Satoshi Takeda

Different feeding and gustatory responses to ecdysone and 20-hydroxyecdysone by larvae of the silkworm,Bombyx mori.

The feeding and gustatory responses to ecdysone and 20-hydroxyecdysone were investigated in the silkworm,Bombyx mori. 20-Hydroxyecdysone reduced feeding response strongly in fourth- and fifth-instar larvae, whereas ecdysone had no effect on feeding response. 20-Hydroxyecdysone stimulated the R receptor, the receptor to feeding deterrents, to a great degree. By contrast, ecdysone was much less effective for stimulating the R receptor. These results indicate that ecdysone and 20-hydroxyecdysone have different effects on feeding response due to different interactions with mouthpart chemoreceptors.

Ecdysone and 20-hydroxyecdysone supplements to the diet affect larval development in the silkworm, Bombyx mori, differently

Abstract Ecdysone and 20-hydroxyecdysone were added to artificial diets of the silkworm, Bombyx mori , to evaluate their effects on larval development and the ecdysteroid titer. Ecdysone at more than 50 p.p.m. induced extra larval ecdyses. In contrast, extra larval ecdyses did not occur at any concentration of 20-hydroxyecdysone. 20-Hydroxyecdysone present at a high concentration from hatching onward caused mortality during the second instar. In larvae reared on an ecdysone-supplemented diet the ecdysteroid titer rapidly increased, then declined sharply in each instar. In larvae reared on 20-hydroxyecdysone-supplemented diet, the ecdysteroid titer increased and remained high throughout the second instar. These results suggest that the effect of ecdysone on the mechanism regulating the ecdysteroid titer is qualitatively different from that of 20-hydroxyecdysone.

In vitro release of ecdysteroids by an endoparasitoid, Ascogaster reticulatus Watanabe

Abstract Ascogaster reticulatus larvae removed from their host Adoxophyes sp. and held in vitro released immunoreactive ecdysteroids into Graces medium. Initially 20-hydroxyecdysone and an unidentified polar ecdysteroid were released, but ecdysone was also present after 24 h incubation. Regardless of the age of the host or size of the parasitoid larva, the maximal release of immunoreactive ecdysteroids occurred when a parasitoid larva developed opaque, fat body spots. We discuss the possibility of direct manipulation of the host haemolymph ecdysteroid titre and subsequent apolysis of the host integument, all initiated by the release of ecdysteroids by the parasitoid larva.

Induction of egg diapause by implantation of corpora cardiaca and corpora allata in Bombyx mori

Abstract Diapause egg production was examined in non-diapause egg producers by implantation of various cephalic organs into pharate adults 4 days after larval-pupal ecdysis. The implantation of five pairs of corpora cardiaca or corpora allata induced a great amount of egg diapause. Implantation of these organs was effective in inducing egg diapause even when the suboesophageal ganglion of the recipients had been removed, although the effect of the corpora allata decreased moderately. The injection of juvenile hormone into 4-day-old pharate adults did not greatly increase production of diapause eggs.

Alteration of egg diapause in Bombyx mori by ouabain injected into diapause egg producers

Abstract Ouabain, an inhibitor of the active transport of some inorganic cations, functioned to produce non-diapause eggs in diapause egg producers. The effectiveness of this chemical related to non-diapause egg production was evident in 40 nmole injection per 4-day-old pharate adult. Simultaneous injections of ouabain with diapause hormone preparation or K+-ion suppressed non-diapause egg production to as a great extent as though they functioned competitively. Other experiments indicate that ouabain does not affect the ovaries directly but appears to inhibit the release of endogenous diapause hormone from the suboesophageal ganglion by affecting the central nervous system. The shortage of 3-hydroxykynurenine in non-diapause eggs produced by ouabain is thought not to be the result of the blockage of active transport at the ovaries but the result of a lack of diapause hormone.

Induction of ultranumerary larval ecdyses by ecdysone does not require and active prothoracic gland in the silkworm, Bombyx mori

Abstract When larvae of Bombyx mori were reared on an artificial diet supplemented with ecdysone, they ecdysed to the seventh instar. Their prothoracic gland was inactive in all instars, when tested in vitro. By contrast, when larvae were reared on a diet supplemented with 20-hydroxyecdysone, they ecdysed to the fifth instar and all of them died. The prothoracic gland of larvae fed 20-hydroxyecdysone was active during the fourth instar and ecdysone was found in the hemolymph, but during the fifth instar, gland activity greatly diminished and little ecdysone was detected in the hemolymph. We propose that an active prothoracic gland is not required for the induction of “ultranumrary larval ecdyses” by ecdysone and that ecdysone, or its metabolites other than 20-hydroxyecdysone, has a critical role in the molting process.

The adult eclosion rhythm in Hyphantria cunea (Lepidoptera: Arctiidae): Endogenous and exogenous light effects

Abstract Endogenous and exogenous effects of light on adult eclosion in Hyphantria cunea were tested by exposure to various light regimes. Regression analysis showed that the position of the eclosion peak after lights on was proportional to the length of the photophase, and that the peak was influenced by the timing of both lights‐on and lights‐off. Under photoperiods of 2–12 hours LD cycle, the eclosion peak was situated after lights‐off, but moved into the light phase as the photophase increased to 22 hours. Pupae were exposed to 3 “skeleton”; photoperiods of LDLD2:2:6:14, 4:2:4:14 and 6:2:2:14. Under the first of these, most adults emerged at the start or just before the longest dark period. Under the second and third skeleton regimes, 20% and 70% respectively of pupae emerged during the shorter dark period. When the compound eyes of the pharate adults were covered, adults smerged 1–4 hours before lights‐off under LD10:14, compared to a control group which emerged just after lights‐off. When pupae were...

Induction of egg diapause in Bombyx mori by some cephalo-thoracic organs of the cockroach, Periplaneta americana

Abstract Induction of egg diapause in the silkworm, Bombyx mori by some cephalo-thoracic organs of the cockroach, Periplaneta americana was examined. All tissues tested such as brain, corpora cardiaca, corpora allata, suboesophageal and thoracic ganglia and nerve cords between thoracic ganglia were able to produce diapause eggs in non-diapause egg producers both by transplantation and injection of their crude homogenates. The homogenate of thoracic ganglia was effective even in pharate adults with the suboesophageal ganglion removed or in isolated abdomens of pharate adults. From these results, it was surmised that some endocrine organs, as well as the central nervous system in the cephalo-thorax of Periplaneta americana, contained the active principle responsible for egg diapause in Bombyx mori.

Larval development of a larval parasitoid (Apanteles kariyai) forced to oviposit in a pupal host (Pseudaletia separata)

There have been many reports on larval parasitoids, usually carried out using hosts in the penultimate and/or last instar. Indeed, host development is in these cases terminated prior to pupation and the parasitoid completes its endoparasitic larval stage in the arrested host larva (see Beckage, 1991). In contrast, little is known about the development of parasitoid larvae in pupal hosts. In the present study, egg and larval development of Apanteles kariyai in their pupal host (Pseudaletia separata) were investigated. We compared the physiological, environmental and humoral factors related to embryonic and post-embryonic development of a larval parasitoid forced to develop in a pupal host with that of the same parasitoid developing in a larval stage host.