Haemolymph ecdysteroid titres at metamorphosis in the fruit fly Ceratitis capitata: multiple peaks not apparent in whole body extracts

Abstract. The titre profile of haemolymph ecdysteroids in the fruit fly Ceratitis capitata was constructed from determinations of haemolymph taken from single animals and compared with ecdysteroid levels in whole body extracts. Larvae were sampled throughout the period from the late third instar larva until eclosion and were synchronized using a conspicuous behavioural marker (‘leaping’) that occurs at the end of the wandering period. Extracts of the whole body exhibit two peaks of ecdysteroids, one associated with pupariation (‘pupariation peak’ of other authors) and the other with pharate adult development. However, the ‘pupariation peak’ corresponded with three temporally distinct peaks in the titre of haemolymph ecdysteroids. The first peak occurs at the time of head retraction (lh before formation of the white puparium) and may represent the initial response to release of prothoracicotropic hormone. The second peak occurs 2–3 h later at the onset of tanning and may be responsible for induction of dopa‐decarboxylase. These peaks are brief (c. 2h each), whereas the third is much longer (16 h) and occupies most of the ‘pupariation peak’. The first two peaks have not been reported previously in any dipteran. Their existence illustrates that extremely brief pulses of ecdysteroids occur in vivo, apparently with profound developmental consequences. The fact that brief pulses in the haemolymph titre are not apparent in whole body extracts emphasizes that results obtained using the latter method must be interpreted with caution. Copyright © 1993, Wiley Blackwell. All rights reserve

Haemolymph ecdysteroid titres at metamorphosis in the fruit fly Ceratitis capitata: multiple peaks not apparent in whole body extracts

Abstract. The titre profile of haemolymph ecdysteroids in the fruit fly Ceratitis capitata was constructed from determinations of haemolymph taken from single animals and compared with ecdysteroid levels in whole body extracts. Larvae were sampled throughout the period from the late third instar larva until eclosion and were synchronized using a conspicuous behavioural marker (‘leaping’) that occurs at the end of the wandering period. Extracts of the whole body exhibit two peaks of ecdysteroids, one associated with pupariation (‘pupariation peak’ of other authors) and the other with pharate adult development. However, the ‘pupariation peak’ corresponded with three temporally distinct peaks in the titre of haemolymph ecdysteroids. The first peak occurs at the time of head retraction (lh before formation of the white puparium) and may represent the initial response to release of prothoracicotropic hormone. The second peak occurs 2–3 h later at the onset of tanning and may be responsible for induction of dopa‐decarboxylase. These peaks are brief (c. 2h each), whereas the third is much longer (16 h) and occupies most of the ‘pupariation peak’. The first two peaks have not been reported previously in any dipteran. Their existence illustrates that extremely brief pulses of ecdysteroids occur in vivo, apparently with profound developmental consequences. The fact that brief pulses in the haemolymph titre are not apparent in whole body extracts emphasizes that results obtained using the latter method must be interpreted with caution. Copyright © 1993, Wiley Blackwell. All rights reserve

Testis ecdysiotropin, an insect gonadotropin that induces synthesis of ecdysteroid

Testes of lepidoptera synthesized ecdysteroid in a somewhat different temporal pattern than the prothoracic glands that release ecdysteroid to the hemolymph. Brain extracts from Heliothis virescens and Lymantria dispar induced testes to synthesize ecdysteroid, but did not affect prothoracic glands. The testis ecdysiotropin (LTE) was isolated from L. dispar pupal brains by a series of high-pressure chromatography steps. Its sequence was Ile-Ser-Asp-Phe-Asp-Glu-Tyr-Glu-Pro-Leu-Asn-Asp-Ala-Asp-Asn-Asn-Glu-Val-Leu-Asp-Phe-OH, of molecular mass 2,473 Daltons. The predominant signaling pathway for LTE was via Gi protein, IP3, diacylglycerol and PKC; a modulating pathway, apparently mediated by an angiotensin II-like peptide, was controlled via G. protein, cAMP, and PKA. Testis ecdysteroid caused isolated testis sheaths to also synthesize a growth factor that induced development of the male genital tract. The growth factor appeared to be a glycoprotein similar to vertebrate alpha-l-glycoprotein. A polyclonal antibody to LTE indicated LTE-like peptide in L. dispar brain medial neurosecretory cells, the suboesophageal, and other ganglia, and also in its target organ, the testis sheath. LTE immunoreactivity was also seen in testis sheaths of Rhodnius prolixus. LTE-like immunoactivity was also detected in developing optic lobes, antennae, frontal ganglia, and elongating spermatids of developing L. dispar pupae. This may indicate that LTE has a role in development as well as stimulation of testis ecdysteroid synthesis.status: publishe

Circadian rhythms in insect disease vectors

Organisms from bacteria to humans have evolved under predictable daily environmental cycles owing to the Earth's rotation. This strong selection pressure has generated endogenous circadian clocks that regulate many aspects of behaviour, physiology and metabolism, anticipating and synchronising internal time-keeping to changes in the cyclical environment. In haematophagous insect vectors the circadian clock coordinates feeding activity, which is important for the dynamics of pathogen transmission. We have recently witnessed a substantial advance in molecular studies of circadian clocks in insect vector species that has consolidated behavioural data collected over many years, which provided insights into the regulation of the clock in the wild. Next generation sequencing technologies will facilitate the study of vector genomes/transcriptomes both among and within species and illuminate some of the species-specific patterns of adaptive circadian phenotypes that are observed in the field and in the laboratory. In this review we will explore these recent findings and attempt to identify potential areas for further investigation