TRPA1 modulates noxious odor responses in Lygus hesperus

RNAi-Mediated Knockdown of Tektins Does Not Affect Male Fertility in Lygus hesperus

Mirid plant bugs (Hemiptera: Miridae), including Lygus hesperus (western tarnished plant bug), are key pests of numerous agricultural crops. While management of this pest relies heavily on chemical insecticides, the evolution of resistance and environmental concerns underscore the need for new and more effective approaches. Genetic-based strategies that target male fertiliy are currently being evaluated for population suppression. However, a lack of candidate gene targets with appropriate function, specifically in non-model species like L. hesperus, has hindered progress in the development and application of such approaches. Given their conserved role in stabilization of the flagella axoneme and association with sperm motility in many organisms, members of the tektin gene family represent logical targets for genetic-based sterilization. Here, we identified four homologs of the non-vertebrate tektin family from L. hesperus and used RNA interference-mediated knockdown to assess their roles in male fertility. Although transcription of the four tektins was predominantly in the testis, knockdown had negligible effects on either sperm abundance or male fertility. Our results suggest that tektins do not play a critical role in sperm fertilization of eggs in L. hesperus and are thus likely poor targets for genetic-based sterilization approaches in this species.

Exploiting TRP channel diversity in insects: a pathway to next-generation pest management

Transient Receptor Potential (TRP) channels, a diverse family of over 30 ion channel subtypes, are pivotal in regulating sensory perception, thermoregulation, and feeding in insects. In Drosophila melanogaster, 13 TRP channels have been identified, while Aedes aegypti and Anopheles gambiae possess 11 and 10, respectively, showcasing evolutionary adaptations to their ecological niches. This review explores recent advancements in understanding the structure, classification, and physiological functions of TRP channels, emphasizing their evolutionary divergence across Diptera, Lepidoptera, and Hymenoptera. Key TRP subfamilies, such as TRPA, TRPC, TRPM, TRPV, TRPN, and TRPP, are discussed, highlighting their roles in chemo-sensation, gustation, and stress responses. Examples include TRPA1's involvement in thermal sensing and TRPV's role in osmoregulation, critical for insect survival under fluctuating environmental conditions. The review highlights the potential of TRP channels as targets for pest control, focusing on TRP-specific insecticides like pymetrozine, afidopyrifen, and flonicamid, which impact feeding and sensory pathways. RNA interference (RNAi) techniques targeting TRP genes are highlighted as promising tools for innovative pest management. TRP channels' role in mediating thermal tolerance is particularly significant in the context of climate change, where variable temperatures challenge pest dynamics and agricultural sustainability. Understanding these mechanisms is vital for developing climate-resilient pest control strategies. The review also evaluates methodologies used in TRP channel studies, including genomic, transcriptomic, and functional assays, alongside behavioural analyses. Despite progress, challenges remain in studying TRP channels in non-model insects and elucidating their regulation. Future research should integrate multidisciplinary approaches to fully harness TRP channels for sustainable pest management.

β-tubulin functions in spermatogenesis in Lygus hesperus Knight

Lygus hesperus Knight is an important insect pest of crops across western North America, with field management heavily reliant on the use of chemical insecticides. Because of the evolution of resistance to these insecticides, effective and environmentally benign pest management strategies are needed. Traditional sterile insect technique (SIT) has been successfully employed to manage or eradicate some insect pests but involves introducing irradiated insects with random mutations into field populations. New genetically-driven SIT techniques are a safer alternative, causing fixed mutations that manipulate individual genes in target pests to produce sterile individuals for release. Here, we identified seven β-tubulin coding genes from L. hesperus and show that Lhβtub2 is critical in male sperm production and fertility. Lhβtub2 is expressed primarily in the male testes and targeting of this gene by RNA interference or gene editing leads to male sterility.

Mining Lygus hesperus (western tarnished plant bug) transcriptomic data for transient receptor potential channels: Expression profiling and functional characterization of a Painless homolog

The transient receptor potential (TRP) family of cation channels are evolutionarily conserved proteins with critical roles in sensory physiology. Despite extensive studies in model species, knowledge of TRP channel functional diversity and physiological impact remains limited in many non-model insect species. To assess the TRP channel repertoire in a non-model agriculture pest species (Lygus hesperus), publicly available transcriptomic datasets were mined for potential homologs. Among the transcripts identified, 30 are predicted to encompass complete open reading frames that encode proteins representing each of the seven TRP channel subfamilies. Although no homologs were identified for the Pyrexia and Brivido channels, the TRP complement in L. hesperus exceeded the 13-16 channels reported in most insects. This diversity appears to be driven by a combination of alternative splicing, which impacted members of six subfamilies, and gene expansion of the TRPP subfamily. To validate the in silico data and provide more detailed analyses of L. hesperus TRP functionality, the putative Painless homolog was selected for more in depth analysis and its functional role in thermosensation examined in vitro. RT-PCR expression profiling revealed near ubiquitous expression of the Painless transcript throughout nymphal and adult development. Electrophysiological data generated using a Xenopus oocyte recombinant expression system indicated activation parameters for L. hesperus Painless homolog that are consistent with a role in noxious heat (40°-45 °C) thermosensation.

RNAi-Mediated Manipulation of Cuticle Coloration Genes in Lygus hesperus Knight (Hemiptera: Miridae)

Cuticle coloration in insects is a consequence of the accumulation of pigments in a species-specific pattern. Numerous genes are involved in regulating the underlying processes of melanization and sclerotization, and their manipulation can be used to create externally visible markers of successful gene editing. To clarify the roles for many of these genes and examine their suitability as phenotypic markers in Lygus hesperus Knight (western tarnished plant bug), transcriptomic data were screened for sequences exhibiting homology with the Drosophila melanogaster proteins. Complete open reading frames encoding putative homologs for six genes (aaNAT, black, ebony, pale, tan, and yellow) were identified, with two variants for black. Sequence and phylogenetic analyses supported preliminary annotations as cuticle pigmentation genes. In accord with observable difference in color patterning, expression varied for each gene by developmental stage, adult age, body part, and sex. Knockdown by injection of dsRNA for each gene produced varied effects in adults, ranging from the non-detectable (black 1, yellow), to moderate decreases (pale, tan) and increases (black 2, ebony) in darkness, to extreme melanization (aaNAT). Based solely on its expression profile and highly visible phenotype, aaNAT appears to be the best marker for tracking transgenic L. hesperus.

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.