Growth and development of agnostids Pentagnostus proanabarensis Fedoseev, 1999

Juvenile development of the Middle Cambrian agnostid trilobite Pentagnostus proanabarensis Fedoseev, 1999 is studied. A sequence of eight juvenile stages is defined based on changes in morphology and measurements. Three of them belong to meraspid degree 0, another three refer to meraspid degree 1, and two represent early holaspid stages. Neither the frequency distribution of the length of cephalons and pygidia nor the length-width scatter diagrams give clear clusters of molts; the number of juvenile molts can be estimated through the analysis of the posteroaxis length distribution. Thus, the measurements and morphology of some juvenile pygidia with vestiges of the pleural and postaxial furrows allow reconstruction of the number of segments during individual growth. At the initial stage of development, the pygidial axis of P. proanabarensis probably had four segments, the pygidial axis increased up to no less than six segments in adults.     

Ontogeny of Agnostida

Evidence about ontogeny of the miomerid trilobite groups Eodiscina and Agnostina is summarizied and unified in terminology. There appear to be strong similarities in the juvenile development of both suborders. They both have prolonged meraspid degree 0 and 1 stages, including two to six molts. The degree 0 stage tends to shorten from six to four molts in Eodiscina, and probably from three to two in Agnostina, while degree 1 tends to lengthen whithin Eodiscina. During degree 0 and 1 moltings, none of the segments are liberated into the thorax, and one segment is added into the transitory pygidium. The liberation of thoracic segments marks the beginning of the meraspid degrees and the holaspid period. This developmental scenario contrasts with that of the classical polymerid—in the latter case, the liberation of thoracic segments is accompanied by insertion of new segments in the transitory pygidium. In the Eodiscina, during meraspid degree 2, the polymerid scheme is present.     

Effect of white grub developmental stage on susceptibility to entomopathogenic nematodes

The pathogenicity of the entomopathogenic nematodes Heterorhabditis bacteriophora Poinar and Steinernema scarabaei Stock & Koppenh?fer against different developmental stages of the Japanese beetle, Popillia japonica Newman, and the oriental beetle, Anomala (=Exomala) orientalis Waterhouse, were studied under laboratory conditions. The efficacy of S. scarabaei did not differ between second and third instars in P. japonica or A. orientalis or between small (young) and large (older) third instars in A. orientalis. However, H. bacteriophora efficacy decreased from first over second to third instar and also from small third instars to large third instars in A. orientalis but did not differ significantly between P. japonica larval stages. Once A. orientalis third instars had purged their intestines in preparation for pupation, no significant mortality by S. scarabaei and H. bacteriophora was observed. In contrast, P. japonica susceptibility to both nematode species gradually decreased from stage to stage from actively feeding third instars to pupae. In two additional experiments, we found no difference in Steinernema glaseri (Steiner) susceptibility between second and third instars of A. orientalis but an increase in S. scarabaei susceptibility from the second to third instar of Asiatic garden beetle, Maladera castanea (Arrow). Our observations combined with those of previous studies with other nematode and white grub species show that nematode efficacy against white grub developmental stages varies with white grub and nematodes species, and no generalization can be made.     

低温对小菜蛾实验种群的影响

研究了低温(<8℃)对小菜蛾的发育、存活和繁殖的影响结果表明,卵和蛹在4℃和6℃下死亡率随处理时间的延长而增加,在分别处理55d和70d后,卵和蛹全部死亡;经4℃和6℃处理的蛹,在16℃下羽化成虫的平均产卵量随处理时间的延长而减少,处理45d时,产卵量均为0小菜蛾幼期各虫态在0℃以下,死亡率随低温强度加大和处理时问的延长而增高就耐寒力而言,3龄幼虫和蛹最强,其次是2龄和4龄幼虫,卵和1龄幼虫的耐寒力最弱不同低温和时间处理小菜蛾幼期虫态对其后继虫态的发育历期有较大影响,总体说来,经过处理的小菜蛾幼期虫态,其后继虫态的发育历期普遍延长,一般处理某一虫态对其相邻虫态发育历期的影响最大小菜蛾蛹经低温处理后其羽化成虫的产卵量随着蛹期所经历低温强度的增强和时间延长而减少。     

Shifts in developmental diet breadth of Lymantria xylina (Lepidoptera: Lymantriidae)

