Control of corpus allatum activity in the adult Colorado potato beetle

M.A. Khan

Research output: Thesisinternal PhD, WU

Abstract

Control of corpus allatum activity was investigated in adult <em>Leptinotarsa decemlineata</em> (Say) under various external conditions. Gland activity was measured <em>in vitro</em> utilizing the incorporation of ( <sup>14</sup> C)-methyl-Methionine into juvenile hormone III by individual pairs of corpora allata.<br/>The activities of corpora allata during adult maturation were found to be significantly higher in reproductive, long-day animals than in prediapause, short-day beetles. The activities of male and female glands were similar. During diapause no activity was detectable, whereas corpora allata from post-diapause beetles were totally reactivated within 5 days. There was no clear correlation between the spontaneous rate of juvenile hormone biosynthesis and gland volume although larger glands appeared to be capable of higher activities. Corpora allata from a population of beetles of similar age did not display any synchronous diurnal rhythmicity.<br/>During starvation, young long-day females displayed reduced corpus allatum activities as well as low juvenile hormone titres in the haemolymph. Denervation and implantation studies revealed that intact nervous connections between the central nervous system and corpora allata are essential for restraining juvenile hormone biosynthesis during a 5 days starvation period. The initial activation of corpora allata from newly-emerged long-day females was not dependent on the first feeding.<br/>When the titre of juvenile hormone III in long-day females was elevated by implantation of 3 pairs of supernumerary corpora allata or by injection of 50 pg of the hormone dissolved in 1 μ1 olive oil, the rate of endogenous hormone production was significantly restrained. Denervation experiments indicated that this restrainment occurred predominantly via the neural pathway but humoral factors were also implicated. There was no direct effect of 10 <sup>-5</sup> m juvenile hormone III on gland activity <em>in vitro.</em> 20-Hydroxyecdysone tested <em>in</em> vivo and precocene II tested <em>in vivo</em> and <em>in vitro</em> had no apparent effect on corpus allatum activity.<br/>Corpus allatum activities <em>in vitro,</em> substantiated by juvenile hormone titres (determined by gas chromatography /mass spectroscopy and radioimmunoassay) showed that under short-day conditions both neural and humoral factors are involved in corpus allatum inhibition. This was indicated by the temporary activation of short-day glands after denervation in early prediapause and the gradual restrainment of active corpora allata from long-day females implanted into short-day hosts. Transfer of short- day beetles to long-day photoperiod completely activated the corpora allata and this process was independent of gland innervation. Starvation leads to neural restrainment of intact glands but to possible stimulation of loose corpora allata since implanted glands in starved hosts were fully activated irrespective of the photoperiod.<br/>Studies with farnesenic acid as a precursor in the <em>in vitro</em> assay indicated that the rate limiting enzymes in the biosynthetic pathway probably occur prior to the last two steps in juvenile hormone biosynthesis, namely the methylation and epoxidation of the farnesyl precursor. However, the final 2 enzymatic steps were also diminished during prolonged neural or humoral restrainment of the corpora allata.<br/>The innervation of the corpus allatum as revealed by retrograde diffusion with horse radish peroxidase seems to be restricted to a group of about eight cells in the ipsilateral protocerebral lobe of the brain. It is suggested that the neurally mediated inhibitory signals controlling corpus allatum activity may originate from these lateral neurosecretory cells.<p/>
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • de Wilde, J., Promotor, External person
  • de Kort, C.A.D., Co-promotor, External person
Award date28 Oct 1983
Place of PublicationWageningen
Publisher
Publication statusPublished - 1983

Keywords

  • chrysomelidae
  • endocrinology
  • hormones
  • insects
  • plant pests
  • cum laude

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