Larval-larval Ecdysis Research Articles

Characterization of Molting Process during the Different Developmental Stages of the Diamondback Moth Plutella xylostella.

Simple SummaryThe diamondback moth, Plutella xylostella (L.) is the most important pests of cruciferous crops worldwide. Although there are numerous studies on the general life cycle of P. xylostella, the detailed descriptions of the morphological transformation and behavioral sequence during molting are rarely provided and visualized. In this paper, we provided the duration and photographic details of staging criteria of each stage of egg hatching, larval–larval ecdysis, larval–pupal metamorphosis and adult eclosion, and post-eclosion behavior of P. xylostella. Several new characters in the molting process that were previously not described in other lepidopteran insects were found, i.e., the larvae contracted anterior-posteriorly then dorsal-ventrally during pre-ecdysis, and the antennae waved backward then forward in the post-eclosion behavior. Our findings add an important piece of knowledge about the molting biology of lepidopteran insects.The molting process of the lepidopteran insects is observed for many species. However, the detailed description of the morphological transformation and behavioral sequence during molting are rarely provided and visualized. Here, we described the molting process of the diamondback moth Plutella xylostella by providing the duration and photographic details of staging criteria of each stage using stereo microscopy and a digital video camera. We divided the morphological transformation of egg development and hatching into five stages, the larval–larval ecdysis and the larval–pupal metamorphosis into five stages, the pupal development and eclosion into three stages, and the post-eclosion behavior into four stages. Several new characters in the molting process that were not previously described in other lepidopteran insects were found, i.e., the larvae contracted anterior-posteriorly then dorsal-ventrally during pre-ecdysis, and the antennae waved backward then forward in the post-eclosion behavior. Our findings will deepen the knowledge of the molting biology of lepidopteran insects and facilitate the study of the underlying mechanisms.

The Biological Effects of Venom Derived from the Ectoparasitic Wasp Eulophus pennicornis (Nees) (Hymenoptera: Eulophidae): Evidence for Dual Endocrine Regulation~!2008-08-08~!2009-05-30~!2010-02-11~!

The venom of the ectoparasitoid Eulophus pennicornis is known to induce developmental arrest in parasitized hosts through the prevention of moulting. However, little work has explored how the venom affects different host stages, whether the observed effects vary with different doses, and whether the venom has activity in non-host species. Injections of venom doses of � 0.5 � g protein prevented the development of >90% of both fifth and sixth instar Lacanobia oleracea larvae. In fifth instars, developmental arrest at doses of � 1.0 � g occurred prior to ecdysis to the sixth stadium, whilst the 0.5 and 0.25 � g treatments allowed 36% and 77% of injected larvae, respectively, to moult although most sub- sequently failed to pupate. Although naturally parasitized hosts always showed reduced growth, lower doses of venom of- ten prevented pupation without affecting this parameter, particularly in sixth instar larvae where only the highest dose (2.0 � g) reduced the mean maximum weights achieved. Two factitious lepidopteran hosts, Manduca sexta and Spodoptera lit- toralis, were also affected by injection of the venom at w/w doses equivalent to those used for L. oleracea although larval- larval moulting was only prevented in the former. Fractionation of venom using gel-filtration FPLC indicated the presence of at least two factors that markedly affected host development. One series of contiguous fractions, on injection, prevented larval-larval ecdysis in a similar way to whole venom. A second series of fractions had no effect on larval-larval ecdysis but resulted in the formation of deformed pupae, an effect that closely resembled the application of a juvenile hormone (JH) analogue, which may indicate the presence of a factor within the venom that modulates host levels of this hormone.

Strains in the common cutworm, Spodoptera litura (Lepidoptera: Noctuidae) with differing host ranges

The larvae of two strains of Spodoptera litura, Ishihara and Sumitomo, supplied by Ishihara Sangyo Co. Ltd. and Sumitomo Chemical Co. Ltd., respectively, were raised on an artificial diet until last larval-larval ecdysis, and their growth and survival were compared when fed on leaves from 15 different plants known as host plants of this species. The Ishihara strain grew better and a higher percentage of larvae pupated when fed on spinach, leaf mustard, tomato, Chinese kale, taro, green pepper, red pepper or eggplant, compared with the Sumitomo strain. Whereas, much lower percentage of the larvae of the Sumitomo strain pupated especially on the last four plants, indicating that these plants were not suitable diets for larvae of this strain. The presence of strains differing in their host ranges is discussed in relation to the migration of S. litura.

