- Drosophila suzukii (Diptera: Drosophilidae), a pest of thin-skinned fruits, has been detected worldwide recently, with new locations of establishment determined annually since it first became a concern on continental North America in 2008. Drosophila suzukii females are different from most other drosophilids as being one of two known species capable of economic injury in fruit. This is achieved via a serrated ovipositor that pierces the skin of ripening susceptible fruit, depositing eggs that will then hatch into larvae, utilizing the fruit as a food source. Current control methods involve the application of pesticides on a weekly basis upon the coloring of fruit, ending when harvest is complete. To shift back towards IPM, knowledge of D. suzukii development under different environmental factors is necessary to improve upon current management options.
The first objective of this research project was to determine the developmental period, longevity, and fecundity of D. suzukii when exposed to seven constant temperatures and separately, five constant relative humidities (RHs) at 22 ± 2 ºC. Temperature had an influence on these parameters, with decreasing developmental periods as temperatures increased from 10 to 28ºC. Developmental period increased above 28ºC. The highest net reproductive rate and intrinsic rate of population increase was 22 ºC. Estimations using linear and nonlinear fit for the minimum, optimal and maximum were 7.2, 28.1, and 42.1 ºC, respectively. The minimal, optimal, and maximal temperatures for intrinsic rate of population increase were 13.4, 21.0, and 29.0 ºC . Relative humidity also had a significant influence on these parameters. The estimated minimum, optimal and maximum development thresholds for RH were 27, 79, and 100% RH, respectively. Fecundity appeared to increase with RH, with a maximum observed at 93%, however ovary dissections indicated that no differences in ovary maturation occurred between 78 and 93% RH.
The second objective of this research was conducted to determine the effect of floral resource feeding on nutrient levels in female D. suzukii when provided cherry or blueberry blossoms as well as lifespan over an observed feeding period. When adults were provided cherry blossoms, they had significantly longer lifespans than their water-fed counterparts over a 41-day observation period. Adults provided blueberry blossoms exhibited longer lifespans, however, this observation could not be statistically compared with the cherry and water treatments due to availability of blossoms and a staggered start date. A nutritional assay showed higher levels of glycogen and sugar levels amongst female flies provided either blossom type or sucrose over water-fed flies. Lipid levels tended to be the same across treatments.
Overall, this research discovered new information about D. suzukii biology that can be incorporated into future management strategies. The temperature-related development and fecundity study contributed to the development of a population prediction model. The humidity work will be incorporated into the D. suzukii model to refine estimates across different locations. The model will provide a tool for growers to determine management timing. The nutritional work may aide in the development of a bait spray and timing of bait spray application.