Insect Science最新文献

Urbanization, one of the most significant global environmental issues of our time, causes significant environmental and structural changes in natural or seminatural habitat patches. These urbanization-related changes trigger significant impact on ecological interactions and functioning. Predation is one of the most important ecological interactions, and urbanization-related changes on predation pressure may have substantial ecological consequences. We studied predation pressure over a full season (from April to October) in rural versus urban forests using the sentinel approach in and around a large city (Debrecen) in the eastern part of the Great Hungarian Lowland. Model caterpillars made of nondrying green plasticine were readily attacked by arthropods, birds and mammals. From attack marks left by potential predators, a relatively high predation pressure was documented: up to 36% of the caterpillars exposed for 24 h showed attack marks. Seasonal differences were also obvious, with predation pressure during summer being significantly higher than in spring or autumn. This trend held for overall attack rates, also for attacks by arthropods and mammals but not birds. Surprisingly, attack rates were often higher in urban than rural habitats, contradicting the general hypothesis that predation pressure is lower in urbanized areas. As attack rates depend on both predator abundance and activity, and general data indicate lower predator abundances in urban habitats, this phenomenon may have been caused by hungrier predators in urban forest fragments or by the predator relaxation/safe habitat hypothesis that argues that a reduced need for vigilance allows more time to search for prey.

Termites are not only social insects but also significant global insect pests. Investigating the molecular mechanisms regulating immune defense response in termites is beneficial for developing novel approaches to termite management. Currently, research mainly focuses on coding RNAs in termite immunity, with limited exploration of non-coding RNAs. Here, we identified miR-701, a markedly downregulated microRNA (miRNA) in the globally significant termite pest Coptotermes formosanus after Metarhizium anisopliae infection, which targets the immune gene Toll4. Transcriptome analysis of termites injected with miR-701 agomir revealed that miR-701 affects the immune-related response, growth, and development of termites. Treatment with miR-701 agomir, either through injection or ingestion, resulted in a notably reduced survival rate of termites infected with M. anisopliae compared to the control group infected with M. anisopliae alone. Additionally, termites injected with miR-701 agomir exhibited a significant decrease in the expression of antimicrobial peptide genes termicin and lysozyme, alongside a notable increase in the colony-forming units of M. anisopliae in the infected termites. Subsequent investigations demonstrated that miR-701 suppressed the expression of the target gene Toll4, consequently inhibiting the Toll signaling pathway and diminishing the expression of antimicrobial peptides. These findings suggest that termites can combat M. anisopliae by downregulating miR-701 expression to activate the Toll signaling pathway and enhance antimicrobial peptides synthesis. This discovery improves our comprehension of the role of miRNAs in termites' immune responses and the mechanism of termites managing miRNAs to boost their pathogen resistance. Additionally, it reveals a new molecular target for termite biological control.

Resource partitioning among sympatric species is crucial for assembling ecological communities, such as caterpillar-ant assemblages in tropical forests. Myrmecophilous caterpillars use behavioral and chemical strategies to coexist with ants, avoiding attacks. While these strategies are well-understood in single pair of interacting species, such as those involving myrmecophiles and ants, their role in complex multitrophic interactions that include several species of plants, herbivores and ants remains unclear. We aimed to identify the role of cuticular hydrocarbons and specialized morphological structures that caterpillars use to interact with ants (called ant organs) in the recognition process between two riodinid caterpillar species and their respective ant-plant systems. We hypothesized that caterpillars' cuticular profiles would be conspicuous, possessing cues of rewards to ants, allowing specific ants to recognize and not attack them on plants. We performed experiments exposing caterpillars to ants to assess the role of larval ant organs and the specificity of caterpillar-ant interactions on plants. We analyzed cuticular hydrocarbons of caterpillars, ant workers and plants using gas chromatography/mass spectrometry. Our experiments showed that larval ant organs were activated according to each treatment and caterpillars were consistently accepted by their associated ants when transferred to host plants occupied by the same ant species. However, caterpillars transferred to plants with a non-associated ant species that do not tend them were often killed. This highlights the specificity of these interactions. Caterpillar cuticular hydrocarbon profiles, while present in far lower amounts than those of ant workers and plants, were distinctive, suggesting a strategy of chemical conspicuousness that helps caterpillars to be recognized by ants and prevents attacks in specific ant-plant systems. Our results indicate that ants recognize conspicuous cuticular hydrocarbons, while caterpillars convey multimodal signals from ant organs during interactions, which are essential for caterpillar survival in these specific interactions.

