Identification and testing of oviposition attractant chemical compounds for Musca domestica

Coordinated mediation of the response to ethyl linoleate by two odorant-binding proteins in Plodia interpunctella larvae

The Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae), is a ubiquitous pest in stored products, with the larvae inflicting the most damage. The molecular mechanisms underlying larval olfaction and associated behaviors remain poorly understood. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis revealed two odorant binding proteins of P. interpunctella (PintOBPs) with antenna-biased expression in larvae. Competitive binding assays revealed that both PintOBP18 and PintOBP19 bind to a variety of volatile compounds emitted from stored food products, with ethyl linoleate identified as the best ligand for both proteins. According to RNA interference tests, the attractiveness of ethyl linoleate to P. interpunctella larvae was not significantly affected by the silencing of PintOBP18 or PintOBP19 separately. Nevertheless, the attractiveness of this odorant to larvae was severely impaired when both OBPs were knocked down. Furthermore, molecular docking and site-directed mutagenesis studies demonstrated that Ser66 in PintOBP18 and Val62 in PintOBP19 play crucial roles in binding ethyl linoleate. These findings advance our understanding of olfactory recognition in P. interpunctella larvae and provide potential targets for developing olfactory disruption strategies to control storage pests.

Electrophysiological Responses and Field Attractants of Plutella xylostella Adults to Volatiles from Brassica oleracea

The diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae), is a major pest of crucifers. Many volatile compounds emitted by cruciferous vegetables are known to mediate the attraction of DBM adults to host plant and oviposition sites. However, development of highly effective attractants for DBM management is still needed. Here, we first analyzed the volatile compounds emitted by macerated broccoli leaves with gas chromatographic-electroantennographic detection and gas chromatography/mass spectrometry. Eight compounds, including benzaldehyde, limonene, phenylacetaldehyde, acetophenone, linalool, 2-phenylethyl alcohol, methyl salicylate, and methyl 2-methoxybenzoate, elicited robust responses from the antennae. Then, we conducted multiple field trapping experiments involving the "addition approach" (individually adding components to the most abundant component, D-limonene) and the "subtraction approach" to evaluate the attractiveness of different blends. We found that a 3-component blend of D-limonene, 2-phenylethyl alcohol, and methyl 2-methoxybenzoate (3:2:1) is the most effective attractant. This blend holds great potential for monitoring and management of P. xylostella populations.

Evaluation of the Control Efficacy of Bt Maize Expressing Cry1Ab and Vip3Aa Proteins Against Agrotis ypsilon (Rottemberg)

Bt maize is the main means to control many lepidopteran pests in the world, but its control efficacy against Agrotis ypsilon (Rottemberg), an important insect pest of maize seedlings, remains unclear until now. The interaction between the insect and Bt transgenic maize events (DBN9936 (expressing Cry1Ab), DBN9501 (expressing Vip3Aa), and DBN3601T (expressing Cry1Ab and Vip3Aa)) was investigated using bioassay and insect behavioral tests. The results show that the Cry1Ab contents in different tissues of DBN9936 were 47.78-82.60 μg·g-1, and the Vip3Aa contents in DBN9501 were 15.29-27.78 μg·g-1. The contents of Cry1Ab and Vip3Aa in DBN3601T were 32.08-79.08 and 10.16-17.52 μg·g-1, respectively. There was no significant difference in total Bt protein content between the leaves and stems; however, that the content in both was significantly higher than that in the roots. The larvae were most sensitive to the Vip3Aa protein, and the corrected mortalities of larvae feeding on DBN9501 and DBN3601T were greater than 89.65% at the seedling stage, significantly higher than those feeding on DBN9936 (16.46-76.13%). The corrected mortalities of the third to the fifth instar larvae feeding on Bt maize root were as follows: DBN3601T (54.00-96.60%) > DBN9501 (24.67-70.88%) > DBN9936 (6.67-53.31%). The results of behavioral tests for Bt/non-Bt maize plant selection indicated that the larvae mainly fed on non-Bt maize while showing antifeedant behavior toward Bt maize, and the moth preferred to lay eggs on undamaged or slightly damaged Bt maize. It is concluded that DBN3601T maize has a strong control efficacy for A. ypsilon, which can play an important role in building an integrated pest management strategy for the insect.

