Sexual differentiation in adult insects: male-specific cuticular yellowing in Schistocerca gregaria as a model for reevaluating some current (neuro)endocrine concepts

Sexual repurposing of juvenile aposematism in locusts

Adaptive plasticity requires an integrated suite of functional responses to environmental variation, which can include social communication across life stages. Desert locusts (Schistocerca gregaria) exhibit an extreme example of phenotypic plasticity called phase polyphenism, in which a suite of behavioral and morphological traits differ according to local population density. Male and female juveniles developing at low population densities exhibit green- or sand-colored background-matching camouflage, while at high densities they show contrasting yellow and black aposematic patterning that deters predators. The predominant background colors of these phenotypes (green/sand/yellow) all depend on expression of the carotenoid-binding "Yellow Protein" (YP). Gregarious (high-density) adults of both sexes are initially pinkish, before a YP-mediated yellowing reoccurs upon sexual maturation. Yellow color is especially prominent in gregarious males, but the reason for this difference has been unknown since phase polyphenism was first described in 1921. Here, we use RNA interference to show that gregarious male yellowing acts as an intrasexual warning signal, which forms a multimodal signal with the antiaphrodisiac pheromone phenylacetonitrile (PAN) to prevent mistaken sexual harassment from other males during scramble mating in a swarm. Socially mediated reexpression of YP thus adaptively repurposes a juvenile signal that deters predators into an adult signal that deters undesirable mates. These findings reveal a previously underappreciated sexual dimension to locust phase polyphenism, and promote locusts as a model for investigating the relative contributions of natural versus sexual selection in the evolution of phenotypic plasticity.

A male steroid controls female sexual behaviour in the malaria mosquito

Insects, unlike vertebrates, are widely believed to lack male-biased sex steroid hormones¹. In the malaria mosquito Anopheles gambiae, the ecdysteroid 20-hydroxyecdysone (20E) appears to have evolved to both control egg development when synthesized by females² and to induce mating refractoriness when sexually transferred by males³. Because egg development and mating are essential reproductive traits, understanding how Anopheles females integrate these hormonal signals can spur the design of new malaria control programs. Here we reveal that these reproductive functions are regulated by distinct sex steroids through a sophisticated network of ecdysteroid-activating/inactivating enzymes. We identify a male-specific oxidized ecdysteroid, 3-dehydro-20E (3D20E), which safeguards paternity by turning off female sexual receptivity following its sexual transfer and activation by dephosphorylation. Notably, 3D20E transfer also induces expression of a reproductive gene that preserves egg development during Plasmodium infection, ensuring fitness of infected females. Female-derived 20E does not trigger sexual refractoriness but instead licenses oviposition in mated individuals once a 20E-inhibiting kinase is repressed. Identifying this male-specific insect steroid hormone and its roles in regulating female sexual receptivity, fertility and interactions with Plasmodium parasites suggests the possibility for reducing the reproductive success of malaria-transmitting mosquitoes.

Knockdown of ecdysone receptor in male desert locusts affects relative weight of accessory glands and mating behavior

Locusts have been known as pests of agricultural crops for thousands of years. Recently (2018-2021) the world has faced the largest swarms of desert locusts, Schistocerca gregaria, in decades and food security in large parts of Africa and Asia was under extreme pressure. There is an urgent need for the development of highly specific bio-rational pesticides to combat these pests. However, to do so, fundamental research is needed to better understand the molecular mechanisms behind key physiological processes underpinning swarm formation, such as development and reproduction. The scope of this study is to investigate the possible role(s) of the ecdysteroid receptor in the reproductive physiology of male S. gregaria. Ecdysteroids and juvenile hormones are two important classes of insect hormones and are key regulators of post-embryonic development. Ecdysteroids are best known for their role in moulting and exert their function via a heterodimer consisting of the nuclear receptors ecdysone receptor (EcR) and retinoid-X receptor (RXR). To gain insight into the role of SgEcR and/or SgRXR in the male reproductive physiology of S. gregaria we performed RNAi-induced knockdown experiments. A knockdown of SgEcR, but not SgRXR, resulted in an increased relative weight of the male accessory glands (MAG). Furthermore, the knockdown of these genes, either in combination or separately, caused a significant delay in the onset of mating behavior. Nevertheless, the MAG appeared to mature normally and the fertility of mated males was not affected. The high transcript levels of SgEcR in the fat body, especially towards the end of sexual maturation in both males and females, represent a remarkable finding since as of yet the exact role of SgEcR in this tissue in S. gregaria is unknown. Finally, our data suggest that in some cases SgEcR and SgRXR might act independently of each other. This is supported by the fact that the spatiotemporal expression profiles of SgEcR and SgRXR do not always coincide and that knockdown of SgEcR, but not SgRXR, significantly affected the relative weight of the MAG.

