Target for lipid-to-carbohydrate intake minimizes cost of growth.

Many theoretical treatments of foraging use energy as currency, with carbohydrates and lipids considered interchangeable as energy sources. However, herbivores must often synthesize lipids from carbohydrates since they are in short supply in plants, theoretically increasing the cost of growth. We tested whether a generalist insect herbivore (Locusta migratoria) can improve its growth efficiency by consuming lipids, and whether these locusts have a preferred caloric intake ratio of carbohydrate to lipid (C : L). Locusts fed pairs of isocaloric, isoprotein diets differing in C and L consistently selected a 2C : 1L target. Locusts reared on isocaloric, isoprotein 3C : 0L diets attained similar final body masses and lipid contents to locusts fed the 2C : 1L diet, but they ate more and had a ~12% higher metabolic rate, indicating an energetic cost for lipogenesis. These results demonstrate that some animals can selectively regulate carbohydrate-to-lipid intake and that consumption of dietary lipids can improve growth efficiency.

Risk of migration: not all gregarious locust nymphs reach appropriate refuges.

Sedentary animals choose appropriate refuges against predators, while migratory ones may not necessarily do so. In ectotherms, refuge selection is critical during low temperatures, because they cannot actively evade predators. To understand how migratory ectotherms alter their defensive behaviors depending on refuge quality in cold temperatures, we evaluated migratory gregarious desert locust nymphs (Schistocerca gregaria) in the Sahara Desert, where daily thermal constraints occur. We recorded how roosting plant type (bush/shrub) and its height influenced two alternative defense behaviors (dropping/stationary) during cold mornings, in response to an approaching simulated ground predator. Most locusts in bushes dropped within the bush and hid irrespective of their height, whereas those roosting > 2 m height in shrubs remained stationary. These defenses are effective and match with refuge plant types because dynamic locomotion is not required. When nymphs roosted on shrubs < 1.5-m height, which was an unsafe position, nearly half showed both defensive behaviors, indicating that escaping decisions become ambiguous when the refuges are inappropriate. These results suggest that locusts display flexible defensive behaviors when finding appropriate refuges and selecting refuge before daily thermal limitations occur could be critical for migratory ectotherms, which is a risk associated with migration.

Study on the prediction method of grasshopper occurrence risk in Inner Mongolia based on the maximum entropy model during the growing period.

Grasshoppers represent a significant biological challenge in Inner Mongolia's grasslands, severely affecting the region's animal husbandry. Thus, dynamic monitoring of grasshopper infestation risk is crucial for sustainable livestock farming. This study employed the Maxent model, along with remote sensing data, to forecast Oedaleus decorus asiaticus occurrence during the growing season, using grasshopper suitability habitats as a base. The Maxent model's predictive accuracy was high, with an AUC of 0.966. The most influential environmental variables for grasshopper distribution were suitable habitat data (34.27%), the temperature-vegetation dryness index during the spawning period (18.81%), and various other meteorological and vegetation factors. The risk index model was applied to calculate the grasshopper distribution across different risk levels for the years 2019-2022. The data indicated that the level 1 risk area primarily spans central, eastern, and southwestern Inner Mongolia. By examining the variable weights, the primary drivers of risk level fluctuation from 2019 to 2022 were identified as accumulated precipitation and land surface temperature anomalies during the overwintering period. This study offers valuable insights for future O. decorus asiaticus monitoring in Inner Mongolia.

