Bdor\Orco is important for oviposition-deterring behavior induced by both the volatile and non-volatile repellents in Bactrocera dorsalis (Diptera: Tephritidae)

Reproductive behavior of fruit flies: courtship, mating, and oviposition

Many species of the Tephritidae family are invasive and cause huge damage to agriculture and horticulture, owing to their reproductive characteristics. In this review, we have summarized the existing studies on the reproductive behavior of Tephritidae, particularly those regarding the genes and external factors that are associated with courtship, mating, and oviposition. Furthermore, we outline the issues that still need to be addressed in fruit fly reproduction research. The review highlights the implications for understanding the reproductive behavior of fruit flies and discusses methods for their integrated management and biological control. © 2023 Society of Chemical Industry.

Enhancement of Pathogen Toxicity by Feeding Reticulitermes chinensis Snyder Sonicated Bacteria Expressing Double-Stranded RNA That Interferes with Olfaction

Reticulitermes chinensis Snyder is a serious pest in China, and the odorant receptor co-receptor gene RcOrco plays a crucial role in olfaction. However, the function of RcOrco in the resistance of termites to entomopathogens has not been reported. We constructed dsRcOrco-HT115 engineered bacteria based on the RcOrco sequence from the full-length transcriptome data of R. chinensis. The engineered bacteria expressed dsRNA of RcOrco. Sonication was used to inactivate the dsRNA-HT115 strain and obtain a large amount of dsRcOrco. The dsRcOrco produced using this method overcame the problem that genetically engineered bacteria could not be applied directly and improved its effectiveness against termites. Bioassays using the dsRcOrco generated using this method showed that dsRcOrco significantly increased the toxicity of the bacterial and fungal pathogens to R. chinensis. The present study showed, for the first time, the function of Orco in termite resistance to pathogens, and the results provide a theoretical basis for the development and application of termite RNA biopesticides.

TRPA1-mediated repellency behavior in the red flour beetle Tribolium castaneum

The sensory perception of irritant chemicals results in escape and repellency behavioral patterns in insects. Transient receptor potential channels are cation channels that function as sensor proteins for several types of signals, such as light, sound, temperature, taste, as well as chemical and physical stimuli; among these, the TRPA channel is widely conserved and activated by irritant chemicals. Certain plant-derived essential oils (EOs), produced by secondary metabolism, are mixtures of volatile compounds, which are used as repellents because they contain environmentally sustainable ingredients. Citronellal, which is present in citronella EO from Cymbopogon species, is a potentially viable insect repellent; however, the repellency capability against coleopteran beetles remains limited. We investigated the citronellal-derived repellency behavior for the red flour beetle Tribolium castaneum, in which TcTRPA1 and odorant receptor co-receptor (Orco) expressions were mediated by RNA interference. Area-preference tests showed dose-dependent repellency behavior for citronellal; additionally, both TcTRPA1 and TcOrco double-strand RNA (dsRNA) micro-injection showed clear TcTRPA1 and TcOrco transcript reductions, and only TcTRPA1 dsRNA treatment significantly impaired repellency behavior. The relative expression level of the TcTRPA1 transcripts, evaluated by quantitative reverse-transcription PCR (qRT-PCR), revealed dominant expression in the antennae, indicating the antennae-expressed TcTRPA1-mediated repellency behavior.

The Odorant Binding Protein, SiOBP5, Mediates Alarm Pheromone Olfactory Recognition in the Red Imported Fire Ant, Solenopsis invicta

Olfaction is crucial in mediating various behaviors of social insects such as red imported fire ants, Solenopsis invicta Buren. Olfactory receptor (OR) complexes consist of odor-specific ORs and OR co-receptors (Orco). Orcos are highly conserved across insect taxa and are widely co-expressed with ORs. Odorant binding proteins (OBPs) can transport semiochemicals to ORs as protein carriers and thus constitute the first molecular recognition step in insect olfaction. In this study, three OBP genes highly expressed in S. invicta antenna, OBP1, OBP5, OBP6, and Orco were partially silenced using RNA interference (RNAi). RNAi SiOBP5- and Orco-injected ants showed significantly lower EAG (electroantennography) responses to fire ant alarm pheromones and the alkaloid, 2,4,6-trimethylpyridine than water- or GFP-injected ants 72 h post injection. Subsequent qRT-PCR analysis demonstrated that the transcript level of the OBP1, OBP5, OBP6, and Orco significantly decreased 72 h after ants were injected with dsRNAs; however, there were no transcript level or EAG changes in ants fed dsRNAs. Our results suggest that S. invicta Orco and SiOBP5 are crucial to fire ants for their responses to alarm pheromones. RNAi knocking down SiOBP5 can significantly disrupt alarm pheromone communication, suggesting that disrupting SiOBP5 and Orcos could be potentially useful in the management of red imported fire ants.