Yellowing and YPT gene expression in the desert locust, Schistocerca gregaria: Effects of developmental stages and fasting

The yellow protein of the takeout family (YPT) controls the development of yellow body color in the desert locust. This study focused on two aspects related to YPT in the locust. We first examined the expression pattern of YPT during nymphal stages because yellowing was not obvious during the early instars. YPT expression levels were extremely low in the second and third instars compared with the last two nymphal instars. Warm rearing temperature and juvenile hormone (JH) injection, which stimulated YPT expression in the late instars, had little effect in the second instar, suggesting that YPT expression during the early instars was suppressed and could not be stimulated by either of these factors. We also investigated delayed yellowing in fasting male adults, under the hypothesis that fasting decreased the JH titers and delayed the onset of YPT expression. Yellowing was delayed in fasting adults compared with well-fed adults and YPT expression was stimulated by JH injections at Day 15. However, we failed to obtain evidence that fasting significantly influenced the expression levels of YPT and the JH early-inducible gene Krüppel homolog 1 at Days 15 and 20 post-adult emergence. Results suggest that a YPT-independent mechanism possibly induces delayed yellowing in fasting males.

Nitrate: An Environmental Endocrine Disruptor? A Review of Evidence and Research Needs

Nitrate is heavily used as an agricultural fertilizer and is today a ubiquitous environmental pollutant. Environmental endocrine effects caused by nitrate have received increasing attention over the last 15 years. Nitrate is hypothesized to interfere with thyroid and steroid hormone homeostasis and developmental and reproductive end points. The current review focuses on aquatic ecotoxicology with emphasis on field and laboratory controlled in vitro and in vivo studies. Furthermore, nitrate is just one of several forms of nitrogen that is present in the environment and many of these are quickly interconvertible. Therefore, the focus is additionally confined to the oxidized nitrogen species (nitrate, nitrite and nitric oxide). We reviewed 26 environmental toxicology studies and our main findings are (1) nitrate has endocrine disrupting properties and hypotheses for mechanisms exist, which warrants for further investigations; (2) there are issues determining actual nitrate-speciation and abundance is not quantified in a number of studies, making links to speciation-specific effects difficult; and (3) more advanced analytical chemistry methodologies are needed both for exposure assessment and in the determination of endocrine biomarkers.

Environmental and hormonal control of body color polyphenism in late-instar desert locust nymphs: Role of the yellow protein

Locusts show body color polyphenism that is considered to be an adaptation to various biotic and abiotic environmental changes. In Schistocerca gregaria, wild-type late-instar nymphs growing under crowded conditions (gregarious form) develop yellow and black body coloration, whereas they assume various body colors under isolated conditions (solitarious form). Black and green body colorations are induced by the neuropeptide corazonin (Crz) and juvenile hormone (JH), respectively. To characterize the molecular mechanisms controlling body color polyphenism, we investigated factors influencing body coloration in S. gregaria. We report here that yellow body coloration in the last nymphal instar is caused by the yellow protein of the takeout family (YPT) in this locust. YPT transcription was enhanced under high-temperature conditions during which the nymphs turned bright yellow and had little black patterning. RNAi-mediated YPT knockdown suppressed the appearance of yellow individuals and yellow staining in the exuviae. In albino nymphs, injection of JH induced yellow and green coloration and enhanced the YPT expression levels in both yellow and green individuals. YPT knockdown also suppressed yellow staining in the exuviae but did not prevent the appearance of yellow individuals. Therefore, another factor or pigment may contribute to the observed yellow body color. Injection of Crz into wild-type nymphs caused darkening and suppressed yellowing and YPT expression at high temperatures. Thus, Crz signaling could inhibit yellowing by suppressing YPT expression. Rearing cup substrate color significantly influenced YPT expression in albino nymphs both under isolated and crowded conditions. In contrast, substrate color affected YPT expression in wild-type nymphs only under isolated conditions. From these results, we conclude that YPT is an important factor in the control of body color polyphenism in S. gregaria, and its expression is influenced by temperature, JH, Crz, and substrate color of the growing environment.