Chewing insects, pollinators, and predators on Acacia auriculiformis A. Cunn. ex Beth (Fabales: Fabaceae) plants fertilized with dehydrated sewage sludge / Insetos mastigadores, polinizadores e predadores em plantas de Acacia auriculiformis A. Cunn. ex Beth (Fabales: Fabaceae) fertilizada com lodo de esgoto desidratado

Fertilization with dehydrated sewage sludge can speed up the recovery process of degraded areas due to nutrients concentration, favoring the development of pioneer plants such as Acacia auriculiformis A. Cunn. ex Beth (Fabales: Fabaceae) and the emergence of insects. This study aimed the evaluation of chewing, pollinating insects, predators, their ecological indices and relationships on A. auriculiformis plants fertilized with dehydrated sewage sludge. The experimental design was completely randomized with two treatments (with and without dehydrated sewage sludge) and 24 repetitions. The prevalence of chewing insects Parasyphraea sp. (Coleoptera: Chrysomelidae), Nasutitermes sp. (Blattodea: Termitidae), and Tropidacris collaris (Stoll, 1813) (Orthoptera: Romaleidae), defoliation, and ecological indices of abundance of Coleoptera and Orthoptera were observed on fertilized A. auriculiformis. Acacia auriculiformis plants, with a superior number of branches/tree, revealed greater abundance of Coleoptera and Orthoptera, species richness of pollinating insects, defoliation, numbers of Parasyphraea sp. and T. collaris. The ones with larger leaves/branches displayed greater abundance of species richness of Coleoptera and Diabrotica speciosa (Germar, 1824) (Coleoptera: Chrysomelidae). Therefore, the use of A. auriculiformis plants, fertilized with dehydrated sewage sludge, is promising in the recovery of degraded areas due to the ecological indices increase of chewing and pollinators insects and spiders in the analyzed area.

A fertilização com lodo de esgoto desidratado pode acelerar o processo de recuperação de áreas degradadas devido à concentração de nutrientes, favorecendo o desenvolvimento de plantas pioneiras tais como Acacia auriculiformis A. Cunn. ex Beth (Fabales: Fabaceae) e de seus insetos. O objetivo deste trabalho foi avaliar os insetos mastigadores, polinizadores e predadores e seus índices e relações ecológicas em plantas de A. auriculiformis fertilizadas com lodo de esgoto desidratado, em área degradada, durante 24 meses. O delineamento foi inteiramente casualizados com dois tratamentos (com e sem adubação com lodo de esgoto desidratado) e 24 repetições (uma repetição = uma planta). O maior número de insetos mastigadores Parasyphraea sp. (Coleoptera: Chrysomelidae), Nasutitermes sp. (Blattodea: Termitidae) e Tropidacris collaris (Stoll, 1813) (Orthoptera: Romaleidae), de desfolha, e do índice ecológico abundância de Coleoptera e de Orthoptera foram maiores em plantas de A. auriculiformis fertilizadas do que nas não fertilizadas com lodo de esgoto desidratado. Plantas de A. auriculiformis, com maior quantidade de galhos/árvore, apresentaram maiores abundâncias de Coleoptera e Orthoptera, riqueza de espécies de insetos polinizadores, desfolha e números de Parasyphraea sp. e T. collaris, e as com maior folhas/galho os de riqueza de espécies de Coleoptera e Diabrotica speciosa (Germar, 1824) (Coleoptera: Chrysomelidae). Por tanto, a utilização de A. auriculiformis, adubada com lodo de esgoto desidratado, é promissora na recuperação de áreas degradadas devido ao aumento dos índices ecológicos de insetos mastigadores, polinizadores e aranhas na área.

Predicting the current and future distribution of the edible long-horned grasshopper Ruspolia differens (Serville) using temperature-dependent phenology models.

