Wildfire smoke exposure impacts wing development of two pest outbreaking moths in boreal forests

Wildfires and insect outbreaks are major natural disturbances in boreal forests, and both are intensifying with climate change. Since insects are sensitive bio-indicators, wildfire smoke may alter their role in forest ecosystems. In 2023, wildfires in Eastern Canada caused extreme smoke events, with fine particulate matter (PM_2.5) reaching hazardous air quality levels above 400 µg/m³. We investigated how smoke exposure during larval development affects wing morphology, body mass, and flight capacity in two outbreaking forest defoliators: the eastern spruce budworm (Choristoneura fumiferana Clemens) and forest tent caterpillar moth (Malacosoma disstria Hübner). Spruce budworm larvae were collected from white spruce (Picea glauca (Moench) Voss) pre-wildfire and after smoke exposure. Wing malformations were categorized as folded, crumpled, or undeveloped. Smoke exposure significantly increased malformation rates, particularly folded and crumpled wings, while undeveloped wings decreased. Malformation was unaffected by sex but more common in forewings. Forest tent caterpillars collected from trembling aspen (Populus tremuloides Michx.) after smoke events also showed higher wing deformity rates compared to clean-air lab and later field samples. Males were especially affected, showing more malformations and reduced flight activity, indicated by lower pheromone trap captures. In both species, wing malformation correlated with higher body mass, regardless of sex. These findings reveal that wildfire smoke can disrupt insect development, altering morphology, physiology, and behavior in ways that are poorly understood. As wildfires intensify, smoke-driven effects may have complex and unpredictable consequences for forest ecosystems.