Number Of Larval Instars Research Articles

Larval instars of Apion Clavipes gerst. (coleoptera: apionidae)

Morphological measurements such as head capsule width are being employed for classifying larval instars of insects. For successful IPM of larval stages of pests, assessment of the life history stage is very important. Apion clavipes Gerst. (Coleoptera: Apionidae) is an important pest of mungbean in the lowland areas of north Shewa, Ethiopia. Few studies have been made on specific parameters of its life history. The present study determines the number of larval instars of A.clavipes. Different growth stages of larvae were collected from mungbean fields on the commencement of pod formation to maturity during the main season of 2015 and preserved in 70% ethyl alcohol. Head capsule width of each larva was measured under a stereozoom microscope fitted with ocular micrometer. For analysis of data, the frequency distribution method and Dyar's Law were used. The frequency distribution showed three different peaks which represents the three layers of the head capsule width. These observations agreed with Dyar's Law that revealed a perfect geometric larval growth pattern for each instar by regression analysis. The excellent fit to a linear model, indicates that no instar was overlooked. Thus, this study brings out the morphometrics of the three larval instars for A.clavipes.

Preimaginal Phases and Development of Spalangia gemina and Pachycrepoideus vindemiae (Hymenoptera: Pteromalidae) on House Fly (Diptera: Muscidae)

The development and morphology of immature phases of Spalangia gemina Boucek and Pachycrepoideus vindemiae Rondani are described from a laboratory reared culture maintained on the house fly Musca domestica L. (Diptera: Muscidae). Body width and length of pupal parasitoid were recorded. These 2 characteristics were determined for each larval instar and classified using cluster analysis in the SAS program. Developmental time from egg to adult of S. gemina and P. vindimiae was approximately 18 - 24 days and 15 - 18 days respectively at 25±3 °C and 45 - 65 % relative humidity. Eggs of S. gemina and P. vindemiae are hymenopteriform. Their incubation times are 24 - 48 h. The results show that the different numbers of larval instars in these parasitoids are well classified. The larvae of S. gemina has 3 instars with protuberances present on the last instar, whereas, P. vindemiae has 4 larval instars and the final instar lacks proturberances. The instars of P. vindemiae are morphologically similar except size and color of internal organs. Prepupae of both species are exarate and noticeably excrete meconium from the body. This information on preimaginal stages can be useful in the production and identification of parasitoids of the house fly.

Larvae of trap-jaw ants, Odontomachus Latreille, 1804 (Hymenoptera: Formicidae): morphology and biological notes

This study aims to contribute to the neglected topic of larval biology in ants. The number of larval instars for three different species of trap-jaw ants, Odontomachus meinerti Forel, 1905, Odontomachus bauri Emery, 1892, and Odontomachus brunneus (Patton, 1894) was estimated to three based on the maximum width frequency distributions of head capsules from worker and male larvae. The obtained number of larval instars was smaller than from a previous report with another species in the genus, indicating possible interspecific variation. Larvae of different sexes and instars among the three different species were generally identical, differing merely by relative dimensions and patterns of hair distribution. Dorsal doorknob protuberances were recorded for the first time in the genus, and observed being used to fix larvae onto nest walls. From observing several individuals, we suggest the ornamentation of spiracle peritremes and the types of body protuberances are useful characters for larval taxonomy within this group. Moreover, a few individuals were found possessing anomalous structures which are reminiscent of characters from related taxa. Finally, some brief observations are made on an unidentified parasite found inside some mature larvae of O. bauri.

Cross-species comparison of the gut: Differential gene expression sheds light on biological differences in closely related tenebrionids

The gut is one of the primary interfaces between an insect and its environment. Understanding gene expression profiles in the insect gut can provide insight into interactions with the environment as well as identify potential control methods for pests. We compared the expression profiles of transcripts from the gut of larval stages of two coleopteran insects, Tenebrio molitor and Tribolium castaneum. These tenebrionids have different life cycles, varying in the duration and number of larval instars. T. castaneum has a sequenced genome and has been a model for coleopterans, and we recently obtained a draft genome for T. molitor. We assembled gut transcriptome reads from each insect to their respective genomes and filtered mapped reads to RPKM>1, yielding 11,521 and 17,871 genes in the T. castaneum and T. molitor datasets, respectively. There were identical GO terms in each dataset, and enrichment analyses also identified shared GO terms. From these datasets, we compiled an ortholog list of 6907 genes; 45% of the total assembled reads from T. castaneum were found in the top 25 orthologs, but only 27% of assembled reads were found in the top 25 T. molitor orthologs. There were 2281 genes unique to T. castaneum, and 2088 predicted genes unique to T. molitor, although improvements to the T. molitor genome will likely reduce these numbers as more orthologs are identified. We highlight a few unique genes in T. castaneum or T. molitor that may relate to distinct biological functions. A large number of putative genes expressed in the larval gut with uncharacterized functions (36 and 68% from T. castaneum and T. molitor, respectively) support the need for further research. These data are the first step in building a comprehensive understanding of the physiology of the gut in tenebrionid insects, illustrating commonalities and differences that may be related to speciation and environmental adaptation.