The edible long-horned grasshopper Ruspolia differens (Serville) is widely distributed and consumed in sub-Saharan Africa. Efficient mass rearing of the edible grasshopper is critical to ensure their sustainable supply for food and nutritional security. Hence, we investigated the effect of temperature on development, survival and reproduction of R. differens under six constant (15, 20, 25, 30, 32 and 35 °C) and fluctuating temperatures. Using Insect Life Cycle Modeling software we fitted, linear and non-linear models to R. differens development, mortality, longevity, and fecundity. The best-fitted functions were compiled for each life stage to yield a phenology model, which was stochastically simulated to estimate the life table parameters. We used the process-based climatic phenology models, and applied establishment risk index (ERI) and generation index (GI) in a geographic information system to map the potential distribution of R. differens under current and future climates. At optimum temperatures of 30-32 °C, egg incubation period was 14-15 days and the developmental time was shortest at 52.5-58 days. Lowest nymphal mortality (3.4-13%) and the highest female fecundity was obtained at 25-30 °C. The optimum temperature for the reproduction ranged between 27 and 30 °C. Most simulated lifetable parameters were at their maximum at 28 °C. Predictive models showed that countries in the East, Central, West, Southern and the Horn of Africa were suitable for establishment of R. differens under current climate scenarios (2000). However, by 2050, climatically suitable areas for the establishment of R. differens were predicted to shrink in the West, Southern and the Horn of Africa than its current distribution. We predict up to three generations per year for R. differens in sub-Saharan Africa under current scenarios which can increase to 4 under future scenarios. The optimum rearing temperatures identified can guide optimization of mass rearing of R. differens.

Infectivity of Paranosema locustae (Microsporidia) against gregarious-phase South American locust (Orthoptera) when treated en masse.

En masse inoculations with Paranosema locustae, an intracellular parasite of adipose tissue of grasshoppers and locusts and the only microsporidium registered as a biocontrol agent, were conducted against crowded fourth-instar nymphs of the South American locust Schistocerca cancellata and the grasshoppers Dichroplus schulzi and Ronderosia bergii. Infection did not develop in the locust, but was highly prevalent in the two grasshopper species. We hypothesize that absolute absence of infection in S. cancellata may constitute a case of density-dependent prophylactic resistance, an elevation of the baseline immunity of an organism in order to cope with disease that is prevalent in species exhibiting phase polyphenism.

Oxygen supply limits the chronic heat tolerance of locusts during the first instar only.

Although scientists know that overheating kills many organisms, they do not agree on the mechanism. According to one theory, referred to as oxygen- and capacity-limitation of thermal tolerance, overheating occurs when a warming organism's demand for oxygen exceeds its supply, reducing the organism's supply of ATP. This model predicts that an organism's heat tolerance should decrease under hypoxia, yet most terrestrial organisms tolerate the same amount of warming across a wide range of oxygen concentrations. This point is especially true for adult insects, who deliver oxygen through highly efficient respiratory systems. However, oxygen limitation at high temperatures may be more common during immature life stages, which have less developed respiratory systems. To test this hypothesis, we measured the effects of heat and hypoxia on the survival of South American locusts (Schistocerca cancellata) throughout development and during specific instars. We demonstrate that the heat tolerance of locusts depends on oxygen supply during the first instar but not during later instars. This finding provides further support for the idea that oxygen limitation of thermal tolerance depends on respiratory performance, especially during immature life stages.

Designing monitoring protocols to measure population trends of threatened insects: A case study of the cryptic, flightless grasshopper Brachaspis robustus.

Statistically robust monitoring of threatened populations is essential for effective conservation management because the population trend data that monitoring generates is often used to make decisions about when and how to take action. Despite representing the highest proportion of threatened animals globally, the development of best practice methods for monitoring populations of threatened insects is relatively uncommon. Traditionally, population trend data for the Nationally Endangered New Zealand grasshopper Brachaspis robustus has been determined by counting all adults and nymphs seen on a single ~1.5 km transect searched once annually. This method lacks spatial and temporal replication, both of which are essential to overcome detection errors in highly cryptic species like B. robustus. It also provides no information about changes in the grasshopper's distribution throughout its range. Here, we design and test new population density and site occupancy monitoring protocols by comparing a) comprehensive plot and transect searches at one site and b) transect searches at two sites representing two different habitats (gravel road and natural riverbed) occupied by the species across its remaining range. Using power analyses, we determined a) the number of transects, b) the number of repeated visits and c) the grasshopper demographic to count to accurately detect long term change in relative population density. To inform a monitoring protocol design to track trends in grasshopper distribution, we estimated the probability of detecting an individual with respect to a) search area, b) weather and c) the grasshopper demographic counted at each of the two sites. Density estimates from plots and transects did not differ significantly. Population density monitoring was found to be most informative when large adult females present in early summer were used to index population size. To detect a significant change in relative density with power > 0.8 at the gravel road habitat, at least seventeen spatial replicates (transects) and four temporal replicates (visits) were required. Density estimates at the natural braided river site performed poorly and likely require a much higher survey effort. Detection of grasshopper presence was highest (pg > 0.6) using a 100 m x 1 m transect at both sites in February under optimal (no cloud) conditions. At least three visits to a transect should be conducted per season for distribution monitoring. Monitoring protocols that inform the management of threatened species are crucial for better understanding and mitigation of the current global trends of insect decline. This study provides an exemplar of how appropriate monitoring protocols can be developed for threatened insect species.

