A nonpeptide provides insight into mechanisms that regulate Drosophila melanogaster heart contractions

Here we report the effect of a nonpeptide, benzethonium chloride (bztc), on Drosophila melanogaster larval, pupal, and adult heart rates in vivo. Benzethonium chloride reduced the frequency of spontaneous contractions in the D. melanogaster pupal heart, but not in the larval heart or the adult heart as measured in noninvasive whole animal preparations. When applied directly to the D. melanogaster heart, in the absence of hemolymph, bztc reduced the frequency of spontaneous contractions in larval, pupal, and adult hearts. These findings are consistent with the conclusion that bztc acts through or is regulated by different mechanisms in these three developmental stages. An alternative explanation is that larval hemolymph and adult hemolymph contain a material that interferes with the effect of the nonpeptide on heart contractions. Bztc mimicked the effect of the peptide dromyosuppressin (DMS) on the heart at an equivalent concentration; in contrast, 103-fold more nonpeptide is required to mimic the effect of DMS on fly gut. These findings are consistent with the presence of tissue-specific myosuppressin receptors or mechanisms.     

Body size and cell size in Drosophila: the developmental response to temperature

In Drosophila, like most ectotherms, development at low temperature reduces growth rate but increases final adult size. Cultures were shifted from 25 degrees C to low (16.5 degrees C) or to high (29 degrees C) temperature at regular intervals through larval and pupal stages, and the flies of both sexes showed an increase or decrease, respectively, in the size of thorax, wing and abdominal tergite. Size changes in the wing blade resulted from changes in the size of the epidermal cells (with only a small increase in cell number in males reared at low temperature). The temperature-shifts became less effective as they were made at successively later developmental stages, demonstrating a cumulative effect of temperature on adult size. The thorax and wing develop from the same imaginal disc, with most cell division occurring in larval stages, but they differ in timing of temperature sensitivity, which extends only to pupariation or into the late pupal stage, respectively. Growth of the adult abdomen occurs largely after pupariation but its size is temperature-sensitive through both larval and pupal stages. We discuss growth control in Drosophila and the likely effects of temperature on food assimilation, growth efficiency and allocation of nutrients to the production of different tissues.     

幼虫密度对甜菜夜蛾生长发育与繁殖的影响

为了研究甜菜夜蛾Spodoptera exigua(Hübner)幼虫的密度对其发育及繁殖的影响,本实验观察了5种幼虫密度下（1,5,10,20,30头/瓶）,幼虫发育和成虫繁殖情况。结果表明：幼虫和蛹历期、存活率和蛹重均差异显著。幼虫和蛹历期均以20头/瓶的最短,1头/瓶的最长,其余随幼虫密度增加而延长;幼虫至蛹存活率以10头/瓶的最高,其余随幼虫密度增加而降低;1头/瓶的蛹最重,显著高于其他密度的,其余随幼虫密度增加而下降。尽管密度间成虫羽化率和产卵前期均无显著差异,但成虫产卵量、寿命和畸形率差异显著。1头/瓶的产卵量最多,其次为10头/瓶的,其余随幼虫密度增加而减少,30头/瓶的产卵量显著少于其他密度的; 密度在1～20头/瓶范围内,雌蛾寿命均较短,显著短于30头/瓶的,而雄蛾寿命以5头/瓶的最短,显著短于其他密度的（10头/瓶除外）,10头/瓶的次之,其余密度间差异不显著;不同幼虫密度下羽化的成虫畸形率差异显著,10头/瓶的最低,其余随幼虫密度增加而升高; 生命表结果表明甜菜夜蛾在10头/瓶下世代存活率和种群增长指数均最高,幼虫密度过低或过高均不利于种群增长;世代存活率（S）和种群增长指数（I）与幼虫密度之间的关系均呈抛物线关系：S =－0.2087x²+2.5694x+211.52 (R²=0.88),I=－0.0552x²+0.9166x+54.168 (R²=0.95)。结果提示幼虫密度影响甜菜夜蛾种群动态的重要生态因子之一。     

