Short Communication Evidence for a Brain Factor That Stimulates Deposition of Puparial Hydrocarbons in Diapausing Flesh Flies

Puparia from diapausing pupae of the flesh fly Sarcophaga crassipalpis are lined with twice as much hydrocarbon as puparia from nondiapausing pupae (J. A. Yoder, D. L. Denlinger, M. W. Dennis and P. E. Kolattukudy, unpublished observations). The additional hydrocarbon favors water conservation during diapause by reducing water loss, enhancing water vapor absorptivity and elevating the critical transition temperature (Yoder and Denlinger, 1991). In this study we seek to identify the source of a hormonal modulator that would account for this difference in hydrocarbons. Our results suggest that a factor unique to the brains of diapause-programmed larvae is responsible for increasing the quantity of hydrocarbon deposited on the puparium. Cyclic AMP elicits the same effect, suggesting that the factor is probably a neuropeptide or another modulator that uses cyclic AMP as a second messenger. A colony of the flesh fly Sarcophaga crassipalpis Macquart was maintained in the laboratory as previously described (Denlinger, 1972). Parental adults were reared under nondiapausing (L:D 15h:9h, 25°C) or diapausing (L:D 12h:12h, 25°C) conditions. All larvae and pupae were maintained at L:D 12h:12h and 20°C. Under these conditions, a high incidence of pupal diapause (>95%) was observed in the progeny of short-day mothers, while none of the progeny from long-day mothers entered diapause. The photosensitive stage is actually the embryo that develops within the uterus of the female (Denlinger, 1971). Thus, diapausing and nondiapausing groups in this experiment differed only in maternal photoperiod. Brain extracts, hemolymph and known hormonal agents were tested for their efficacy in stimulating hydrocarbon deposition. Methoprene (Zoecon Corp., Palo Alto, CA), a juvenile hormone (JH) analog, was diluted in acetone and applied topically to larvae. 20-Hydroxyecdysone (Sigma, St Louis, MO) was diluted in 10 % ethanol and injected using a finely drawn glass capillary, and the dibutyryl