Growth Performance and Enzymatic Response of the Grasshopper, Calliptamus abbreviatus (Orthoptera: Acrididae), to Six Plant-Derived Compounds.

Plant-derived compounds are sources of biopesticides for the control of insect pests. We compared the growth performance and enzymatic response of the grasshopper Calliptamus abbreviatus Ikonn to six plant-derived compounds (rutin, quercetin, nicotine, matrine, azadirachtin, and rotenone) in laboratory and field trials. When exposed to the six compounds, C. abbreviatus had significantly reduced growth and survival. All the compounds significantly induced an elevated level of reactive oxygen species, indicating oxidative damage. The activity of detoxifying enzymes, including cytochrome P450s, carboxylesterase, glutathione-S-transferase, and UDP-glucuronosyltransferase, and the antioxidant enzymes, including superoxide dismutase, catalase, and peroxidase, all significantly increased after exposure to the six compounds. These data suggest that the six plant-derived compounds had negative effects on C. abbreviatus. Of the six compounds, matrine, azadirachtin, and rotenone were more toxic to C. abbreviatus, followed by nicotine, quercetin, and rutin. These results show the potential of these compounds as botanical pesticides, which can be applied for the biological control of the grasshopper C. abbreviatus.

Physiological responses to gravity in an insect.

Gravity is one of the most ubiquitous environmental effects on living systems: Cellular and organismal responses to gravity are of central importance to understanding the physiological function of organisms, especially eukaryotes. Gravity has been demonstrated to have strong effects on the closed cardiovascular systems of terrestrial vertebrates, with rapidly responding neural reflexes ensuring proper blood flow despite changes in posture. Invertebrates possess open circulatory systems, which could provide fewer mechanisms to restrict gravity effects on blood flow, suggesting that these species also experience effects of gravity on blood pressure and distribution. However, whether gravity affects the open circulatory systems of invertebrates is unknown, partly due to technical measurement issues associated with small body size. Here we used X-ray imaging, radio-tracing of hemolymph, and micropressure measurements in the American grasshopper, Schistocerca americana, to assess responses to body orientation. Our results show that during changes in body orientation, gravity causes large changes in blood and air distribution, and that body position affects ventilation rate. Remarkably, we also found that insects show similar heart rate responses to body position as vertebrates, and contrasting with the classic understanding of open circulatory systems, have flexible valving systems between thorax and abdomen that can separate pressures. Gravitational effects on invertebrate cardiovascular and respiratory systems are likely to be widely distributed among invertebrates and to have broad influence on morphological and physiological evolution.

Rhythmic change of adipokinetic hormones diurnally regulates locust vitellogenesis and egg development.