Steroid hormone signaling during development has a latent effect on adult male sexual behavior in the butterfly Bicyclus anynana

It is well established that steroid hormones regulate sexual behavior in vertebrates via organizational and activational effects. However, whether the organizational/activational paradigm applies more broadly to the sexual behavior of other animals such as insects is not well established. Here we describe the hormonal regulation of a sexual behavior in the seasonally polyphenic butterfly Bicyclus anynana is consistent with the characteristics of an organizational effect. By measuring hormone titer levels, quantifying hormone receptor gene expression in the brain, and performing hormone manipulations, we demonstrate steroid hormone signaling early in pupal development has a latent effect on adult male sexual behavior in B. anynana. These findings suggest the organizational/activational paradigm may be more highly conserved across animal taxa than previously thought.

Comparing the impacts of sediment-bound bifenthrin on aquatic macroinvertebrates in laboratory bioassays and field microcosms

We conducted two laboratory bioassays and two field microcosm exposures with bifenthrin (a synthetic pyrethroid) in order to evaluate the capacity of single-species laboratory bioassays to predict lethal and sublethal impacts on aquatic invertebrates in microcosms. For the laboratory species, Chironomus tepperi, larval survival was reduced by 24% at 53.66µg/g OC, while adult emergence was reduced at concentrations of 33.33µg/g OC and higher, with a 61% decrease at 77.78µg/g OC and no emergence at 126.67µg/g OC. The abundance of several other microcosm taxa was reduced in the microcosms at a similar concentration range (33.33µg/g OC and above), however there was no impact on the abundance of the congeneric species, Chironomus oppositus. The differences in impacts between test systems were potentially due to both differing species sensitivity and the interaction of ambient temperature with bifenthrin toxicity. Bifenthrin also was associated with early emergence of Chironomus sp. in both test systems, at concentrations of 10µg/g OC and higher (laboratory) and 43.90µg/g OC (microcosm), and with a significant decrease in the proportion of C. oppositus males in a microcosm. These findings indicate that while laboratory bioassays accurately predict many impacts in the field, there are some limitations to the predictive capacity of these tests.

Foxl2 and Its Relatives Are Evolutionary Conserved Players in Gonadal Sex Differentiation

Foxl2 is a member of the large family of Forkhead Box (Fox) domain transcription factors. It emerged during the last 15 years as a key player in ovarian differentiation and oogenesis in vertebrates and especially mammals. This review focuses on Foxl2 genes in light of recent findings on their evolution, expression, and implication in sex differentiation in animals in general. Homologs of Foxl2 and its paralog Foxl3 are found in all metazoans, but their gene evolution is complex, with multiple gains and losses following successive whole genome duplication events in vertebrates. This review aims to decipher the evolutionary forces that drove Foxl2/3 gene specialization through sub- and neo-functionalization during evolution. Expression data in metazoans suggests that Foxl2/3 progressively acquired a role in both somatic and germ cell gonad differentiation and that a certain degree of sub-functionalization occurred after its duplication in vertebrates. This generated a scenario where Foxl2 is predominantly expressed in ovarian somatic cells and Foxl3 in male germ cells. To support this hypothesis, we provide original results showing that in the pea aphid (insects) foxl2/3 is predominantly expressed in sexual females and showing that in bovine ovaries FOXL2 is specifically expressed in granulosa cells. Overall, current results suggest that Foxl2 and Foxl3 are evolutionarily conserved players involved in somatic and germinal differentiation of gonadal sex.