Coordinated Morphological Changes in Midgut, Imaginal Discs, and Respiratory Trumpets During Metamorphosis of <I>Aedes aegypti</I> (Diptera: Culicidae)

Abstract The study of mosquito metamorphosis has relevance to understanding the mosquitocidal mechanisms of juvenile hormone analogues and may provide information concerning dipteran evolution. This report details the chronology and coordination of morphological changes in imaginal disc growth and differentiation, respiratory trumpet morphogenesis, and midgut remodeling that occur during Aedes aegypti (L.) metamorphosis. These observations were facilitated by the transparent A. aegypti larval cuticle and the relatively synchronous development of individually grown larvae. The results indicate that within 12 h of the last larval-larval ecdysis, leg imaginal discs start to grow and differentiate, pupal respiratory trumpets start their morphogenesis, and midgut remodeling starts in that programmed death of midgut polytene cells and division of midgut diploid cells are initiated. Morphological changes in all of these structures continue throughout the fourth stadium and are concomitant with substantial larval...

Comparison of the Response of Heliothis virescens to Parasitism by Euplectrus comstockii and Euplectrus plathypenae

Two major similarities were observed in larvae of Heliothis virescens parasitized by either Euplectrus comstockii or Euplectrus plathypenae. Parasitism by either parasitoid arrested larval-larval ecdysis and caused comparable alterations in the titer of storage proteins found in the host hemolymph. However, each larval stadium responded differently to parasitism. Parasitized 3rd-instar larvae increased in weight to ca. twice that of control larvae while parasitized 4th- and 5th-instar larvae increased in weight to ca. 1.3 times the maximum observed in control larvae for that stadium. The titer of storage proteins present in the hemolymph increased in parasitized 3rd- and 4th-instar larvae but decreased in parasitized 5th-instar larvae, by comparison to the titers found in control 3rd-, 4th- and 5th-instar larvae, respectively. Feeding by the parasitoids did not cause further alteration in the composition of the hemolymph proteins of the host. A plausible explanation for the increase in weight and/or increase in the storage protein titer in the younger host larvae is to provide a sufficient nutritional source to extend the viability of the host while it remains in that stadium and is fed upon by the developing parasitoids.

Characteristics of a developmental arrestant in the venom of the ectoparasitoid wasp Euplectrus comstockii

Parasitic Hymenoptera regulate their hosts in order to provide a suitable source of nutrition and dwelling for their offspring. Few regulatory factors known to cause a specific effect on the host have been structurally characterized. The larval ectoparasitoid Euplectrus comstockii Howard (Hymenoptera: Eulophidae) arrests larval-larval ecdysis in its lepidopteran hosts. Prior to oviposition, the female wasp injects a venom into the hemocoel of the host and that venom alone is effective in causing the arrestment. A venom gland-reservoir structure connected to the lower reproductive tract of the wasp contains a complex mixture of proteins. There are no obvious similarities among the electrophoretic banding pattern (native or denatured) for venom proteins of E. comstockii and several other parasitic hymenopteran species. Venomous protein, separated by electrophoretic techniques, with a native mol. wt of c. 66,000, was capable of arresting larval-larval ecdysis in 4th instar larvae of Trichoplusia ni (Lepidoptera : Noctuidae). Nanogram quantities of the protein were sufficient to cause arrestment. The activity of the protein was sensitive to temperature, pH, organic solvent, and protease.

Developmental changes in urea in the haemolymph (determined by a urease-indophenol method) in hybrid strains of the silkworm, Bombyx mori and the effect of starvation in the fifth instar larvae, fed an artificial diet, on urea level in subsequent development