Adipokinetic hormones (AKHs), the neurohormones synthesized in the insect corpora cardiaca are known to mobilize lipids and carbohydrates for energy-consuming activities including reproduction. However, both inhibitory and stimulatory effects of AKHs on insect reproduction have been reported, and the underlying mechanisms remain elusive. Using the migratory locust, Locusta migratoria, as a model system, we report here that AKHs are expressed in response to rhythmic diel change, and AKH III expression increases markedly at photophase. Diurnal injection of AKH III but not AKH I or AKH II in adult females stimulates vitellogenesis and egg development. In contrast, AKH treatment at scotophase represses female reproduction. RNA interference-mediated knockdown of AKH receptor (AKHR) results in significantly reduced vitellogenin (Vg) expression in the fat body at photophase along with reduced Vg deposition in the ovary. AKHR knockdown also leads to decreased expression of Brummer, triacylglycerol lipase and trehalose transporter, accompanied by suppressed mobilization of triacylglycerol and trehalose. We propose that in addition to stimulating Vg expression at photophase, AKH/AKHR signalling is likely to regulate ovarian uptake of Vg via triacylglycerol mobilization and trehalose homeostasis. This study provides new insights into the understanding of AKH/AKHR signalling in the regulation of insect reproduction.

Diet-Induced Plasticity of Linear Static Allometry Is Not So Simple for Grasshoppers: Genotype-Environment Interaction in Ontogeny Is Masked by Convergent Growth.

Grasshoppers, Melanoplus sanguinipes (Orthoptera: Acrididae), develop larger head width (HW) and shorter leg length, relative to body size, when fed low nutrient, lignin-rich grasses compared to sibs fed a diet of high nutrient grasses. To elucidate how underlying genetic variation and plasticity of growth generate plasticity of this linear static allometry within coarse-grained environments, I measured head and leg size of three nymphal instars and adult grasshoppers raised on either a low or high nutrient diet within a half-sib quantitative genetic experiment. Doubly-multivariate repeated measures multiple analysis of variance (MANOVA) of head, mandible, and hind leg size and their rate of growth (mm/period) and growth period (days) through ontogeny were used to analyze how the ontogeny of diet-induced plasticity for these variables and additive genetic variation for plasticity (genotype × environment interaction [G×E]) contribute to plasticity in functional linear static allometry. Genetic variation for diet-induced plasticity (G×E) of head and leg size varied through ontogeny, as did genetic variation for plasticity of growth in third and fourth instar nymphs. Despite extensive genetic variation in plasticity of HW and leg length in fourth instar nymphs, the static allometry between head and leg was stable within each diet because the patterns of G×E were similar for HW, leg length and their coordinated growth. Nutrient sensitive plasticity in growth shifted the intercept but not the slope of static allometry, a result consistent with one outcome of a graphical model of the relationships between G× E and plasticity of within environment static allometry. In addition, G×E of fourth instar head and leg size was reduced in adults by negatively size-dependent, convergent growth in the last period of ontogeny. Consequently, the bivariate reaction norms of head and leg size for adults exhibited no G×E and, again, plasticity in the intercept but not in the slope of static allometry. The ontogeny of seemingly simple diet-induced linear static allometry between functional body parts in grasshoppers arises from a complex combination of differing patterns of nutrient-sensitive growth, duration of growth, convergent growth, and G×E, all relevant to understanding the development and evolution of functional allometry in hemimetabolous insects.

Aryl hydrocarbon receptor regulates the expression of LmGSTd7 and is associated with chlorpyrifos susceptibility in Locusta migratoria.

