Number Of Instars Research Articles

Determining the Number of Instars in Simulium quinquestriatum (Diptera: Simuliidae) Using k-Means Clustering via the Canberra Distance

Simulium quinquestriatum Shiraki (Diptera: Simuliidae), a human-biting fly that is distributed widely across Asia, is a vector for multiple pathogens. However, the larval development of this species is poorly understood. In this study, we determined the number of instars in this pest using three batches of field-collected larvae from Guiyang, Guizhou, China. The postgenal length, head capsule width, mandibular phragma length, and body length of 773 individuals were measured, and k-means clustering was used for instar grouping. Four distance measures-Manhattan, Euclidean, Chebyshev, and Canberra-were determined. The reported instar numbers, ranging from 4 to 11, were set as initial cluster centers for k-means clustering. The Canberra distance yielded reliable instar grouping, which was consistent with the first instar, as characterized by egg bursters and prepupae with dark histoblasts. Females and males of the last cluster of larvae were identified using Feulgen-stained gonads. Morphometric differences between the two sexes were not significant. Validation was performed using the Brooks-Dyar and Crosby rules, revealing that the larval stage of S. quinquestriatum is composed of eight instars.

How to become larger: ontogenetic basis of among‐population size differences in a moth

AbstractEvolutionary studies on animal body size have primarily focussed on selective pressures operating during the adult life. In contrast, ontogenetic pathways leading to differently sized adults have received less attention. In the present study, based on a common garden experiment, we report considerable genetic differences in body size among European populations of Ematurga atomaria (L.) (Lepidoptera: Geometridae). In terms of body mass, the moths from a southern (Georgian) population are twice as large as their northern (Estonian) conspecifics. Detailed monitoring of larval growth schedules revealed that the size difference arises through a longer development period of the Georgian larvae, with no difference in the number of instars. Differential (instantaneous) growth rates of the larvae do not differ between the populations. Eggs and newly hatched larvae are larger in the Georgian population but the difference vanishes in the second instar. The larger size of the Georgian moths is regained through higher relative mass increments during each of the three final instars. Such gradual ‘accumulation of the difference’ confirms the idea about constraints on substantial evolutionary changes in growth patterns within a single instar. The larger Georgian moths were found to be considerably more fecund which implies a strong selection for large female size. It remains unclear which counteracting selective pressures have favored the smaller size of Estonian conspecifics. As the associated difference in egg size appears not to be carried over to larger larval size, the adaptive value of larger eggs is not likely in contributing to the prospective large adult size. The larger eggs of the Georgian population should have an adaptive value per se, or represent a mechanistic consequence of larger maternal body size.

Immature Stages of the Masked Birch Caterpillar, Drepana arcuata (Lepidoptera: Drepanidae) With Comments on Feeding and Shelter Building

The masked birch caterpillar, Drepana arcuata (Lepidoptera: Drepanidae) is an excellent model for studying vibratory communication and sociality in larval insects. Vibratory communication occurs throughout development, but the functions of signals are reported to change as larvae change from gregarious to solitary lifestyles. To better understand the sensory ecology of these caterpillars, it is important to study their life history. Here, we describe the morphological and behavioral characteristics of larvae by confirming the number of instars, identifying their distinguishing morphological features, and noting changes in feeding and shelter construction. Five instars were confirmed based on the number of head capsules collected for individuals throughout development, and by using Dyar’s rule, which predicts the number of instars based on geometric growth patterns of head capsules. Frequency distributions of head capsule widths showed five separate peaks, indicating that this is a useful parameter for distinguishing between instars. Other morphological features including body length, shape, and banding patterns of head capsules, and morphology of thoracic verrucae are helpful in distinguishing among instars. Feeding behavior changes from leaf skeletonization in first and second instars to leaf cutting in fourth and fifth instars, with third instars transitioning between these feeding styles as they grow. Early instars typically construct communal silken shelters whereas late instars live solitarily in leaf shelters. These results provide essential life history information on the masked birch caterpillar that will enable future investigations on the proximate and ultimate mechanisms associated with social behavior and communication in larval insects.

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.

Influence of Temperature on Development ofNesidiocoris tenuis(Reuiter) Preying onTrialeurodes vaporariorum(WESTWOOD) on Tomato

The relationship between insect development rate and temperature represents an important ecological variable for modeling the population dynamics of insects. The development time of different stages of Nesidiocoris tenuis (Reuiter) (Hemiptera: Miridae) was determined at 15, 20, 25, 30, and 35°C by using Trialeurodes vaporariorum (Westwood) as prey on tomato (Solanum esculentum (Miller). N. tenuis was able to complete development with a similar (five) number of nymphal instars at temperatures between 15 and 35°C. Development rate of the insect was temperature-dependent and temperatures above 25°C were suitable for faster development. The developmental threshold varied from 6.66°C for third instar nymphs to 12.12°C for the first instar nymphs. The thermal constant also varied with developmental stage and was lowest (26.25 degree-days) for the first instar nymphs, and highest (200 degree-days) for the egg stage. The degree-day requirements were 250 for the entire nymphal stage and 500 for the egg to adult stage. The information generated can be used for developing phenological models based on temperature and development rate relationships, and for programming mass breeding for commercial purposes.