1. 1. Developmental changes in urea in the haemolymph in hybrid strains of the silkworm, Bombyx mori were determined by a urease-indophenol method in silkworms fed an artificial diet or fed fresh mulberry leaves. 2. 2. Lower concentrations of urea in the haemolymph compared to our previous results determined by a chemical method (Suraida et al., 1990; Comp. Biochem. Physiol. 97A, 373–379) were observed in the fourth and fifth larval instars, approximately 0.1–0.2 and 0–0.05 mg urea N/ml haemolymph in the silkworms fed an artificial diet and fed fresh mulberry leaves, respectively. 3. 3. Concentrations of urea in the haemolymph in pharate adults, approximately 0.7–0.8 and 0.001 mg urea N/ml haemolymph in the silkworms fed an artificial diet and fed fresh mulberry leaves, were similar to our previous results. 4. 4. Based on evaluation of the assay method, it was concluded that the changes in urea in the haemolymph in a hybrid strain of the silkworm, Bombyx mori in the larval stage was established for the first time in the present study. 5. 5. Starvation from 72 hr after the fourth larval-larval ecdysis in the silkworms fed an artificial diet resulted in a further elevated concentration of urea, approximately 1 mg urea N/ml haemolymph in the pharate adult stage, a 20% increase against non-starved control silkworms.

Isolation of cDNA clones coding for humoral lectin of silkworm, Bombyx mori, larvae

In the hemolymph of the silkworm, Bombyx mori, lectin with hemagglutinating activity against sheep red blood cells increases at larval-larval ecdysis and at spinning stage ( Suzuki and Natori, 1983) and is induced by infection with cytoplasmic polyhedrosis virus. A Bombyx lectin polypeptide with molecular weight approx 280K is responsible for hemagglutinating activity, since antiserum raised against this polypeptide inhibited hemagglutinating activity. The site of synthesis of Bombyx lectin was determined by primary tissue cultures of fat body and hemocytes. A hemagglutinating activity assay demonstrated that hemocyte is responsible for the release of hemagglutinin into the culture medium. Isolation of cDNA clones coding for Bombyx lectin was carried out on the cDNA library prepared in an expression vector α gt11 starting with poly(A) + RNA from spinning larval hemocytes. As a result of immunoscreening, several positive clones were obtained, and the cDNA clones were characterized.

Changes in urea in the haemolymph of the silkworm, bombyx mori in the fourth and the fifth larval instars and effect of starvation in th fifth instar on the level of urea in the pharate adults

1. 1. Urea in the haemolymph was determined during the development in the silkworms, Bombyx mori that were reared on artificial diet and on fresh mulberry leaves. 2. 2. In the fourth and the fifth larval instars, the changing pattern and the level of urea were similar in the silkworms reared on artificial diet and on fresh mulberry leaves. A peak of concentration of urea, approx. 0.7 mg urea N/ml, was observed in each instar. These were the new observations. 3. 3. In the pharate adult development, a high level of urea, a maximum of approx. 1.0 mg urea N/ml, was observed in the silkworms reared on artificial diet and a low level, approx. 0.05 mg urea N/ml, was observed in the silkworms reared on fresh mulberry leaves. These results were similar to the reported results (Inokuchi et al., 1983 Appl. Ent. Zool. 27, 99–105). 4. 4. In the fifth larval instar, starvation experiments were carried out, beginning from 48, 72 and 96 hr after the fourth larval-larval ecdysis in the silkworms reared on fresh mulberry leaves. 5. 5. Starvation from 72 hr let the silkworm larvae transform themselves to pharate adults and produced a changing pattern of urea in the pharate adult that is closely similar to the changes in the silkworms reared on artificial diet only. This result might support the hypothesis (Yamada et ai, 1984 Appl. Em. Zool. 28, 49–56) that urease in mulberry leaves enters into the haemolymph in the mature larvae through the midgut tissue in the fifth instar.

The ecdysteroid titres during the last-larval instar of Ephestia kuehniella Z. (Lepidoptera: Pyralidae)

The ecdysteroid titre and the body weight during the last-larval instar of Ephestia kuehniella were determined. Slightly elevated ecdysteroid titres occur during the first 12 h following the last larval-larval ecdysis (38 ng/g) and again some 120 h later, lasting about 48 h (33 ng/g). A high ecdysteroid peak (750 ng/g) with a maximum in prepupae of the eye-class A4 precedes the larval-pupal ecdysis. The basal levels between these increased ecdysteroid titres are between 13 ng/g and 15 ng/g. Compared with the body weight, the first sligtly increased ecdysteroid titre 12 h after ecdysis is associated with the beginning of food intake, the second increase at 144 h after ecdysis with reduced gain in body weight. The prepupal ecdysteroid peak occurs whilst the body weight remains constant. Correlations between the varying ecdysteroid titre and morphological and physiological events accompanying the progress in larval-pupal development are discussed.

