HsTRPA of the Red Imported Fire Ant, Solenopsis invicta, Functions as a Nocisensor and Uncovers the Evolutionary Plasticity of HsTRPA Channels

Hymenopteran-specific TRPA channel from the Texas leaf cutter ant (Atta texana) is heat and cold activated and expression correlates with environmental temperature

Leaf cutting ants of the genus Atta cultivate fungal gardens, carefully modifying environmental conditions to maintain optimal temperature for fungal growth. Antennal nerves from Atta are highly temperature sensitive, but the underlying molecular sensor is unknown. Here, we utilize Atta texana (Texas leaf cutter ant) to investigate the molecular basis of ant temperature sensation and how it might have evolved as the range expanded northeast across Texas from ancestral populations in Mexico. We focus on transient receptor potential (TRP) channel genes, the best characterized temperature sensor proteins in animals. Atta texana antennae express 6 of 13 Hymenopteran TRP channel genes and sequences are under a mix of relaxed and intensified selection. In a behavioral assay, we find A. texana workers prefer 24 °C (range 21-26 °C) for fungal growth. There was no evidence of regulatory evolution across a temperature transect in Texas, but instead Hymenoptera-specific TRPA (HsTRPA) expression highly correlated with ambient temperature. When expressed in vitro, HsTRPA from A. texana is temperature activated with Q10 values exceeding 100 on initial exposure to temperatures above 33 °C. Surprisingly, HsTRPA also appears to be activated by cooling, and therefore to our knowledge, the first non-TRPA1 ortholog to be described with dual heat/cold activation and the first in any invertebrate.

Harnessing Insect Chemosensory and Mechanosensory Receptors Involved in Feeding for Precision Pest Management

Chemosensation and mechanosensation are vital to insects' survival and behavior, shaping critical physiological processes such as feeding, metabolism, mating, and reproduction. During feeding, insects rely on diverse chemosensory and mechanosensory receptors to distinguish between nutritious and harmful substances, enabling them to select suitable food sources while avoiding toxins. These receptors are distributed across various body parts, allowing insects to detect environmental cues about food quality and adjust their behaviors accordingly. A deeper understanding of insect sensory physiology, especially during feeding, not only enhances our knowledge of insect biology but also offers significant opportunities for practical applications. This review highlights recent advancements in research on feeding-related sensory receptors, covering a wide range of insect species, from the model organism Drosophila melanogaster to agricultural and human pests. Additionally, this review examines the potential of targeting insect sensory receptors for precision pest control. Disrupting behaviors such as feeding and reproduction emerges as a promising strategy for pest management. By interfering with these essential behaviors, we can effectively control pest populations while minimizing environmental impacts and promoting ecological balance.

A long-read draft assembly of the Chinese mantis (Mantodea: Mantidae: Tenodera sinensis) genome reveals patterns of ion channel gain and loss across Arthropoda

Praying mantids (Mantodea: Mantidae) are iconic insects that have captivated biologists for decades, especially the species with cannibalistic copulatory behavior. This behavior has been cited as evidence that insects lack nociceptive capacities and cannot feel pain; however, this behaviorally driven hypothesis has never been rigorously tested at the genetic or functional level. To enable future studies of nociceptive capabilities in mantids, we sequenced and assembled a draft genome of the Chinese praying mantis (Tenodera sinensis) and identified multiple classes of nociceptive ion channels by comparison to orthologous gene families in Arthropoda. Our assembly-produced using PacBio HiFi reads-is fragmented (total size = 3.03 Gb; N50 = 1.8 Mb; 4,966 contigs), but is highly complete with respect to gene content (BUSCO complete = 98.7% [odb10_insecta]). The size of our assembly is substantially larger than that of most other insects, but is consistent with the size of other mantid genomes. We found that most families of nociceptive ion channels are present in the T. sinensis genome; that they are most closely related to those found in the damp-wood termite (Zootermopsis nevadensis); and that some families have expanded in T. sinensis while others have contracted relative to nearby lineages. Our findings suggest that mantids are likely to possess nociceptive capabilities and provide a foundation for future experimentation regarding ion channel functions and their consequences for insect behavior.

TRPA5 encodes a thermosensitive ankyrin ion channel receptor in a triatomine insect

As ectotherms, insects need heat-sensitive receptors to monitor environmental temperatures and facilitate thermoregulation. We show that TRPA5, a class of ankyrin transient receptor potential (TRP) channels absent in dipteran genomes, may function as insect heat receptors. In the triatomine bug Rhodnius prolixus (order: Hemiptera), a vector of Chagas disease, the channel RpTRPA5B displays a uniquely high thermosensitivity, with biophysical determinants including a large channel activation enthalpy change (72 kcal/mol), a high temperature coefficient (Q10 = 25), and in vitro temperature-induced currents from 53°C to 68°C (T0.5 = 58.6°C), similar to noxious TRPV receptors in mammals. Monomeric and tetrameric ion channel structure predictions show reliable parallels with fruit fly dTRPA1, with structural uniqueness in ankyrin repeat domains, the channel selectivity filter, and potential TRP functional modulator regions. Overall, the finding of a member of TRPA5 as a temperature-activated receptor illustrates the diversity of insect molecular heat detectors.