Head Capsule Width is Useful for Determining Larval Instar inHeilipus lauri(Coleoptera: Curculionidae)

SummaryThe purpose of this study was to determine the number of larval instars for Heilipus lauri Boheman (Coleoptera: Curculionidae). We reared 385 larvae under laboratory conditions and measured the width of the larval head capsules from digital images. Data were analyzed using the Hcap program and Dyar’s rule. Analysis of the frequency distribution showed the existence of 4 distinct peaks. The mean Dyar’s constant was 1.42, where the relationship between the natural logarithm of the head capsule widths and the number of larval instars resulted in a near-perfect geometric growth for each instar. The excellent fit of the data to a linear model suggests that there was nearly no overlap among the 4 instars in the head capsule measurements, making it possible to distinguish the 4 instars of H. lauri accurately. SumarioEl objetivo de este estudio fue determinar el numero de estadios larvarios de Heilipus lauri Boheman (Coleoptera: Curculionidae). Un total de 385 larvas fueron criadas en condiciones de laboratorio. El ancho de la capsula cefalica de cada larva fue medido por medio de un sistema computarizado de analisis de imagenes. Los datos fueron analizados con el programa HCap y la regla de Dyar. El grafico de distribucion de frecuencias mostro cuatro picos de distribucion del ancho de la capsula cefalica. El promedio de la constante de Dyar fue de 1.42 donde la relacion entre el logaritmo natural del ancho de la capsula cefalica y el numero de estadio larvario resulto en un perfecto crecimiento geometrico de cada estadio larvario. El excelente ajuste lineal de las datos sugiere que no existen instares traslapados y es posible distinguir cuatro estadios larvarios en H. lauri.View this article in BioOne

External Morphology of Immatures of Mischocyttarus nomurae Richards (Hymenoptera, Vespidae) during the Post-embryonic Development

The work on this paper aimed to perform the description of the immatures and determine the number of larval instars in the post-embryonic development of Mischocyttarus nomurae Richards, a social wasp which the only works performed were the description of the specie and of the male. Twenty colonies were collected in the city of Rio de Contas, in the region of the Chapada Diamantina, Bahia, Brazil and there were dimensioned 145 eggs, 349 larvae, 12 pre-pupae and 59 pupae. The eggs presented an average length of 1.03 ± 0.12mm and diameter of 0.40 ± 0.03mm. The average rate of growth of the larvae that presented five instars was 1.49. The width of the cephalic capsule of the larvae was: 1st instar 0.32 ± 0.08, 2nd instar 0.54 ± 0.06, 3rd instar 0.77 ± 0.07, 4th instar 1.05 ± 0.10 and 5th instar 1.55 ± 0.07. The average width of the larvae of 5th instar and pre-pupae were close, where larvae of the 1st instar differed from the egg, being smaller. The average measure of the pupae was 1.85 ± 0.08. The specie presents two abdominal lobes highly projected towards and the first thoracic spiracle is 3.1 times higher than the second one. This is the first work on the biology of the specie.

Biological Strategies of Dermestes maculatus DeGeer (Coleoptera: Dermestidae) at Larval Stages in Different Temperatures.

The intraspecific variation in larval instars is a widely distributed phenomenon amongst holometabolous insects. Several factors can affect the number of instars, such as temperature, humidity, and density. Only a few references could be found in the literature because the invariability in the number of larval instars is considered normal, and the issue has raised little to no interest. Despite this, no study to date has intended to assess or focus on the larval development. Here, we analyzed the effect of different rearing temperature on the larval stage of Dermestes maculatus DeGeer (Coleoptera: Dermestidae). The results indicated that at all temperatures, L5 represented a decisive point for individuals as well as the other later larval instars, because the next step to follow was to pupate or molt to the next larval instar. Furthermore, there were mainly two populations, L5 and L6, although in different proportions according to temperature. We also found that at a greater number of instars, the larval development at all temperatures lasted longer. Moreover, the exponential model was the best adjustment in the developmental time of all populations as well as for the accumulated developmental time of L1-L4. Thus, we conclude that random factors such as genetics could probably cause interspecific variability in D. maculatus larval development.

