Wing Morph Determination Research Articles

Postnatal Wing Morph of Pea Aphids Regulates Hemolymph Trehalose Levels.

Trehalose, a nonreducing disaccharide composed of two glucose molecules, functions as a critical energy source in various insect tissues and organs and is the predominant sugar component of the hemolymph. The pea aphid, Acyrthosiphon pisum, exhibits higher hemolymph trehalose levels than other insects. However, the dynamics of hemolymph trehalose levels throughout its life stages remain unclear owing to the challenges associated with obtaining hemolymph from these small insects. Therefore, this study was conducted to quantify hemolymph trehalose levels in A. pisum using a fluorescent trehalose sensor (Tre-C04), which enhances green fluorescent protein fluorescence through the binding of trehalose to a ligand-binding protein fused to the fluorophore. Trehalose levels were successfully quantified in minimal hemolymph samples from individual aphids, with measurements spanning from the first nymphal stage to the adult stage in both the winged and wingless forms of A. pisum. Hemolymph trehalose levels remained relatively stable throughout the life cycle but exhibited a gradual increase with each developmental stage. Notably, adult winged aphids exhibited significantly higher hemolymph trehalose levels than wingless aphids. Given that wing morph determination occurs early in the nymphal stage, these findings suggest that hemolymph trehalose levels are regulated post-wing morph development. Further investigation of the expression of genes associated with trehalose metabolism revealed that trehalose phosphate synthase 2 levels were downregulated in early-stage wingless adults, whereas insulin-related peptide 5 levels were upregulated in wingless aphids. These findings indicate that A. pisum synthesizes trehalose during the winged adult stage to serve as an energy source for flight.

Phenotypically plastic responses to environmental variation are more complex than life history theory predicts.

For insects that exhibit wing polyphenic development, abiotic and biotic signals dictate the adult wing morphology of the insect in an adaptive manner such that in stressful environments the formation of a flight-capable morph is favored and in low-stress environments, a flightless morph is favored. While there is a relatively large amount known about the environmental cues that dictate morph formation in wing polyphenic hemipterans like planthoppers and aphids, whether those cues dictate the same morphs in non-hemipteran (i.e., cricket) wing polyphenic species has not been explicitly investigated. To experimentally test the generality of environmental cue determination of wing polyphenism across taxa with diverse life histories, in this study, we tested the importance of food quantity, parasitic infection, and tactile cues on wing morph determination in the wing polyphenic sand field cricket, Gryllus firmus. Our results also show that certain stress cues, such as severe diet quantity limitation and parasitic infection, actually led to an increase in the production of flightless morph. Based on these findings, our results suggest that physiological and genetic constraints are important to an organism's ability to respond to environmental variation in an adaptive manner beyond simple life history trade-offs.

Transcriptomic Analysis Suggests Genes Expressed Stage-Independently and Stage-Dependently Modulating the Wing Dimorphism of the Brown Planthopper.

Wing dimorphism is considered as an adaptive trait of insects. Brown planthoppers (BPHs) Nilaparvata lugens, a serious pest of rice, are either macropterous or brachypterous. Genetic and environmental factors are both likely to control wing morph determination in BPHs, but the hereditary law and genes network are still unknown. Here, we investigated changes in gene expression levels between macropterous and brachypterous BPHs by creating artificially bred morphotype lines. The nearly pure-bred strains of macropterous and brachypterous BPHs were established, and their transcriptomes and gene expression levels were compared. Over ten-thousand differentially expressed genes (DEGs) between macropterous and brachypterous strains were found in the egg, nymph, and adult stages, and the three stages shared 6523 DEGs. The regulation of actin cytoskeleton, focal adhesion, tight junction, and adherens junction pathways were consistently enriched with DEGs across the three stages, whereas insulin signaling pathway, metabolic pathways, vascular smooth muscle contraction, platelet activation, oxytocin signaling pathway, sugar metabolism, and glycolysis/gluconeogenesis were significantly enriched by DEGs in a specific stage. Gene expression trend profiles across three stages were different between the two strains. Eggs, nymphs, and adults from the macropterous strain were distinguishable from the brachypterous based on gene expression levels, and genes that were related to wing morphs were differentially expressed between wing strains or strain × stage. A proposed mode based on genes and environments to modulate the wing dimorphism of BPHs was provided.