Ferroptotic cyanobacteria as biocontrol agent of the southern house mosquito Culex quinquefasciatus

Culex quinquefasciatus is a hematophagous mosquito, widely distributed around the world, that plays a crucial role in public and veterinary health. As an efficient vector of etiological agents, it exhibits a marked preference for urban environments and human blood. Despite advances in mosquito-borne disease control, managing mosquito populations remains an economically efficient and safe strategy to reduce the impact of epidemic outbreaks. However, achieving this goal requires ecologically acceptable tools that ensure sustainability and minimize adverse environmental impacts. In the present work, we investigated the effect of a non-toxigenic model cyanobacterium on Cx. quinquefasciatus larvae through regulated cell death. We observed that heat stress treatment of Synechocystis PCC 6803 inducing ferroptosis, results in larval lipid oxidation, leading to their death. This effect can be mitigated by rearing larvae in an environment containing canonical inhibitors of ferroptosis, such as ferrostatin 1, or antioxidants, like glutathione and ascorbic acid. Furthermore, larval cell death induced by ferroptotic cyanobacteria is closely linked to oxidative dysregulation and lipid peroxidation, both hallmarks of ferroptosis. Moreover, while ferroptotic Synechocystis significantly affects larval development, it does not influence oviposition site selection by gravid females.

A review of Musca sorbens (Diptera: Muscidae) and Musca domestica behavior and responses to chemical and visual cues

Musca flies (Diptera: Muscidae) have been found culpable in the mechanical transmission of several infectious agents, including viruses, bacteria, protozoans, and helminths, particularly in low-income settings in tropical regions. In large numbers, these flies can negatively impact the health of communities and their livestock through the transmission of pathogens. In some parts of the world, Musca sorbens is of particular importance because it has been linked with the transmission of trachoma, a leading cause of preventable and irreversible blindness or visual impairment caused by Chlamydia trachomatis, but the contribution these flies make to trachoma transmission has not been quantified and even less is known for other pathogens. Current tools for control and monitoring of house flies remain fairly rudimentary and have focused on the use of environmental management, insecticides, traps, and sticky papers. Given that the behaviors of flies are triggered by chemical cues from their environment, monitoring approaches may be improved by focusing on those activities that are associated with nuisance behaviors or with potential pathogen transmission, and there are opportunities to improve fly control by exploiting behaviors toward semiochemicals that act as attractants or repellents. We review current knowledge on the odor and visual cues that affect the behavior of M. sorbens and Musca domestica, with the aim of better understanding how these can be exploited to support disease monitoring and guide the development of more effective control strategies.

Inundative practice for screening siRNA management candidates against a notorious predatory beetle using olfactory silencing

Calosoma maximoviczi, a predatory pest beetle, poses a significant threat to wild silk farm production due to its predation on wild silkworms. Given the coexistence of this species with beneficial silkworms in the farm orchards, chemical pesticides are not an ideal solution for controlling its population. In this study, we employed a comprehensive multi-target RNA interference (RNAi) approach to disrupt the olfactory perception of C. maximoviczi through independently silencing 16 odorant receptors (ORs) in the respective genders. Specifically, gene-specific siRNAs were designed to target a panel of ORs, allowing us to investigate the specific interactions between odorant receptors and ligands within this species. Our investigation led to identifying four candidate siOR groups that effectively disrupted the beetle's olfactory tracking of various odorant ligands associated with different trophic levels. Furthermore, we observed sex-specific differences in innate RNAi responses reflected by subsequent gene expression, physiological and behavioral consequences, underscoring the complexity of olfactory signaling and emphasizing the significance of considering species/sex-specific traits when implementing pest control measures. These findings advance our understanding of olfactory coding patterns in C. maximoviczi beetles and establish a foundation for future research in the field of pest management strategies.

