Insect Science最新文献

Identifying cryptic species poses a substantial challenge to both biologists and naturalists due to morphological similarities. Bemisia tabaci is a cryptic species complex containing more than 44 putative species; several of which are currently among the world's most destructive crop pests. Interpreting and delimiting the evolution of this species complex has proved problematic. To develop a comprehensive framework for species delimitation and identification, we evaluated the performance of distinct data sources both individually and in combination among numerous samples of the B. tabaci species complex acquired worldwide. Distinct datasets include full mitogenomes, single-copy nuclear genes, restriction site-associated DNA sequencing, geographic range, host speciation, and reproductive compatibility datasets. Phylogenetically, our well-supported topologies generated from three dense molecular markers highlighted the evolutionary divergence of species of the B. tabaci complex and suggested that the nuclear markers serve as a more accurate representation of B. tabaci species diversity. Reproductive compatibility datasets facilitated the identification of at least 17 different cryptic species within our samples. Native geographic range information provides a complementary assessment of species recognition, while the host range datasets provide low rate of delimiting resolution. We further summarized different data performances in species classification when compared with reproductive compatibility, indicating that combination of mtCOI divergence, nuclear markers, geographic range provide a complementary assessment of species recognition. Finally, we represent a model for understanding and untangling the cryptic species complexes based on the evidence from this study and previously published articles.

Our previous study shows that Coptotermes formosanus (Blattodea: Rhinotermitidae) preferred to stay on filter paper treated with ethyl 2,4-dioxovalerate, a metabolite in the soil fungus Trichoderma virens. Here, we hypothesized that adding ethyl 2,4-dioxovalerate in sand could trigger aggregation and tunneling preferences of C. formosanus and improve the effectiveness of liquid termiticide. In aggregation-choice tests, significantly more termites were found on/in sand blocks containing ethyl 2,4-dioxovalerate (250 µg/g) than untreated blocks throughout the 24-h experiments. In the tunneling-choice tests, termites also excavated significantly more tunnels in the sand treated with ethyl 2,4-dioxovalerate (2.5, 25, or 250 µg/g) than untreated sand. However, in no-choice tests, ethyl 2,4-dioxovalerate (2.5, 25, or 250 µg/g) did not significantly affect tunneling activities, termite survival, wood consumption, or activities of detoxification enzymes (peroxidase, superoxide dismutase, and catalase) compared to controls. Interestingly, in aggregation- and tunneling-choice tests, termites preferred to stay and made more tunnels in sand treated with both ethyl 2,4-dioxovalerate (250 µg/g) and fipronil (1 µg/g) than untreated sand. In addition, in choice tests, sand treated with the combination of ethyl 2,4-dioxovalerate (250 µg/g) and fipronil (1 µg/g) caused significantly higher termite mortality than the sand treated with only fipronil (1 µg/g). Our study showed that ethyl 2,4-dioxovalerate may enhance the effectiveness of fipronil (1 µg/g in sand) by triggering aggregation and tunneling preferences of termites, thereby increasing the contact between termites and fipronil.

Oviposition behavior in insects has received considerable attention, but studies have mainly focused on the antennae, neglecting the role of the ovipositor. In this study, we investigated the functional characteristics of the ovipositor in oviposition site selection by the fall armyworm (FAW) Spodoptera frugiperda, a destructive invasive pest of maize and other cereals. In oviposition choice assays females exhibited significant repellency to isothiocyanate (ITC), volatiles specific to non-preferred cruciferous plants. Females retained repellency to ITC or attraction to maize volatiles even after antennae removal. Scanning electron microscopy indicated the presence of olfactory-associated sensilla on the ovipositor. Comparative transcriptome analysis and in vitro functional studies showed that S. frugiperda odorant binding protein 30 (SfruOBP30), exclusively expressed in the ovipositor, displayed a broad sensitivity toward 18 maize volatiles and 10 ITC compounds. Site-directed mutant assay revealed that Ser71 and Ser85 were the key binding sites for SfruOBP30 interacting with ITCs and key maize volatiles, respectively. Silencing the expression of SfruOBP30 resulted in the loss of bias in oviposition of FAW, significantly inhibiting their ability to avoid ITCs and locate the maize substrate. Overall, we propose that the ovipositor does not just seek out advantageous conditions for immature stages but more importantly, avoids potential risks during the oviposition process. Apparently, the involvement of SfruOBP30 plays a critical role in detecting both beneficial and harmful substances during this intricate process.

