Implications of sub-lethal rates of insecticides and daily time of application on Drosophila suzukii lifecycle

The circadian clock is responsible for time keeping within an organism and influences not only behavioural patterns, but also physiological rhythms including toxin susceptibility. Drosophila suzukii Matsumura is a global horticultural pest, and identifying rhythms in insecticide susceptibility could contribute to improving integrated pest management practices. To determine whether time of application influences mortality, LC50 rates of cyantraniliprole, lambda-cyhalothrin, pyrethrum and spinosad were applied to groups of adult D. suzukii at two different times of day. Insecticides were directly applied using a benchtop sprayer. We found no influence of time on mortality or oviposition for any of the four insecticides applied. However, several discoveries were made regarding the impact of sub -lethal and lethal rates on D. suzukii mortality, oviposition and offspring survival over time. In most cases, all surviving females recovered from insecticide rates, and laid the same number of eggs as females treated with the water control. Seven days after application, females that were treated with the field rate of spinosad laid the same number of eggs as the control. The lowest rate of cyantraniliprole resulted in more eggs being laid, initially, with no negative impact on survival of eggs through to adult emergence. However, there were transgenerational impacts of egg to adult survival when parents were treated with sub -lethal rates of spinosad and lambda-cyhalothrin. Although no impact of daily phase of application was detected within this assay, the information surrounding how D. suzukii interacts with lethal and sub -lethal rates of insecticides is of great importance, especially for the resistance management of D. suzukii.