Circadian rhythms of insect pheromone titer, calling, emission, and response: a review

Many insect species have circadian rhythms of pheromone production/titer, calling, emission, and response that are involved in intraspecific communication and impact pest management practices. Rhythms of pheromone biosynthesis, most studied in moths affecting forestry and agriculture, contribute to a periodicity of pheromone concentration or titer within glands or hemolymph. Calling rhythms by the pheromone-emitting sex are physical movements (pumping, vibrating wings) that aid in release and dispersion of the volatile pheromone components attractive to the opposite conspecific sex or both sexes. Circadian rhythms of emission of pheromone also occur as a result of an interaction between calling and the titer of pheromone available for release. Responding individuals usually show a coincidental rhythm of dispersal flight while seeking pheromone plumes in which, by orienting upwind, the insects find mates or food resources. However, some species begin searching an hour or more before the emitting sex initiates calling and emission, which benefits mass trapping control programs because the baited traps do not compete initially with natural pheromone sources. In our review, data of daily rhythms of moths and other insects were extracted from the literature by screen capture software to calculate mean time of activity and standard deviation and fit to normal curves. These methods are illustrated for various insects and as a basis for discussion of interactions of pheromonal circadian rhythms of the well-studied gypsy moth Lymantria dispar, spruce budworm moth Choristoneura fumiferana, turnip moth Agrotis segetum, and cabbage looper moth Trichoplusia ni. The various circadian rhythms are discussed in relation to application of species-specific sex and aggregation pheromones for benign biological control and management of pest insects.