Toxics or Lures? Biological and Behavioral Effects of Plant Essential Oils on Tephritidae Fruit Flies

The family Tephritidae (Diptera) includes species that are highly invasive and harmful to crops. Due to globalization, international trade, and human displacement, their spread is continuously increasing. Unfortunately, the control of tephritid flies is still closely linked to the use of synthetic insecticides, which are responsible for detrimental effects on the environment and human health. Recently, research is looking for alternative and more eco-friendly tools to be adopted in Integrated Pest Management (IPM) programs. In this regard, essential oils (EOs) and their main compounds represent a promising alternative to chemical insecticides. EOs are made up of phytoconstituents formed from the secondary metabolism of many plants and can act as attractants or toxics, depending on the dose. Because of this unique characteristic, EOs and their main constituents are promising tools that can be used both in Sterile Insect Technique (SIT) programs and in the "lure and kill" technique, exploiting the attractiveness of the product in the former case and its toxicity in the latter. In this article, current knowledge on the biological and behavioral effects of EOs and their main constituents on tephritid fruit flies is reviewed, mainly focusing on species belonging to the Anastrepha, Bactrocera, Ceratitis, and Zeugodacus genera. The mechanisms of action of EOs, their real-world applications, and challenges related to their use in IPM are critically discussed.

Ultrastructure of the Olfactory Sensilla across the Antennae and Maxillary Palps of Bactrocera dorsalis (Diptera: Tephritidae)

Simple Summary

The environmentally friendly methods have been employed to control the serious pest, Bactrocera dorsalis, based on chemical communications. However, their olfaction mechanism has not been unveiled. In this study, the ultrastructure of the sensilla on the antennae and maxillary palps was examined by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results showed that three types of olfactory sensilla (trichodea, basiconica and coeloconica) and two types of non-olfactory sensilla (chaetica and microtrichia) located on the antennae. These findings will benefit the olfactory research and the integrated management of this pest.

Abstract

The sensilla on the antennae and maxillary palps are the most important olfactory organs, via which the insect can perceive the semiochemicals to adjust their host seeking and oviposition behaviors. The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a major agricultural quarantine pest infesting more than 250 different fruits and vegetables. However, the sensilla involved in olfaction have not been well documented even though a variety of control practices based on chemical communication have already been developed. In this study, the ultrastructure of the sensilla, especially the olfactory sensilla on the antennae and maxillary palps of both males and females, were investigated with field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Three types of olfactory sensillum types including trichodea, basiconica, and coeloconica, and two non-olfactory sensilla including both chaetica and microtrichia, were observed. Each of these three types of olfactory sensilla on the antennae of B. dorsalis were further classified into two subtypes according to the morphology and number of receptor cells. For the first time, the pores on the sensilla trichodea and basiconica cuticular wall were observed in this species, suggesting they are involved in semiochemical perception. This study provides new information on B. dorsalis olfaction, which can be connected to other molecular, genetic, and behavioral research to construct an integral olfactory system model for this species.

Anosmic flies: what Orco silencing does to olive fruit flies

Background

The olive fruit fly (Bactrocera oleae) is the most destructive pest of the olive cultivation worldwide causing significant production losses and olive fruit impoverishment, as its larvae feed exclusively on the olive fruit. Reproductive and sexual behavior, as well as host-plant recognition of the fly, are highly dependent on its chemosensory system. Therefore, exploring the role of genes that play a critical role in olfaction, could reveal potential molecular targets that determine species-specific features on chemical communication and could be used to impair sexual behavior.

Results

In this study we identified the gene that encodes the conserved olfactory co-receptor Orco (Odorant receptor co-receptor), which interacts with all divergent insect odorant receptors, and investigated how disruption of its expression affects chemoreception. We initially searched the expression profile of Bo-Orco in both sexes during sexual maturation, as well as pre- and post-mating communication by relative quantitative real time PCR (qRT-PCR) analysis suggesting that Bo-Orco was abundantly expressed in sexually mature adults.

