Sirex noctilio flight behavior: toward improving current monitoring techniques

Sirex noctilio Fabricius (Hymenoptera: Siricidae), an invasive woodwasp from Spain and North Africa, has an expanding global presence in pine forests. Although their populations are managed in most parts of the world, the success rate of existing prevention and control strategies has been historically variable, and there is consensus that monitoring techniques could be improved with increased knowledge about the behavioral biology of this insect. We conducted descriptive field studies in pine plantations in northern Patagonia to establish the flight behavior of S. noctilio. Specifically, the aim was to characterize male and female vertical flight distributions to assess ideal trap placement in pest monitoring programs. Our results indicated that males fly higher than females. A post-hoc analysis revealed two distinct flight patterns of females; when males are present, females fly higher than when males are absent. This behavioral variance is likely linked to (1) oviposition substrate location and (2) mate location. Results suggest that the most effective trapping and monitoring strategies for females should be deployed at 1.8 m height, whereas monitoring of males or females that are searching for mates would occur at greater heights. Results also suggest that if future techniques involving pheromones are developed, trap placement should be reassessed.