Assessing the Potential of Tropospheric Oxidants to Interfere with Insect Host Location, Mate Location, and Foraging Choice

Insects can use long distance olfactory cues, like floral scents or sex pheromones, as ‘scent-pathways’ that can lead them to either floral hosts or mate-ready conspecifics. These plumes or comprised of blends of different chemical compounds, and can be used to identify as well as locate a specific floral host or mate. However, tropospheric oxidants, including the pollutant ozone, could react with the chemical compounds that make up these olfactory cues, potentially causing compositional changes to these plumes that damage or alter the information they convey to insects. As highly reactive compounds, oxidants like ozone could also alter floral scents by damaging plants and causing changes in the composition of floral plumes emitted or by directly reacting with and damaging insect antenna and thus the insect’s ability to detect odors. Here, we find that tropospheric oxidants cause floral plumes to be initially less attractive to a foraging hawkmoth, Manduca sexta, a specialist bee, Peponapis pruinosa, and a specialist beetle, Acalymma vittatum. However, we further test whether these insects can learn to associate ozone-altered floral plumes with rewards, and find that M. sexta and A. vittatum can learn initially unattractive ozone-altered floral plumes. Insects are unlikely to have an opportunity to learn sex pheromones however, and we find that M. sexta finds conspecific pheromone plumes less attractive when they are exposed to ozone vs. air. Finally, we find that elevated ozone exposure to Cucurbita pepo squash plants changes the production of the plant’s floral volatiles and rewards, and that ozone-exposed squash plants are initially less attractive to the squash bee P. pruinosa. Overall, this work finds that ozone poses a threat to insects on several fronts: insects initially find ozone-altered plumes less attractive, and find ozone-altered sex pheromones less attractive. However, the work also shows that learning may provide a means for some insects, even including a specialist insect, to cope with polluted plumes, and further work investigating the impacts of air pollution on insect foraging and mate-searching success should incorporate insect behavioral plasticity.