Desiccant dusts have been shown to be effective materials in the management of bed bugs (Cimex spp.). Past research primarily focused on exploring the direct lethal effect of dusts against bed bugs, whereas information on their sublethal effects on bed bugs are limited. In this study, we evaluated the lethal effect of 3 dust products (Johnson's^® Baby powder, Vazor DE powder^™, and CimeXa™; abbreviated as Baby powder, DE, and CimeXa) against the tropical bed bug, Cimex hemipterus (F.), under laboratory conditions. Results showed that the 3 dust products caused 97%-100% mortality to tropical bed bugs within 14 d, both in no-choice and choice experiments. However, in a brief exposure experiment (crossing a 2.5-cm-wide band), Baby powder exposure caused a significantly lower mortality (23%) than DE (88%) and CimeXa (100%). The more effective dusts (DE and CimeXa) were selected for further evaluation of their sublethal effects on C. hemipterus. DE and CimeXa caused significantly higher mortality (48%-58%) through horizontal transfer than that of control (6%). Brief exposure to DE and CimeXa dusts did not affect tropical bed bug activity and their response to CO₂. However, CimeXa-exposed tropical bed bugs exhibited reduced feeding and lowered survival rate after feeding. Moreover, both DE and CimeXa dust bands showed strong barrier effects on the crawling of tropical bed bugs. Our results indicate that both DE and CimeXa have great potential for preventing C. hemipterus from reaching protected areas and for controlling C. hemipterus.

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.

Distinct lineages of the grasshopper Chorthippus parallelus (Orthoptera: Acrididae) form well-known hybrid zones (HZs) both in the Pyrenees and the Alps mountain ranges in South Europe. These HZs represent unique experimental systems to identify "key genes" that maintain genetic boundaries between emerging species. The Iberian endemism C. p. erythropus (Cpe) and the subspecies C. p. parallelus (Cpp), widely distributed throughout the rest of Europe, overlap and form the Pyrenean HZ. Both subspecies differ morphologically, as well as in behavioral, mitochondrial, nuclear, and chromosomal traits, and in the strains of the maternally transmitted bacterial endosymbiont Wolbachia infecting them. This results in either unidirectional and bidirectional cytoplasmic incompatibility between both grasshopper subspecies, pointing out that Wolbachia clearly affects gene expression in the infected individuals. Here we explore how Wolbachia may modify the expression of some major genes involved in relevant pathways in Cpp in the Pyrenean HZ. We have analyzed, through molecular biomarkers, the physiological responses in C. parallelus individuals infected by Wolbachia, with particular attention to the energy metabolism, the immune system response, and the reproduction. qPCR was used to evaluate the expression of selected genes in the gonads of infected and uninfected adults of both sexes, since this tissue constitutes the main target of Wolbachia infection. Transcriptional analyses also showed differential sex-dependent responses in most of the analyzed biomarkers in infected and noninfected individuals. We identified for the first time new sensitive biomarkers that might be involved in the reproductive barrier induced by Wolbachia in the hybrid zone.