The potential and prospects of proximal remote sensing of arthropod pests

Bench-top or proximal remote sensing applications are widely used as part of quality control and machine vision systems in commercial operations. In addition, these technologies are becoming increasingly important in insect systematics and studies of insect physiology and pest management. This paper provides a review and discussion of how proximal remote sensing may contribute valuable quantitative information regarding identification of species, assessment of insect responses to insecticides, insect host responses to parasitoids and performance of biological control agents. The future role of proximal remote sensing is discussed as an exciting path for novel paths of multidisciplinary research among entomologists and scientists from a wide range of other disciplines, including image processing engineers, medical engineers, research pharmacists and computer scientists. © 2015 Society of Chemical Industry.

Remote Sensing and Reflectance Profiling in Entomology

Remote sensing describes the characterization of the status of objects and/or the classification of their identity based on a combination of spectral features extracted from reflectance or transmission profiles of radiometric energy. Remote sensing can be benchtop based, and therefore acquired at a high spatial resolution, or airborne at lower spatial resolution to cover large areas. Despite important challenges, airborne remote sensing technologies will undoubtedly be of major importance in optimized management of agricultural systems in the twenty-first century. Benchtop remote sensing applications are becoming important in insect systematics and in phenomics studies of insect behavior and physiology. This review highlights how remote sensing influences entomological research by enabling scientists to nondestructively monitor how individual insects respond to treatments and ambient conditions. Furthermore, novel remote sensing technologies are creating intriguing interdisciplinary bridges between entomology and disciplines such as informatics and electrical engineering.

Initiation of metamorphosis and control of ecdysteroid biosynthesis in insects: The interplay of absence of Juvenile hormone, PTTH, and Ca(2+)-homeostasis

The paradigm saying that release of the brain neuropeptide big prothoracicotropic hormone (PTTH) initiates metamorphosis by activating the Torso-receptor/ERK pathway in larval prothoracic glands (PGs) is widely accepted nowadays. Upon ligand-receptor interaction Ca(2+) enters the PG cells and acts as a secondary messenger. Ecdysteroidogenesis results, later followed by apoptosis. Yet, some data do not fit in this model. In some species decapitated animals can still molt, even repeatedly, and metamorphose. PTTH does not universally occur in all insect species. PGs may also have other functions; PGs as counterpart of the vertebrate thymus? There are also small PTTHs. Finally, PTTH remains abundantly present in adults and plays a role in control of ecdysteroidogenesis (=sex steroid production) in gonads. This is currently documented only in males. This urges a rethinking of the PTTH-PG paradigm. The key question is: Why does PTTH-induced Ca(2+) entry only result in ecdysteroidogenesis and apoptosis in specific cells/tissues, namely the PGs and gonads? Indeed, numerous other neuropeptides also use Ca(2+) as secondary messenger. The recent rediscovery that in both invertebrates and vertebrates at least some isoforms of Ca(2+)-ATPase need the presence of an endogenous farnesol/juvenile hormone(JH)-like sesquiterpenoid for keeping cytosolic [Ca(2+)]i below the limit of apoptosis-induction, triggered the idea that it is not primarily PTTH, but rather the drop to zero of the JH titer that acts as the primordial initiator of metamorphosis by increasing [Ca(2+)]i. PTTH likely potentiates this effect but only in cells expressing Torso. PTTH: an evolutionarily ancient gonadotropin?

Detection of temporal changes in insect body reflectance in response to killing agents