Comparative transcriptional analysis provides insights of possible molecular mechanisms of wing polyphenism induced by postnatal crowding in Aphis gossypii

BackgroundAphis gossypii is a worldwide sap-sucking pest with a variety of hosts and a vector of more than 50 plant viruses. The strategy of wing polyphenism, mostly resulting from population density increasing, contributes to the evolutionary success of this pest. However, the related molecular basis remains unclear. Here, we identified the effects of postnatal crowding on wing morph determination in cotton aphid, and examined the transcriptomic differences between wingless and wing morphs.ResultsEffect of postnatal crowding on wing determination in A. gossypii was evaluated firstly. Under the density of 5 nymphs·cm− 2, no wing aphids appeared. Proportion of wing morphs rised with the increase of density in a certain extent, and peaked to 56.1% at the density of 20 nymphs·cm− 2, and reduced afterwards. Then, transcriptomes of wingless and wing morphs were assembled and annotated separately to identify potentially exclusively or differentially expressed transcripts between these two morphs, in which 3 126 and 3 392 unigenes annotated in Nr (Non-redundant protein sequence) database were found in wingless or wing morphs exclusively. Moreover, 3 187 up- and 1 880 down-regulated genes were identified in wing versus wingless aphid. Pathways analysis suggested the involvement of differentially expressed genes in multiple cellular signaling pathways involved in wing morphs determination, including lipid catabolic and metabolism, insulin, ecdysone and juvenile hormone biosynthesis. The expression levels of related genes were validated by the reverse transcription quantitative real time polymerase chain reaction (RT-qPCR) soon afterwards.ConclusionsThe present study identified the effects of postnatal crowding on wing morphs induction and demonstrated that the critical population density for wing morphs formation in A. gossypii was 20 nymphs·cm− 2. Comparative transcriptome analysis provides transcripts potentially expressed exclusively in wingless or wing morph, respectively. Differentially expressed genes between wingless and wing morphs were identified and several signaling pathways potentially involved in cotton aphid wing differentiation were obtained.

Silencing of juvenile hormone epoxide hydrolase gene (Nljheh) enhances short wing formation in a macropterous strain of the brown planthopper, Nilaparvata lugens

The rice brown planthopper, Nilaparvata lugens, is an important migratory pest in many rice planting areas of Asia. The typical wing dimorphism of N. lugens gives them flexibility to adapt to different environmental cues. As an important hormone in the insect’s endocrine regulation, juvenile hormone (JH) has previously been shown to participate in the wing morph determination of N. lugens. In this paper, we investigated the possible wing morph determination roles of two JH metabolic enzymes, JH esterase (JHE) and JH epoxide hydrolase (JHEH). A 1957-bp full-length cDNA sequence encoding JHEH in N. lugens (NlJHEH) was first cloned from a hemipteran insect. Except for an uncertain transmembrane segment prediction, the deduced 454-amino-acid sequence of Nljheh has all of the conserved domains of JHEHs such as the H147GWP150, Tyr293 and Tyr368 motif corresponding to the oxyanion hole and the residues Asp222, Glu398, and His425 in the catalytic triad. qRT-PCR results showed that both Nljhe and Nljheh had different expression timeframes between a predominantly brachypterous strain (BS) and a macropterous strain (MS) of N. lugens, indicating that these two enzymes may participate in wing dimorphism regulation in brown planthopper. Silencing Nljheh expression by dsRNA injection enhanced short wing formation in the macropterous strain of N. lugens, while the brachypterizing individuals were mainly females. Compared to the dsgfp injection control, silencing Nljhe had no brachypterizing effect. Our results indicated that NlJHEH plays an important role in the wing morph determination of N. lugens.