Studies of transovum and transstadial transmission of a granulosis virus of the codling moth

Capsules of a granulosis virus of the codling moth were never found in codling moth eggs, although they were observed in the larval, pupal, and adult stages. However, eggs obtained from a British Columbia codling moth colony were found to have virus on the egg surface.Transstadial transmission of the virus from the larval to the pupal stage occasionally occurred after intact capsules had been inoculated per os into the larva. The virus was also occasionally transmitted from the pupal to the adult stage, but only after virions had been injected into the hemocoel of the pupa.Fertile eggs obtained from virus-injected insects were not shown to contain active virus. Eggs were tested by maceration in antiserum, by the fluorescent-antibody technique, and by bioassay of their contents.Only one larva of the F₁ and F₂ generations obtained from virus-injected insects succumbed to granulosis even when the larvae were exposed to various types of stressors.Circumstantial evidence supports the hypothesis of transovum transmission, but such transmission cannot be attributed to injections of virus into larvae and pupae in this study.     

幼虫密度对草地螟生长发育及繁殖的影响

为了明确幼虫密度对草地螟Loxostege sticticalis种群增长的影响, 对室内条件下（温度22±1℃, RH 70%±5%, 光周期16L∶ 8D）不同幼虫密度[1, 10, 20, 30和40头/瓶（650 mL）］饲养的草地螟生长发育及繁殖进行了研究。结果表明: 幼虫密度对草地螟幼虫体色、 发育历期和存活率, 以及蛹重和成虫生殖等有显著影响。随着幼虫密度的增加, 幼虫体色黑化程度呈增强趋势, 幼虫密度大于10头/瓶时的体色黑化值均显著大于幼虫密度为1头/瓶时的体色黑化值（P<0.05）。20头/瓶的幼虫和蛹历期最短, 且随幼虫密度的增加而显著延长（P<0.05）。幼虫存活率以10头/瓶最高, 其他幼虫密度的幼虫存活率显著较低（P<0.05）。蛹重以1头/瓶的最重, 并随幼虫密度增加而显著下降（P<0.05）。成虫产卵量和交配率分别以1和20头/瓶的幼虫密度最高, 幼虫密度升高则产卵量、 交配率逐渐降低。成虫产卵历期随着幼虫密度的增加逐渐缩短。雌、 雄蛾寿命分别以10和20头/瓶幼虫密度时最长, 幼虫密度过高时雌雄蛾寿命又显著缩短（P<0.05）。生命表分析表明, 幼虫密度对草地螟种群增长指数有显著影响, 以10头/瓶幼虫密度的种群增长指数最高, 幼虫密度过高或过低时种群增长指数下降。据此认为, 幼虫密度是影响草地螟种群增长的重要因子之一。     

Effects of larval competition on survival and growth in Mediterranean fruit flies

1. Larval success was compared when one, two, or three egg clutches were laid in kumquat fruits (≈ 10 ml in volume) either successively on the same day or at the rate of one clutch per day. 2. Increased clutch density was associated with a significant decrease in larval survival rate and non‐significant decreases in larval growth rate and pupal mass. 3. Larval and pupal parameters showed significantly larger variance when clutches were laid on successive days than on the same day, suggesting a competitive advantage for older larvae over younger larvae. 4. The results suggest that, in small fruit, reduced fitness due to larval competition may act against possible fitness benefits due to social facilitation among adult females, hence reducing the likelihood of non‐linear population dynamics caused by processes such as the Allee effect.     

