Search Results (27)

Insect metamorphosis is a complex developmental process regulated by hormonal signaling and gene transcription. To elucidate its transcriptional regulatory mechanisms, we examined chromatin accessibility dynamics during metamorphosis in two holometabolous insects, Harmonia axyridis and Drosophila melanogaster, using ATAC-seq. Our analysis revealed distinct stage-specific chromatin accessibility patterns, with peak accessibility during the prepupal stage in H. axyridis and the wandering larval to prepupal transition in D. melanogaster. Through analysis of differential accessibility regions (DARs), we identified enrichment of metamorphosis-related processes including cell morphogenesis, tissue remodeling, and hormone signaling pathways via Gene Ontology and KEGG pathway analyses. Integration of chromatin accessibility with gene expression data revealed 608 conserved genes exhibiting coordinated accessibility and expression changes across both species. Additionally, we constructed a regulatory network centered around four key transcription factors (dsx, E93, REPTOR, and Sox14) that form core regulatory modules controlling metamorphosis. This study provides novel insights into the epigenetic landscape of insect metamorphosis and establishes a foundation for understanding the transcriptional regulatory mechanisms governing this critical developmental process. Full article

Holometabolous insects display drastically different morphologies across life stages (i.e., larvae vs. adults). Morphological differences across life stages, such as different sizes and coloration, likely result in differential survival, as predators may find individuals of one life stage more conspicuous and/or more energetically profitable than another. Furthermore, prey conspicuousness may vary temporally because both the sensory environment and predator sensory abilities differ between day and night. Here, we investigated how the interaction between life stage (caterpillar vs. moth) and time of day (day vs. night) influences predation of the white-lined sphinx (Lepidoptera: Hyles lineata). We predicted that caterpillars would be less susceptible to predation than adult moths, as adults are larger and have a more conspicuous shape. After quantifying predation for 72 h during dawn and dusk using 199 plasticine replicas each of adults and caterpillars, predation on adult replicas was twice that of predation on caterpillar replicas. Furthermore, replicas were six times more likely to be predated on during the day than during the night. Lastly, attacks were made mainly by birds, which carried out 86% of the attacks on adult models and 85% of those on caterpillar models. These data support the hypothesis that predation rates differ across life stages in holometabolous insects. This research lays a foundation for further investigation into how specific differences in morphology across life stages affect predation and survival in holometabolous insects. Full article

Callobruchus maculatus is a major quarantine pest of stored legumes in China. As a holometabolous insect, it lives inside the bean it burrows into in both its larval and pupal stages. This study utilized micro-CT and 3D reconstruction to document thoracic morphological transformation during larval and pupal stages. The multi-peak fitting of cranial width was applied to determine larval instars. The results indicate that the first-instar larvae bore into beans using prothoracic muscles and those connecting the head to the mesothorax. The second-instar larva possessed the highest number of thoracic muscles, likely correlating with peak boring activity. The prepupa and the initial pupa exhibited minimal musculature, suggesting larval muscle degradation prior to pupation. Muscles unique to prepupae might homologize with indirect flight muscles in pupae, implying that adult flight capability is determined in the final larval stage. The muscles of both larvae and pupae undergo changes in attachment site, shape and curvature throughout development. At the same time, changes also occur in the larval cuticle and pupal endoskeleton. During the larval stage, muscle growth and degradation occur simultaneously, influencing muscle volume. In the pupal stage, the progressive increase in both absolute and relative thoracic muscle volumes prepare the weevil for movement after emergence. Meanwhile, the other thoracic organs, including the gut, air sacs and nerves, also change during development. Full article

Juvenile environments can influence adult phenotypes in holometabolous insects. This study examines the effects of larval rearing substrates on the reproductive outcomes of Black Soldier Flies (BSFs) at a semi-industrial scale. Larvae were reared on five substrates. Larval growth, adult size, and reproductive performance were monitored, with a specific focus on egg production and hatching rates across 17 continuous egg collection days. Egg production was positively correlated with female body weight, while male body weight appeared to influence the egg production peak. Extended larval feeding stages and shorter non-feeding periods were associated with an earlier onset of egg-laying, suggesting life-history traits as predictors for reproductive timing. Diets high in carbohydrates but low in protein and fat positively influenced larval growth, egg production, and female body weight, while diets rich in both protein and carbohydrates negatively affected all measured parameters. Notably, higher fecundity did not necessarily correlate with fertility (i.e., more viable larvae for bioconversion), highlighting the need to optimize diets for both egg quantity and hatchability to maximize productivity. These findings provide valuable insights for optimizing larval nutrition and egg collection practices, enhancing reproductive efficiency and overall productivity in industrial BSF farming. Full article