The Effect of Combinations of Food Insects for Continuous Rearing of the Wing Polymorphic Water Strider Limnogonus Fossarum fossarum (Hemiptera: Gerridae).

The water strider Limnogonus fossarum fossarum (F.) (Hemiptera: Gerridae) shows a macropterous, micropterous, and apterous polymorphism. Although a long photoperiod condition induces winged morphs, preliminary studies have revealed that crossing between winged morphs increased the proportion of macropterous individuals, suggesting that the genetic factors also affect wing-morph determination in this species. Assessing the genetic backgrounds of wing polymorphism requires constant and repeatable methods for rearing. This study attempts to establish a continuous rearing method for L. f. fossarum under constant diet conditions. Initially, we maintain the water striders with two Drosophila species as a food, but viability until adulthood is less than 20%. We then add the storage pest Plodia interpunctella (Hübner), which are readily reared in the laboratory, to the diets. As a result, nymphs fed on P. interpunctella (even only until the second instar) show significantly higher viability and shorter developmental period than nymphs fed on Drosophila alone. Moreover, feeding on D. melanogaster (Meigen) reared on cholesterol-enriched medium instead of a normal medium significantly increases viability in the next generation. This means that only the two food-insect species are enough for establishing a substantial number of individuals in segregating generations (F2 and backcross), limiting DNA and RNA contaminations from food insects with genome information. Thus, the present rearing method opens the way to elucidating the genetic backgrounds of the wing polymorphism in L. f. fossarum.

Two insulin receptors determine alternative wing morphs in planthoppers.

Wing polyphenism is an evolutionarily successful feature found in a wide range of insects. Long-winged morphs can fly, which allows them to escape adverse habitats and track changing resources, whereas short-winged morphs are flightless, but usually possess higher fecundity than the winged morphs. Studies on aphids, crickets and planthoppers have revealed that alternative wing morphs develop in response to various environmental cues, and that the response to these cues may be mediated by developmental hormones, although research in this area has yielded equivocal and conflicting results about exactly which hormones are involved. As it stands, the molecular mechanism underlying wing morph determination in insects has remained elusive. Here we show that two insulin receptors in the migratory brown planthopper Nilaparvata lugens, InR1 and InR2, have opposing roles in controlling long wing versus short wing development by regulating the activity of the forkhead transcription factor Foxo. InR1, acting via the phosphatidylinositol-3-OH kinase (PI(3)K)-protein kinase B (Akt) signalling cascade, leads to the long-winged morph if active and the short-winged morph if inactive. InR2, by contrast, functions as a negative regulator of the InR1-PI(3)K-Akt pathway: suppression of InR2 results in development of the long-winged morph. The brain-secreted ligand Ilp3 triggers development of long-winged morphs. Our findings provide the first evidence of a molecular basis for the regulation of wing polyphenism in insects, and they are also the first demonstration--to our knowledge--of binary control over alternative developmental outcomes, and thus deepen our understanding of the development and evolution of phenotypic plasticity.

Screening of Upregulated Genes Induced by High Density in the Vetch Aphid Megoura crassicauda

Aphids exhibit several polyphenisms in which discontinuous, alternative phenotypes are produced depending on environmental conditions. One representative example is the wing polyphenism, where winged and wingless females are produced through parthenogenesis. Previous work has shown that, in some aphid species, the density condition sensed by the mother aphid determines the developmental fate of embryos in her ovary, with high densities leading to winged progeny and low densities to wingless progeny. However, little is known about the molecular and physiological mechanisms underlying the wing polyphenism. To identify genes involved in the wing-morph determination in the vetch aphid, Megoura crassicauda, we compared maternal and embryonic transcripts between high- and low-density conditions using differential display, followed by quantitative real-time PCR (qRT-PCR). Under the high-density condition, two genes (Uba1 and Naca) were found to be upregulated in maternal tissues without ovaries, while one gene (ClpP) was upregulated in ovaries containing embryos. Uba1 and Naca encode factors that function in protein modification or transcriptional/translational regulation, respectively. In addition to differential display, candidate gene approaches focusing on morphogenetic and endocrine genes, i.e., wg, dpp, ap, hh, InR, IRS, Foxo, EcR, and USP, were also carried out. We found that wg was upregulated in maternal tissues under the high-density condition. The identified genes from both approaches are candidates for further study of their involvement in the transduction of density signals in mother aphids and/or the initial process of wing differentiation in embryos.