Maturation and degeneration of the fat body in the Drosophila larva and pupa as revealed by morphometric analysis

Using morphometric and cytochemical techniques we have described changes taking place in the fat body cells during three different stages of development. The cell number remains constant at about 2200 cells during larval life and then decreases gradually and continuously throughout metamorphosis and the first 3 days of the adult stage until no more cells can be observed. Cell size increases rapidly during the larval period and decreases steadily during metamorphosis and adult stage. The size of the nuclei increases during the larval instars and decreases during the pupal interval. The change in nuclear size is correlated with the amount of DNA present throughout development implying the nuclear DNA is synthesized during the larval period and degraded gradually during metamorphosis. The cell size changes are due in large part to accumulation or loss of reserve substances: lipid droplets, glycogen deposits and protein granules. During metamorphosis the amount of lipid decreases slightly whereas glycogen experiences two loss cycles. The protein granules in the form of lysosomes continue to increase in amount during the first day of metamorphosis because of a short period of massive autophagy. Then the lysosomes decrease in amount throughout the remainder of metamorphosis. The lysosomes stain positively for lipofuscin.     

Metamorphic changes in the central projects of hair sensilla inTenebrio molitor L. (Insecta: Coleoptera)

Summary This paper describes the afferent projections of hair sensilla of the pro- and mesothoracic legs and the lateral thoracic sclerites of larval and adultTenebrio molitor and the corresponding set of pupal hair sensilla. The sensory neurons that innervate the hair sensilla of larval or adult insects project somatotopically into the thoracic neuropil. Different types of sensilla on the same region of the body surface project to the same zone of the ipsilateral thoracic ventral neuropil but exhibit different arborization patterns. Although there is a profound reorganization of body surface sensilla, the basic somatotopic layout of the larva is maintained in the adult. The sensory neurons that innervate the pupal hair sensilla possess central projections similar to those of the corresponding adult sensory neurons. The central projections of pupal sensory neurons are somatotopically oriented. Their projection pattern is serially homologous in the thoracic and the abdominal ganglia. The central projection pattern of the described pupal sensory neurons is constant throughout pupation. MAb 22C10 immunoreactivity allows an estimate of the timing of the early differentiation of the imaginal sensory neurons originating during pupation. Ablation experiments indicate that pupal sensory neurons influence the central projection pattern of the differentiating imaginal sensory neurons.     

Neuronal control of heart reversal in the hawkmoth Manduca sexta

Cardiograms demonstrate that heart activity of Manduca sexta changes from larva, to pupa, to adult. The larval heart has only anterograde contractions. During metamorphosis, heart activity becomes a cyclic alternation of anterograde and retrograde contractions. Thus, the adult heart has both an anterograde and a retrograde pacemaker. External stimuli also can initiate cardiac reversal. Cardiac reversal is blocked by tetrodotoxin, indicating that reversal is under neuronal control. A branch of each dorsal nerve 8 innervates the posterior chamber of the heart, the location of the anterograde pacemaker. Only retrograde contractions occur when dorsal nerves 8 are cut. Stimulation of ml(-1) 8 initiates anterograde contractions; when stimulation ceases, the heart reverses to retrograde contractions. These experiments indicate that the anterograde pacemaker receives neural input that makes it the dominant pacemaker. In the absence of neural input this pacemaker is inactive, and the retrograde pacemaker becomes active. Application of crustacean cardioactive peptide accelerates the heart but does not eliminate cardiac reversal. The terminal chamber of the heart is also innervated by a branch of each dorsal nerve 7; stimulation of this nerve increases the strength of contraction of the terminal chamber but has no effect on contractions of the remainder of the heart or on cardiac reversal.     

Reprogramming in the absence of DNA synthesis in Galleria larval epidermis.

Larval epidermal cells from a day-1 penultimate instar Galleria larva on implantation into day-5 last instar larva metamorphose and deposit a pupal cuticle at the same time as the host pupates. DNA synthesis in the implanted larval cell was monitored with 3-H-thymidine. Various regimens of 3-H-thymidine application were used and under no conditions did the larval cells incorporate label during the period from implantation to deposition of pupal cuticle. This suggests that a wax moth larval ectoderm cell can reprogram its genome to secrete a pupal cuticle without a precedent cell division.     