Olfactory plays an important role in insect behaviors. Pheromone binding proteins (PBPs) are thought to play a certain role in the transport of pheromone molecules in the olfactory recognition process for courtship and mating. Mythimna separata is one of the most serious cereal pests in Asia. The sexual pheromone components of M. separata were clarified; however, to date, little evidence in vivo or in vitro has disclosed the binding properties of PBPs toward the pheromone components of M. separata. To address this research gap, the functional characterization of PBPs in M. separata, spectroscopic investigations were conducted by using recombinant MsepPBPs. Subsequently, MsepPBP1 and MsepPBP3 were selected for RNA interference to assess changes in behavioral responses of male mutants toward normal females. Fluorescence displacement binding assays, combined with fluorescence quenching assays, revealed that MsepPBP3, among the 3 MsepPBPs, exhibited the strongest affinity for Z11-16:Ald, the primary component of sex pheromone in M. separata. Static quenching was observed only between MsepPBP1 and Z9-16:Ald, as well as between MsepPBP3 and Z11-16:Ald or Z9-16:Ald. Transcript levels of MsepPBP1 or MsepPBP3 of male adults were significantly reduced compared to the control when injected with dsMsepPBPs. Both dsPBP1- and dsPBP3-treated males displayed a notable decrease in successful calling behaviors, with this reduction being more pronounced in dsMsepPBP3 injected groups than in dsMsepPBP1 injected groups. These experiments indicated the specificity of MsepPBP1 and MsepPBP3, with both contributing to the sensitivity of female detection. MsepPBP3 appeared to be a key protein for recognizing the sex pheromones of M. separata.

The western flower thrips (Frankliniella occidentalis) is a significant agricultural pest, causing severe global yield losses due to extensive feeding damage and the transmission of plant pathogenic viruses. Despite recent advancements in RNA interference (RNAi) in thrips species, its application has been mostly limited to the adult stage. Given the crucial role of first instar larval thrips in acquiring and transmitting orthotospoviruses, achieving gene silencing in these larvae is critical for studying virus entry and acquisition. While thoracic and abdominal injections have proven effective in adult thrips, the low post-injection survival rate hinders their use in larval thrips. This study addresses this challenge by presenting a microinjection methodology to deliver dsRNA into the hemolymph of first instar larval thrips through the coxa, the first proximal segment of the foreleg. This method significantly improved larval survival rate by preventing detrimental damage to the internal tissues. Significant knockdown of V-ATPase-B, cytochrome P450 (CYP3653A2), and apolipophorin-II/I (ApoLp-II/I) transcripts was confirmed after 48 and/or 72 h post injection (hpi), corresponding to the first and second instar larval stages, respectively. Silencing CYP3653A2 or ApoLp-II/I significantly increased larval mortality. These findings demonstrate proof-of-principle of gene silencing and associated silencing phenotype (mortality) for first instar larval thrips and highlight the essential role of CYP3653A2 and ApoLp-II/I in larval vitality. Our RNAi-based tool offers an opportunity to investigate the molecular mechanisms of thrips-orthotospovirus interactions, as the virus must be acquired by young larval thrips for successful transmission to plants, thus presenting potential targets for thrips pest management.

Insecticide contamination and climate change are key factors driving the global decline in insect populations. However, how these factors interact to impact insect survival remains uncertain. In this study, we examined the effects of sex and genotype on the response to long-term low insecticide exposure at two temperatures, 18 °C and 28 °C, using the Drosophila melanogaster model. We focused on a polymorphic gene, Cyp6g1, known for conferring broad insecticide resistance. We found that while temperature and insecticide have a synergistic effect on mortality of susceptible flies (Cyp6g1-M allele), they act additively on resistant flies (Cyp6g1-BA allele). And whereas the mortality of BA flies exposed to insecticides is strongly dependent on sex at 18 °C, no sex bias is found at 28 °C. Under no insecticide exposure, BA females showed shorter median lifespan than males regardless of temperature, possibly reflecting a cost associated with the resistant allele. Surprisingly, across all genotypes, females showed lower Cyp6g1 gene expression levels than males, which contrasts with their higher insecticide tolerance. Temperature and insecticide exposure had small effects on Cyp6g1 expression levels, suggesting the presence of additional mechanisms of resistance. Our results indicate that the effect of high insecticide doses on insect mortality cannot be used to predict how insects will respond to low contaminating doses, especially when considering the strong interactions between sex, temperature, and genotype. The combined effects of temperature and long-term low insecticide exposure are complex and can have major impacts on insect population dynamics and survival.