Environmental conditions terminate reproductive diapause and influence pheromone perception in the long‐lived moth Caloptilia fraxinella

Abstract

Reproductive diapause enables long‐lived insects to time mating with environmental conditions suitable for offspring development. Plasticity in the perception of pheromones used in sexual communication may enable mate‐finding at the appropriate time of year. The moth Caloptilia fraxinella (Ely) (Lepidoptera: Gracillariidae) undergoes a 9‐month reproductive diapause, during which the male response to pheromone is plastic and is highest during the period of reproductive activity. The mechanisms controlling this pheromone response plasticity are not well‐understood, and the aim of the present study is to determine the main factors involved. In the present study, the impact of temperature, photoperiod, juvenile hormone analogue (JHA) and adult nutrition on diapause termination are tested using electroantennogram (EAG) and behavioural response to pheromone in male C. fraxinella. Eclosion in a state of reproductive diapause occurs in most males; diapause is maintained under short‐day or cool conditions indoors, or under natural conditions outdoors. Exposure to long‐day, warm conditions over a period of 4 weeks causes a small number of males to become behaviourally responsive to pheromone; a larger number of males become behaviourally responsive over a period of 3 months of post‐eclosion. Treatment with a JHA impacts male EAG and the behavioural response to pheromone during the period of reproductive diapause. A carbohydrate food source is not required by reproductively active adult male C. fraxinella to respond to pheromone and express mate location behaviours. The main factors involved in controlling male pheromone response plasticity and the implications of these factors for the C. fraxinella population in its expanded range are discussed.

The roles of juvenile hormone and biogenic amines on pheromone response plasticity and diapause termination in male Caloptilia fraxinella

“…In the summer, treatment with octopamine or serotonin lowered EAG response compared to non-treated males, but not compared to those treated with the solvent control, whether the BA was applied alone or in combination with methoprene. Evenden, 2009Evenden, , 2015; however, in the current study, acetone treatment significantly lowered EAG response to pheromone compared to males that were not treated in the summer, and increased EAG response in the fall in Experiment 2. Organic solvents applied topically to insects can disrupt or partially destroy the cuticular wax layer, and can disrupt cell membranes inside the insect (Denlinger et al, 1980), which can subsequently impact insect physiology and behaviour.…”

“…The environmental cues that males receive when held outdoors prepare them for overwintering, and male C. frax-inella held outdoors express lower pheromone orientation in a wind tunnel than males held indoors under long day, warm conditions (Lemmen & Evenden, 2015). The environmental cues that males receive when held outdoors prepare them for overwintering, and male C. frax-inella held outdoors express lower pheromone orientation in a wind tunnel than males held indoors under long day, warm conditions (Lemmen & Evenden, 2015).…”

“…Overall more males held indoors expressed pheromonemediated behaviours in the wind tunnel compared with males held outdoors, whereas males held outdoors had higher EAG responses compared with males held indoors. The environmental cues that males receive when held outdoors prepare them for overwintering, and male C. frax-inella held outdoors express lower pheromone orientation in a wind tunnel than males held indoors under long day, warm conditions (Lemmen & Evenden, 2015). Male C. fraxinella should have a low pheromone response in the fall as all moths that overwinter are in reproductive diapause (Evenden et al, 2007).…”

Will climate change affect insect pheromonal communication?

“…For instance, male moths C. fraxinella reared under increased temperature during their reproductive diapause and subsequently exposed to female sex pheromones in a wind tunnel show more pronounced sexual responses [39]. At higher temperatures, male moths also show a lower level of specificity towards their sex pheromones, due to shifts in behavioural thresholds related to plume orientation and to the elicitation of upwind flight [51].…”

“…Very few data are available on how environmental changes will impact pheromone perception, but one recent study showed that the sex pheromone perception was altered in male moth Caloptilia fraxinella under elevated temperature [39].…”