Seasonal plasticity in growth and development of the speckled wood butterfly, Pararge aegeria (Satyrinae)

Regulation of growth and development by photoperiod was studied in a population of the speckled wood butterfly, Purarge aegeria L. (Lepidoptera: Satyrinae), from southern Sweden. Individuals were reared in a range of photoperiodic regimes (9L. to 22L) and temperatures (13°C to 21° C). Plasticity was found for important life-history traits- generation time, growth rate and final weight and seasonal regulation of development in response to photoperiod was found to occur at two levels. Purarge aegeria hibernates as a third instar larva or in the pupal stage, cantering one of four major developmental pathways in response to photoperiod: (1) direct development in both the larval and pupal stages, (2) pupal winter diapause with or (3) without a preceding larval summer diapause, or (4) larval winter diapause. In addition to this high-level regulation of individual development, larval growth rate and pupal development rate also appear to be finally regulated by photoperiod within each major pathway. As photoperiods decreased from 22 h to 17 h at 17° C, growth rate among directly developing larvae increased progressively, as was the case for larva? developing according to a univoltine life cycle from 17 h to 14 h. At two photoperiods, 13 h and 16 h (corresponding to shifts between major pathways), both larval and pupal development were extremely variable with the fastest individuals developing directly and the slowest developing with a diapause. This indicates a gradual nature of diapause itself, suggesting that the two level may not he fundamentally different.     

GENESIS OF MITOCHONDRIA IN INSECT FAT BODY

Electron microscopy and stereological methods have been used to study the time course and mechanism of mitochondrial genesis in the adult fat body of Calpodes ethlius, (Lepidoptera, Hesperiidae). Most of the larval mitochondria are destroyed during a phase of autolysis shortly before pupation, so that pupal and early adult fat body cells have few mitochondria. The number of mitochondria per cell increases rapidly at the end of the 1st day after the adult emerges. Characteristic partitioned mitochondria appear during the period when the number is rapidly increasing. This evidence, coupled with the results of morphometric analyses of mitochondrial diameter, volume, and surface area, confirms the view that the genesis of adult mitochondria involves the growth and division of mitochondria surviving from the larva.     

Regulation of drosophila folylpolyglutamates during development

The polyglutamate status of reduced folates during the larval, pupal and adult stages of Drosophila melanogaster development was investigated. The chain length distribution is very similar and is predominantly pentaglutamate. Half-life estimates of the hydrolytic degradation to the monoglutamate showed larva < pupa < adult. This raises the possibility that polyglutamate hydrolase may have a role in regulating the total intracellular reduced folate content of the different developmental stages.     

PROTEIN AND NUCLEIC ACID METABOLISM IN INSECT FAT BODY

1. The appearance of larval fat body as seen under the light or electron microscope depends on the nutritional state of the larva and on the stage of larval development at which the fat body is observed. 2. Early in the last larval instar the cells usually possess a well-developed endo-plasmic reticulum rich in ribosomes, numerous mitochondria, glycogen granules, a Golgi complex and fat droplets, while later in the instar the endoplasmic reticulum is much reduced and mitochondria are few, but glycogen and fat droplets are present in greater amount together with the appearance of large numbers of proteinaceous spheres. 3. Early in the last instar the fat body synthesizes proteins and exports them into the blood, while later in the instar proteins are sequestered from the blood into the fat body. 4. The rate of protein synthesis by the fat body is high in the early to mid part of the last instar, but then falls off rapidly to a low level, at which it remains until the larva pupates. In diapausing pupae, protein synthesis remains at this low level. 5. The similarity between the electrophoretic patterns of proteins from the fat body and those from the blood provides strong evidence that the fat body is the site of synthesis of many of the blood proteins. 6. Some of the blood proteins have been shown to possess enzymic properties, while others are thought to play a role in the transportation of various types of compounds. 7. Ecdysone and juvenile hormone both stimulate the rate of protein synthesis by larval fat body. Protein synthesis in fat body from diapausing pupae is stimulated after injury to the pupae. 8. The appearance of adult fat body and the amount of protein it contains is often closely linked with the nutritional and reproductive states of the insect. 9. An important role of the fat body in the adult female insect is the synthesis of yolk proteins, which are released into the blood and then taken up by the developing oocytes. This synthesis and uptake are under the control of hormones secreted by the corpora allata and by the median neurosecretory cells of the pars intercerebralis. 10. The RNA content of fat body in final-instar larvae is not constant throughout the instar. In some larvae it is at its highest level early in the instar, falling to a low level as the instar progresses, while in other larvae (e.g. Calliphora) the level of RNA in fat body does not decrease as the instar progresses. 11. In some dipterous insects the base composition of total RNA is DNA-like in that the guanine + cytosine content is low, accounting for 40 % of the bases. A similar composition is seen in rapidly labelled RNA isolated from insects of other orders (Coleoptera and Lepidoptera), but the base content of total RNA from these latter insects resembles ribosomal RNA from vertebrate tissues in that it has a high (ca. 60 %) guanine + cytosine content. 12. The RNA/DNA ratios in blowfly larval tissues are high compared with those found in any vertebrate tissue. 13. In larval fat body, RNA synthesis is low at the time of a moult, increases during the early and mid-instar period and subsequently falls during the latter part of the instar. During the pupal period, especially during pupal diapause, the rate of RNA synthesis is very low and then increases during the subsequent development of the pharate adult. Injury to diapausing pupae results in an increased rate of RNA synthesis in most of their tissues. 14. Ecdysone and juvenile hormone both stimulate RNA and DNA synthesis in larval and adult fat body and in other tissues, although there is evidence that in some tissues these two hormones may act antagonistically to each other. The insecticide DDT also has been shown to stimulate RNA synthesis in tissues of adult insects.     

