae, and larvae to adults respectively. A predictive degree-day model was developed using trap catches of T. japonensis adult emergence during 1991–1995. The model accounted for 84.6% of year-to-year variation in adult emergence and predicted accurately the median emergence time in 1996.
Abstract: 1 We conducted a laboratory experiment to quantify the stage-specific effects of temperature on development time and survival of Otiorhynchus sulcatus (Fabricius) (Coleoptera: Curculionidae), a serious economic pest of horticultural crops. Quantification of the relationship between stage development and temperature is required to predict seasonal occurrence of particular life stages and to optimize the timing of monitoring and control tactics.
2 Temperature-dependent survival rate was quantified using an extreme value function and showed a skewed bell shape, due to the vulnerability of the insect to high temperature in all stages.
3 The development times of O. sulcatus decreased with increasing temperature up to 27 °C for eggs and 24 °C for larvae and pupae. The nonlinear relationship between development rate and temperature was described using the Logan model, and enabled us to estimate the optimum temperature for development.
4 The inherent variation of development time was estimated from the cumulative frequency of stage emergence, which was modelled using the cumulative Weibull function.
5 The stage emergence model, which simulated the transition from one stage to the next in relation to temperature and cohort age, was constructed by incorporating stage-specific survival and development rate submodels with the Weibull model of stage frequency.
6 Our results show a difference in optimal temperature regime among developmental stages of O. sulcatus.
Abstract: Otiorhynchus sulcatus (F.) (Coleoptera: Curculionidae) is one of the most serious pests of horticultural crops but despite this, the effects of temperature on its reproduction are not fully understood. This study investigates the effects of temperature on the full set of reproductive traits of O. sulcatus at nine temperatures between 11 and 36 °C and develops descriptive models for each trait. Cohorts of newly eclosed adults were subjected to these temperatures and fed on Rhododendron spec. leaves. Adults oviposited at temperatures from 11 to 27 °C. Significant differences among treatments were found in the preoviposition period, oviposition period, longevity, per capita egg production, and egg viability. The preoviposition period was the shortest at 24 °C and the longest at 11 °C. With a non-linear model fitted to the data across the full range of experimental temperatures, the lower and upper threshold temperatures and optimum temperature for reproductive maturation were estimated to be 6.8, 30.0, and 22.7 °C, respectively. The developmental threshold and calculated thermal constant were estimated to be 6.7 °C and 505.0 degree-days, respectively, using a linear model at temperatures between 11 and 21 °C. Maximum per capita egg production (1094.1 eggs) and highest egg viability (90.1%) were both observed at 21 °C. The median longevity of O. sulcatus adults in the 18–36 °C range decreased linearly as temperatures increased. At 27 °C or above, the reproductive success of O. sulcatus was substantially impaired, and the optimum temperature range was 21–22 °C. Production of viable eggs in relation to temperature and weevil age was simulated by incorporating four models of life history traits, including egg production, egg viability, cumulative pattern of egg production, and adult survival. Overall, the present study demonstrates that temperature is a key factor in determining the reproductive success of O. sulcatus adults. We hypothesize that temperature may influence the phenology and geographic distribution of O. sulcatus populations.
Abstract: The glassy-winged sharpshooter (GWSS), <i>Homalodisca vitripennis</i> (Germar), is an economically important pest of grapevine, stone fruits, nursery trees, and ornamental plants in California because it transmits <i>Xylella fastidiosa</i> (Xf). Two related studies examined whether GWSS feeding behaviors that control Xf acquisition and inoculation are affected by environmental stresses such as plant water stress, cold ambient temperature, and diel light conditions. Both studies monitored feeding via electrical penetration graph (EPG). Effects of ambient air temperatures and light intensities on GWSS feeding on Euonymus japonica plants were studied outdoors (in Bakersfield, CA; a certified infested, non-agricultural area) during early spring. Effects of plant water stress were studied indoors, comparing feeding on well-watered vs. water-stressed citrus under high-pressure sodium vapor lamps. For both studies, EPG waveforms representing pathway phase (searching for xylem), X waves (xylem contact, likely to control Xf inoculation), and waveform C (ingestion of xylem fluid, Xf acquisition) were analyzed. Results showed no significant differences in feeding duration on Euonymus japonica for daylight vs. nighttime light intensities. However, xylem-sap ingestion occurred for significantly longer duration when ambient temperatures were higher than 10°C, and only occurred at temperatures below 10°C when ingestion was continued from a preceding, warmer period. Xylem-sap ingestion also was longer on well-watered than water-stressed citrus plants. Frequencies of X waves were higher, both at high temperatures and when plants were well-watered. Thus, both acquisition and inoculation behaviors are increased during warm air temperatures and when plants are well-watered.