Aphid wing dimorphisms: linking environmental and genetic control of trait variation.

Both genetic and environmental factors underlie phenotypic variation. While research at the interface of evolutionary and developmental biology has made excellent advances in understanding the contribution of genes to morphology, less well understood is the manner in which environmental cues are incorporated during development to influence the phenotype. Also virtually unexplored is how evolutionary transitions between environmental and genetic control of trait variation are achieved. Here, I review investigations into molecular mechanisms underlying phenotypic plasticity in the aphid wing dimorphism system. Among aphids, some species alternate between environmentally sensitive (polyphenic) and genetic (polymorphic) control of wing morph determination in their life cycle. Therefore, a traditional molecular genetic approach into understanding the genetically controlled polymorphism may provide a unique avenue into not only understanding the molecular basis of polyphenic variation in this group, but also the opportunity to compare and contrast the mechanistic basis of environmental and genetic control of similar dimorphisms.

A sex-linked locus controls wing polymorphism in males of the pea aphid, Acyrthosiphon pisum (Harris).

Discrete variation in wing morphology is a very common phenomenon in insects and has been used extensively in the past 50 years as a model to study the ecology and evolution of dispersal. Wing morph determination can be purely genetic, purely environmental, or some combination of the two. The precise genetic determinants of genetically based wing morph variation are unknown. Here we explore the genetic basis of wing polymorphism in the pea aphid, which can produce either winged or wingless males. We confirm that three types of pea aphid clones coexist in natural populations, those producing winged males only, those producing wingless males only, and those producing a mixture of both. A Mendelian genetic analysis reveals that male wing polymorphism in pea aphids is determined by a single locus, two alleles system. Using microsatellite loci of known location, we show that this locus is on the X chromosome. The existence of a simple genetic determinism for wing polymorphism in a system in which genetic investigation is possible may help investigations on the physiological and molecular mechanisms of genetically-based wing morph variation. This locus could also be used in the search for genes involved in the wing polyphenism described in parthenogenetic females and to investigate the interplay between polymorphisms and polyphenisms.

Coevolution of traits determining migratory tendency: correlated response of a critical enzyme, juvenile hormone esterase, to selection on wing morphology

AbstractMigratory tendency in insects is a complex trait, composed of a suite of correlated behavioural, physiological, morphological and life history traits. We investigate the genetic and physiological basis of the coevolution of this suite of traits using laboratory lines of the wing dimorphic cricket, Gryllus firmus, selected for increasing and decreasing incidence of macroptery. Selection on wing morphology has produced strong direct responses in proportion macropterous as well as correlated (indirect) responses in wing muscle histolysis, flight propensity and fecundity. We investigate the hypothesis that these responses have been mediated by changes in the metabolism of juvenile hormone (JH) during the final nymphal stadium (the critical period for wing morph determination). Previous studies of Gryllus sp. have established that JH titre in this period is determined primarily by the activity of the degradative enzyme, juvenile hormone esterase (JHE). Assays of JHE activity in the final nymphal stadium of the replicated control and selected lines demonstrate highly significant differences in both mean activity and the probability of macroptery for a given level of activity (i.e., the threshold activity required to induce wing formation). These correlated responses in JH metabolism support the general hypothesis that the correlations among traits determining migratory tendency result at least in part from the common influence of JH during the final nymphal stadium. We discuss these results in the context of the quantitative genetic model for the evolution of polygenic, dichotomous traits (the threshold model), and present four general predictions concerning the coevolution of traits associated with ecological (i.e., trophic, life history, behavioural) dimorphisms.