Avoidance of thiazoline compound depends on multiple sensory pathways mediated by TrpA1 and ORs in Drosophila

Transient receptor potential (TRP) channels are primary sensory molecules in animals and are involved in detecting a diverse range of physical and chemical cues in the environments. Considering the crucial role of TRPA1 channels in nocifensive behaviors and aversive responses across various insect species, activators of TRPA1 are promising candidates for insect pest control. In this study, we demonstrate that 2-methylthiazoline (2MT), an artificial volatile thiazoline compound originally identified as a stimulant for mouse TRPA1, can be utilized as a novel repellent for fruit flies, Drosophila melanogaster. We observed that 2MT induced strong, dose-dependent avoidance behaviors in adult males, regardless of their feeding states, as well as egg laying behavior in females. These aversive responses were mediated by contact chemosensation via TrpA1 and olfaction via odorant receptors. Knocking down TrpA1 revealed the essential roles of bitter taste neurons and nociceptive neurons in the legs and labellum. Furthermore, among five isoforms, TrpA1-C and TrpA1-D exclusively contributed to the aversiveness of 2MT. We also discovered that these isoforms were directly activated by 2MT through covalent modification of evolutionarily conserved cysteine residues. In conclusion, we have identified 2MT as a stimulant for multiple sensory pathways, triggering aversive behaviors in fruit flies. We propose that 2MT and related chemicals may serve as potential resources for developing novel insect repellents.

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.

Identification of an arthropod molecular target for plant-derived natural repellents

Rational control of arthropod pests is important for animal and human health as well as biodiversity preservation. As an alternative to synthetic chemical pesticides, natural repellents represent an ecological method of pest control. Through an exceptional gene library screening in Mesobuthus martensii scorpions, we here uncover a transient receptor potential ion channel as the chemosensory sensor for plant-derived repellents. Its ortholog ion channel in Drosophila melanogaster also acts as a molecular receptor of natural repellents and mediates avoidance behavior. This work thus identifies a molecular basis for arthropod chemosensing and should help update the ecological strategies for pest control while preserving biodiversity.

Arthropods maintain ecosystem balance while also contributing to the spread of disease. Plant-derived natural repellents represent an ecological method of pest control, but their direct molecular targets in arthropods remain to be further elucidated. Occupying a critical phylogenetic niche in arthropod evolution, scorpions retain an ancestral genetic profile. Here, using a behavior-guided screening of the Mesobuthus martensii genome, we identified a scorpion transient receptor potential (sTRP1) channel that senses Cymbopogon-derived natural repellents, while remaining insensitive to the synthetic chemical pesticide DEET. Scrutinizing orthologs of sTRP1 in Drosophila melanogaster, we further demonstrated dTRPγ ion channel as a chemosensory receptor of natural repellents to mediate avoidance behavior. This study sheds light on arthropod molecular targets of natural repellents, exemplifying the arthropod–plant adaptation. It should also help the rational design of insect control strategy and in conserving biodiversity.

Contact repellency by l-menthol is mediated by TRPM channels in the red flour beetle Tribolium castaneum

BACKGROUND

Among insects, beetles are one of the most destructive pests of agricultural and stored products. Researchers have been investigating alternatives to pesticides for more sustainable pest management. Here, we focused on insect transient receptor potential (TRP) channel-targeted repellency. Among transient receptor potential melastatin (TRPM) channels, mammalian TRPM8 is activated by menthol and its derivatives, but few previous studies have reported on whether the insect TRPM channel is activated by chemical compounds. Here, we investigated whether the TRPM channel (TcTRPM) of the red flour beetle Tribolium castaneum (Herbst), a major stored-products pest, mediated the repellent behavior of l-menthol and its derivatives.

RESULTS

We initially investigated the repellent activity of l-menthol and menthoxypropanediol (MPD) against T. castaneum. The laboratory bioassay revealed that the repellent activities of l-menthol and MPD were dose dependent. RNA interference was used for transcriptional knockdown of TcTRPM and revealed that a reduced transcript level resulted in a significant decrease in l-menthol and MPD repellent activities. However, no significant decrease was observed for N,N-diethyl-3-methylbenzamide (DEET) repellency. The most abundant TcTRPM transcripts were observed in the antennae. However, antennae-plucked beetles maintained their repellent behavior with l-menthol.

CONCLUSION

The repellent activities of l-menthol and MPD for T. castaneum are mediated by TcTRPM, and it was suggested that the olfactory response is not adequate for avoidance, but that contact repellency might be a more important repellant method. © 2020 Society of Chemical Industry.

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.

Drosophila menthol sensitivity and the Precambrian origins of transient receptor potential-dependent chemosensation

Transient receptor potential (TRP) cation channels are highly conserved, polymodal sensors which respond to a wide variety of stimuli. Perhaps most notably, TRP channels serve critical functions in nociception and pain. A growing body of evidence suggests that transient receptor potential melastatin (TRPM) and transient receptor potential ankyrin (TRPA) thermal and electrophile sensitivities predate the protostome-deuterostome split (greater than 550 Ma). However, TRPM and TRPA channels are also thought to detect modified terpenes (e.g. menthol). Although terpenoids like menthol are thought to be aversive and/or harmful to insects, mechanistic sensitivity studies have been largely restricted to chordates. Furthermore, it is unknown if TRP-menthol sensing is as ancient as thermal and/or electrophile sensitivity. Combining genetic, optical, electrophysiological, behavioural and phylogenetic approaches, we tested the hypothesis that insect TRP channels play a conserved role in menthol sensing. We found that topical application of menthol to Drosophila melanogaster larvae elicits a Trpm- and TrpA1-dependent nocifensive rolling behaviour, which requires activation of Class IV nociceptor neurons. Further, in characterizing the evolution of TRP channels, we put forth the hypotheses that three previously undescribed TRPM channel clades (basal, αTRPM and βTRPM), as well as TRPs with residues critical for menthol sensing, were present in ancestral bilaterians. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.