Chironomids have a number of characteristics that make them a useful group for investigating the impact of environmental and chemical stressors on their life cycle stages. It is crucial to first understand sensitivities to environmental factors and provide a basis for interpreting the results of toxicity tests. We focused on Chironomus riparius–one of the most studied species in aquatic toxicity tests—to understand the changes during the larval stage under conditions of food abundance and limitation. We developed a model based on Dynamic Energy Budget (DEB) theory, a framework to capture the entire life cycle of an individual under varying food and temperature conditions. Available information from this study and the literature pointed out that the first three larval instars are immature and the fourth larval instar is mature, during which the organism saves, in two phases, energy for essential processes occurring during the subsequent non-feeding stages. The model can successfully predict the observed prolonged fourth instar duration under food limitation, the times of life history events (e.g., pupation and emergence), and egg production. This model has the potential to be integrated with toxicokinetic–toxicodynamic models to study the effects of toxicants on a variety of biological traits. Full article

Insect farming generates a new type of chitinous waste in the form of dead specimens that have died of natural causes and insect moults (puparia), particularly large amounts of which are generated during the rearing of holometabolous insects. Following the circular economy paradigm, we treated waste in the form of puparia and dead adults of H. illucens as a valuable material, i.e., as sources of chitin, and tested it as a sorbent for cerium, a lanthanide of great industrial importance. For comparison, non-treated, raw insect materials and commercial chitosans were also investigated. Chitin extracted from H. illucens showed an adsorption capacity at the same level as commercially available, marine-source chitin (approximately 6 mg Ce·g⁻¹). However, more interestingly, raw materials exhibited much higher adsorption capacities—dead adults were similar to commercial chitosans (approximately 32 mg Ce·g⁻¹), while puparia demonstrated twice the performance (approximately 60 mg Ce·g⁻¹). This indicates that unprocessed waste can be used as environmentally friendly, cost-effective Ce biosorbents with comparable or even better sorption capacity than chitosans, whose production requires intense chemical processing. Full article

In holometabolous insects, such as Drosophila and Bombyx, prothoracicotropic hormone (PTTH) is well established to be critical in controlling developmental transitions and metamorphosis by stimulating the biosynthesis of ecdysone in the prothoracic glands (PGs). However, the physiological role of PTTH and the receptor Torso in hemimetabolous insects remains largely unexplored. In this study, homozygous PTTH- and Torso-null mutants of the brown planthopper (BPH), Nilaparvata lugens, were successfully generated by employing clustered regularly interspaced short palindromic repeats/CRISPR-associated 9 (CRISPR–Cas9). Further characterization showed that both NlPTTH^−/− and NlTorso^−/− mutants exhibited prolonged nymphal duration and increased final adult size. Enzyme-linked immunosorbent assay (ELISA) revealed that NlPTTH^−/− and NlTorso^−/− mutants exhibited a significant reduction in 20-hydroxyecdysone (20E) in fifth-instar nymphs at 48 h post-ecdysis compared to Wt controls. Furthermore, our results indicated that both NlPTTH^−/− and NlTorso^−/− mutants had shortened lifespan, reduced female fecundity, and reduced egg hatching rates in adults. These findings suggest a conserved role for the PTTH–Torso signaling system in the regulation of developmental transitions by stimulating ecdysone biosynthesis in hemimetabolous insects. Full article

Animals with different life histories budget their intake energy differently when food availability is low. It has been shown previously that hornworm (larva of Manduca sexta), a holometabolous insect species with a short development stage, prioritizes growth at the price of metabolism under food restriction, but it is unclear how hemimetabolous insect species with a relatively long development period budget their intake energy under food scarcity. Here, we use orange head cockroaches (Eublaberus posticus) to investigate this question. We found that for both species under food restriction, rates of metabolism and growth were suppressed, but the degree of reduction was more severe in growth than that of metabolism for cockroaches. Under both free-feeding and food restriction conditions, hornworms allocated a larger fraction of assimilated energy to growth than to metabolism, and cockroaches were the opposite. More importantly, when food availability was low, the fraction of assimilated energy allocated to growth was reduced by 120% in cockroaches, and the energy from growth was channeled to compensate for the reduction in metabolism; but, the fraction of assimilated energy allocated to growth was only reduced by 14% in hornworms. These results suggest that, compared to hornworms, cockroaches prioritize metabolism over growth. Full article