Temporal organization of endocrine events underlying larval-larval ecdysis in the silkworm, Bombyx mori

The timing of ecdysis in the penultimate instar of Bombyx mori was demonstrated to be under the control of a circadian clock. The temporal organization of secretion of prothoracicotropic hormone (PTTH), ecdysone and juvenile hormone was studied with particular attention to the circadian control of the timing of hormone release. PTTH release occurs, at least, in the second and third night. The latter is responsible for evoking the larval ecdysis. Prothoracic gland initiates ecdysone secretion abruptly with a very short span after the second PTTH release and secrete enough amount of ecdysone for larval moulting, which takes place 11 h later. Juvenile hormone titer is relatively high before the second PTTH release and corpus allatum becomes dispensable for ensuring the larval moulting in 1.5 h. Based on these findings, interpretations for the endocrine system underlying precocious pupation and formation of intermediates, which are produced by neck ligation, are presented.

Circadian clock and prothoracicotropic hormone secretion in relation to the larval-larval ecdysis rhythm of the saturniid Samia cynthia ricini

Observations on the timing of ecdysis and neck ligation experiments on larvae of Samia cynthia ricini under various light-dark conditions show that an endogenous circadian clock controls the timing of larval ecdysis and prothoracicotropic hormone (PTTH) secretion preceding it. The clock, upon reaching a specific phase point, causes the brain to secrete PTTH provided that the brain has acquired the secretory competence. This time may vary, in relation to a previous ecdysis, according to the light-dark conditions by which the clock phase is specifically determined, but is fixed relative to a subsequent ecdysis. Thus, in the case of the ecdysis to the 5th instar, PTTH is secreted [15+nτ] hr (τ: free-running period, slightly less than 24 hr) after the clock has started when the rhythm is free-running, and in the second and third nights of the 4th instar under a photoperiod of 12 hr light and 12 hr dark. Full secretion of ecdysone occurs 6 hr after PTTH secretion and ecdysis ensues 34 hr thereafter to complete the ultimate sequence of ecdysis.

Control of corpora allata function in larvae of Galleria mellonella.

1. The implantation of three brains into freshly ecdysed last instar larvae which possess at least one of the two corpora allata induces extra larval development. Implanted brains appear to produce a neurohumoral allatotropic factor.2. Corpora allata seem to be inhibited via their nervous connections 48-60 hours after the last larval-larval ecdysis and become insensitive to the allatotropic factor. Severance of the nerves innervating the corpora allata and adjacent corpora cardiaca induces extra larval development in 7% of the experimental insects and restores sensitivity to the implanted brains in as many as 20%.3. Severance of the nerves to the corpora cardiaca—corpora allata complexes or implantation of corpora cardiaca—corpora allata complexes into allatectomized larvae in some instances causes a considerable prolongation of the last larval instar. It is suggested that disconnection of the corpora allata from the brain partly removes their inhibition and induces secretion of a low titer of juvenile ho...

Spatial and feeding requirements for pupation of last instar larval Galleria mellonella (Lepidoptera)

The emergence of pupae from lightly spun-up last stage larvae can be significantly delayed simply by depriving the larvae of sufficient free space. The effect is upon pupation, and apparently not upon larval-pupal ecdysis. The inhibition may be prolonged for months without restricting larval movement when free space is practically eliminated by use of food-filled containers. The quality of the free space is most important: with containers of approximately equal volumes, those having more flat area seem more conducive to emergence, and those with a highly restrictive dimension inhibit it. The inhibition does not seem to be due to such factors as humidity, population density, the availability of room for cocoon construction, or the build-up of chemical inhibitors. In the last larval instar a minimum of 2 days' exposure to standard diet is needed for metamorphosis. Isolated last stage larvae would pupate if they were provided after the last larval-larval ecdysis with nothing more than any one of the following substances: beeswax, palmitic acid, ceryl alcohol, myristyl ester of palmitic acid, or mixtures of cellulose, casein, glucose, and glycerine. Such larvae die within 3 weeks if given only methyl palmitate, myristyl alcohol, hexadecanol, myricyl alcohol, cellulose and water, or any of three waxes.