Physiology and ecology of dispersal polymorphism in insects.

Studies of dispersal polymorphism in insects have played a pivotal role in advancing our understanding of population dynamics, life history evolution, and the physiological basis of adaptation. Comparative data on wing-dimorphic insects provide the most definitive evidence to date that habitat persistence selects for reduced dispersal capability. The increased fecundity of flightless females documents that a fitness trade-off exists between flight capability and reproduction. However, only recently have studies of nutrient consumption and allocation provided unequivocal evidence that this fitness trade-off results from a trade-off of internal resources. Recent studies involving wing-dimorphic insects document that flight capability imposes reproductive penalties in males as well as females. Direct information on hormone titers and their regulation implicates juvenile hormone and ecdysone in the control of wing-morph determination. However, detailed information is available for only one species, and the physiological regulation of wing-morph production remains poorly understood. Establishing a link between the ecological factors that influence dispersal and the proximate physiological mechanisms regulating dispersal ability in the same taxon remains as a key challenge for future research.

The role of juvenile hormone and juvenile hormone esterase in wing morph determination in Modicogryllus confirmatus

The role of juvenile hormone (JH) and juvenile hormone esterase (JHE) in regulating wing morph determination was studied in the cricket Modicogryllus confirmatus. JHE activities were significantly higher in nascent long-winged (LW) vs short-winged (SW) crickets during the latter half but not during the first half of the last stadium. The magnitude and direction of the activity differences were similar to those previously documented between wing morphs of the cricket, Gryllus rubens. In contrast, activities of general esterase, an enzyme or group of enzymes with no demonstrated role in regulating the JH titer in insects, showed no or only minor differences between morphs. The magnitude and direction of the JHE activity variation is consistent with a regulatory role for this enzyme in some aspect of wing dimorphism. However, the timing of the differences (exclusively during the last half of the last stadium) argue against a role in regulating wing length development per se. Single or multiple applications of juvenile hormone-III to nascent LW individuals during the first few days of the last stadium significantly redirected development from long to short wings. Multiple applications of acetone, by itself, also increased the production of short-winged adults. For most treatments, all individuals with shortened wings also had undeveloped flight muscles. These data suggest that JH may play a role in wing morph determination in M. confirmatus but that it affects a different aspect of the polymorphism from JHE.

The Relation of Adult Wing-Form in the Brown Planthopper, Nilaparvata lugens STÅL (Homoptera : Delphacidae) to Wing-Pad Length of Last Instar Nymphs

Relationships between adult wing-form and wing-pad length in Nilaparvata lugens were examined under laboratory conditions (25±1°C). Most of the last instar female nymphs with wing-pads shorter than 0.94 mm developed to brachypterous adults, but female nymphs with wing-pads longer than 0.94 mm became both brachypterous and macropterous adults. Thus the brachypterous females of this insect consisted of short wing-pad brachypters and long wing-pad brachypters. In females, with the increase of rearing density during the nymphal stage, short wing-pad brachypters decreased with the increase of long wing-pad brachypters. This was followed by an increase of macropters. Male nymphs with shorter wing-pads tended to become brachypterous adults, but a critical wing-pad size for induction of macropters was not detected. Male nymphs emerged as macropterous adults over the wide density range studied. Relationships between weight and wing-pad length of last instar nymphs were different between sexes. Body weight tended to be heavier in female nymphs with short wing-pads than in those with long wing-pads. The wing morph determination mechanism in N. lugens females was hypothesized to consist of 2 sequential processes. The first process may affect development of wing-pads, while the second process influences development of adult wings.