Life-cycle nitrogen budget for the gypsy moth, Lymantria dispar, reared on artificial diet

Lymantria dispar larvae were reared on a wheat germ-based artificial diet from egg eclosion until pupation. Utilization efficiency of dietary nitrogen underwent an age-specific decrease from 75% in the first instar to 54 and 43% for last-instar female and male larvae, respectively. Relative rates (mg/day/mg biomass) of nitrogen consumption and assimilation also decreased during larval development, but the excretion rate of nitrogen was constant for all instars and both sexes. Larval % nitrogen decreased as the larvae matured, while the percentage in the frass increased. These data suggest that need for nitrogen decreases as the larva matures. While L. dispar is comparatively inefficient at assimilating dietary nitrogen, over one-half of that assimilated by the female larva is transferred to egg production by the adult.     

Reproductive under-performance of tsetse flies in the laboratory, related to feeding frequency

Abstract. The rates of development of the eggs and larvae in utero and the next two developing ovarioles were measured by ovarian dissection on each day of the pregnancy cycle in tsetse, Glossina morsitans, subject to different feeding regimes. Compared with flies fed four times per pregnancy cycle, flies fed three times per cycle showed a lower pupal production rate (70%), the same (zero) adult mortality, a slightly slower growth rate of the larva and second ovariole only from day 8 onwards, but the same growth rate of the first ovariole. Flies fed only twice per pregnancy cycle produced no pupae, suffered 18% adult mortality and showed a significantly slower growth rate of the larva and second ovariole from days 6 and 7 respectively, but still the growth rate of the first ovariole was barely affected. Flies offered food three times or twice per pregnancy cycle engorged fully at every opportunity, but 16.5% of the flies offered food four times per cycle did not feed on every occasion, while 12–22% did not engorge fully on days 3, 5 or 7. In assessing the applicability of these laboratory results to the field situation the following points must be borne in mind: in the laboratory flies take smaller mean blood meals than in the field; during protein production associated with larval growth the proportion of the blood meal lost to transformation and excretory costs is less than during normal lipid metabolism; the balance between the tsetse's known fertility rate and adult and pupal mortality rates reveals that the abortion rate in the field must be extremely low. The high abortion rates usually observed in laboratory colonies, even when flies are offered food daily_l would be quite untenable in the field and indicate that laboratory conditions impose physiological stresses on the flies that are quite different from those in the field. These facts indicate that three field-sized meals may be sufficient to meet the energy demands of normal larval development in the field.     

