Impact of short- and long-term heat stress on reproductive potential of Drosophila suzukii Matsumura (Diptera: Drosophilidae).

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is an invasive vinegar fly of Asian origin now distributed throughout North America. Due to the unique morphology of females, this fly has become one of the most serious pests of thin-skinned fruits including blueberry, blackberry, cherry, raspberry, and strawberry. Prophylactic insecticide applications are commonly used to control this fly. A more sustainable approach to managing this invasive pest may not be possible without a clear understanding of the biology of this species under extreme environmental conditions. Specifically, high temperature is known to interfere with development and reproduction of drosophilids; however, the impact of high temperature on D. suzukii needs to be further investigated. The objective of the present study was to investigate the impact of exposure to constant and relatively short-term heat stress on reproductive success of D. suzukii, and potential for recovery. Results show that the development and reproduction of D. suzukii were negatively affected by constant and relatively short-term heat stress. Under constant heat stress, oviposition rate and adult lifespan decreased as temperature increased from 24 °C to 33 °C and reproduction was completely absent at 33 °C. Under relatively short-term heat stress, oviposition, pupation, and adult eclosion were significantly decreased as temperature increased from 28 °C to 34 °C. The short-term heat stress greatly reduced the fertility of both male and female D. suzukii which was recovered eight days after treatment. This study provides basic information on thermal biology of D. suzukii to help us better understand the trends commonly observed in D. suzukii trap captures in regions with hot summer conditions, and the results can be used in population models to predict its population dynamics in regions where high temperatures prevail during the field season.

Mulching as a cultural control strategy for Drosophila suzukii in blueberry.

BACKGROUND: Fruit growers largely depend on chemical control to reduce populations of the economically damaging invasive fly, Drosophila suzukii (Matsumura). Drosophila suzukii is susceptible to high temperatures and low humidity; therefore, it may be possible to implement cultural control practices that create microclimates unfavorable for its development and survival. In addition to other fruit production benefits, in-row mulches may impede the development of D. suzukii immatures when larvae leave the fruit to pupate in the soil. This study compared the effects of different mulches (black polypropylene fabric weedmats, sawdust, and wood chips) on temperature and relative humidity (RH), and on adult emergence of D. suzukii from larvae in blueberries and pupae, both above and below the ground surface in blueberry plantings (Vaccinium corymbosum L.). RESULTS: Across regions, both lower larval survival and longer periods with high suboptimal temperatures occurred above the ground in comparison to buried below the ground, regardless of mulch type. Fewer D. suzukii adults emerged from larvae on weedmat mulch at one site, but there was no effect of mulch type on temperature, RH, or D. suzukii emergence at most sites. The relationships between temperature, RH, and the emergence of adults from larvae and pupae varied by region. Natural infestation by D. suzukii in blueberries was lower over weedmat compared to wood-based mulches at one site. Greenhouse experiments showed that larvae burrowed to pupate underneath sawdust mulch, but were unable to pupate underneath a weedmat mulch. CONCLUSIONS: Although weedmats may not modify temperatures or RH enough to consistently affect D. suzukii emergence, they can reduce field suitability for D. suzukii by providing a barrier that prevents larvae from reaching favorable pupation microhabitats underground. © 2019 Society of Chemical Industry.

Diel periodicity of Drosophila suzukii (Diptera: Drosophilidae) under field conditions.

Drosophila suzukii Matsumura (Diptera: Drosophilidae), an economically important pest of blueberry and other thin-skinned fruits, persists and prolifically reproduces under seemingly lethal climatic conditions in the field. However, behavioral and physiological mechanisms employed by D. suzukii to tolerate such extreme climatic conditions in the field are unknown. The primary objective of this project was to investigate diel periodicity of D. suzukii and their reproductive success under field conditions as related by climatic factors such as temperature and relative humidity. Results show that D. suzukii reproductive success was significantly higher during the night (including dawn and dusk periods) than the day in terms of oviposition, pupation, adult eclosion, and the number of progeny per female. Female D. suzukii reproductive success was not significantly different between specific regions of a blueberry bush in relation to the amount of shade provided by the canopy. Our studies indicate that D. suzukii flight activity is crepuscular and is sensitive to fluctuations in temperature and relative humidity. Results also suggest that the majority of fly activity during peak hours is concentrated in areas around the border and within the center of blueberry orchards with little activity in the surrounding wooded areas. These findings suggest that D. suzukii prefers microclimate with mild temperatures and high humidity, and does not function well when exposed to direct sunlight with extreme heat. The authors propose that D. suzukii management strategies should be implemented during the early morning and immediately before darkness to maximize efficacy.