Changes in lipid droplet localization during embryogenesis of the silkworm, Bombyx mori

Lipid droplets are considered one of the most important energy sources in lepidopteran eggs during late embryogenesis, but the process of their incorporation into the embryo is as yet unknown. The present study focused on the process of transition of lipid droplets from the extraembryonic yolk to the embryo of the silkworm Bombyx mori, using morphological and biochemical approaches. The morphological study revealed that the incorporation of lipid droplets from the extraembryonic yolk into the embryo occurs at three points and in three different ways during the development of the embryo. Some lipid droplets were translocated directly from the extraembryonic yolk to the embryo before the blastokinesis stage. However, the majority of lipid droplets together with the other components of the extraembryonic yolk were incorporated in the embryo via both morphogenetic inclusion during dorsal closure and ingestion of the extraembyonic yolk by the developing caterpillar prior to hatching. Similar results were obtained from the biochemical study. Thus, we propose that there are three steps in the incorporation of lipid droplets from the extraembryonic yolk into the embryo. In addition, morphological and biochemical data concerning the total amount of lipid droplets in the egg suggested that lipid droplets were mainly consumed during late embryogenesis, seeming to synchronize with tracheal development.     

Gregariousness affects performance and defensive reactions in swallowtail caterpillars

1. Group living in caterpillars may enhance individual performance due to sharing of costs associated with individual tasks when dealing with biotic or abiotic ecological factors. 2. In the gregarious caterpillar Battus polydamas archidamas (Papilionidae) egg clusters and caterpillar groups vary in size. We hypothesized that individual survival would be higher in larger groups and that group living would enhance individual performance: shorter development time and/or reduced frequency of (presumably costly) defensive reactions in larvae and larger adult size. We also tested whether the group size conferring the highest survival to laboratory-reared caterpillars matched the most frequent egg clutch size in the field. 3. We collected egg clutches in the field and reared caterpillars in groups of 1, 6, 10, and 14 individuals. We quantified larval survival and stage duration as well as adult mass under laboratory conditions, excluding natural enemies. We also recorded the frequency of larval defensive reactions (thrashing and osmeterium display) against a tactile stimulus of first-instar larvae. 4. Group living enhanced caterpillar survival, particularly during the first instars, when caterpillars are 100% gregarious. Groups of intermediate size reduced larval development time but group living did not affect adult mass. Individual caterpillars in groups showed defensive reactions less frequently than solitary individuals, revealing a cost-saving feature of gregariousness for this swallowtail species. The most frequent clutch size in the field (9–10 eggs) did not match the larval group with highest survival (14 individuals), but did match the group with shortest development time.     

Comparative analysis of proteome maps of silkworm hemolymph during different developmental stages

Background  

The silkworm Bombyx mori is a lepidopteran insect with four developmental stages: egg, larva (caterpillar), pupa, and adult. The hemolymph of the silkworm is in an open system that circulates among all organs, and functions in nutrient and hormone transport, injury, and immunity. To understand the intricate developmental mechanisms of metamorphosis, silkworm hemolymph from different developmental stages, including the 3^rd day of fifth instar, the 6^th day of fifth instar, the 3^rd day of pupation, the 8^th day of pupal stage and the first day of the moth stage, was investigated by two-dimensional electrophoresis and mass spectrometry.     

Does tent caterpillar attack reduce the food quality of red alder foliage?

Summary We assayed the quality of red alder trees for western tent caterpillar growth and survival to test the hypothesis that caterpillar feeding stimulates plant defenses in both attacked and adjacent trees. Three years of high tent caterpillar density were necessary before deterioration in foliage quality occurred, and even then only foliage from trees which were almost completely defoliated in the current year reduced the growth of caterpillars. Both tent size and mean egg mass size increased after the second year of high density which indicates that good conditions still existed for tent caterpillars after 2 to 3 years of heavy feeding.Egg masses which were moved to areas where trees had not recently supported a high caterpillar population produced significantly smaller tents than endemic controls in 1982. Therefore the small tent and egg mass size of the high density population in 1982 was inherent to the insects rather than modified by food source. In 1983 the tents from introduced egg masses were as large as naturally occurring tents.If lightly attacked trees within areas of high caterpillar density are better defended against insect attack, this does not show up in their ability to support caterpillar growth and survival. We found no evidence to support the hypothesis that trees communicate insect attack and stimulate chemical defenses in adjacent trees. Reduced foliage quality seems to be a result of extensive insect damage rather than a defense against insect damage.     