Biology and Seasonality of the Reemergent Pest Rhynchaenus pallicornis (Coleoptera: Curculionidae) and Methods for Monitoring Its Abundance.

Rhynchaenus pallicornis (Say) is a pest of commercially grown apples in the upper Midwest. This historic pest has resurged and caused severe yield loss on farms using certified organic production practices. The life history and potential monitoring methods of R. pallicornis are presented. Seasonal abundance data were collected through beat and visual sampling. A phenological model was developed for R. pallicornis. The minimum developmental threshold of R. pallicornis was determined to be 3.5°C with a required degree-day accumulation of 125°D for first adult emergence. Larval damage was observed on >60% of leaves in unmanaged orchards and affected significantly fewer basal leaf clusters (near the trunk), than medially or apically located clusters. Of 2,900 R. pallicornis larval mines collected over two years at three different sites, 18.0% produced at least one adult parasitoid, but the targeted larval stage is unknown. Measurements of R. pallicornis larval head capsules and the simple frequency method were used to determine three larval instars of R. pallicornis The number of larval instars could also be accurately determined by observing the presence or absence of two sets of thoracic sclerites. Pyramid traps, yellow sticky cards baited with olfactory cues (pear essence, benzaldehyde, and an aggregation of adult R. pallicornis) were evaluated as R. pallicornis monitoring tools. None of the traps or lures tested significantly affected the number of adult R. pallicornis per trap.

Larva, nymph and naiad – for accuracy's sake

Larva, nymph and naiad – for accuracy's sake

The life cycle of the emerald ash borer Agrilus planipennis in European Russia and comparisons with its life cycles in Asia and North America

Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), native to Asia, is a destructive invasive pest of ash Fraxinus spp. in U.S.A., Canada and European Russia. It is spreading quickly and will probably soon be detected in other European countries. Information about the life cycle of the pest is needed for detection and survey efforts, development of control options and predicting the potential range in Europe. The life cycle has been studied in North America and Asia, although it has not previously been studied in European Russia. The number of larval instars and the duration of development of A. planipennis in European Russia were determined. Distributions of width of epistome and length of urogomphi indicated four larval instars. The number of excretory ducts and the presence of ledges did not provide a clear differentiation between instars. Development in most of the specimens took 2 years. Generation time is flexible. In warmer regions (Tianjin), most individuals finish development in 1 year, whereas, in colder regions (Moscow, Changchun, Harbin), it takes 2 years. In intermediate climatic regions (Michigan), the ratio of 1 : 2‐year life cycles depends on additional factors. The flexibility of the life cycle allows A. planipennis to establish in regions with different climates.

Convergent Reduction of Ovariole Number Associated with Subterranean Life in Beetles.

BackgroundSome species of obligate cavernicolous beetles are known to possess a unique feature—a contraction of the larval cycle. In contrast to many other subterranean beetles, life-cycle contraction in Trechini ground beetles (Carabidae) is correlated with a reduction in the number of eggs and a drastic reduction in the number of ovarioles. This remarkable peculiarity has only been reported for a small number of closely related species.ResultsWe give a description of the female internal reproductive system for six species of Trechini, including five subterranean species, with a particular focus on the western Pyrenean radiation of Aphaenops, a group for which nothing is known regarding the early life stages. We redescribe the internal female genitalia of A. crypticola Linder. Study of the ovarioles allowed us to infer the postembryonic development of the larvae for each species examined. We then used a phylogenetic framework to recognize two independent reductions in the number of ovarioles in the Pyrenean lineage. We discuss the multiple convergent evolutions in ovariole number and the potential link between a reduction of ovariole number and troglobiomorphism in a phylogenetic context.ConclusionsThere is an extreme reduction in ovariole number and size within the species studied; the eggs produced by small ovarioles have a remarkably large size. A reduction to one ovariole has occurred independently at least twice in this subterranean group. A reduction in the number of ovarioles in ground beetles is one of the striking consequences of subterranean specialization and it is correlated with another remarkable adaptation of subterranean beetles, a reduction in the number of larval instars.