Resilin is an elastic protein that is vital to insects’ vigorous movement. Canonical resilin proteins possess the R&R Consensus, a chitin-binding domain conserved in a family of cuticular proteins, and highly repetitive sequences conferring elastic properties. In the malaria vector mosquito, Anopheles gambiae, however, a cuticular protein has been found that has an R&R Consensus resembling that of resilin but lacks the repetitive sequences (here, we call it resilin-related or resilin-r). The relationship between resilin-r and resilin was unclear. It was also unknown whether resilin-r is conserved in mosquitoes. In this paper, phylogenetic and structural analyses were performed to reveal the relationship of resilin homologous proteins from holometabolous insects. Their chitin-binding abilities were also assessed. A resilin-r was found in each mosquito species, and these proteins constitute a clade with resilin from other insects based on the R&R Consensus sequences, indicating an evolutionary relationship between resilin-r and resilin. The resilin-r showed chitin-binding activity as same as resilin, but had distinct structural features from resilin, suggesting that it plays specialized roles in the mosquito cuticle. Another resilin-like protein was found to exist in each holometabolous insect that possesses resilin-like repetitive sequences but lacks the R&R Consensus. These results suggest that similar evolutionary events occurred to create resilin-r and resilin-like proteins. Full article

In most holometabolous insects, transformer-2 (tra-2) is an auxiliary gene required for sex determination, exerting a crucial role in regulating sexual differentiation; however, the study of tra-2 in hemimetabolous insects remains very sparse and limited to just a few species. In this study, we investigated the sequence and expression profile of the tra-2 gene in the bean bug, Riptortus pedestris, an agricultural pest belonging to the Heteroptera order. Three non-sex-specific splicing isoforms of Rptra-2 were found, Rptra-2²⁹³, Rptra-2²⁸⁴, and Rptra-2²⁹⁹, which shared most exons and exhibited similar expression throughout all stages of development, with particularly elevated levels in the embryo, ovary, and testis. RNAi knockdown experiments revealed that the suppression of Rptra-2 in nymphs led to abnormal females, characterized the formation of male-specific external genital, and also caused longer nymph duration. Knockdown of the expression of the Rptra-2 gene in newly emergent virgin females would cause ovarian arrest, and injecting the 8th-day virgin females with dsRptra-2 also caused a noticeable decline in the offspring numbers. Conversely, in dsRptra-2-treated males, the testes maintained normal morphology but experienced impaired reproductive capacity, attributed to diminished sperm viability. These findings highlight the crucial role of Rptra-2 in the sex determination and fertility of R. pedestris, providing valuable insights into the sex determination mechanisms of hemimetabolous insects. Full article

Insects are renowned for their remarkable diversity of reproductive modes. Among these, the largest non-holometabolous order, Hemiptera, stands out with one of the most diversified arrays of parthenogenesis modes observed among insects. Although there are extensive reviews on reproduction without fertilization in some hemipteran higher taxa, no such analysis has been conducted for the large suborders Fulgoromorpha (planthoppers) and Cicadomorpha (leafhoppers). In both groups, there are species that reproduce by true parthenogenesis, specifically thelytoky, and in Fulgoromorpha, there are species that reproduce by pseudogamy or, more specifically, sperm-dependent parthenogenesis. In this review paper, we give and discuss the only currently known examples of true parthenogenesis in Fulgoromorpha and Cicadomorpha, mainly from the planthopper family Delphacidae and the leafhopper family Cicadellidae. We analyze patterns of distribution, ecology, mating behavior, acoustic communication, and cytogenetic and genetic diversity of parthenoforms and discuss hypotheses about the origin of parthenogenesis in each case. We also highlight examples in which natural populations show a shift in sex ratio toward females and discuss possible causes of this phenomenon, primarily the influence of endosymbiotic bacteria capable of altering the reproductive strategies of the hosts. Our review is mainly based on studies in which the authors have participated. Full article

