Effects of Juvenoids and Retinoic Acid on Development of Larvae and Nymphs in the Tick Ixodes ricinus L. (Acari,Ixodidae) and Regeneration of Haller's Organ during Metamorphosis

Larvae and nymphs of the tick Ixodes ricinus L. display similar reactions to analogs of the insect juvenile hormones (methoprene and pyriproxyfen), which induce at both stages juvenalization of the Haller's sense organ regenerates. Similar effects were also described for retinoic acid. Unlike juvenoids, retinoic acid can affect not only regeneration, but also normal development of the Haller's organ and cause changes corresponding to so-called regenerative induction. Amputation of the leg and treatment with retinoic acid do not affect the duration of larval or nymphal development, while juvenoids somewhat accelerate their development.     

Partial purification and characterization of locust allatotropin I

Methanol extracts of locust brains, corpora cardiaca (CC), and suboesophageal ganglia (SOG) were separated by gradient and/or isocratic reverse-phase high-performance liquid chromatography (HPLC) and allatotropic activity monitored in the eluted fractions. A major peak of activity, separated by isocratic separation with 12% 2-propanol, designated allatotropin I, exhibited identical retention times in the three tissue extracts. Doseresponse curves of allatotropin I indicate similar content in brain and CC-equivalents, whereas optic lobes, similarly separated by isocratic HPLC, contain only one-tenth of this amount of allatotropin. Allatotropin I is resistant to boiling and is susceptible to tryptic and chymotryptic digestion. Methanol extracts of thoracic muscle, Malpighian tubules, fat body or ovaries, similarly prepared and boiled, did not exhibit allatotropic activity at high doses of tissue equivalents.     

Effects of a juvenile hormone analogue on the eggs, post-embryonic development, metamorphosis and diapause induction of the Colorado potato beetle, Leptinotarsa decemlineata

The effect of a juvenile hormone analogue, S-71639, was tested on the eggs, four larval instars and adults of the Colorado potato beetle, Leptinotarsa decemlineata Say, by topical application or after treatment of the foodplant. The last larval instar is very sensitive to S-71639. Treatment of this instar delayed the onset of pupation and prevented adult emergence. Treated animals showed severe abnormalities, but they were not immediately killed at the doses used in this study. Treatment of larvae also interfered with the photoperiodic induction of diapause. Adults, kept under diapausing conditions, started to lay eggs after treatment with S-71639. The ovicidal effect of the compound was rather weak. The implications for practical use of S-71639 in control of the Colorado potato beetle are being discussed.

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Résumé L'effet d'un analogue de l'hormone juvénile, S-71639, a été testé sur les oeufs, les quatre stades larvaires et les adultes du doryphore, Leptinotarsa decemlineata Say, par application topique ou après traitement de la plante-hôte. Le dernier stade larvaire est très sensible au S-71639. Le traitement de ce stade retarde le début de la métamorphose et empêche l'émergence adulte. Les animaux traités montrent de graves anomalies, mais ne sont pas immédiatement tués par les doses utilisées dans cette étude. Le traitement des larves perturbe aussi l'induction photopériodique de la diapause. Les adultes placés dans des conditions de diapause, commencent à pondre après traitement au S-71639. L'effet ovicide de la substance est plutôt faible. Les implications pour l'utilisation pratique du S-71639 dans la lutte contre le doryphore sont discutées.

     

Critical roles for juvenile hormone and its esterase+ in the prepupa of Trichoplusia ni

In the caterpillar Trichoplusia ni (Lepidoptera: Noctuidae) it has been demonstrated by allatectomy that the appearance of juvenile hormone during the prepupal stage is crucial for the successful larval-pupal ecdysis of most larvae. Application of juvenile hormone or juvenile hormone esterase inhibitors at key times disrupted normal development as well. Thus the subsequent disappearance of juvenile hormone is regulated by degradation by juvenile hormone esterase in addition to a hypothetical reduction in biosynthesis. This reduction in juvenile hormone titer in the prepupa is just as critical for normal development as was its previous appearance. These observations on the critical role of juvenile hormone in the prepupa are in contrast to observations in some other species. For instance, in the case of Manduca sexta (Lepidoptera: Sphingidae), juvenile hormone is considered only supplementary to the action of prothoracicotropic hormone in the postwandering stage and primarily is required for normal pupal development. It thus appears that even within the Lepidoptera the role of juvenile hormone in prepupal development can vary dramatically.     

Tentacle structure and feeding processes in life stages of the commercial sea cucumber Parastichopus californicus (Stimpson)

Tentacle structure and function in the pentacula larva, juvenile, and adult life stages of Parastichopus californiens (Stimpson) were examined via light and electron microscopy. Food particle adherance to the tentacle surface is mediated by an adhesive material in the case of the pentacula larva and additionally by mechanical entrapment in juvenile and adult animals. Mechanical entrapment is of secondary importance to adhesion during feeding.     

Factors responsible for the initiation of a second oöcyte maturation cycle in the ovoviviparous cockroach Nauphoeta cinerea

The factors responsible for the initiation of a second oöcyte maturation cycle were investigated by measuring oöcyte growth, vitellogenin titre, and corpus allatum activity after injection of juvenile hormone and/or removal of the egg-case from pregnant females and by performing ovary and corpus allatum transplant experiments.Egg-case removal in late pregnancy results in immediate oöcyte growth, whereas in early pregnancy oöcyte growth is resumed only after a lapse of time, even after injection of juvenile hormone. This, however, induces an immediate increase in the haemolymph vitellogenin titre. A single injection of 2 or 10 μg of juvenile hormone II first stimulates some oöcyte growth after this lapse of time and later activates the corpora allata, which in turn leads to completion of oöcyte maturation. A repeat injection of 10 μg stimulates continuous oöcyte growth without activating the corpora allata. In the presence of an egg case, activation of the corpora allata is suppressed, even after injection of 2 μg of juvenile hormone III, and the oöcytes do not grow. Injection of higher doses stimulates oöcyte growth and leads to expulsion of the egg case in up to 95% of the females. This, however, is not a direct consequence of the increase in size of the ovaries. Ovary transplant experiment show that in young pregnant females the second generation of oöcyte is not yet competent for growth and that ovaries which are competent can mature in young pregnant females, treated with juvenile hormone, whose egg case has been removed.The results are summarized in a model demonstrating the various factors involved in regulating corpus allatum activity in oöcyte maturation and pregnancy and after application of juvenile hormone. We prepose that the corpus allatum activating effect of exogenous juvenile hormone is mediated by the growing oöcyte and that this activation can be suppressed by the continuous presence of exogenous juvenile hormone.