We further investigated the functional role of Bo-Orco in mating and oviposition behavior via transient gene silencing that was performed through in vivo dsRNA hemolymph injections in sexually mature flies 7 days after eclosion. Orco-knockdown phenotypes in both sexes showed reduced copulation rates in mating competitiveness tests, possibly through impaired olfactory-mediated detection of sex pheromone. In addition, oviposition was significantly inhibited in dsRNA-Orco injected females in a post-mating behavior test.

Conclusions

Our results demonstrate that Orco plays a crucial role in the reproductive behavior of the olive fruit fly, since pre- and post-mating processes were affected. This is the first report in the olive fruit fly that links the chemosensory pathway with the mating behavior and the reproductive potential at a molecular basis, rendering this gene a potential target for the improvement of the olive fruit fly population control techniques.

Silencing Orco Impaired the Ability to Perceive Trail Pheromones and Affected Locomotion Behavior in Two Termite Species

Sophisticated social behaviors in termite colonies are mainly regulated via chemical communication of a wide range of pheromones. Trail pheromones play important roles in foraging behavior and building tunnels and nests in termites. However, it is almost unclear how termites perceive trail pheromones. Here, we cloned and sequenced of olfactory co-receptor (Orco) genes from the two termites Reticulitermes chinensis Snyder (Isoptera: Rhinotermitidae) and Odontotermes formosanus (Shiraki) (Isoptera: Termitidae), and then examined their responses to trail pheromones after silencing Orco through RNA interference (RNAi). We found that Orco knockdown impaired their ability to perceive trail pheromones and resulted in the disability of following pheromone trails in the two termite species. Our locomotion behavior assays further showed that Orco knockdown significantly decreased the distance and velocity in the two termite species, but significantly increased the angular velocity and turn angle in the termite R. chinensis. These findings strongly demonstrated that Orco is essential for termites to perceive their trail pheromones, which provides a potential way to control termite pests by damaging olfactory system.

TRPA1 modulates noxious odor responses in Lygus hesperus

Lygus hesperus isa key pest of many economically important crops across western North America. Central to many aspects of the lives of these insects is chemical signalling, with identified roles in host plant selection, aggregation and passive mate guarding. The development of novel monitoring and control approaches for this insect will rely on a sound understanding of how these cues are perceived and processed, and their impact on behavior. Towards this end, we investigated allyl isothiocyanate, cinnamaldehyde and citronellal, compounds that are noxious repellents to other insects. We found that L. hesperus avoided areas containing the three compounds and that exposure induced increases in movement velocity and duration in both nymphs and adults. This suggests these compounds may work as repellents. To better understand the underlying physiology of this response, RNA interference by dsRNA injection was used to inhibit the expression of two chemosensory-associated proteins, the odorant receptor co-receptor (Orco) and the transient receptor potential A (TRPA1) channel. While knockdown of Orco did not change the reaction of adult females to citronellal, TRPA1 silencing effectively eliminated the induced increase to movement, suggesting a chemoperceptory role in citronellal detection.

Molecular and Functional Characterization of Odorant Binding Protein 7 From the Oriental Fruit Moth Grapholita molesta (Busck) (Lepidoptera: Tortricidae)

Odorant-binding proteins (OBPs) are widely and abundantly distributed in the insect sensillar lymph and are essential for insect olfactory processes. The OBPs can capture and transfer odor molecules across the sensillum lymph to odorant receptors and trigger the signal transduction pathway. In this study, a putative OBP gene, GmolOBP7, was cloned using specific-primers, based on the annotated unigene which forms the antennal transcriptome of Grapholita molesta. Real-time PCR (qRT-PCR) analysis revealed that GmolOBP7 was highly expressed in the wings of males and the antennae of both male and female adult moths, while low levels were expressed in other tissues. The recombinant GmolOBP7 (rGmolOBP7) was successfully expressed and purified via Ni-ion affinity chromatography. The results of binding assays revealed that rGmolOBP7 exhibited a high binding affinity to the minor sex pheromone 1-dodecanol containing K_i of 7.48 μM and had high binding capacities to the host-plant volatiles, such as pear ester, lauraldehyde and α-ocimene. RNA-interference experiments were performed to further assess the function of GmolOBP7. qRT-PCR showed that the levels of mRNA transcripts significantly declined in 1 and 2 day old male and female moths, treated with GmolOBP7 dsRNA, compared with non-injection controls. The EAG responses of dsRNA-injected males and females to pear ester, as well as the EAG responses of dsRNA-injected males to 1-dodecanol, were significantly reduced compared to the GFP-dsRNA-injected and non-injected controls. We therefore infer that GmolOBP7 has a dual function in the perception and recognition of the host-plant volatiles and sex pheromones.