Individual and mixture effects of selected pharmaceuticals on larval development of the estuarine shrimp Palaemon longirostris

Few ecotoxicological studies incorporate within the experimental design environmental variability and mixture effects when assessing the impact of pollutants on organisms. We have studied the combined effects of selected pharmaceutical compounds and environmental variability in terms of salinity and temperature on survival, development and body mass of larvae of the estuarine shrimp Palaemon longirostris. Drug residues found in coastal waters occur as mixture, and the evaluation of combined effects of simultaneously occurring compounds is indispensable for their environmental risk assessment. All larval stages of P. longirostris were exposed to the nonsteroidal anti-inflammatory drug (NSAID) diclofenac sodium (DS: 40 and 750μgL−1), the lipid regulator clofibric acid (CA: 17 and 361μgL−1) and the fungicide clotrimazole (CLZ: 0.14 and 4μgL−1). We observed no effect on larval survival of P. longirostris with the tested pharmaceuticals. However, and in contrast to previous studies on larvae of the related marine species Palaemon serratus, CA affected development through an increase in intermoult duration and reduced growth without affecting larval body mass. These developmental effects in P. longirostris larvae were similar to those observed in the mixture of DS and CA confirming the toxic effects of CA. In the case of CLZ, its effects were similar to those observed previously in P. serratus: high doses affected development altering intermoult duration, tended to reduce the number of larval instars and decreased significantly the growth rate. This study suggests that an inter-specific life histories approach should be taken into account to assess the effect of emergent compounds in coastal waters.

A Quantitative Analysis of Growth and Size Regulation in Manduca sexta: The Physiological Basis of Variation in Size and Age at Metamorphosis.

Body size and development time are important life history traits because they are often highly correlated with fitness. Although the developmental mechanisms that control growth have been well studied, the mechanisms that control how a species-characteristic body size is achieved remain poorly understood. In insects adult body size is determined by the number of larval molts, the size increment at each molt, and the mechanism that determines during which instar larval growth will stop. Adult insects do not grow, so the size at which a larva stops growing determines adult body size. Here we develop a quantitative understanding of the kinetics of growth throughout larval life of Manduca sexta, under different conditions of nutrition and temperature, and for genetic strains with different adult body sizes. We show that the generally accepted view that the size increment at each molt is constant (Dyar’s Rule) is systematically violated: there is actually a progressive increase in the size increment from instar to instar that is independent of temperature. In addition, the mass-specific growth rate declines throughout the growth phase in a temperature-dependent manner. We show that growth within an instar follows a truncated Gompertz trajectory. The critical weight, which determines when in an instar a molt will occur, and the threshold size, which determines which instar is the last, are different in genetic strains with different adult body sizes. Under nutrient and temperature stress Manduca has a variable number of larval instars and we show that this is due to the fact that more molts at smaller increments are taken before threshold size is reached. We test whether the new insight into the kinetics of growth and size determination are sufficient to explain body size and development time through a mathematical model that incorporates our quantitative findings.

Aromia bungii

Aromia bungii

Larval and pupal morphology of three species of the genus Psammoecus Latreille (Coleoptera: Silvanidae: Brontinae) in Japan with reference to the number of larval instars.

The last instar larva and the pupa of Psammoecus scitus Yoshida & Hirowatari, all instar larvae of P. simoni Grouvelle, and the last instar larva of P. hiranoi Yoshida & Hirowatari are described, and their morphologies are compared among species and instars. Larval association for P. simoni was confirmed by DNA barcoding. Apart from a brief description of the pupa of Cryptamorpha brevicornis (White) illustrated by Hudson (1924), the pupal morphology of Brontinae is described in detail for the first time. Potentially informative characters for phylogeny of larval and pupal morphology of Silvanidae are discussed.

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.

Reproductive biology and postembryonic development of a polyphagid cockroach Eucorydia yasumatsui Asahina (Blattodea: Polyphagidae)

Reproductive biology, including mating behavior, ootheca deposition, ootheca rotation, and postembryonic development, were examined and described in a Japanese polyphagid, Eucorydia yasumatsui Asahina, 1971. E. yasumatsui lacks elaborate pre-copulation behaviors, in contrast to most cockroaches. On encountering a female, the male rushes to her, chases her, touching her with his antennae, and finally the pair initiates “tail-to-tail” copulation. The ootheca bears a well-developed, serrated keel along its dorsal median line and a flange on its anterior end, which is grasped with the female’s paraprocts while she carries the ootheca. The ootheca formed in the vestibulum emerges from her caudal end, with its keel upwards. Several hours later, she rotates the ootheca clockwise by 90°, viewed from the female’s side, into a horizontal position. After rotation, she carries the ootheca, maintaining this horizontal position for a few days, and then deposits it on the ground. The number of larval instars was 9 or 10 in females and 8 or 9 in males. Addition of annuli to the antennal flagellum occurs from the 2nd instar molting onwards, and annular division occurs both in the 1st annulus of the flagellum (meriston) and in the annulus following it (called “meristal annulus” from the 3rd instar on): one to several annuli from the former and a single annulus from the latter are added. Sexes can be distinguished from the 3rd instar on according to the changes of the postabdominal structures. Regarding exposed structures, in the female the posterior margin of abdominal coxosternum VIII becomes incised medially, the abdominal coxosterna VIII and IX retract, and the styli of segment IX disappear. The male does not undergo marked externally visible changes.