Juvenile hormone-III biosynthesis in presumptive long-winged and short-winged Gryllus rubens: Implications for the endocrine regulation of wing dimorphism

In vitro rates of juvenile hormone-III biosynthesis were quantified for corpora allata from nascent long-winged and short-winged Gryllus rubens. Rates were measured during the penultimate and last stadia, two juvenile-hormone-sensitive periods of wing morph determination. This was done to assess the contribution of differences in rates of hormone biosynthesis to juvenile-hormone-mediated morph determination. Corpora allata from individuals of the same morph, sex and stage of development exhibited low variability in juvenile hormone-III biosynthetic rates. Developmental profiles of these biosynthetic rates for each sex and morph were U-shaped during each stadium. Rates varied from 1 to 5 and 0 to 5 pmol juvenile hormone-III/h/pair corpora allata during the penultimate and last stadium, respectively. Juvenile hormone-III biosynthetic rates did not differ significantly between morphs of the same sex on any day in development, except for a few cases at the beginning or end of each stadium. In general, developmental patterns of juvenile hormone-III biosynthesis were similar between the sexes of each morph. These data (1) provide no evidence that morph-specific differences in rates of juvenile hormone-III biosynthesis underlie juvenile-hormone-mediated morph determination, and (2) further implicate previously documented variation in juvenile hormone esterase activity in morph determination. Data on juvenile hormone biosynthesis, degradation and titre also collectively implicate cessation of biosynthesis rather than elevation of juvenile hormone esterase activity in producing the steep decline in the juvenile hormone titre early in the last stadium; this decline presumably initiates metamorphosis. Alternate morph development appears to result at least in part from differential clearance of low levels of juvenile hormone following the steep decline.

Wing dimorphism in Gryllus rubens: genetic basis of morph determination and fertility differences between morphs.

The genetic basis of wing morph determination and fertility differences between wing morphs were studied in the wing-dimorphic cricket, Gryllus rubens. Using pair corsses, a significant effect of genotype on morph determination was documented in F3 progeny of field-collected crickets. The effect of genotype was significantly stronger in females than in males. Results are consistent with an earlier study (Zera and Tiebel 1988) showing that wing development is more strongly buffered from environmental variation in females. Segregation patterns were consistent with a polygenic mode of inheritance and provided no evidence for the existence of genes of major effect, maternal effects, or sex linkage. Only a weak morph x sex association was observed. These results contrast those of Walker (1987) where sex-linked loci of major effect on morph determination were identified in crosses between long-wing and short-wing-selected strains of G. rubens. Short-winged female G. rubens began ovipositing earlier and oviposited significantly more eggs than long-winged females during the first 24 days after adult eclosion. The greater reproductive output of the short-winged morph was due entirely to greater oviposition during the first two weeks after adult eclosion. Preliminary results indicate that flight may further accentuate the reduced reproductive output of long-winged versus short-winged females. These data provide the foundation for investigating the endocrine basis of morph-associated fertility variation in G. rubens and its mechanistic relationship with morph determination.

Phenological studies on the wing dimorphism of a semi‐aquatic bug, Microvelia douglasi (Heteroptera: Veliidae)

SummarySeasonal changes in the percentage of macropterous individuals in natural population of Microvelia douglasi in permanent habitats were investigated in Shimane, western part of Japan. Macropterous forms of 5th instar nymphs occurred most frequently from late June to early July. However, the seasonal appearance of macropterous adults differed between habitats and years. There were significant effects of density, temperature, photoperiod and food availability on the percentage of macropters under laboratory conditions. The percentage of macropterous forms generally increased with density, but the mode of the response was modified by temperature, photoperiod and food availability. When insects were reared under long day photperiod (16L8D) with abundant food (0.5–1.0 g/container/day), the percentage of macroptery varied most among the different density treatments at the intermediate temperature (24°C) and the difference was reduced at higher temperature (28° and 32°C). Effects of temperature were small under the short day photoperiod (12L12D). Under 12L12D photoperiod sensitivity of density responses were higher at 32°C and lower at 24°C than those under 15L8D photoperiod. When the insects were supplied with food every other day, the density response became obscure. Ecological significance of environmental responses in the wing morph determination was discussed in relation to the heterogeneous environment of water surface.