The moth Lymantria xylina Swinhoe (1903) (Lepidoptera: Lymantriidae) is a major defoliator of hardwood and fruit trees in Taiwan. Although the plants identified as host plants of L. xylina usually refer to plants used as food or as shelter, most of the host plant identifications have not considered the role of these hosts on larval development. This study investigated various instars feeding on different plants to assess the developmental diet breath of L. xylina. Forty-seven plant species, belonging to 25 families were used in feeding trials. Various bioassays, including first instar survival and long-term feeding trials, indicated the most suitable host plants for the different developmental stages. Results of the first instar survival trial indicated that first instars could survive only on 13 of the tested plant species. In addition, first instars could only successfully grow to pupa on seven of these 13 test plants species. To assess the developmental diet breath shifts of this moth, 38 plant species (excluding those nine plant species that the first instars did not feed upon) were fed to third and fifth instars in long-term feeding trials. Survival to pupa was noted on 12 and 13 test plant species for the third and fifth instars, respectively. In short, we found that the larvae performed differently when fed on various host plants and that the host plant range increased with the larval stage. Therefore, it is necessary to adjust the host plant range of this moth and to consider host plant breadth together with the developmental stages of caterpillars.     

Stage-dependent effects of 20-hydroxyecdysone on DNA synthesis of corpus allatum cells in the silkworm,Bombyx mori

DNA synthesis in cells of the corpus allata (CA) of the silkworm, Bombyx mori, was studied immunocytochemically after in vivo labeling with 5-bromo-2'-deoxyuridine (BrdU); developmental changes during the 3rd, 4th, and last larval instars and effects of 20-hydroxyecdysone treatment were examined. During both the 3rd and 4th larval instars, the number of DNA-synthesizing cells fluctuated, and relatively low levels were observed during the middle stages. On day 0 of the last larval instar, the number of DNA-synthesizing cells per gland was 9.2, which then increased on day 1 and remained at levels ranging from 12.9 and 16.9 cells per gland. A major peak level (28 BrdU-labeled cells per gland) occurred on day 8, two days after larvae entered the wandering stage. When last instar larvae were fed 20-hydroxyecdysone-supplemented mulberry leaves starting on day 0 or 1, the number of DNA-synthesizing cells dramatically decreased to very low levels and these low levels were maintained throughout the remainder of the instar. However, no effect was observed when last instar larvae were fed 20-hydroxyecdysone-supplemented mulberry leaves starting on day 3, indicating the stage-specific action of 20-hydroxyecdysone. The mechanism by which 20-hydroxyecdysone treatment inhibits DNA synthesis of CA cells was further examined by using continuous in vitro BrdU labeling for a 2-day incubation. It was found that the decrease in responsiveness of DNA synthesis of CA cells of 20-hydroxyecdysone-treated larvae to stimulation by growth factors from hemolymph may have been, at least in part, responsible for the indirect inhibitory effects of 20-hydroxyecdysone.     

贵州寒武纪杷榔组Changaspis elongata Chien,1961个体发育研究及意义

根据采自贵州剑河辣子寨杷榔组的张氏虫Changaspis 296块标本,采用传统形态测量方法,对头部及躯干特征进行度量;结合散点图、简化主轴回归分析及线性拟合对比分析后,确认这些标本均为长形张氏虫Chang-aspis elongata的标本,厘定出从分节6期至成虫期共计12个连续个体发育序列,揭示其形态变化特点。从分节6期至10期,背壳长、头鞍长、头盖长和宽的增长幅度相对小;随着体节的增多,头盖长度与背壳长度的比值从50%减少至34%;随着头鞍长度的增长,头鞍前部及后部宽均呈线性关系的连续增长趋势;个体发育序列确认该种成虫期有17节胸节,不同以往认为的16节胸节。对比分析及线性拟合的数据比较论证,确认原为C.micropyge和C.placenta 2个种的特征应为C.elongata在个体发育变化中的种内差异,确认先前命名的这2种应为C.elongata的晚出同义名。     

Susceptibility of immature stages of Chrysoperla rufilabris (Neurop., Chrysopidae) to pyriproxyfen, a juvenile hormone analog

Effects of pyriproxyfen (Knack), a juvenile analog, at three concentrations (10, 50 and100 mg [AI]/l), on survival and development of all immature stages of Chrysoperla rufilabris (Burmeister), were determined in the laboratory. Pyriproxyfen significantly reduced the survival rates when eggs, first and third instars were treated, but not when the second instars and pupae were treated. When eggs were treated, the two higher concentrations reduced the eggs viability by 33.3–50%, and only 0.0–6.7% developed to adults. The lowest concentration of pyriproxyfen (10 mg [AI]/l) caused high mortality on third instars, not on other stages, indicating the third instar was the most vulnerable stage. Pyriproxyfen had significant effects on development for all immature C. rufilabris that successfully developed to adults with variations among the developmental stages and concentrations. The overall developmental duration from eggs to adults when eggs, first, and third instars were treated were 2.6–4.2, 2.4–4.1 respectively, and 6.0–7.1 d longer than those in water control, respectively. However, the overall developmental durations from eggs to adults were 0.5–1.2 d shorter than in water control when the second instars were treated with pyriproxyfen. The compatibility of pyriproxyfen with natural enemies in integrated pest management programs is discussed.     