Computer vision and reflectance-based analyses are becoming increasingly important methods to quantify and characterize phenotypic responses by whole organisms to environmental factors. Here, we present the first study of how a non-destructive and completely non-invasive method, body reflectance profiling, can be used to detect and time stress responses in adult beetles. Based on high-resolution hyperspectral imaging, we acquired time series of average reflectance profiles (70 spectral bands from 434-876 nm) from adults in two beetle species, maize weevils (Sitophilus zeamais) and larger black flour beetles (Cynaus angustus). For each species, we acquired reflectance data from untreated controls and from individuals exposed continuously to killing agents (an insecticidal plant extract applied to maize kernels or entomopathogenic nematodes applied to soil applied at levels leading to ≈100% mortality). In maize weevils (exposed to hexanic plant extract), there was no significant effect of the on reflectance profiles acquired from adult beetles after 0 and 12 hours of exposure, but a significant treatment response in spectral bands from 434 to 550 nm was detected after 36 to 144 hours of exposure. In larger black flour beetles, there was no significant effect of exposure to entomopathogenic nematodes after 0 to 26 hours of exposure, but a significant response in spectral bands from 434-480 nm was detected after 45 and 69 hours of exposure. Spectral bands were used to develop reflectance-based classification models for each species, and independent validation of classification algorithms showed sensitivity (ability to positively detect terminal stress in beetles) and specificity (ability to positively detect healthy beetles) of about 90%. Significant changes in body reflectance occurred at exposure times, which coincided with published exposure times and known physiological responses to each killing agent. The results from this study underscore the potential of hyperspectral imaging as an approach to non-destructively and non-invasively quantify stress detection in insects and other animals.

Neuropeptides affecting the transfer of juvenile hormones from males to females during mating in Spodoptera frugiperda

In the polyandric moth, Spodopterafrugiperda, juvenile hormone (JH) is transferred from the male accessory reproductive glands (AG) to the female bursa copulatrix (BC) during copulation (see Hassanien et al., 2014). Here we used the RNA interference technique to study the role of allatoregulating neuropeptides in controlling the synthesis and transfer of JH during mating. Knockdown of S. frugiperda allatostatin C (Spofr-AS type C) in freshly emerged males leads to an accumulation of JH in the AG beyond that in the control and mating results in a higher transport of JH I and JH II into the female BC. Knockdown of S. frugiperda allatotropin 2 (Spofr-AT2) significantly reduces the amount of JH in the AG as well as its transfer into the female BC during copulation. Knockdown of S. frugiperda allatostatin A (Spofr-AS type A) and S. frugiperda allatotropin (Spofr-AT; Hassanien et al., 2014) only slightly affects the accumulation of JH in the AG and its transfer from the male to the female. We conclude that Spofr-AS type C and Spofr-AT2 act as true allatostatin and true allatotropin, respectively, on the synthesis of JH I and JH II in the male AG. Moreover, both peptides seem to control the synthesis of JH III in the corpora allata of adult males and its release into the hemolymph.

The essence of insect metamorphosis and aging: electrical rewiring of cells driven by the principles of juvenile hormone-dependent Ca(2+)-homeostasis

In holometabolous insects the fall to zero of the titer of Juvenile Hormone ends its still poorly understood "status quo" mode of action in larvae. Concurrently it initiates metamorphosis of which the programmed cell death of all internal tissues that actively secrete proteins, such as the fat body, midgut, salivary glands, prothoracic glands, etc. is the most drastic aspect. These tissues have a very well developed rough endoplasmic reticulum, a known storage site of intracellular Ca(2+). A persistent high [Ca(2+)]i is toxic, lethal and causal to apoptosis. Metamorphosis becomes a logical phenomenon if analyzed from: (1) the causal link between calcium toxicity and apoptosis; (2) the largely overlooked fact that at least some isoforms of Ca(2+)-ATPases have a binding site for farnesol-like endogenous sesquiterpenoids (FRS). The Ca(2+)-ATPase blocker thapsigargin, like JH a sesquiterpenoid derivative, illustrates how absence of JH might work. The Ca(2+)-homeostasis system is concurrently extremely well conserved in evolution and highly variable, enabling tissue-, developmental-, and species specificity. As long as JH succeeds in keeping [Ca(2+)]i low by keeping the Ca(2+)-ATPases pumping, it acts as "the status quo" hormone. When it disappears, its various inhibitory effects are lifted. The electrical wiring system of cells, in particular in the regenerating tissues, is subject to change during metamorphosis. The possibility is discussed that in vertebrates an endogenous farnesol-like sesquiterpenoid, probably farnesol itself, acts as a functional, but hitherto completely overlooked Juvenile anti-aging "Inbrome", a novel concept in signaling.

