The roles of juvenile hormone and biogenic amines on pheromone response plasticity and diapause termination in male Caloptilia fraxinella Joelle K. Lemmen* & Maya L. Evenden Department of Biological Sciences, University of Alberta, CW405 Biological Sciences Building, Edmonton, AB, Canada T6G 2E9 Accepted: 22 September 2015 Key words: methoprene, pyriproxyfen, reproductive diapause, electroantennogram, wind tunnel, octopamine, dopamine, serotonin, Lepidoptera, Gracillariidae Abstract In insects that exhibit a period of delayed reproduction, the timing of mating and reproduction is controlled by environmental conditions that regulate endogenous factors such as hormones and bio- genic amines (BAs). Caloptilia fraxinella (Ely) (Lepidoptera: Gracillariidae) undergoes a 9-month reproductive diapause from adult eclosion in the summer until diapause termination the following spring when adults mate. Male response to female sex pheromone is plastic, and is most acute when moths are reproductively active. The aim of this study is to further elucidate the mechanisms involved in the regulation of male response to pheromone in C. fraxinella, and to test whether the application of BAs with and without a juvenile hormone analogue (JHA) to males in different physio- logical states impacts pheromone responsiveness, as measured by electroantennogram and wind tun- nel bioassays. Treatment of male C. fraxinella in reproductive diapause with one application of a JHA induces the highest subsequent pheromone response in the fall, but does not alter pheromone response earlier in reproductive diapause in the summer. The JHAs methoprene and pyriproxyfen similarly enhance pheromone response in the fall. Treatment with methoprene alone or in combina- tion with one of the BAs octopamine, dopamine or serotonin increases male pheromone responsive- ness in the fall. The increase in pheromone response can be attributed to methoprene only, as treatment with any of the BAs alone does not enhance male response to pheromone. Biogenic amine treatment lowers male responsiveness to pheromone in some experiments, indicating that there may be a role for BAs in maintaining low pheromone response during reproductive diapause in this species. Introduction Long-lived insects can experience a reproductive inactivity as adults during migration or diapause. In these species, signalling systems for finding mates and oviposition loca- tions should be plastic and most acute at reproductive maturity and under suitable environmental conditions for mating and offspring development (Anton et al., 2007). In insects studied to date, induction of sexual communica- tion with pheromones after reproductive inactivity is under the regulation of exogenous factors such as temper- ature and photoperiod that trigger endogenous regulating factors including hormones (Goehring & Oberhauser, 2002; Anton et al., 2007). Juvenile hormone (JH) is a sesquiterpenoid hormone that regulates insect growth and development at all life stages, and is well studied as an important gonadotropic hormone in many Lepidoptera (Ramaswamy et al., 1997; Minakuchi & Riddiford, 2006). Juvenile hormone regu- lates male sex pheromone response and sex accessory gland development in lepidopterans with delayed repro- duction (Cusson et al., 1993; Duportets et al., 1996, 1998; Ramaswamy et al., 1997; Denlinger, 2002; Anton et al., 2007). The reproductive diapause of migratory monarch butterflies, Danaus plexippus (L.), can be terminated with JH application (Barker & Herman, 1976). Treatment with a JH analogue (JHA) induces pheromone response of newly eclosed male Agrotis ipsilon Hufnagel in a wind tun- nel (Gadenne et al., 1993). Treatment with JHA affects the sensitivity of central but not peripheral olfactory neurons *Correspondence: E-mail: jlemmen@ualberta.ca 184 © 2016 The Netherlands Entomological Society Entomologia Experimentalis et Applicata 158: 184–201, 2016 DOI: 10.1111/eea.12391