Position of the labrum in agnostid trilobites

Specimens of Peronopsis and Ptychagnostus from the House Range of western Utah provide new information on the location of the labrum (hypostoma) of agnostid trilobites. A labral position as that described here, beneath the second glabellar lobe, has two implications: (1) anomalous cephalic muscle scars described by previous workers may be interpreted as attachment areas for labral muscles; and (2) the mouth probably migrated posteriorly in agnostids. Posterior displacement of the mouth was probably one of several feeding modifications associated with a pelagic mode of life.     

Apseudopsis adami, a new species of tanaidacean (Crustacea: Peracarida) from the NW Iberian Peninsula: postmarsupial development and remarks on morphological characters

A new species of apseudomorph tanaidacean, Apseudopsis adami sp. nov., is described, including intraspecific variation, from specimens collected in the seagrass meadows of O Grove inlet (NW Iberian Peninsula, NE Atlantic). The new species is characterized by the unique combination of the following characters: pointed rostrum with rounded shoulders, four ventral propodal spines on pereopod 1, and posterolateral pointed apophyses on pereonites 2–5, regardless of the developmental stage of the individual. Two juvenile stages were identified before reaching maturity; early juvenile limbs are scarcely ornamented in comparison to the adults. Advanced juveniles represent the vast majority of the studied population, and the limb ornamentation is similar to that of the adults. Males show two different cheliped morphologies. After a preparatory stage, females pass through a sequence of copulatory instars followed by intermediate stages in which the female loses the ovisac after manca release. The number of segments of the antennular and antennal flagella and uropod endopods, as well as the development and ornamentation of the mandibular palp, are meristic changes that occur during development and allow rapid identification of the developmental instar.     

Ontogeny of the Upper Cambrian (Furongian) Olenid trilobite Protopeltura aciculate (Angelin, 1854) from Skåne and Västergötland,Sweden

Abstract: The ontogeny of the trilobite Protopeltura aciculata (Angelin, 1854) is described on the basis of material from the upper Cambrian (Furongian) of Andrarum (Skåne) and Hjelmsäter (Västergötland), Sweden. P. aciculata is present in the Parabolina brevispina and Parabolina spinulosa zones. Protopeltura aciculata is represented by all stages of growth, from early protaspides to holaspides, although most of the specimens are disarticulated and precise degrees are unknown. The cranidia have therefore been allocated to five morphological groups. Cuticular sculpture of the cranidia changes throughout ontogeny. Large tubercles are present in earlier stages, disappear gradually in middle meraspid stages and are replaced with a very faint granulation. The transitory pygidium, relatively large and shield‐shaped with upwardly and backwardly directed marginal spines in early meraspides, later becomes very small, triangular‐shaped and lacking spines as a late meraspid and holaspid. The development of hypostomes and librigenae is also described. Protopeltura aciculata shows major intraspecific variations throughout development, especially regarding the pygidium where variation is much less constrained than in many other olenids. This high developmental plasticity may be a survival strategy for a trilobite living in a stressed environment. Protopeltura inhabited a dysoxic environment, possibly unusually prone to localised spreading of anoxic or toxic water. Some morphs may have been less vulnerable than others to such stresses, surviving by chance and thus enabling the species to continue.     

Temporal changes in DNA synthesis of prothoracic gland cells during larval development and their correlation with ecdysteroidogenic activity in the silkworm, Bombyx mori

DNA synthesis in prothoracic gland cells of the silkworm, Bombyx mori, was studied immunocytochemically after in vivo labeling with 5-bromo-2'-deoxyuridine (BrdU), and its developmental changes during the 3rd, 4th, and last larval instars were examined. During the early stages of both the 3rd and 4th larval instars, a dramatic increase in the number of DNA-synthesizing cells of the prothoracic glands was detected. However, during the latter stages of each instar, the number of DNA-synthesizing cells greatly decreased. The determination of glandular protein content showed that dramatic increases occurred during the latter stages of each larval instar. Comparison of changes in prothoracic gland cell DNA synthesis with ecdysteroidogenic activity showed that the increase in DNA synthesis precedes ecdysteroidogenesis. The cellular mechanism underlying changes in prothoracic gland cell DNA synthesis during the last two larval instars was further analyzed by determining the in vitro DNA synthesis of the glands, their responsiveness to hemolymph growth factors, and changes in the growth-promoting activity of hemolymph during development. It was found that both growth factors and the responsiveness of the prothoracic gland cells to growth factors from hemolymph may play roles in regulating DNA synthesis of gland cells.     