Juvenile hormone and ecdysteroid titres during critical periods of wing morph determination in Gryllus rubens

Juvenile hormone and ecdysteroid titre developmental profiles were compared between Gryllus rubens that were genetically-determined to develop into long-winged vs short-winged adults. Hormone titres were measured during the penultimate and last stadia, two periods during which wing length development is sensitive to exogenous juvenile hormone. No large differences in juvenile hormone titres were observed between nascent wing morphs during any stage in development. Slightly elevated titres were observed in long-wing vs short-wing-destined crickets during the middle third of the penultimate stadium. However, titre differences were opposite those inferred from earlier experiments involving topical application of juvenoids. An earlier decline in the juvenile hormone titre was also suggested in presumptive long-winged crickets during the last stadium. The earlier decline in macropters is consistent with previous juvenile hormone topical application experiments as well as with morph specific differences in juvenile hormone esterase activity. Peak ecdysteroid titres were higher in presumptive macropterous vs brachypterous males, while an elevated ecdysteroid titre occurred for a longer duration in macropterous females during the penultimate stadium. In both sexes, ecdysteroid titres were higher in presumptive long-winged vs short-winged morphs throughout the last stadium; peak titres were significantly higher in macropterous vs brachypterous females but not males. Both the longer duration of elevated ecdysteroid titres and the higher hormone titres in presumptive long-winged crickets are consistent with a regulatory role of ecdysteroids in wing morph determination.

Differences in juvenile hormone esterase activity between presumptive macropterous and brachypterous Gryllus rubens: Implications for the hormonal control of wing polymorphism

The developmental profile of haemolymph juvenile hormone esterase activity was compared between presumptive macropterous and brachypterous morphs of the cricket, Gryllus rubens. Activities were measured during the penultimate and last stadia, two stadia where winglength development is sensitive to both exogenous juvenile hormone and crowding. Ester hydrolysis was the exclusive or nearly exclusive route of juvenile hormone degradation in the haemolymph. Individuals of a genetic stock nearly pure-breeding for long wings exhibited substantially higher enzyme activity during the last stadium compared with individuals of a stock pure-breeding for short wings. High juvenile hormone esterase activity strongly cosegregated with long wings in F 1 interstock crosses and in F 2 backcrosses. Crickets of the macropterous stock whose winglength development was redirected to short wings by crowding exhibited low juvenile hormone esterase activity during the last stadium, similar to individuals of the brachypterous stock. Rates of juvenile hormone hydrolysis (epoxide hydrase plus esterase activity) were also higher in wingbud homogenates from last-stadium macropterous versus brachypterous females. In contrast, haemolymph enzyme activity was similar in presumptive macropterous and brachypterous morphs during the penultimate stadium. Results suggest that variation in haemolymph juvenile hormone esterase activity during the last stadium may play an important role in wingmorph determination in Gryllus rubens.

The influence of environmental factors on wing polymorphism in females of Leptopterna dolobrata (Heteroptera, Miridae).

The females of Leptopterna dolobrata (Heteroptera, Miridae) occur either as flightless brachypters or as macropterous individuals, whereas all the males are longwinged and capable of flight. The expression of this alary dimorphism is influenced by both genetic and environmental factors. Population density and temperature conditions prevailing during larval development both affect the formation of macropterous females. The larval instars L4 and/or L5 are particularly sensitive to these environmental stimuli and are thus decisive for the determination of wing-morphs.Experimentally crowded larvae developed a greater proportion of macropterous females than individuals reared at lower densities, and lower temperatures seem to counteract the stimulating effect of crowding. Larvae from different local populations varied in the proportion of macropters which developed, which could be ascribed to differences in the genetic constitution, although the genetic basis of wing-morph determination in L. dolobrata is not yet understood.There is strong evidence that in crowded populations a high percentage of the emerging macropterous females will emigrate and perform dispersal flights to new habitats. The sexual maturation of macropterous females is retarded compared with the brachypterous morph, and the dispersal flights are likely to occur during the pre-reproductive period.The underlying physiological mechanism of wingmorph determination and the adaptive significance of its environmental control are discussed on the basis of information available from other polymorphic species.