Deciphering the Chemical Fingerprint of Astragalus membranaceus: Volatile Components Attractive to Bruchophagus huonchili Wasps

Bruchophagus huonchili is a pest that poses a serious threat to the yield and quality of Astragalus membranaceus seeds. In this study, we employed solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) to identify volatile organic compounds (VOCs) in A. membranaceus pods during the pod-filled period. Additionally, we utilized a Y-tube olfactometer to measure the behavioral response of B. huonchili to different individual VOCs and specific VOC-based formulations. The most effective formulations were further evaluated for their effectiveness in attracting wasps in the field. Our findings revealed that A. membranaceus pods emit 25 VOCs, including green leaf volatiles (GLVs) and terpenoid and aromatic compounds. Among these compounds, five were found to be most attractive to B. huonchili at the following concentrations: 10 µg/µL cis-β-ocimene, 500 µg/µL hexyl acetate, 100 µg/µL hexanal, 1 µg/µL decanal, and 10 µg/µL β-caryophyllene, with respective response rates of 67.65%, 67.74%, 65.12%, 67.57%, and 66.67%. In addition, we evaluated 26 mixed VOC formulations, and three of them were effective at attracting B. huonchili. Furthermore, field experiments showed that one of the formulations was significantly more effective than the others, which could be used for monitoring B. huonchili populations.

Characterizations of botanical attractant of Halyomorpha halys and selection of relevant deorphanization candidates via computational approach

Halyomorpha halys has been recognized as a global cross-border pest species. Along with well-established pheromone trapping approaches, there have been many attempts to utilize botanical odorant baits for field monitoring. Due to sensitivity, ecological friendliness, and cost-effectiveness for large-scale implementation, the selection of botanical volatiles as luring ingredients and/or synergists for H. halys is needed. In the current work, botanical volatiles were tested by olfactometer and electrophysiological tests. Results showed that linalool oxide was a potential candidate for application as a behavioral modifying chemical. It drove remarkable attractiveness toward H. halys adults in Y-tube assays, as well as eliciting robust electroantennographic responsiveness towards antennae. A computational pipeline was carried out to screen olfactory proteins related to the reception of linalool oxide. Simulated docking activities of four H. halys odorant receptors and two odorant binding proteins to linalool oxide and nerolidol were performed. Results showed that all tested olfactory genes were likely to be involved in plant volatile-sensing pathways, and they tuned broadly to tested components. The current work provides insights into the later development of field demonstration strategies using linalool oxide and its molecular targets.

Culex quinquefasciatus larvae development arrested when fed on Neochloris aquatica

Culex quinquefasciatus is a cosmopolitan species widely distributed in the tropical and subtropical areas of the world. Due to its long history of close association with humans, the transmission of arboviruses and parasites have an important role in veterinary and public health. Adult females feed mainly on birds although they can also feed on humans and other mammals. On the other hand, larvae are able to feed on a great diversity of microorganisms, including microalgae, present in natural or artificial breeding sites with a high organic load. These two particularities, mentioned above, are some of the reasons why this mosquito is so successful in the environment. In this work, we report the identification of a microalga found during field sampling in artificial breeding sites, in a group of discarded tires with accumulated rainwater. Surprisingly, only one of them had a bright green culture without mosquito larvae while the other surrounding tires contained a large number of mosquito larvae. We isolated and identified this microorganism as Neochloris aquatica, and it was evaluated as a potential biological control agent against Cx. quinquefasciatus. The oviposition site preference in the presence of the alga by gravid females, and the effects on larval development were analyzed. Additionally, microalga effect on Cx. quinquefasciatus wild type, naturally infected with the endosymbiotic bacterium Wolbachia (w⁺) and Wolbachia free (w⁻) laboratory lines was explored. According to our results, even though it is chosen by gravid females to lay their eggs, the microalga had a negative effect on the development of larvae from both populations. Additionally, when the larvae were fed with a culture of alga supplemented with balanced fish food used as control diet, they were not able to reverse its effect, and were unable to complete development until adulthood. Here, N. aquatica is described as a biological agent, and as a potential source of bioactive compounds for the control of mosquito populations important in veterinary and human health.

Culex quinquefasciatus, known as a southern house mosquito, is a domestic and cosmopolitan species widely distributed in the tropical and subtropical regions of the Americas, Asia, Africa, and Oceania. It is strongly associated with humans and other vertebrates, and it has been given a relevant role in the transmission of arboviruses and parasitic diseases, some of them very important in veterinary and human health. Adult females feed mainly on birds, although they can also feed on humans and other mammals, being effective not only in surviving in the environment, but in vectoring pathogens as well. In addition, Culex pipiens and Cx. quinquefasciatus, members of the Cx. pipiens complex, coexist in a distribution hybrid zone and their mating produces viable offspring, expanding its distribution even more. Moreover, larvae can be developed in different environments, including standing water generated by humans and livestock, being able to exploit food sources found in them. This ability to get adapted to different conditions make it a successful host with great potential to initiate and facilitate the transmission of pathogens, therefore it is essential to develop environmentally friendly control systems that can be used in integrated vector management programs. In this context, the use of microorganisms, like microalgae, with the capability to alter or slow down the development of insects such as Cx. quinquefasciatus must be exhaustively explored.