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.

Effects of Insect Growth Regulators on Bagrada hilaris (Hemiptera: Pentatomidae).

Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae) is a serious pest of cruciferous crops in the central coast of California. Management of B. hilaris primarily involves the use of broad spectrum insecticides, such as pyrethroids and neonicotinoids, when the pest invades a crop field. Insect growth regulators (IGRs) are known for their efficacy on nymphal stages of B. hilaris, but little is known about their transovarial effects. Thus, the major objective of this study was to determine the transovarial effects of IGRs such as novaluron, diflubenzuron, and azadirachtin, when adults are exposed to direct topical spraying and dried residues. In addition, a direct topical spray of IGRs on older instars (fourth and fifth instars) was examined at 1-, 3-, and 7-d post-treatment. The number of young instars (first and second instars) and adults was recorded up to ~31 d after exposure. In the topical spray assays, the number of young instars was significantly lower for novaluron, diflubenzuron, and azadirachtin than for the nontreated control. The number of young instars that emerged after novaluron treatment was low (0-11%). In the assays with dried residues, the number of young instars that developed was significantly lower for novaluron treatment than for the other IGRs and the nontreated control. There was no significant difference among diflubenzuron, azadirachtin, and nontreated control treatments in the development of young instars. In the assays with a topical spray of IGRs on older instars, significantly more nymphs died at 3 and 7 d after exposure. The IGRs had no clear impact on adults.

New insect pest at the culture of peach: Biology of Lagria villosa Fabricius, 1783 (Coleoptera: Tenebrionidae) fed with peach

The Idiamim ( Lagria villosa Fabricius, 1783) is an opportunist detritivore insect, but recently the young stage this inscet has been fed into peaches, making them unfit for consumption, in Chapeco, Santa Catarina. Given the lack of information on this species of insect, the aim of this study was evaluate the biology of this insect fed with peach cultivar BRS Libra in physiological maturity. The study was conducted in the Fruit Laboratory of the Federal University of Fronteira Sul, in Chapeco, Santa Catarina. The insects were collected in the adult stage in the field and isolated to obtain the eggs, and from that, we evaluated the duration of young stage and number of instars, reproductive period and fecundity, egg viability, incubation period, longevity and overall cycle. The food was efficient for the development of Idiamin in the laboratory, but the oviposition and egg viability were negatively affected.

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.

Analysis of the life stages of Cimex lectularius captured within a medical centre suggests that the true numbers of bed bug introductions are under-reported

Little is known about the epidemiology of bed bugs within the healthcare system, but nymphal stages predominate in natural infestations. This study determined the life stages of bed bugs captured within a medical centre, and found that older bed bugs were more likely to be captured than younger insects. The numbers of first instars, third-fifth instars and adult females captured were significantly different compared with the numbers of each life stage found in a natural infestation (P<0.01). A significant number of early-instar bed bugs introduced into the medical centre may go unnoticed by hospital staff.

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.

Variability in development of the striped rice borer, Chilo suppressalis (Lepidoptera: Pyralidae), due to instar number and last instar duration.

The striped stem borer, Chilo suppressalis (Walker), is an important insect pest of rice which shows substantial variation in developmental duration among individuals. This variation is currently poorly characterized but it is important from a control perspective because pesticides can only target early sensitive instars. It is unclear whether there are key stages that determine the length of developmental duration of individuals and/or whether variation in instar number contributes to this variation. In this study, a laboratory population and a population recently established from the field were used to test variation in development time across instar stages. The duration of developmental time of C. suppressalis started to diverge from the 5th instar onward. Individuals pupated at the 5th, 6th, 7th or even 8th instar stage. In both populations, both the instar at which the larva pupated and the duration of the last larval instar stage determined total developmental time of an individual. There was little impact of the developmental time of early instars on total developmental duration or on instar number prior to pupation. Sex influenced the number of instars but not development time within this number. The biological and applied significance of uneven development in C. suppressalis are discussed.