Morphology and ontogeny of the eodiscoid trilobite Sinodiscus changyangensis from the lower Cambrian of South China

Abstract: A large number of complete specimens together with numerous disarticulated sclerites of the eodiscinid trilobite Sinodiscus changyangensis Zhang in Zhou et al., 1977 have been collected from the lower Cambrian Shuijingtuo Formation in Changyang, Hubei Province, South China. An ontogenetic series is established based on the immature and mature exoskeletons including the previously unknown protaspides and meraspides, in particular. No further substages can be differentiated in the protaspid specimens herein. Changes that took place during the meraspid period include the addition of postcephalic segments and prominent pygidial larval notches in early meraspid development which became progressively less distinct and disappeared in degree 2. Two holaspid stages are recognized based on the addition of a new pygidial segment, indicating that the start of the holaspid phase preceded the onset of the epimorphic phase and accordingly, its developmental mode is attributed to the protarthrous pattern. The trunk segmentation schedule of S. changyangensis is discussed, which is similar to other primitive eodiscoid trilobites, that is, as the boundary between the thorax and pygidium migrated posteriorly, there is no change in the number of the trunk segments. The processes of liberation of the thoracic segment and segment insertion into the pygidium are separated from one another, and the two different mechanisms, somitogenesis and tagmosis, progress independently during the ontogenetic development of the postcephalic region of these primitive eodiscinids.     

Postembryonic development of Tanystylum bealensis (Pycnogonida, Ammotheidae) from Barkley Sound, British Columbia, Canada

All developmental stages of Tanystylum bealensis are described. This is the first complete developmental series of a pycnogonid species collected from a natural, rather than a laboratory-reared population. Development proceeds through a series of nine instars from egg to adult, with major defining characteristics of the instars being the addition of walking legs, loss of chelifores, and modification of larval appendages into adult palps and ovigers. All stages are free-living on the hydroid Plumularia setacea, except for the first instar (protonymphon), which remains on the ovigers of the adult male for a short time after hatching. Development in T. bealensis is compared to development in both the closely related species T. orbiculare and to the more distantly related Achelia alaskensis.     

Population growth and development of the psocid Liposcelis rufa (Psocoptera: Liposcelididae) at constant temperatures and relative humidities

We investigated the effects of eight temperatures (22.5, 25.0, 27.5, 30.0, 32.5, 35.0, 37.5, and 40.0 degrees C) and four relative humidities (43, 55, 63, and 75%) on population growth and development of the psocid Liposcelis rufa Broadhead (Psocoptera: Liposcelididae). L. rufa did not survive at 43% RH, at all temperatures tested; at 55% RH, at the highest four temperatures; and at 63% RH and 40.0 degrees C. The greatest population growth was recorded at 35.0 degrees C and 75% RH (73-fold growth). At 40.0 degrees C, L. rufa populations declined or barely grew. L. rufa males have two to four nymphal instars, and the percentages of males with two, three, and four instars were 31, 54, and 15%, respectively. Female L. rufa have two to five instars, and the percentages of females with two, three, four, and five instars were 2, 44, 42, and 12%, respectively. The life cycle was shorter for males than females. We developed temperature-dependent developmental equations for male and female eggs, individual nymphal, combined nymphal, and combined immature stages. The ability of L. rufa to reproduce at a relative humidity of 55% and temperatures of 22.5-30.0 degrees C and at relative humidities of 63-75% and temperatures of 22.5-37.5 degrees C, in addition to being able to survive at 40.0 degrees C, suggests that this species would be expected to have a broader distribution than other Liposcelis species. These data provide a better understanding of L. rufa population dynamics and can be used to help develop effective management strategies for this psocid.     