BACKGROUND: The aryl hydrocarbon receptor (AhR) belongs to the bHLH-PAS (basic Helix-Loop-Helix - Period/ARNT/Single minded) family of transcription factors. AhR is a ligand-activated transcription factor, which participates in the sensing and transmitting stimuli of endogenous and exogenous chemicals, and subsequently activates the transcription of genes related to various physiological and detoxification functions. RESULT: In this study, a single full-length LmAhR sequence was cloned and characterized. RNA interference (RNAi) and insecticide bioassays showed that LmAhR plays a vital role in chlorpyrifos susceptibility. To better identify aryl hydrocarbon receptor from locusta migratoria (LmAhR)-regulated genes involved in chlorpyrifos susceptibility, a comparative transcriptome analysis was performed using double-stranded (ds)GFP- and dsLmAhR-injected Locusta migratoria. Differential gene expression analysis identified 145 down-regulated and 67 up-regulated genes (P ≤ 0.05 and fold change ≥2) in dsLmAhR-knockdown insects. We selected 27 down-regulated genes and verified their expression levels using reverse transcription quantitative PCR. Finally, one glutathione S-transferase (GST) gene (LmGSTd7) was selected as a candidate detoxification gene and was further validated via RNAi and chlorpyrifos bioassays. CONCLUSION: Our data suggest that AhR is associated with chlorpyrifos susceptibility via the regulation of LmGSTd7 expression in L. migratoria. © 2019 Society of Chemical Industry.

The puzzle of locust density-dependent phase polyphenism.

Locust density-dependent phase polyphenism presents a quintessential example of environmentally induced plasticity. Almost a century of research has yielded ample knowledge regarding the multitude of ecological, physiological, and molecular phase-dependent characteristics. This short review highlights the considerable advances that have been made in our understanding of the locust's extreme plasticity and the highly complex nature of the phase phenomenon. Several challenges in locust research resulting from this unique complexity are also presented. It is concluded that the joint, interdisciplinary collaborative efforts, already underway, hold the promise of translating our ample knowledge into a complete solution to untangling the locust phase puzzle.

Aimed limb movements in a hemimetabolous insect are intrinsically compensated for allometric wing growth by developmental mechanisms.

For aimed limb movements to remain functional, they must be adapted to developmental changes in body morphology and sensory-motor systems. Insects use their limbs to groom the body surface or to dislodge external stimuli, but they face the particular problem of adapting these movements to step-like changes in body morphology during metamorphosis or moulting. Locusts are hemimetabolous insects in which the imaginal moult to adulthood results in a sudden and dramatic allometric growth of the wings relative to the body and the legs. We show that, despite this, hind limb scratches aimed at mechanosensory stimuli on the wings remain targeted to appropriate locations after moulting. In juveniles, the tips of the wings extend less than halfway along the abdomen, but in adults they extend well beyond the posterior end. Kinematic analyses were used to examine the scratching responses of juveniles (fifth instars) and adults to touch of anterior (wing base) and posterior (distal abdomen) targets that develop isometrically, and to wing tip targets that are anterior in juveniles but posterior in adults. Juveniles reach the (anterior) wing tip with the distal tibia of the hind leg using anterior rotation of the thoraco-coxal and coxo-trochanteral ('hip') joints and flexion of the femoro-tibial ('knee') joint. Adults, however, reach the corresponding (but now posterior) wing tip using posterior rotation of the hip and extension of the knee, reflecting a different underlying motor pattern. This change in kinematics occurs immediately after the adult moult without learning, indicating that the switch is developmentally programmed.

An intact insect embryo for developmental neurotoxicity testing of directed axonal elongation.

Developmental neurotoxicity (DNT) of chemicals poses a serious threat to human health worldwide. Current in vivo test methods for assessing DNT require the use of high numbers of laboratory animals. Most alternative in vitro testing methods monitor rather simple toxicological endpoints, whereas the formation of a functional brain requires precisely timed navigation of axons within a complex tissue environment. We address this complexity by monitoring defects in axonal navigation of pioneer axons of intact locust embryos after exposure to chemicals. Embryos develop in serum-free culture with test chemicals, followed by immunolabeling of pioneer neurons. Defects in axon elongation of pioneer axons are quantified in concentration-response curves and compared to the general viability of the embryo, as measured by a resazurin assay. We show that selected chemical compounds interfering with calcium signaling, the cytoskeletal organization, and the reference developmental neurotoxicant rotenone, can be classified as DNT positive. The pesticide rotenone inhibits pioneer neuron elongation with a lower IC50 than the viability assay. The rho kinase inhibitor Y27632 can partially rescue outgrowth inhibition, supporting the classification of rotenone as a specific DNT positive compound. Since mechanisms of axonal guidance, such as growth cone navigation along molecular semaphorin gradients are conserved between locust and mammalian nervous systems, we will further explore the potential of this invertebrate preparation as an assay for testing the DNT potential of chemicals in humans.