Biological Responses of Aphids (Hemiptera: Aphididae) When Fed Three Species of Forage Grasses

Abstract In Brazil, the forage species Brachiaria spp., Pennisetum purpureum (Schumacher), and Cynodon dactylon (L.) (Poaceae) are important components in the feed that is used to rear animals for meat and milk production. Aphids are among the insects that feed on these forage species and, at high population levels, greatly reduce the amount and quality of forage. Hence, the aim of this study was to determine the nutritional suitability of the forage species Brachiaria decumbens Stapf, C. dactylon, and P. purpureum for the aphids Sipha flava (Forbes), Rhopalosiphum maidis (Fitch), Hysteroneura setariae (Thomas), and Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Nymphs, which were up to 24 h old, of the 4 aphid species were observed for a biological cycle (1 full generation) on the 3 species of forage. For each association between a species of plant and a species of aphid, 70 aphids were used to create the individual units. The number of instars and the duration and survival of each instar and nymphal st...

Application of a frequency distribution method for determining instars of Eucryptorrhynchus brandti (Coleoptera: curculionidae) from several morphological variables

ABSTRACTEucryptorrhynchus brandti (Harold) (Coleoptera: Curculionidae) is a major pest of Ailanthus altissima (Mill.) Swingle (Simaroubaceae), commonly known as tree-of-heaven, and A. altissima var. Qiantouchun in China. It is considered a potential biological control agent for tree-of-heaven in North America. The aim of this study was to use a frequency distribution method to determine the instars of field-collected larvae of E. brandti. We collected larval samples of various sizes from both the field and the laboratory and measured five morphological variables, including antenna spacing, mandible width, head-capsule width, ocellus spacing, and pronotum width. Based on the results of a frequency distribution method and Dyar’s rule, the larvae of E. brandti were divided into seven instars. Of the five variables measured, the width of the head capsule provided the best measurement for determining instar stage. The regression equation between the head-capsule widths and the instar number was y = 0.324e0.096x (R2 = 0.970).

Monarch Butterflies Use Regenerating Milkweeds for Reproduction in Mowed Hayfields in Northern Virginia

ABSTRACT. The effects of mowing milkweeds in areas visited by monarch butterflies (Danaus plexippus L., Nymphalidae) were studied by counting the eggs and larvae on regenerating common milkweeds (Asclepias syriaca L., Apocyanaceae) in five adjacent mowed hayfields in northern Virginia in late summer 2015. At the same time monarch larvae were counted on mature senescent common milkweeds in unmowed areas adjacent or near to the mowed hayfields. Milkweeds supported populations of immature monarchs in both habitat types with initially many eggs and early instars found on regenerating plants in the mowed hayfields while late instars dominated the unmowed older milkweeds. As September proceeded, the censuses revealed an increase in the numbers of late instars on the mowed regenerating milkweeds whereas the abundance of larvae declined sharply on the older senescing milkweeds, many of which had lost all or most of their leaves. The study showed that late season mowing of hayfields provided adult female monarch b...

&lt;b&gt;Growth and developmental time in the parthenogenetic scorpion &lt;i&gt;Tityus stigmurus&lt;/i&gt; (Thorell, 1876) (Scorpiones: Buthidae)

This study describes variation in ontogenetic development of the parthenogenetic scorpion Tityus stigmurus based on variations in size, intermolt period, and number of instars. Individuals were created under laboratory conditions (28 ± 3oC) and subjected to similar diet regime. Comparative measurements of carapace, segment V of the metasoma, and the movable finger are used to estimate variations in size among instars. The application of Dyar rule shows a growth factor from 1.14 to 1.38 depending on the parameter analysed with intense variations in size between and within the different instars. The duration of the period from birth to adulthood was 871 days, after six moults. These data suggest that T. stigmurus has the longest post-embryonic development of Tityus genus and the existence of an extra molt to reach maturity.

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.

Larval development and growth ratios of Odonata of the Azores

To fully understand odonate life cycles, it is vital to analyse the patterns of larval growth, which are tightly associated with variations in environmental factors. However, the identification of larval instars is often difficult, especially for early development stages. We hypothesise that pond hydroperiod influences odonate larval growth, and test this idea with novel information about the environmental characteristics of 12 study ponds in Terceira Island (Azores). This study, which represents the first analysis of larval development of Odonata in the Azores, involved determining the instars of development and growth ratios. We measured the morphological characteristics of 898 Odonata larvae, and found that they significantly differed between temporary and permanent ponds. To estimate the larval instars, we used two methods: frequency distribution methods and correlation diagrams between body characteristics. The first method was the most effective, allowing the estimation of 17 instars for Anax imperator, 13 for Sympetrum fonscolombii and 10 for Ischnura hastata, as well as growth ratios between instars for head width, total length, abdomen length, wings and antenna length. Our results also suggest that a combination of the two methods is the most appropriate strategy for estimating the number of instars and growth ratios during larval development.