Developmental Profile of Prothoracicotropic Hormone (PTTH) Activity in the Gypsy Moth, Lymantria Dispar

Abstract

A profile of L. dispar brain PTTH activity during late embryonic to adult development has been generated using an in vitro prothoracic gland (PGs) stimulation bioassay. The existence and titer of PTTH in various lepidopteran insects has been discussed (Ishizaki, 1969; Nishiitsujii-Uwo and Nishimura, 1975; O’Brien et al, 1986; and Dorn et al, 1987). Our previous studies (Kelly et al., 1986) showed that in L. dispar the PGs respond to brain extract in vitro during day 3 to 5 of the fifth larval instar. Following a 180-min pre-incubation, day 4 PGs secrete 24 times more ecdysone/gland than their contralateral control glands when incubated for 90 min with 0.25 brain equivalents (Fig. 1). Since the day-4 PGs are equally responsive as those of day-5 glands (Fig. 1), day-4 PGs were used for in vitro assay with larval and pupal brains from day 1–11. Prothoracic gland activation was nearly constant using day 1–11 larval or pupal brain extracts, suggesting a relatively constant titer of PTTH. However, day- 7 and day-8 last-instar larval brain extracts showed maximum and minimum activity, respectively, at 1 brain equivalent/25μl (Fig. 2). Pupal brains showed maximum activity on day 3 at both 1 and 0.25 brain equivalents/25μl. Boiled extract from prehatch embryonic eggs showed mimimum activity at both concentrations.