Developmental constraints in cave beetles

In insects, whilst variations in life cycles are common, the basic patterns typical for particular groups remain generally conserved. One of the more extreme modifications is found in some subterranean beetles of the tribe Leptodirini, in which the number of larval instars is reduced from the ancestral three to two and ultimately one, which is not active and does not feed. We analysed all available data on the duration and size of the different developmental stages and compared them in a phylogenetic context. The total duration of development was found to be strongly conserved, irrespective of geographical location, habitat type, number of instars and feeding behaviour of the larvae, with a single alteration of the developmental pattern in a clade of cave species in southeast France. We also found a strong correlation of the size of the first instar larva with adult size, again regardless of geographical location, ecology and type of life cycle. Both results suggest the presence of deeply conserved constraints in the timing and energy requirements of larval development. Past focus on more apparent changes, such as the number of larval instars, may mask more deeply conserved ontogenetic patterns in developmental timing.     

Ontogeny of the redlichiid trilobite Eoredlichia intermediata from the Chengjiang Lagerstätte,lower Cambrian,southwest China

A detailed investigation of the morphology and ontogeny of the redlichioid trilobite Eoredlichia intermediata (Bulletin of the Geological Society of China, 3–4, 1940, 333) from the lower Cambrian Yu'anshan Member of the Heilinpu Formation, in Kunming, Yunnan Province, southwest China, is presented. The new material comprises a relatively complete ontogenetic series ranging from the early meraspid to the holaspid period, which reveals more details on morphological variation such as the appearance of bacculae in some holaspid specimens, contraction and disappearance of fixigenal spines, and macropleural spines of the first and second thoracic segments, which are all documented for the first time and can also be used as developmental markers defining ontogenetic phases. Two distinct morphotypes, possibly an expression of intraspecific variation or sexual dimorphism, are distinguished by the morphology of pleural spines of the second thoracic segment in meraspid degree 14 and holaspides. The trunk segmentation schedule of E. intermediata is also discussed and conforms to the protarthrous developmental mode. The distinction of the thoracic region into two portions can be observed during late meraspid and early holaspid periods, which might be considered as a reference for a better understanding on the relationship of tagmosis and growth segmentation among the Cambrian redlichiid trilobites.     

Caste morphology and development in Termitogeton nr. planus (Insecta,Isoptera, Rhinotermitidae)

The termite family Rhinotermitidae displays a wide diversity in its patterns of social organization in castes. The genus Termitogeton probably branched off early in the evolution of this family. We studied the developmental pathways of a putative undescribed species from New Guinea, Termitogeton nr planus. The development begins with two white inactive instars (larvae), the second of which possesses small wing buds. These are followed by a relatively homogenous group of active immature stages (pseudergates) among which a biometric study revealed the presence of four instars. The first of these instars possesses wing buds that regress at subsequent molts. The external morphology of older instars resembles that of higher termite workers. Older pseudergates can differentiate into presoldiers and then into soldiers, but they are also able to molt into a unique stage with long wing pads (nymph), preceding the imago. Colony maturity can be reached with about 10(3) individuals. The sex ratio is near 1:1 in all castes except soldiers, among which females are more numerous than males. The caste pattern of T. nr. planus is reminiscent of those of the Kalotermitidae and Termopsidae, and of Prorhinotermes among the Rhinotermitidae. None of these taxa possess a true worker caste, permanently diverted from imaginal development: social tasks are done by unspecialized immatures that retain a full array of developmental options, including that of proceeding to the imago. The most remarkable trait of T. nr. planus is the presence in all second-instar individuals of wing buds that later regress to reappear in the single nymphal stage. We suggest that the traditional definitions of the terms larvae, nymphs, and pseudergates should be revised because they cannot be satisfactorily applied to the castes of Termitogeton.     

Intraspecific variability in number of larval instars in insects

The number of larval instars varies widely across insect species. Although instar number is frequently considered to be invariable within species, intraspecific variability in the number of instars is not an exceptional phenomenon. However, the knowledge has remained fragmentary, and there are no recent attempts to synthesize the results of relevant studies. Based on published case studies, we show that intraspecific variability in the number of larval instars is widespread across insect taxa, occurring in most major orders, in both hemimetabolous and holometabolous insects. We give an overview of various factors that have been observed to affect the number of instars. Temperature, photoperiod, food quality and quantity, humidity, rearing density, physical condition, inheritance, and sex are the most common factors influencing the number of instars. We discuss adaptive scenarios that may provide ultimate explanations for the plasticity in instar number. The data available largely support the compensation scenario, according to which instar number increases in adverse conditions when larvae fail to reach a species-specific threshold size for metamorphosis. However, in Orthoptera and Coleoptera, there are some exceptional species in which instar number is higher in favorable conditions. In more specific cases, the adaptive value of the variability in instar number may be in reaching or maintaining the developmental stage adapted to hibernation, producing additional generations in multivoltine species, or increasing the probability of surviving in long-lasting adverse conditions.