Aedes albopictus (Ae. albopictus) is widely distributed and can transmit many infectious diseases, and insecticide-based interventions play an important role in vector control. However, increased insecticide resistance has become a severe public health problem, and the clarification of its detailed mechanism is a matter of urgence. This study found that target-site resistance and metabolic resistance could not fully explain insecticide resistance in field Ae. albopictus, and there were likely other resistance mechanisms involved. The 16S and internal transcribed spacer sequencing revealed significant differences in the species compositions of the cuticle surface symbiotic bacteria and fungi between deltamethrin (DM)-resistant (DR) and DM-susceptible (DS) Ae. albopictus. Additionally, the abundances of Serratia spp. and Candida spp. significantly increased after DM treatment. Furthermore, 2 fungi (Rhodotorula mucilaginosa and Candida melibiosica) and 3 bacteria (Serratia marcescens, Klebsiella aerogenes, and Serratia sp.) isolated from DR Ae. albopictus can use DM as their sole carbon source. After reinoculation onto the cuticle surface of DS Ae. albopictus, R. mucilaginosa and C. melibiosica significantly enhanced the DM resistance of Ae. albopictus. Moreover, transcriptome sequencing of the surviving Ae. albopictus after DM exposure revealed that the gene expression of cytochrome P450 enzymes and glutathione-S-transferases increased, suggesting that besides the direct degradation, the candidate degrading microbes could also cause insecticide resistance via indirect enhancement of mosquito gene expression. In conclusion, we demonstrated that the cuticle surface symbiotic microbes were involved in the development of insecticide resistance in Ae. albopictus, providing novel and supplementary insights into insecticide resistance mechanisms.

The fall armyworm (FAW), an important migratory pest native to the Americas, was first detected in a nonnative region (West Africa) in 2016. In the following years, it quickly spread to multiple regions worldwide. FAW exhibits long-distance seasonal migration in both the Americas and Asia, primarily to take advantage of suitable seasonal habitats as they appear along the migratory pathways. Tropical West Africa experiences minimal annual temperature variation and has widely distributed potential year-round habitats, leading us to hypothesize that the migration capacity of FAW populations in this region may be substantially reduced. To test our hypothesis, we assessed the flight performance of FAW collected from Ghana in West Africa with tethered flight mills and compared it to that of a FAW population from southern China. Additionally, we quantified the relationships between morphological characteristics and flight performance of the FAW from Ghana. Based on observed flight behaviors, we categorized FAW into migratory and non-migratory types. The flight capabilities of first-generation Ghanaian FAW bred in the laboratory were similar to that of the field population from Yunnan, Southwest China, with migrants making up the majority. However, after several generations of laboratory rearing, the flight capability of the Ghanaian population significantly declined, primarily due to a marked increase in the proportion of non-migratory individuals. The low correlation between morphological variables and flight duration suggests that genetic factors likely determine most variations in flight propensity. The results of this study indicate that FAW with high migratory capacity in West Africa is likely to pose a threat to crops in eradication zones and neighboring uninvaded areas and may possibly be capable of crossing the Sahara Desert and invading Europe. Therefore, it is crucial to establish comprehensive pest early warning and management systems.

Host expansion facilitates tephritid flies to expand their ranges. Unraveling the mechanisms of host expansion will help to efficiently control these pests. Our previous works showed mitochondrial complex I genes Ndufs1, Ndufs3, and Ndufa7 being upregulated during host expansion of Bactrocera tau (Walker), one of the highly hazardous species of tephritids. However, their roles in the host expansion of B. tau remain unknown. Here, using clustered regularly interspaced short palindromic repeats (CRISPR) / CRISPR-associated nuclease 9 (Cas9) editing system for the first time, a stable homozygous Ndufa7 strain (Btndufa7^-/-), heterozygous Ndufs1 (Btndufs1^+/-), and Ndufs3 strains (Btndufs3^+/-) were obtained from F3 generation of B. tau, after gene knockout. Reduced sizes of larvae and pupae of the Ndufa7 knockout strain were first observed. Notably, the mean values of fitness estimation (pupal numbers, single-pupal weight and emergence rate) and Ndufa7 gene expression in the Ndufa7 knockout strain were slightly reduced on 2 native hosts (summer squash and cucumber), while it sharply decreased on the novel host banana and the potential host pitaya, compared with those of the wild-type strain. Furthermore, the Ndufa7 knockout strain did not survive on the novel host guava. These results suggested that Ndufa7 disturbs the survival on native hosts, expansion to novel hosts, and further expansion to potential hosts of B. tau. Homozygous lethality occurred after the knockout of Ndufs1 or Ndufs3, suggesting that these 2 genes play a role in the early development of B. tau. This study revealed that Ndufa7 is a target gene for the management of tephritids and opens a new avenue for pest control research.