A possible role of 20-hydroxyecdysone in embryonic development of the silkworm Bombyx mori

It has been well established that eggs of insects, including those of the silkworm Bombyx mori, contain various ecdysteroids and the amounts of these ecdysteroids fluctuate during embryonic development. In order to know the function of egg ecdysteroids in embryonic development of B. mori, we examined the biological activities of various egg ecdysteroids by in vitro ligand-binding assay and bioassay using B. mori eggs. First, using the ecdysteroid receptor of B. mori (BmEcR-B1/BmUSP heterodimer) prepared by yeast and Escherichia coli expression systems, the interaction between the ecdysteroid receptor and various egg ecdysteroids of B. mori was analyzed. The relative binding affinities of egg ecdysteroids to the BmEcR-B1/BmUSP heterodimer decreased in the order of 20-hydroxyecdysone > 2-deoxy-20-hydroxyecdysone > 22-deoxy-20-hydroxyecdysone > ecdysone > 2-deoxyecdysone > ecdysone 22-phosphate. Next, several egg ecdysteroids of B. mori were injected into the prospective diapause eggs, which show a very low level of free ecdysteroids at the onset of embryonic diapause (gastrula stage). Approximately 7% of them (P < 0.002, chi(2)-test) developed beyond the gastrula stage without entering diapause by the injection of 20-hydroxyecdysone (25 ng/egg). In contrast, the injection of other ecdysteroids was not effective in inducing embryonic development. These results suggest that 20-hydroxyecdysone, via the ecdysteroid receptor, is responsible for the developmental difference between diapause and non-diapause in B. mori embryos. Furthermore, it was suggested that continuous supply of 20-hydroxyecdysone may be required to induce embryonic development.     

Ultrastructure and role of the aeropyle and shell of the egg of Galleria mellanella

The structure of the eggshells and particularly the morphogenesis and the fine structure of an aeropyle were studied in the wax moth Galleria mellonella.Galleria has eggs whose chorion shows an inner trabecular layer and the walls of aeropyles are coated by threads. During oviposition air enters the trabecular layer in a sufficient quantity to allow the development of the caterpillar if the egg is immersed in boiled water or paraffin oil. This layer is in communication with the atmosphere by means of 150 to 200 aeropyles.     

Macrogeographic clines in fecundity, reproductive allocation, and offspring size of the forest tent caterpillar Malacosoma disstria

1. The fecundity of the forest tent caterpillar varies considerably across its geographic range. Field data indicate that populations in the southern United States (Gulf States) produce nearly twice as many eggs as females from Canada or the Lake States, with little or no difference in the size of adult females. 2. In controlled rearing experiments, female forest tent caterpillar from the southern United States (Louisiana) had much larger clutch sizes than same sized females from northern populations in Michigan or Manitoba, Canada. Increased fecundity in Louisiana females was achieved through a significant reduction in egg size and a concomitant increase in the allocation of resources to egg production. 3. Comparison of 10 forest tent caterpillar populations spanning a 27° latitudinal gradient, validated the results of detailed comparisons among the three populations above by confirming the strong negative correlation between latitude and clutch size. 4. Neonate forest tent caterpillars from Manitoba were significantly larger than larvae from either Michigan or Louisiana. Michigan larvae were intermediate in size. It is postulated that large neonates are advantageous in thermally limiting environments. More than three times as many degree‐days are available to Louisiana neonates during the first 2 weeks after hatching. A consistently favourable climate during the vulnerable post‐hatching period may have allowed the evolution of larger clutches at the expense of neonate size in southern populations.     

A maternal gene mutation correlates with an ovary phenotype in a parthenogenetic wasp population.

