Climate change-fueled heat waves reduce the susceptibility of the agricultural pest oblique banded leaf roller (Choristoneura rosaceana) to chemical control.

Heat waves are becoming a more frequent experience throughout Canada. For agricultural pests, it is unknown how exposure to a heat wave will impact their ability to withstand chemical controls and if timing of these heat waves in relation to their exposure to chemical controls will further influence efficacy. Using three commonly used commercially available products for leafroller control, oblique banded leafroller were exposed to heat waves and treated with these products (at label rates) at four different times: before heat wave exposure, on day 3 of the 5 day heat wave, immediately following the heat wave and 3 days following a heat wave. Results found that exposure to heat waves accelerated larval development. If a third instar went into the heat wave, by day 3 or upon removal from the heat wave, development had accelerated such that the treatment was applied to a fourth instar. This acceleration has implications for the window of opportunity for growers to get a treatment applied for maximum effect. Additionally, two of the three products showed reduced efficacy when larvae were exposed to heat waves, likely due to the accelerated growth rate of the larvae. Only one product showed increased efficacy and this is likely due to increased feeding and ingestion of more product. Studies are continuing to evaluate the impact when 2nd instars are introduced to heat waves and to tease apart the effect of the product and larval physiology.