Responses of the putative trachoma vector, Musca sorbens, to volatile semiochemicals from human faeces

The putative vector of trachoma, Musca sorbens, prefers to lay its eggs on human faeces on the ground. This study sought to determine whether M. sorbens females were attracted to volatile odours from human faeces in preference to odours from the faeces of other animals, and to determine whether specific volatile semiochemicals mediate selection of the faeces. Traps baited with the faeces of humans and local domestic animals were used to catch flies at two trachoma-endemic locations in The Gambia and one in Ethiopia. At all locations, traps baited with faeces caught more female M. sorbens than control traps baited with soil, and human faeces was the most successful bait compared with soil (mean rate ratios 44.40, 61.40, 10.50 [P<0.001]; 8.17 for child faeces [P = 0.004]). Odours from human faeces were sampled by air entrainment, then extracts of the volatiles were tested by coupled gas chromatography-electroantennography with laboratory-reared female M. sorbens. Twelve compounds were electrophysiologically active and tentatively identified by coupled mass spectrometry-gas chromatography, these included cresol, indole, 2-methylpropanoic acid, butanoic acid, pentanoic acid and hexanoic acid. It is possible that some of these volatiles govern the strong attraction of M. sorbens flies to human faeces. If so, a synthetic blend of these chemicals, at the correct ratios, may prove to be a highly attractive lure. This could be used in odour-baited traps for monitoring or control of this species in trachoma-endemic regions.

A chromosome-level genome assembly of Cydia pomonella provides insights into chemical ecology and insecticide resistance

The codling moth Cydia pomonella, a major invasive pest of pome fruit, has spread around the globe in the last half century. We generated a chromosome-level scaffold assembly including the Z chromosome and a portion of the W chromosome. This assembly reveals the duplication of an olfactory receptor gene (OR3), which we demonstrate enhances the ability of C. pomonella to exploit kairomones and pheromones in locating both host plants and mates. Genome-wide association studies contrasting insecticide-resistant and susceptible strains identify hundreds of single nucleotide polymorphisms (SNPs) potentially associated with insecticide resistance, including three SNPs found in the promoter of CYP6B2. RNAi knockdown of CYP6B2 increases C. pomonella sensitivity to two insecticides, deltamethrin and azinphos methyl. The high-quality genome assembly of C. pomonella informs the genetic basis of its invasiveness, suggesting the codling moth has distinctive capabilities and adaptive potential that may explain its worldwide expansion.

The codling moth, Cydia pomonella, is one of the major pests of pome fruit (apples and pears) and walnuts. Here, the authors sequence and analyze its genome, providing insights on olfactory and detoxification processes that may underlie its worldwide expansion.

Behavioral Evidence and Olfactory Reception of a Single Alarm Pheromone Component in Halyomorpha halys

Halyomorpha halys is a major herbivore insect in the fruit orchards of China that has become a devastating invasive pest in North America and Europe since its accidental introductions in the 1990s and 2000s, respectively. Like other hemipteran insects, H. halys releases defensive chemicals against natural enemies, including (E)-2-decenal, which is an aldehyde associated with alarm pheromones. In this study, a series of electrophysiological and behavioral tests were conducted to characterize the alarm functions of (E)-2-decenal among H. halys adults and nymphs. An antennal transcriptome was obtained from a Chinese H. halys population, and 44 odorant-binding protein (OBP) genes were annotated. Among them, five putative alarm pheromone-binding proteins were screened and were extremely consistent with their homologs from US populations. These five OBPs were later expressed in a heterologous expression system, harvested, and then challenged with (E)-2-decenal in a binding assay. All five OBPs showed high binding activities to (E)-2-decenal, which demonstrated its behavioral significance as a defensive component in H. halys, as well as being the first report of its olfactory reception. These findings will help develop behavioral-mediating tools as part of integrated pest management approaches to control this invasive pest.