Molecular characterization and evolution of a chemosensory receptor gene family in three notorious rice planthoppers, Nilaparvata lugens, Sogatella furcifera and Laodelphax striatellus, based on genome and transcriptome analyses

BACKGROUND

The white-backed planthopper (WBPH) Sogatella furcifera, the brown planthopper (BPH) Nilaparvata lugens, and the small brown planthopper (SBPH) Laodelphax striatellus (Hemiptera: Delphacidae) are rice pests that damage rice plants by sap-sucking and by transmitting viruses. Host-seeking behavior involves chemosensory receptor genes that include odorant receptors (ORs), ionotropic receptors (IRs) and gustatory receptors (GRs).

RESULTS

We used genome and transcriptome data to identify 141 ORs, 28 GRs and 25 IRs in BPH; 135 ORs, 18 GRs and 16 IRs in WBPH; and 37 ORs, 14 GRs and 6 IRs in SBPH. A phylogenetic analysis identified several specific OR clades of rice planthoppers, the results indicating that these OR members might be used to respond to specific host volatiles. OR co-receptor (Orco) is the most conserved and essential OR gene among these species and RNA interference (RNAi) can decrease their mRNA expression level to <50%. RNAi knockdown rice planthoppers were anosmia and were unable to seek or locate rice plants in behavioral tests.

CONCLUSION

The results demonstrate the importance of the planthopper Orco genes in locating rice plants. This information may aid in the development of RNAi-based transgenic rice and other pest management technologies. © 2018 Society of Chemical Industry.

Characterization and Comparative Analysis of Olfactory Receptor Co-Receptor Orco Orthologs Among Five Mirid Bug Species

The phytophagous mirid bugs of Apolygus lucorum, Lygus pratensis as well as three Adelphocoris spp., including Adelphocoris lineolatus, A. suturalis, and A. fasciaticollis are major pests of multiple agricultural crops in China, which have distinct geographical distribution and occurrence ranges. Like many insect species, these bugs heavily rely on olfactory cues to search preferred host plants, thereby investigation on functional co-evolution and divergence of olfactory genes seems to be necessary and is of great interest. In the odorant detection pathway, olfactory receptor co-receptor (Orco) plays critical role in the perception of odors. In this study, we identified the full-length cDNA sequences encoding three putative Orcos (AsutOrco, AfasOrco, and LpraOrco) in bug species of A. suturalis, A. fasciaticollis, and L. pratensis based on homology cloning method. Next, sequence alignment, membrane topology and gene structure analysis showed that these three Orco orthologs together with previously reported AlinOrco and AlucOrco shared high amino acid identities and similar topology structure, but had different gene structure especially at the length and insertion sites of introns. Furthermore, the evolutional estimation on the ratios of non-synonymous to synonymous (Ka/Ks) revealed that Orco genes were under strong purifying selection, but the degrees of variation were significant different between genera. The results of quantitative real-time PCR experiments showed that these five Orco genes had a similar antennae-biased tissue expression pattern. Taking these data together, it is thought that Orco genes in the mirid species could share conserved olfaction roles but had different evolution rates. These findings would lay a foundation to further investigate the molecular mechanisms of evolutionary interactions between mirid bugs and their host plants, which might in turn contribute to the development of pest management strategy for mirid bugs.

Access to the odor world: olfactory receptors and their role for signal transduction in insects

The sense of smell enables insects to recognize and discriminate a broad range of volatile chemicals in their environment originating from prey, host plants and conspecifics. These olfactory cues are received by olfactory sensory neurons (OSNs) that relay information about food sources, oviposition sites and mates to the brain and thus elicit distinct odor-evoked behaviors. Research over the last decades has greatly advanced our knowledge concerning the molecular basis underlying the reception of odorous compounds and the mechanisms of signal transduction in OSNs. The emerging picture clearly indicates that OSNs of insects recognize odorants and pheromones by means of ligand-binding membrane proteins encoded by large and diverse families of receptor genes. In contrast, the mechanisms of the chemo-electrical transduction process are not fully understood; the present status suggests a contribution of ionotropic as well as metabotropic mechanisms. In this review, we will summarize current knowledge on the peripheral mechanisms of odor sensing in insects focusing on olfactory receptors and their specific role in the recognition and transduction of odorant and pheromone signals by OSNs.