Endoparasitoid wasps rely on maternal protein secretions, including viruses and virus-like particles (VLPs), to overcome host defense reactions. In the ichneumonid Venturia canescens, VLPs are assembled in the nuclei of ovarian calyx gland cells, secreted into the lumen of the gland, and eventually transmitted into the host caterpillar together with the parasitoid egg. One of the genes coding for VLP proteins, termed VLP1, exists in two alleles producing two structurally different proteins. Here we describe the establishment and initial phenotypic characterisation of two parthenogenetic laboratory strains, which differ in VLP1 as well as in other genetic markers. A comparison of calyx tissues from the two strains revealed morphological differences that seem to affect egg movement from the ovarioles into the oviduct. The observed histological changes are correlated with differences in egg maturation and embryonic development causing a delay in larval hatching in one of the strains. Under conditions that favour superparasitism, the two strains differ in the number of offspring produced.     

Carbohydrate metabolism and restricted oxygen supply in the eggs of the silkworm, Bombyx mori

Increased oxygen supply to diapause eggs of the silkworm (O₂-incubation) effectively prevented diapause initiation and induced the same pattern of glycogen, polyol and lactate levels as was observed in normal non-diapause eggs. Sensitivity to oxygen decreased as embryonic development proceeded. After the termination of this sensitive period, accumulation of polyols and lactate followed.Experiments were carried out to test whether changes in the oxygen permeability of the egg membranes are involved in restricting the supply of this gas to eggs at the onset of diapause. Oxygen permeability of the chorion was measured with apparatus especially designed for this purpose. Although the chorion of the diapause egg was less permeable than that of the non-diapause egg, the oxygen permeability of the chorion does not change appreciably during the early developmental stages of the diapause eggs. The changes in rate of water loss through the egg membranes were measured during the early developmental stages of the embryos. The level of water loss decreased gradually as the formation of serosal cuticle proceeded. Moreover, it was observed that the water loss up to the time of formation of serosal cuticle was closely related to the oxygen permeability of the chorion.From these results, we suggest that the formation of the serosal cuticle may be an additional cause of the restricted oxygen supply at the onset of the diapause.     

Plant sterols and host plant suitability for generalist and specialist caterpillars

Insects, unlike plants and vertebrates, lack the ability to biosynthesize sterols. Cholesterol is typically the most common sterol found in plant-feeding insects, but it is rarely found in plants above trace levels, so plant-feeding insects must produce the cholesterol they need by metabolizing the sterols found in the plants they eat. Plant-feeding insects are, however, often limited in terms of which sterols can be converted to cholesterol. In the current study we used a transgenic tobacco plant line that displays high levels of atypical plant steroids, specifically stanols and ketone-steroids, to explore how novel steroid structural features affect performance in three economically important caterpillars (Heliothis virescens, Spodoptera exigua, and Manduca sexta). For each species we measured pupation success, larval development, pupal mass, pupal development, and eclosion success. For the two generalists species (H. virescens and S. exigua) we also measured egg production and egg viability. We then used these eggs to replicate the experiment, so that we could examine the effect of parental steroid dietary history on survival, growth and reproduction of 2nd-generation individuals. Significant negative effects of novel steroids on larval and pupal performance were observed for each caterpillar in the first generation, although these were often subtle, and were not consistent between the three species. In the second generation, larval survival estimated by 'pupation number/plant' on the tobacco plants with novel steroids was significantly reduced, while eclosion success was significantly lower for H. virescens. With respect to adult reproduction (i.e. egg production and egg viability) there were no observed differences in the first generation, but novel steroids significantly negatively impacted reproduction in the second generation. The findings from this study, when integrated into a simple population growth model, demonstrate the potential in using plants with modified steroids as a novel approach to manage populations of economically important caterpillar species.     