Reflectance-based identification of parasitized host eggs and adult Trichogramma specimens

A wide range of imaging and spectroscopy technologies is used in medical diagnostics, quality control in production systems, military applications, stress detection in agriculture, and ecological studies of both terrestrial and aquatic organisms. In this study, we hypothesized that reflectance profiling can be used to successfully classify animals that are otherwise very challenging to classify. We acquired hyperspectral images from adult specimens of the egg parasitoid genus Trichogramma (T. galloi, T. pretiosum and T. atopovirilia), which are ~1.0 mm in length. We also acquired hyperspectral images from host eggs containing developing Trichogramma instar and pupae. These obligate egg endoparasitoid species are commercially available as natural enemies of lepidopteran pests in food production systems. Because of their minute size and physical resemblance, classification is time consuming and requires a high level of technical experience. The classification of reflectance profiles was based on a combination of average reflectance and variogram parameters (describing the spatial structure of reflectance data) of reflectance values in individual spectral bands. Although variogram parameters (variogram analysis) are commonly used in large-scale spatial research (i.e. geoscience and landscape ecology), they have only recently been used in classification of high-resolution hyperspectral imaging data. The classification model of parasitized host eggs was equally successful for each of the three species and was successfully validated with independent data sets (>90% classification accuracy). The classification model of adult specimens accurately separated T. atopovirilia from the other two species, but specimens of T. galloi and T. pretiosum could not be accurately separated. Interestingly, molecular-based classification (using the DNA sequence of the internally transcribed spacer ITS2) of Trichogramma species published elsewhere corroborates the classification, as T. galloi and T. pretiosum are closely related and comparatively distant from T. atopovirilia. Our results emphasize the importance of using high-spectral and high-spatial resolution data in the classification of organism relatedness, and hyperspectral imaging may be of relevance to a wide range of commercial (i.e. producers of biocontrol agents), taxonomic and evolutionary research applications.

The mode of action of juvenile hormone and ecdysone: towards an epi-endocrinological paradigm?

In some insect species, two sites of juvenile hormone (JH) synthesis have been reported: the very well documented corpora allata that secrete JH for "general use", and the reproductive system, in particular the male accessory glands, in which the function of the sometimes huge amounts of JH (e.g. in Hyalophora cecropia) remains to be clarified. A recent finding in Schistocerca gregaria, namely that suppression of the ecdysteroid peak preceding a molt by RNAi of the Halloween genes spook, phantom and shade does not impede normal molting, challenges the (never experimentally proven) classical concept that such a peak is causally linked to a molt. Recent developments in epigenetic control of gene expression in both the honey bee and in locusts suggest that, in addition to the classical scheme of hormone-receptor (membrane- and/or nuclear) mode of action, there may be a third way. Upon combining these and other orphan data that do not fit in the commonly accepted textbook schemes, we here advance the working hypothesis that both JH and ecdysone might be important but overlooked players in epigenetic control of gene expression, in particular at extreme concentrations (peak values or total absence). In this review, we put forward how epi-endocrinology can complement classical arthropod endocrinology.

Both cell-autonomous mechanisms and hormones contribute to sexual development in vertebrates and insects

The differentiation of male and female characteristics in vertebrates and insects has long been thought to proceed via different mechanisms. Traditionally, vertebrate sexual development was thought to occur in two phases: a primary and a secondary phase, the primary phase involving the differentiation of the gonads, and the secondary phase involving the differentiation of other sexual traits via the influence of sex hormones secreted by the gonads. In contrast, insect sexual development was thought to depend exclusively on cell-autonomous expression of sex-specific genes. Recently, however, new evidence indicates that both vertebrates and insects rely on sex hormones as well as cell-autonomous mechanisms to develop sexual traits. Collectively, these new data challenge the traditional vertebrate definitions of primary and secondary sexual development, call for a redefinition of these terms, and indicate the need for research aimed at explaining the relative dependence on cell-autonomous versus hormonally guided sexual development in animals.

