Ashfaq A. Sial

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.

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.

Multistate Comparison of Attractants and the Impact of Fruit Development Stage on Trapping Drosophila suzukii (Diptera: Drosophilidae) in Raspberry and Blueberry

Abstract Spotted-wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is an invasive pest of softskinned fruits across the globe. Effective monitoring is necessary to manage this pest, but suitable attractants are still being identified. In this study, we combined lures with fermenting liquid baits to improve D. suzukii trapping specificity and attractiveness. We also measured the efficiency and specificity of baits/lures during different times of the season; the reproductive status of females among baits/lures; and the effects of locations and crop type on these response variables. We developed a metric that combined mating status and fat content to determine differences in types of females attracted. Lures utilizing yeast and sugar-based volatiles trapped the most D. suzukii. The addition of a commercial lure to yeast and sugar-based lures increased catches in most locations, but was also the least specific to D. suzukii. Apple juice-based chemical lures tended to be most specific to D. suzukii, while lures comprised of a singular attractant tended to trap more D. suzukii with a higher reproductive potential than combinations of attractants. Trap catch and lure specificity was lower during fruit development than fruit ripening. While catch amounts varied by geographic location and crop type, attractants performed similarly relative to each other in each location and crop. Based on the metrics in this study, the yeast and sugar-based attractants were the most effective lures. However, further work is needed to improve early season monitoring, elucidate the effects of physiological status on bait attraction, and understand how abiotic factors influence bait attraction.

Natural Enemy Abundance in Southeastern Blueberry Agroecosystems: Distance to Edge and Impact of Management Practices

Abstract Natural enemies are valuable components of agroecosystems as they provide biological control services to help regulate pest populations. Promoting biocontrol services can improve sustainability by decreasing pesticide usage, which is a major challenge for the blueberry industry. Our research is the first to compare natural enemy populations in managed (conventional and organic) and unmanaged blueberry systems, in addition to the effects of non-crop habitat. We conducted our study in 10 blueberry orchards during the growing season across the major blueberry producing counties in Georgia, United States. To estimate the spatial distribution of natural enemies, we conducted suction sampling at three locations in each orchard: within the forested border, along the edge of blueberry orchard adjacent to forested border, and within the interior of the blueberry orchard. Natural enemies maintained higher abundance over the season in unmanaged areas when compared with organic or conventional production systems. In the conventional orchards, natural enemies were more abundant in the surrounding non-crop area compared with the interior of the orchard. Populations were more evenly distributed in less intensive systems (organic and unmanaged). Our results indicate spatial structure in natural enemy populations is related to management practice, and less intensive management can retain higher abundance of natural enemies in blueberry systems. Considerations must be made towards promoting ecologically based management practices to sustain natural enemy populations and potentially increase the delivery of biological control services.

High throughput sequencing reveals Drosophila suzukii responses to insecticides

Global climate change and acquired resistance to insecticides are threats to world food security. Drosophila suzukii, a devastating invasive pest in many parts of the world, causes substantial economic losses to fruit production industries, forcing farmers to apply broad‐spectrum insecticides frequently. This could lead to the development of insecticide resistance. We determined the Lethal Concentration 50 (median lethal concentration, LC50) values of zeta‐cypermethrin, spinosad, and malathion insecticides against D. suzukii colonies established from Clarke and Pierce county Georgia, United States. The LC50 values were 3 fold higher in the Pierce county population for all insecticide treatments. We then used RNA sequencing to analyze the responses of Pierce and Clarke population flies surviving a LC50 treatment of the 3 insecticides. We identified a high number of differentially expressed genes that are likely involved in detoxification and reduced cuticular penetration, especially in the Pierce population, with extensive overlap in differentially expressed genes between the 3 insecticide treatments. Finally, we predicted fewer nonsynonymous single nucleotide variants having deleterious effects on protein function among detoxification, insecticide target, and cuticular protein encoding genes in Pierce flies. Thus a combination of increased gene expression and fewer deleterious single nucleotide variants highlights molecular mechanisms underlying the higher LC50 values for Pierce population flies.

Season-long Management of Drosophila suzukii in Southern Highbush Blueberry, 2014

The objective of these trials was to determine efficacy of season-long insecticide programs against SWD in southern highbush blueberries. Trials were conducted at the University of Georgia Blueberry Research and Demonstration Farm in Alma, GA. We evaluated four treatment programs each consisted of weekly applications of different insecticides (Table 1). Treatments were organized in a randomized complete block design with four blocks of four treatments and an untreated check. The plots were approximately 0.14 acres and included 3–5 rows of blueberry bushes. Insecticides were applied weekly from May 2014 to June 2014 at the manufacturer-recommended maximum field rate with a standard airblast sprayer. Water was used at the rate of …