Insect growth is interrupted by molts, during which the insect develops a new exoskeleton. The exoskeleton confers protection and undergoes shedding between each developmental stage through an evolutionarily conserved and ordered sequence of behaviors, collectively referred to as ecdysis. Ecdysis is triggered by Ecdysis triggering hormone (ETH) synthesized and secreted from peripheral Inka cells on the tracheal surface and plays a vital role in the orchestration of ecdysis in insects and possibly in other arthropod species. ETH synthesized by Inka cells then binds to ETH receptor (ETHR) present on the peptidergic neurons in the central nervous system (CNS) to facilitate synthesis of various other neuropeptides involved in ecdysis. The mechanism of ETH function on ecdysis has been well investigated in holometabolous insects such as moths Manduca sexta and Bombyx mori, fruit fly Drosophila melanogaster, the yellow fever mosquito Aedes aegypti and beetle Tribolium castaneum etc. In contrast, very little information is available about the role of ETH in sequential and gradual growth and developmental changes associated with ecdysis in hemimetabolous insects. Recent studies have identified ETH precursors and characterized functional and biochemical features of ETH and ETHR in a hemimetabolous insect, desert locust, Schistocerca gregaria. Recently, the role of ETH in Juvenile hormone (JH) mediated courtship short-term memory (STM) retention and long-term courtship memory regulation and retention have also been investigated in adult male Drosophila. Our review provides a novel synthesis of ETH signaling cascades and responses in various insects triggering diverse functions in adults and juvenile insects including their development and reproductive regulation and might allow researchers to develop sustainable pest management strategies by identifying novel compounds and targets. Full article

Engrailed (en) and invected (inv) encode paralogous transcription factors found as a closely linked tandem duplication within holometabolous insects. Drosophila en mutants segment normally, then fail to maintain their segments. Loss of Drosophila inv is viable, while loss of both genes results in asegmental larvae. Surprisingly, the knockdown of Oncopeltus inv can result in the loss or fusion of the entire abdomen and en knockdowns in Tribolium show variable degrees of segmental loss. The consequence of losing or knocking down both paralogs on embryogenesis has not been studied beyond Drosophila. To further investigate the relative functions of each paralog and the mechanism behind the segmental loss, Tribolium double and single knockdowns of en and inv were analyzed. The most common cuticular phenotype of the double knockdowns was small, limbless, and open dorsally, with all but a single, segmentally iterated row of bristles. Less severe knockdowns had fused segments and reduced appendages. The Tribolium paralogs appear to act synergistically: the knockdown of either Tribolium gene alone was typically less severe, with all limbs present, whereas the most extreme single knockdowns mimic the most severe double knockdown phenotype. Morphological abnormalities unique to either single gene knockdown were not found. inv expression was not affected in the Tribolium en knockdowns, but hh expression was unexpectedly increased midway through development. Thus, while the segmental expression of en/inv is broadly conserved within insects, the functions of en and inv are evolving independently in different lineages. Full article

Ecdysteroid hormones are key regulators of insect development and metamorphosis. Ecdysone-inducible E75, a major component of insect ecdysone signaling pathway, has been well characterized in holometabolous insects, however, barely in hemimetabolous species. In this study, a total of four full-length E75 cDNAs from the English grain aphid, Sitobion avenae, were identified, cloned, and characterized. The four SaE75 cDNAs contained 3048, 2625, 2505, and 2179 bp open reading frames (ORF), encoding 1015, 874, 856, and 835 amino acids, respectively. Temporal expression profiles showed that SaE75 expression was low in adult stages, while high in pseudo embryo and nymphal stages. SaE75 was differentially expressed between winged and wingless morphs. RNAi-mediated suppression of SaE75 led to substantial biological impacts, including mortality and molting defects. As for the pleiotropic effects on downstream ecdysone pathway genes, SaHr3 (hormone receptor like in 46) was significantly up-regulated, while Sabr-c (broad-complex core protein gene) and Saftz-f1 (transcription factor 1) were significantly down-regulated. These combined results not only shed light on the regulatory role of E75 in the ecdysone signaling pathway, but also provide a potential novel target for the long-term sustainable management of S. avenae, a devastating global grain pest. Full article

Chemical secretions are an effective means by which insects may deter potential enemies, already being studied extensively with regard to their chemicals, synthesis, toxicity, and functions. However, these defensive secretions have been little studied in Megaloptera. Herein, the fluid expelling behavior of adult alderflies (Sialidae), fishflies (Corydalidae: Chauliodinae), and dobsonflies (Corydalidae: Corydalinae), all of the order Megaloptera, is described in detail regarding the timing and possible function of this behavior. When disturbed artificially, both males and females could expel fluid from the anus. However, the frequency of expelling was much lower in alderflies than in fishflies and dobsonflies. The amount of expelled fluid relative to body weight was also smaller in alderflies. In fishflies and dobsonflies, the amount of expelled fluid decreased with adult age, probably because the fluid is little replenished once expelled. The cream-colored fluid seems to be meconial fluid produced via the Malpighian tubules at the pupal stage, which is usually discharged at adult emergence in most other holometabolous insects. However, adult fishflies and dobsonflies often expel it vigorously by bending their abdomen when disturbed after emergence. Thus, the fluid expelling may be an anti-predatory behavior, particularly in younger adults that can expel a relatively large amount of fluid. Full article