The pine processionary moth (Thaumetopoea pityocampa; “PPM”) is a serious pest of pine trees throughout its native range in the Mediterranean Basin, and this range is expanding with climate change. PPM caterpillars are covered in urticating hairs that they can release when disturbed, causing allergic reactions in humans and other vertebrates. Despite its risk to humans, the PPM has primarily been studied in areas where human population density is low. However, cities contain ample host plants, and preliminary evidence suggests that caterpillars in cities may have higher survival during cold periods than caterpillars outside cities as a result of the urban heat island effect. Here, we report the results of studies based in Orléans, France, and the Paris metropolitan region considering whether PPM colonies in cities have altered phenology and/or survival compared to PPM colonies outside urban areas.
Results/Conclusions
The phenology of PPM caterpillars in cities is significantly advanced compared to caterpillars in forests, with urban caterpillars reaching highly-urticating life stages earlier in the season (p < 0.05). At the beginning of the winter cold period, caterpillars in cities are on average twice the size of larvae in forests. Our ongoing analyses consider the survival of PPM caterpillars in urban areas following cold spells as well as variation in the timing of PPM pupations. The PPM is managed primarily with pheromone traps, spray treatments, and traps designed to catch the caterpillars as they leave trees to pupate. These management tactics succeed only when they are deployed at proper times during the PPM’s life cycle. Thus, differences in phenology between cities and forests have important implications for control and for reducing health risks to humans. In addition, the PPM is one of the best-studied examples of an organism shifting its range with climate change. Our results suggest that cities may be especially suitable for the PPM, and future models of the range expansion should account for this.