马尾松诱导抗性对马尾松毛虫幼虫生长发育的影响

利用不同受害方式和受害程度的马尾松 (PinusmassonianaLamb.)针饲养马尾松毛DendrolimuspunctarusWalker虫幼虫 ,研究受害松针对幼虫生长发育的影响。结果表明 :马尾松毛虫取食受害松针后 ,幼虫的取食量下降 ,排粪量减少 ,对食物的消耗和利用指数降低 ,幼虫发育速率缓慢 ,死亡率增加 ,从而影响马尾松毛虫的种群动态     

Traditional Regulation of Edible Caterpillar Exploitation in the Kopa Area of Mpika District in Northern Zambia

The Traditional Ecological Knowledge (TEK) of the Bisa people of northern Zambia on species, life cycles and host plants of the caterpillars they exploit for food and for household income generation, and the traditional control of caterpillar harvesting, were investigated through a household survey. The accessed indigenous knowledge on caterpillar biology was validated through a forest survey, caterpillar collections and identifications. Eight species of caterpillars were harvested from the surrounding miombo woodlands. Their life systems and host plants were well understood by members of local communities and this knoweldge was communicated amongst them orally. Popular commercial species were Gynanisa maya Strand and Gonimbrasia zambesina Walker. Over 20 miombo tree species hosted the two species but the mean numbers of the caterpillars on Julbernadia paniculata Troupin were significantly larger than those on other host plants (p < 0.05), indicating that J. paniculata was probably the main host plant of the two species. Traditional regulation of caterpillar harvesting involved: (i) monitoring for edible caterpillar development and abundance and for changes in caterpillar habitats, (ii) protection of host plants and moth eggs against late bush fires, through use of traditional fire technology, and (iii) temporal restriction of edible caterpillar harvesting. The possibility of the Zambian Government promoting caterpillar harvesting as an economic incentive to the Bisa people to conserve both this renewable edible caterpillar natural resource and their environment is discussed.     

Modeling Spruce Budworm Population Revisited: Impact of Physiological Structure on Outbreak Control

Understanding the dynamics of spruce budworm population is very important for the protection of spruce and balsam fir trees of North American forests, and a full understanding of the dynamics requires careful consideration of the individual physiological structures that is essential for outbreak control. A model as a delay differential equation is derived from structured population system, and is validated by comparing simulation results with real data from the Green River area of New Brunswick (Canada) and with the periodic outbreaks widely observed. Analysis of the equilibrium stability and examination of the amplitudes and frequencies of periodic oscillations are conducted, and the effect of budworm control strategies such as mature population control, immature population control and predation by birds are assessed. Analysis and simulation results suggest that killing only budworm larvae might not be enough for the long-term control of the budworm population. Since the time required for development during the inactive stage (from egg to second instar caterpillar) causes periodic outbreak, a strategy of reducing budworms in the inactive stage, such as removing egg biomass, should also be implemented for successful control.     

Effects of environmental humidity on the survival and development of pine caterpillars, Dendrolimus tabulaeformis (Lepidoptera: Lasiocampidae)

The pine caterpillar, Dendrolimus tabulaeformis is one of the most important pests on Pinus tabulaeformis and other pine species in North China. In the present study, effects of relative humidity (RH) on the development and survival of pine caterpillars and soil moisture (SM) on their diapausing larvae were investigated. Low RH (20%) deferred the development of eggs and larvae, reduced egg hatching and larval surviving compared to 40%, 60% and 80% RH. Both low (20%) and high (100%) RH reduced egg hatching, but only 20% RH deferred the development of larvae, prolonged developmental duration and reduced the body mass and body length of larvae. The SM influenced the survival of diapausing larvae significantly. The dry treatment significantly reduced the supercooling points (SCPs), whereas increased the mortality and reduced body mass from 56.9 to 36.5 mg and body water content from 78% to 63% after 2 weeks' exposure. Therefore, higher RH is more favorable for the development of early instars and survival of diapausing larvae of the pine caterpillars.     

Heat resistance of the eggs of a mulberry silkworm strain adapted to a subtropical climate]

The heat stability of the eggs of a polyvoltine strain of Bombyx mori occurring in the conditions of hot climate was studied. No marked differences between this strain and the moderate climate strains were found in the level of heat stability and the character of its age changes. The mechanisms of heat stability upon the diapause-less egg development are discussed.     