Olfactory Plasticity: Variation in the Expression of Chemosensory Receptors in Bactrocera dorsalis in Different Physiological States

Changes in physiological conditions could influence the perception of external odors, which is important for the reproduction and survival of insect. With the alteration of physiological conditions, such as, age, feeding state, circadian rhythm, and mating status, insect can modulate their olfactory systems accordingly. Ionotropic, gustatory, and odorant receptors (IR, GR, and ORs) are important elements of the insect chemosensory system, which enable insects to detect various external stimuli. In this study, we investigated the changes in these receptors at the mRNA level in Bactrocera dorsalis in different physiological states. We performed transcriptome analysis to identify chemosensory receptors: 21 IRs, 12 GRs, and 43 ORs were identified from B. dorsalis antennae, including almost all previously known chemoreceptors in B. dorsalis and a few more. Quantitative real-time polymerase chain reaction analysis revealed the effects of feeding state, mating status and time of day on the expression of IR, GR, and OR genes. The results showed that expression of chemosensory receptors changed in response to different physiological states, and these changes were completely different for different types of receptors and between male and female flies. Our study suggests that the expressions of chemosensory receptors change to adapt to different physiological states, which may indicate the significant role of these receptors in such physiological processes.

Implementing the sterile insect technique with RNA interference - a review

We review RNA interference (RNAi) of insect pests and its potential for implementing sterile insect technique (SIT)-related control. The molecular mechanisms that support RNAi in pest species are reviewed in detail, drawing on literature from a range of species including Drosophila melanogaster Meigen and Homo sapiens L. The underlying genes that enable RNAi are generally conserved across taxa, although variance exists in both their form and function. RNAi represents a plausible, non-GM system for targeting populations of insects for control purposes, if RNAi effector molecules can be delivered environmentally (eRNAi). We consider studies of eRNAi from across several insect orders and review to what extent taxonomy, genetics, and differing methods of double-stranded (ds) RNA synthesis and delivery can influence the efficiency of gene knockdown. Several factors, including the secondary structure of the target mRNA and the specific nucleotide sequence of dsRNA effector molecules, can affect the potency of eRNAi. However, taxonomic relationships between insects cannot be used to reliably forecast the efficiency of an eRNAi response. The mechanisms by which insects acquire dsRNA from their environment require further research, but the evidence to date suggests that endocytosis and transport channels both play key roles. Delivery of RNA molecules packaged in intermediary carriers such as bacteria or nanoparticles may facilitate their entry into and through the gut, and enable the evasion of host defence systems, such as toxic pH, that would otherwise attenuate the potential for RNAi.

Role of a tachykinin-related peptide and its receptor in modulating the olfactory sensitivity in the oriental fruit fly, Bactrocera dorsalis (Hendel)

Insect tachykinin-related peptide (TRP), an ortholog of tachykinin in vertebrates, has been linked with regulation of diverse physiological processes, such as olfactory perception, locomotion, aggression, lipid metabolism and myotropic activity. In this study, we investigated the function of TRP (BdTRP) and its receptor (BdTRPR) in an important agricultural pest, the oriental fruit fly Bactrocera dorsalis. BdTRPR is a typical G-protein coupled-receptor (GPCR), and it could be activated by the putative BdTRP mature peptides with the effective concentrations (EC₅₀) at the nanomolar range when expressed in Chinese hamster ovary cells. Consistent with its role as a neuromodulator, expression of BdTRP was detected in the central nervous system (CNS) of B. dorsalis, specifically in the local interneurons with cell bodies lateral to the antennal lobe. BdTRPR was found in the CNS, midgut and hindgut, but interestingly also in the antennae. To investigate the role of BdTRP and BdTRPR in olfaction behavior, adult flies were subjected to RNA interference, which led to a reduction in the antennal electrophysiological response and sensitivity to ethyl acetate in the Y-tube assay. Taken together, we demonstrate the impact of TRP/TRPR signaling on the modulation of the olfactory sensitivity in B. dorsalis. The result improve our understanding of olfactory processing in this agriculturally important pest insect.

