Juvenile hormone metabolism during and after diapause in the female Colorado potato beetle, Leptinotarsa decemlineata

Abstract

The corpus allatum activity, juvenile hormone III titre and juvenile hormone-esterase activity in the haemolymph were examined throughout and after adult diapause in Leptinotarsa decemlineata. The influence of external factors (i.e. temperature, photoperiod and food supply) during and after diapause on juvenile hormone metabolism and post-diapause reproduction was studied. During diapause, a phase of true diapause, or “diapause development”, during which beetles are insensitive to temperature increase, is followed by a facultative “post-diapause quiescence” which depends mainly on favourable temperature conditions. The juvenile hormone titre, in good correlation with corpus allatum activity, remains at a constant low level regardless of temperature or time in diapause. Juvenile hormone titre thus does not reflect a transition between two phases during diapause ( sensu lato). Juvenile hormone synthesis rate, however, becomes undetectable soon after the onset of diapause. A gradual inactivation of corpora allata may be one of the physiological traits of diapause development. Shortly before emergence from the soil, a slight increase in the rate of juvenile hormone synthesis occurs in relation to temperature increase. The corpora allata become completely activated only after emergence. The full reactivation of corpora allata is thus a consequence of resumption of activity of the beetles, rather than its cause. Although exposure to light may affect corpora allata activation, food does not seem to play any role. After diapause, the juvenile hormone titre increases progressively. Juvenile hormone-esterase activity in haemolymph is low throughout and after diapause, irrespective of temperature and photoperiod. Sensitivity to photoperiod is lost after diapause development, with regard to oviposition rate. The rate of juvenile hormone synthesis remains, however, dependent of photoperiod in post-diapause.