The influence of per offspring investment (POI) and starvation on larval developmental plasticity within the palaemonid shrimp, Palaemonetes varians

At the inter-specific level, per offspring investment (POI), degree of abbreviated development, and lecithotrophic potential all increase with increasing latitude and freshwater penetration among crustaceans. These traits are considered adaptations to conditions of decreasing growth potential. We hypothesise that this relationship between POI and abbreviated development also occurs at the intra-specific level. We studied the caridean shrimp, Palaemonetes varians, to investigate the hypothesis that under food-limited conditions, higher POI enables development through fewer larval instars. Under starvation stress, larvae from broods of greater POI (measured as hatchling brood average dry weight, DW) generally developed through fewer larval instars. With increasing starvation period, larval development time increased, whilst larval growth rate, juvenile DW, juvenile carbon mass, and juvenile carbon:nitrogen (C:N) ratio all decreased. Larval development time generally decreased with increasing brood average dry weight. In contrast, larval growth rate, juvenile DW, juvenile carbon mass, and juvenile C:N ratio all increased with increasing larval brood average DW. The relationship between POI and larval instar number (abbreviation of development) reported here is consistent with that at the inter-specific level and supports the concept that macro-ecological trends in development modes at the inter-specific level may be driven by selection occurring on POI at the intra-specific level.

Complete tribal sampling reveals basal split in Muscidae (Diptera), confirms saprophagy as ancestral feeding mode, and reveals an evolutionary correlation between instar numbers and carnivory

With about 5000 species in ca. 180 genera, the Muscidae is the most species-rich family in the muscoid grade of Calyptratae (Diptera: Cyclorrhapha), the others being the Fanniidae, Scathophagidae and Anthomyiidae. Muscidae is remarkable for its young age, high species diversity in all biogeographic regions, and an unusually diverse range of feeding habits at the larval stage (e.g., saprophagy, phytophagy, carnivory, endoparasitism, haematophagy). We here review muscid classification and biology and present a molecular phylogeny based on four mitochondrial genes (12S, 16S, COI, CYTB) and three nuclear genes (28S, Ef1a, and CAD) for 84 species from 40 genera. Our analysis is the first to include species from all biogeographic regions and all currently recognised muscid subfamilies and tribes. We provide strong support for the monophyly of the Muscidae, and for the first time also for the first split within this family. The ancestral larval feeding habit is reconstructed to be saprophagy with more specialised coprophagous saprophagy, phytophagy, and carnivory evolving multiple times from saprophagous ancestors. The origins of carnivory in larvae are significantly correlated with a reduction of the number of larval instars from three (ancestral) to two and one. The genus Achanthiptera which was previously in its own subfamily is shown to be closely related to Azeliini. However, it appears that Azeliinae is paraphyletic because Muscinae is sister-group to the Azeliini while the azeliine Reinwardtiini are polyphyletic. Coenosiinae and Muscinae are monophyletic, but Muscini is paraphyletic with regard to Stomoxyini. Because many subfamilies are apparently para- or even polyphyletic, we review the history of muscid classification in order to reveal how the currently used classification originated.

Life-history specialization was not an evolutionary dead-end in Pyrenean cave beetles

Research on subterranean organisms has focused on the colonization process and some of the associated phenotypic changes, but little is known on the long-term evolutionary dynamics of subterranean lineages and the origin of some highly specialized complex characters. One of the most extreme modifications is the reduction of the number of larval instars in some Leptodirini beetles from the ancestral 3 to 2 and ultimately a single instar. This reduction is usually assumed to have occurred independently multiple times within the same lineage and geographical area, but its evolution has never been studied in a phylogenetic framework. Using a comprehensive molecular phylogeny, we found a low number of independent origins of the reduction in the number of instars, with a single transition, dated to the Oligocene-Miocene, from 3 to 2 and then 1 instar in the Pyrenees, the best-studied area. In the Pyrenees, the 1-instar lineage had a diversification rate (0.22 diversification events per lineage per million years) significantly higher than that of 3- or 2-instar lineages (0.10), and similar to that seen in other Coleopteran radiations. Far from being evolutionary dead-ends, ancient lineages fully adapted to subterranean life seem able to persist and diversify over long evolutionary periods.