Effects of nutrition and methoprene treatment upon reproductive diapause in Caloptilia fraxinella (Lepidoptera: Gracillariidae)

Abstract

Female Caloptilia fraxinella exhibit a prolonged reproductive diapause immediately post adult emergence in mid-summer until the next spring when mating, egg development and oviposition on fresh Fraxinus spp. leaflets occur. Factors that effect the termination of reproductive diapause are investigated in this species. Caloptilia fraxinella diapausing adults held in overwintering conditions (2 °C, LD 0 : 24 h) for 24 weeks terminate diapause after placement for 2 weeks in simulated summer conditions (24 °C, LD 16 : 8 h) only if they are provided with 10% sugar water. Exogenous application of the Juvenile Hormone (JH) analogue methoprene to moths in both early-(summer) and mid-(autumn) reproductive diapause demonstrates that JH affects diapause termination but a carbohydrate nutrition source also mediates mating and vitellogenesis. Mating between moth pairs early in diapause occurs only after treatment with methoprene and provision with sugar water. However, there is no impact of mating on the propensity of females to produce vitellogenic oöcytes. Moths collected in the autumn in mid-diapause respond in a dose-dependent fashion to methoprene treatment and the response is greater than that of moths early in diapause collected in the summer. Treatment with methoprene and access to sugar water results in vitellogenic oöcytes in 18.75% of females from mid-diapause moth pairs treated with 0.01 g methoprene per insect and in all females from pairs treated at the two highest doses of methoprene (0.1 and 1 g per insect). Mating occurs only between moths in mid-diapause treated with the two highest doses of methoprene and these doses induce 91% and 100% mating, respectively. Both control and methoprene-treated males in mid-diapause held under summer conditions mate successfully and pass a spermatophore to their methoprene-treated female partner. These data demonstrate that female C. fraxinella undergo a prolonged reproductive diapause in which termination is dependent on JH and further mediated by a carbohydrate nutrition source. The production of vitellogenic oöcytes is independent of mating. These data also provide evidence that response of moths in diapause to exogenous applications of methoprene differs throughout the diapause period and between male and female C. fraxinella .

Peripheral and behavioral plasticity of pheromone response and its hormonal control in a long-lived moth

“…Antennae from males collected and tested in the summer at the beginning of the period of reproductive inactivity responded to the main aldehyde component intermediately between reproductively active spring males and males collected in the autumn prior to overwintering. This may be because a small proportion of the population that eclose in the summer are not in a state of reproductive inactivity (Evenden et al, 2007). Alternatively, the antennal response to the blend may be driven in part by greater plasticity in response to the minor alcohol component.…”

“…However, in species studied to date, sexual receptivity occurs over a period of days after eclosion rather than after months, as is the case in C. fraxinella (Evenden et al, 2007). Pheromone response of male P. unipuncta increases with age and reproductive maturity over 5-7 days post-eclosion (Turgeon et al, 1983;Dumont and McNeil, 1992) and is correlated with JH acid biosynthesis .…”

“…This is probably because gene expression varies during diapause initiation, maintenance and termination, and upregulation of genes involved in diapause termination as a result of JH treatment will vary depending on time of treatment (Tauber and Tauber, 1976;Denlinger, 2002). A greater proportion of female C. fraxinella collected in autumn and treated with methoprene mate and produce eggs than females collected and treated in summer early in the period of reproductive inactivity (Evenden et al, 2007). Similarly, in the lady beetle Coccinella septempunctata bruckii summer aestivation is successfully terminated by JHA treatment, which induces increased respiration and initiation of oogenesis in females (Sakurai et al, 1986).…”

“…Caloptilia fraxinella (Ely) adults eclose in July when the majority of the population is in a reproductively immature state (Evenden et al, 2007), which is maintained until the following spring when adults emerge from overwintering sites to mate and lay eggs on newly flushed ash leaflets (Pohl et al, 2004). JH is important for the initiation of reproduction in female C. fraxinella in the spring (Evenden et al, 2007).…”

“…JH is important for the initiation of reproduction in female C. fraxinella in the spring (Evenden et al, 2007). Male C. fraxinella exhibit plasticity in response to sex pheromone that is dependent on physiological state, and their response is most acute in the spring when females are reproductively active (Evenden and Gries, 2008).…”