Accessory gland as a site for prothoracicotropic hormone controlled ecdysone synthesis in adult male insects

Insect steroid hormones (ecdysteroids) are important for female reproduction in many insect species and are required for the initiation and coordination of vital developmental processes. Ecdysteroids are also important for adult male physiology and behavior, but their exact function and site of synthesis remains unclear, although previous studies suggest that the reproductive system may be their source. We have examined expression profiles of the ecdysteroidogenic Halloween genes, during development and in adults of the flour beetle Tribolium castaneum. Genes required for the biosynthesis of ecdysone (E), the precursor of the molting hormone 20-hydroxyecdysone (20E), are expressed in the tubular accessory glands (TAGs) of adult males. In contrast, expression of the gene encoding the enzyme mediating 20E synthesis was detected in the ovaries of females. Further, Spookiest (Spot), an enzyme presumably required for endowing tissues with competence to produce ecdysteroids, is male specific and predominantly expressed in the TAGs. We also show that prothoracicotropic hormone (PTTH), a regulator of E synthesis during larval development, regulates ecdysteroid levels in the adult stage in Drosophila melanogaster and the gene for its receptor Torso seems to be expressed specifically in the accessory glands of males. The composite results suggest strongly that the accessory glands of adult male insects are the main source of E, but not 20E. The finding of a possible male-specific source of E raises the possibility that E and 20E have sex-specific roles analogous to the vertebrate sex steroids, where males produce primarily testosterone, the precursor of estradiol. Furthermore this study provides the first evidence that PTTH regulates ecdysteroid synthesis in the adult stage and could explain the original finding that some adult insects are a rich source of PTTH.

Do desert locust hoppers develop gregarious characteristics by watching a video?

Various sensory stimuli have been suggested to induce gregarious body coloration in locusts, but most previous studies ignored the importance of substrate color. This study tested the effects of visual, olfactory and tactile stimuli from other locusts on the induction of gregarious body coloration in single (isolated-reared) Schistocerca gregaria nymphs housed in yellow-green cups. Odor from gregarious (crowd-reared) locusts, which is believed to induce black patterns in single locusts, had little effect when applied to visually isolated nymphs at the 2nd stadium onward, and all test nymphs remained green without black patterns at the last stadium, as in controls reared without odor and visual stimuli. Visual stimuli alone induced black patterns when a single solitarious nymph was allowed to see other locusts in another cup. The degree of black patterns increased as the number of locusts shown increased, and some test nymphs developed body coloration typically observed in gregarious forms. A classical morphometric ratio (hind femur length/head width) shifted toward the value typical of gregarious forms when the single nymphs were allowed to see 5 or 10 locusts. Single nymphs also developed black patterns when presented green conspecific nymphs and adults of two hemipteran species kept in another cup. No synergetic effects of visual and odor stimuli were detected. Movies of locusts, crickets and tadpoles were found effective in inducing black patterns in single locusts. Ontogenetic variation in the sensitivity to crowding and experimental methodology might be responsible for some discrepancies in the conclusions among different researchers.

Fruitless RNAi knockdown in males interferes with copulation success in Schistocerca gregaria

In Drosophila melanogaster, the male-specific splice isoform of the fruitless gene (Fru(M)) codes for a set of transcription factors that are involved in the regulation of male courtship and copulation. Fru(M) is expressed in an interconnected neuronal circuit containing central and sensory neurons as well as motor neurons. A partial sequence from the Schistocerca gregaria fru-gene from an EST database allowed quantitative real time analysis of fru-expression in adult locusts, and revealed the highest expression in the testes, accessory glands as well as the brain (and optic lobes). Starting fru specific RNAi knockdown in the third and fourth nymphal stage resulted in a significantly lower cumulative copulation frequency of the RNAi-treated animals compared to controls after 3 h of observation. In addition, the testes of RNAi-treated males weigh less. Analysis of the egg pods resulting from a successful copulation event revealed that egg pods from females that mated with an RNAi-treated male were smaller and contained less fertilized eggs compared to egg pods from females who mated with control males. Starting injections in the fifth nymphal stage showed the complete opposite for the cumulative copulation frequency and testes weight. We conclude that already in the early nymphal phases of male desert locusts, fruitless starts to play an important role in the regulation of successful copulation in the adult. The RNAi treatment in the male has also its effects on fertility and fecundity. It remains unknown whether this effect is coming from aberrant courtship behaviour or from an altered composition of the sperm or seminal fluids.