Positive Allosteric Modulation of Insect Olfactory Receptor Function by ORco Agonists

Insect olfactory receptors (ORs) are heteromeric ligand-gated cation channels composed of a common olfactory receptor subunit (ORco) and a variable subunit (ORx) of as yet unknown structures and undetermined stoichiometries. In this study, we examined the allosteric modulation exerted on Anopheles gambiae heteromeric ORx/ORco olfactory receptors in vitro by a specific class of ORco agonists (OAs) comprising ORcoRAM2 and VUAA1. High OA concentrations produced stronger functional responses in cells expressing heteromeric receptor channels relative to cells expressing ORco alone. These OA-induced responses of ORx/ORco channels were also notably much stronger than those obtained upon administration of ORx-specific ligands to the same receptors. Most importantly, small concentrations of OAs were found to act as strong potentiators of ORx/ORco function, increasing dramatically both the efficacy and potency of ORx-specific odorants. These results suggest that insect heteromeric ORs are highly dynamic complexes adopting different conformations that change in a concerted fashion as a result of the interplay between the subunits of the oligomeric assemblies, and that allosteric modulation may constitute an important element in the modulation and fining tuning of olfactory reception function.

Identification of putative chemosensory receptor genes from yellow peach moth Conogethes punctiferalis (Guenée) antennae transcriptome

The yellow peach moth, Conogethes punctiferalis, is an extremely important polyphagous insect in Asia. The chemosensory systems of moth play an important role in detecting food, oviposition sites and mate attraction. Several antennal chemosensory receptors are involved in odor detection. Our study aims to identify chemosensory receptor genes for potential applications in behavioral responses of yellow peach moth. By transcriptomic analysis of male and female antennae, 83 candidate chemosensory receptors, including 62 odorant receptors, 11 ionotropic receptors and 10 gustatory receptors were identified. Through Blast and sequence alignment, the highly conserved co-receptor Orco was annotated, eight unigenes clustered into pheromone receptors, and two clustered as sugar receptor. Among the IRs, one unigenes was similar with co-receptors IR25a. Expression levels of 50 odorant receptors were further evaluated by quantitative real-time PCR in antennae. All the ORs tested were detected in antennae and some of which were associated with sex-biased expression. The chemosensory receptors identified in C. punctiferalis provide a foundational resource for further analysis on olfaction for behavior. The expression profiles of ORs in antennae indicated variant functions in olfactory recognition, and our results provided the possibility for the potential application of semiochemical to control this pest moth.

Are insect repellents toxic to freshwater insects? A case study using caddisflies exposed to DEET

Stream ecosystems face ever-increasing pressures by the presence of emergent contaminants, such as, personal care products. N, N-diethyl-3-methylbenzamide (DEET) is a synthetic insect repellent that is being found in surface waters environments in concentrations up to 33.4 μg/L. Information concerning DEET's toxicity in the aquatic environment is still limited and focused only on its acute effects on model species. Our main objective was to assess the effects of DEET exposure to a caddisfly non-target species using sub-lethal endpoints. For that, we chose Sericostoma vittatum, an important shredder in Portuguese freshwaters that has been already used in different ecotoxicological assays. Besides acute tests, S. vittatum were exposed during 6 days to a gradient of DEET concentrations (8, 18 and 40.5 mg/L) to assess effects on feeding behaviour and biochemical responses, such as, lipid peroxidation levels (LPO), catalase and acetylcholinesterase (AChE) activities, and also assess effects on energy reserves and consumption. Acute tests revealed a 48 h-LC50 of 80.12 mg/L and DEET exposure caused feeding inhibition with a LOEC of 36.80 mg/L. Concerning the biochemical responses, DEET caused no effects in LPO nor on catalase activity. A non-significant decrease in AChE activity was observed. Regarding energetic reserves, exposure to DEET caused a significant reduction in S. vittatum carbohydrates levels. These results add important information for the risk assessment of insect repellents in the aquatic environment and suggest that reported environmental concentrations of DEET are not toxic to non-target freshwater insects.