Host color preferences and short-range searching behavior of the egg parasitoid Trichogramma ostriniae

The color of lepidopteran eggs often varies by species or egg condition, and parasitoids that attack lepidopteran eggs could therefore potentially use color to obtain information about host identity or quality. The objective of our study was to determine whether females of the egg parasitoid Trichogramma ostriniae Pang & Chen (Hymenoptera: Trichogrammatidae) showed differential responses to egg color when searching for hosts over short distances and when evaluating the suitability of encountered eggs. We examined the wasps’ host‐selection behavior in a Petri dish arena using white, yellow, green, and black clay beads as egg models presented against a green background (to mimic leaf color). In no‐choice tests, bead color had a significant effect on the proportion of tested wasps that accepted a bead for further examination, on the time it took wasps to find and begin examining a bead, and on the time that wasps spent examining the beads. However, bead color had only a marginally significant effect on the proportion of wasps attempting to drill into a bead with their ovipositors, and no significant effect on the amount of time they spent drilling. The wasps also showed significant color preferences when given a choice between two adjacent beads of different colors. The results of the no‐choice and choice trials taken together indicated a color preference ranking of yellow > white > green > black. The wasps’ higher preference for the yellow and white egg models generally corresponds to the white or yellowish‐white egg color of T. ostriniae's target host, the European corn borer moth, Ostrinia nubilalis Hübner (Lepidoptera: Crambidae). The wasps’ strong rejection of black egg models is likely to be an adaptive response that reflects the fact that eggs that are wholly or partially black are often unsuitable for parasitization due to advanced caterpillar development, damage to the egg, or previous parasitization.     

Population fluctuations of the western tent caterpillar in southwestern British Columbia

Cyclic populations of western tent caterpillars fluctuate with a periodicity of 6–11 years in southwestern British Columbia, Canada. Typically, larval survival is high in early stages of the population increase, begins to decline midway through the increase phase, and is low through several generations of the population decline. Fecundity is generally high in increasing and in peak populations but is also reduced during the population decline. Poor survival and low fecundity for several generations cause the lag in recovery of populations that is necessary for cyclic dynamics. The dynamics of tent caterpillar populations vary among sites, which suggests a metapopulation structure; island populations in the rainshadow of Vancouver Island have more consistent cyclic dynamics than mainland populations in British Columbia. Sudden outbreaks of populations that last a single year suggest that dispersal from source to sink populations may occur late in the phase of population increase. Wellington earlier discussed qualitative variation among tent caterpillar individuals as an aspect of population fluctuations. The variation in caterpillar activity he observed was largely statistically nonsignificant. Recent observations show that the frequency of elongate tents as described by Wellington to characterize active caterpillars varies among populations but does not change in a consistent pattern with population density. The level of infection from nucleopolyhedrovirus (NPV) was high in some populations at peak density but was not associated with all population declines. Sublethal infection can reduce the fecundity of surviving moths, and there is a weak association between viral infection and egg mass size in field populations. The impact of weather in synchronizing or desynchronizing populations is a factor to be investigated further. Received: May 25, 1999 / Accepted: March 28, 2000     

家蚕保存系统红色卵的遗传分析

用遗传背景清楚的家蚕Bombyx mori红卵（re）、白卵(w-2、pe)、第4褐卵（b-4）的标志基因系统和正常型黑卵系统与我国家蚕基因库保存的20个红色卵系统杂交,进行顺反测验,分析了它们的卵色支配基因及遗传规律。结果发现：①在03-310系统中存在家蚕卵色新突变pink egg,与红卵re 等位,基因符号为re^p,表型特征为：卵淡红色,成虫蛾眼也为淡红色;②6个系统为红卵（re）的纯合系统,还有５个系统除具有re／re基因型外,还具有支配白色卵或浅红色或橙红色卵的突变基因;③２个系统为第4褐卵（b4）的纯合系统; ④6个系统的红褐色卵为母性影响遗传;⑤发现家蚕卵色基因b-4和r-e的互补关系,b-4/b-4 re/re基因型表现为新的卵色——橙黄色。     

The effect of low level ionizing radiation on embryogenesis of silkworm,Bombyx mori L.

Summary The effect of chronic radiation, 100, 1000 and 4000 times exceeding the natural background radiation, on embryogenesis of silkworm,Bombyx mori has been investigated. It is shown that low level ionizing radiation shortens by several hours the period of embryogenesis while the larva mass increases as the development proceeds. A single preincubational exposure of silkworm eggs to a dose of 2 Gy increases the mass of larvae as well as the cocoon shell weight, silk-bearing and the raw silk production.