Sphingomyelinase activity in mother's milk is essential for juvenile development: a case from lactating tsetse flies

Sphingosine is a structural component of sphingolipids. The metabolism of phosphoethanolamine ceramide (sphingomyelin) by sphingomyelinase (SMase), followed by the breakdown of ceramide by ceramidase (CDase) yields sphingosine. Female tsetse fly is viviparous and generates a single progeny within her uterus during each gonotrophic cycle. The mother provides her offspring with nutrients required for development solely via intrauterine lactation. Quantitative PCR showed that acid smase1 (asmase1) increases in mother's milk gland during lactation. aSMase1 was detected in the milk gland and larval gut, indicating this protein is generated during lactation and consumed by the larva. The higher levels of SMase activity in larval gut contents indicate that this enzyme is activated by the low gut pH. In addition, cdase is expressed at high levels in the larval gut. Breakdown of the resulting ceramide is likely accomplished by the larval gut-secreted CDase, which allows absorption of sphingosine. We used the tsetse system to understand the critical role(s) of SMase and CDase during pregnancy and lactation and their downstream effects on adult progeny fitness. Reduction of asmase1 by short interfering RNA negatively impacted pregnancy and progeny performance, resulting in a 4-5-day extension in pregnancy, 10%-15% reduction in pupal mass, lower pupal hatch rates, impaired heat tolerance, reduced symbiont levels, and reduced fecundity of adult progeny. This study suggests that the SMase activity associated with tsetse lactation and larval digestion is similar in function to that of mammalian lactation and represents a critical process for juvenile development, with important effects on the health of progeny during their adulthood.     

Reciprocal transplantation of wing discs between a wing deficient mutant (fl) and wild type of the silkworm, Bombyx mori

The wingless mutant flügellos ( fl ) of the silkworm lacks all four wings. Although wing discs of the fl seem to develop normally until the fourth larval instar, wing morphogenesis stops after the fourth larval ecdysis, probably caused by aberrant expression of an unidentified factor, referred to as fl . To characterize factor fl , the wing discs dissected from the wild-type (WT) and fl larvae were transplanted into other larvae and developmental changes of the discs were examined. When the wing disc from a WT larva was transplanted into another WT larva and allowed to grow until emergence, a small wing appeared that was covered with scales. Thus, the transplanted wing discs can develop autonomously, form scales and evert from adult skin. The WT wing discs transplanted into the fl larvae also developed at a high rate. However, the fl wing discs transplanted into the WT larvae did not develop during the larval to pupal developmental stages. These data suggest that the fl gene product (factor fl) works in the wing disc cells during wing morphogenesis. Its function cannot be complemented by hemolymph in the WT larva. It is also implied that the level of humoral factors and hormones required for wing morphogenesis are normally maintained in the fl larva.     

Morphological abnormalities and lethality in silkworm (Bombyx mori) larvae treated with high concentrations of insect growth-blocking peptide

Insect growth-blocking peptides (GBPs) exhibit growth-blocking and paralytic activity. Low concentrations of GBP stimulate larval growth, whereas high concentrations of GBP significantly retard larval growth. Here, we show that morphological abnormalities and lethality were induced in silkworm (Bombyx mori) larvae by high concentrations of GBP. Active B. mori GBP (BmGBP) was produced by treating recombinant proBmGBP (expressed in baculovirus-infected insect cells) with bovine factor Xa. When silkworm larvae on day 1 of the fifth-instar stage were injected between the seventh and eight abdominal segments with BmGBP (100 or 500 ng/larva), the larval–pupal and pupal–adult transformations of these silkworms were delayed in a dose-dependent manner. However, a high concentration (2000 ng/larva) of BmGBP or Spodoptera exigua GBP (SeGBP) acutely induced morphological abnormalities and death in silkworm larvae. In silkworm larvae treated with high concentrations of GBPs, the ingested food excessively accumulated in the foregut, which caused extreme swelling in both the thorax and the foregut and resulted in larval death. Therefore, these results not only provide insight into the effect of insect GBPs on gut physiology but also reveal a novel function of insect GBPs.