Responses of the aquatic midge Chironomus riparius to DEET exposure

N,N-diethyl-3-methylbenzamide (DEET) is the active ingredient of many commercial insect repellents. Despite being detected worldwide in effluents, surface water and groundwater, there is still limited information on DEET's toxicity toward non-target aquatic invertebrates. Thus, our main objective was to assess the effects of DEET in the life cycle of Chironomus riparius and assess its biochemical effects. Laboratory assays showed that DEET reduced developmental rates (reduced larval growth, delayed emergence) of C. riparius larvae and also caused a decrease in the size of adult midges. Concerning the biochemical responses, a short exposure to DEET caused no effects in lipid peroxidation, despite the significant inhibition of catalase and glutathione-S-transferase activities and of total glutathione contents. Moreover, inhibition of acetylcholinesterase activity was also observed showing neurotoxic effects. Environmental risk assessment of insect repellents is needed. Our results showed moderate toxicity of DEET toward C. riparius, however, due to their mode of action, indirect ecological effects of DEET and of other insect repellents cannot be excluded and should be evaluated.

Targeted mutagenesis of an odorant receptor co-receptor using TALEN in Ostrinia furnacalis

Genome editing using transcription activator-like effector nuclease (TALEN) has been applied for various model organisms but not yet for agricultural pest insects. In this study, TALEN-mediated mutagenesis of the gene encoding odorant receptor co-receptor (Orco) of an important agricultural pest Ostrinia furnacalis (OfurOrco) was carried out. Of the two pairs of TALEN constructs designed, one generated somatic and germline mutations at rates of 70.8% and 20.8%, respectively. Physiological and behavioral analyses using a gas chromatograph-electroantennographic detector system and a wind tunnel, respectively, revealed that antennal responses to sex pheromone components were decreased to trace levels, and behavioral responses were abolished in OfurOrco mutants. This study demonstrated that TALEN-mediated mutagenesis is applicable to pest insects, and these results will open the way for a better understanding of chemosensory systems in wild insects.

Identification, characterization and target gene analysis of testicular microRNAs in the oriental fruit fly Bactrocera dorsalis

MicroRNAs (miRNAs) are small noncoding RNAs that regulate various diverse biological processes including insect spermatogenesis. The oriental fruit fly, Bactrocera dorsalis, is one of the most destructive horticultural pests in East Asia and the Pacific region. Although developmental miRNA profiles of B. dorsalis have enriched our knowledge, specific testicular miRNAs in this dipteran species are unexplored. In this study, we identified miRNAs from B. dorsalis testes by deep sequencing, which provided an overview of miRNA expression during spermatogenesis. Small RNA libraries were constructed from the testes of fully mature (FM), immature (IM) and middle-aged (MA) adult flies of B. dorsalis. Small RNA sequencing and data analysis revealed 172 known and 78 novel miRNAs amongst these libraries. Pairwise comparisons of libraries led to the identification of 24, 15 and 14 differentially expressed miRNAs in FM vs. IM, FM vs. MA and IM vs. MA insects, respectively. Using a bioinformatic approach, we predicted 124 target genes against the 13 most differentially expressed miRNAs. Furthermore, the expression patterns of six randomly selected miRNAs (from the 13 most differentially expressed miRNAs) and their putative target genes (from the 124 predicted target genes) were analysed in the testis of B. dorsalis by quantitative real-time PCR, which showed that out of six, four tested miRNAs-mRNAs had an inverse expression pattern and are probably co-regulated. This study is the first comparative profile of the miRNA transcriptome in three developmental stages of the testis, and provides a useful resource for further studies on the role of miRNAs in spermatogenesis in B. dorsalis.

Reference genes for accessing differential expression among developmental stages and analysis of differential expression of OBP genes in Anastrepha obliqua

The West Indian fruit fly, Anastrepha obliqua, is an important agricultural pest in the New World. The use of pesticide-free methods to control invasive species such as this reinforces the search for genes potentially useful in their genetic control. Therefore, the study of chemosensory proteins involved with a range of responses to the chemical environment will help not only on the understanding of the species biology but may also help the development of environmentally friendly pest control strategies. Here we analyzed the expression patterns of three OBP genes, Obp19d_2, Obp56a and Obp99c, across different phases of A. obliqua development by qPCR. In order to do so, we tested eight and identified three reference genes for data normalization, rpl17, rpl18 and ef1a, which displayed stability for the conditions here tested. All OBPs showed differential expression on adults and some differential expression among adult stages. Obp99c had an almost exclusive expression in males and Obp56a showed high expression in virgin females. Thereby, our results provide relevant data not only for other gene expression studies in this species, as well as for the search of candidate genes that may help in the development of new pest control strategies.