Serpins (serine protease inhibitors) constitute a superfamily of proteins with functional diversity and unusual conformational flexibility. In insects, serpins act as multiple inhibitors, by forming inactive acyl-enzyme complexes, in regulating Spätzles activation, phenoloxidases (POs) activity, and other cytokines. In this study, we present the cloning and characterization of Octodonta nipae serpin2 (OnSPN2), a 415 residues protein homologous to Tenebrio molitor 42Dd-like. Notably, OnSPN2 features an arginine residue (R364) at the P1 position, and additional arginine residues (R362, R367) at the P3 and P3' positions, respectively which is crucial for protease inhibition. Immunohistochemistry (IHC) and Western blot analyses revealed that OnSPN2 is primarily synthesized in plasmatocytes and then released into the plasma to exert its function. RNA interference results indicated that OnSPN2 knockdown may depress serine protease in melanization and remarkably increase the transcript level of Attacin in hemolymph, but its messenger RNA levels were not changed upon immune induction. Reciprocal co-immunoprecipitation assay results confirmed that OnSPN2 binds to OnPPAF1 and OnSP8, indicating its role as a negative regulator in the PO and AMP pathway. Intriguingly, several cathepsin-L isoforms were identified in the OnSPN2 immunoprecipitated samples. The cathepsin-L inhibition assays and protein-protein docking results, identified cathepsin-L as a potential target of OnSPN2. These results indicate that OnSPN2 is produced as an intracellular resident and additionally is associated with the PO and AMP pathway. OnSPN2 represents a multiple defense tool that may provide multiple antiproteolytic functions.

Cuticular proteins are essential for cuticle formation, molting, and survival in insects. However, functional analysis of cuticular proteins in the melon aphid has been limited. In this study, we identified an endocuticle structural glycoprotein (ESG) AgSgAbd-2-like in the melon aphid Aphis gossypii, which is a member of the RR-1 subfamily of the CPR (cuticular protein containing the conserved Rebers-Riddiford motif) chitin-binding proteins. When double-stranded RNA is delivered epidermally, AgSgAbd-2-like is knocked down, resulting in molting defects and mortality. The expression of AgSgAbd-2-like is comparatively low prior to molting and increases following molting. Ecdysone signaling consistently suppresses AgSgAbd-2-like. Histologically, the endocuticle and whole cuticle are thinner in AgSgAbd-2-like RNA interference (RNAi) aphids, which is a leading cause of molting defects and mortality. Furthermore, knockdown of any other homolog of ESGs, including AgSgAbd-4, AgSgAbd-4-like, AgSgAbd-8-like, and AgSgAbd-9-like, results in molting defects and death, like that by AgSgAbd-2-like RNAi. These results indicate that the melon aphid ESGs are conserved in cuticle formation and could be potential targets for RNAi-based pest management.

Succession is one of the most extensively studied ecological phenomena, yet debates persist about the importance of dispersal and external factors in driving this process. We aimed to quantify the influence of these factors by investigating how wing-related traits evolve across succession of blowfly (Diptera: Calliphoridae) communities in South Brazil. Rat carrion was placed in both forest and grassland habitats, and the associated blowfly communities were documented throughout the decomposition process. Using morphometric analysis, we measured wing and thorax traits and assessed trait changes over succession through mixed models. Our findings revealed that carrion succession follows distinct trajectories in forest and grassland environments. Specifically, we observed that Calliphora lopesi predominantly visited carcasses during the final phase of decomposition, resulting in significant differences in species composition and wing size between habitats. In forests, wing size increased toward the later stages of succession, whereas an opposite trend was observed in grasslands. Notably, these trait patterns were only evident at the species level, indicating that intraspecific trait variation is irrelevant. Stronger dispersers tend to arrive during the later stages of succession, suggesting that dispersal has a negligible role in shaping successional dynamics. Instead, environmental differences between habitats drive trait patterns throughout succession. Our results suggest that community composition in ephemeral resources is governed by deterministic processes and that successional stages can be predicted based on blowfly wing traits. Specifically, the presence of the large-winged C. lopesi indicates late decay, while the small-winged Chrysomia albiceps and Lucilia eximia are indicative of early decay.

Wings are important organs of insects involved in flight, mating, and other behaviors, and are therefore prime targets for pest control. The formation of insect wings is a complex process that is regulated by multiple pathways. The Hedgehog (Hh) pathway regulates the distribution of wing veins, while the Hippo pathway modulates wing size. Any interventions that can manipulate these pathways have the potential to disrupt wing development and could be used for pest control. In this study, we find that overexpression of miR-7 in Drosophila results in smaller wings with disordered veins. Mechanistically, miR-7 directly targets both ci and yki via different mature miRNAs (miR-7-5p and miR-7-3p), thereby disrupting the Hh and Hippo pathways. Importantly, this regulatory mechanism is also observed in another insect species, Helicoverpa armigera. Finally, by utilizing a nanocarrier delivery system, we show that introducing miR-7 via star polycation (SPc) leads to wing defects in H. armigera. In conclusion, these findings uncover that miR-7 inhibits wing formation by targeting both the Hippo and Hh pathways, indicating its potential for use in pest control strategies.