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.

Role of PTP/PTK trans activated insulin-like signalling pathway in regulation of grasshopper (Oedaleus asiaticus) development.

Protein tyrosine phosphatase (PTPs) and protein tyrosine kinase (PTKs) genes are responsible for the regulation of insect insulin-like pathway (ILP), cells growth, metabolism initiation, gene transcription and observing immune response. Signal transduction in insect cell is also associated with PTPs and PTKs. The grasshopper (Oedaleus asiaticus) 'Bey-Bienko' were treated with dsRNA of protein tyrosine non-receptor type 4 (PTPN4) and protein tyrosine kinase 5 (PTK5) along with control (water). Applying dsPTK5 treatments in 5th instar of Oedaleus asiaticus, significant reduction was recorded in body dry mass, growth rate and overall performance except survival rate. Whereas with PTPN4, no such significant impact on all of these growth parameters was recorded. Expression of genes in ILP 5th instar of Oedaleus asiaticus by the application of dsPTPN4 and dsPTK5 revealed that PTK, INSR (insulin receptor), IRS (insulin receptor substrate), PI3K (phosphoinositide 3-kinase), PDK (3-phosphoinositide-dependent protein kinase), Akt (protein kinase B) and FOXO (forkhead transcription factor) significantly expressed with downregulation except PTPN4, which remained non-significant. On the other hand, the phosphorylation level of ILP four proteins in O. asiaticus with the treatment of dsPTPN4 and dsPTK5 significantly affected P-IRS and P-FOXO, while P-INSR and P-AKT remained stable at the probability level of 5%. This indicated that the stress response in the O. asiaticus insulin-like signalling pathway (ILP) reduced. Regarding association of protective enzymatic activities, ROS (relative oxygen species), CAT (catalase) and PO (phenol oxidase) increased significantly with exposure to dsPTK5 as compared to dsPTPN4 and control, while exposure of 5th instar of O. asiaticus to dsPTPN4 treatment slightly raised CAT and PO activities with but significant contribution. No such significant effect on MFO and POD was seen using dsPTPN4 and dsPTK5. This showed that in the ILP of O. asiaticus, PTK5 was detrimental to growth, body mass and overall performance, which ultimately benefited insect detoxification with high-energy cost.

The microRNAs let-7 and miR-278 regulate insect metamorphosis and oogenesis by targeting the juvenile hormone early-response gene Krüppel-homolog 1.

Krüppel-homolog 1 (Kr-h1), a zinc-finger transcription factor, inhibits larval metamorphosis and promotes adult reproduction by transducing juvenile hormone (JH). Although the transcriptional regulation of Kr-h1 has been extensively studied, little is known about its regulation at the post-transcriptional level. Using the migratory locust Locusta migratoria as a model system, we report here that the microRNAs let-7 and miR-278 bound to the Kr-h1 coding sequence and downregulated its expression. Application of let-7 and miR-278 mimics (agomiRs) significantly reduced the level of Kr-h1 transcripts, resulting in partially precocious metamorphosis in nymphs as well as markedly decreased yolk protein precursors, arrested ovarian development and blocked oocyte maturation in adults. Moreover, the expression of let-7 and miR-278 was repressed by JH, constituting a regulatory loop of JH signaling. This study thus reveals a previously unknown regulatory mechanism whereby JH suppresses the expression of let-7 and miR-278, which, together with JH induction of Kr-h1 transcription, prevents the precocious metamorphosis of nymphs and stimulates the reproduction of adult females. These results advance our understanding of the coordination of JH and miRNA regulation in insect development.