Short Trichoid Sensilla Research Articles

A receptor-neuron correlate for the detection of attractive plant volatiles in Helicoverpa assulta (Lepidoptera: Noctuidae)

Plant volatiles are vital cues in the location of hosts for feeding and oviposition for Lepidoptera moths. The noctuid Helicoverpa assulta is a typical polyphagous moth, regarded as a good model for studying the olfactory reception of plant volatiles. In this study, four full-length genes encoding odorant receptors HassOR24, HassOR40, HassOR41, and HassOR55 expressed in antenna in H. assulta were functionally characterized. The highly expressed HassOR40 was narrowly tuned to a few structurally-related plant volatiles: geranyl acetate, geraniol and nerolidol. By systematically analyzing responses of single neuron in both trichoid sensilla and basiconic sensilla using single sensillum recording, the specific neuron B in one type of short trichoid sensilla was found to be mainly activated by the same chemicals as HassOR40 with high sensitivity, and with no significant difference between male and female neurons. Thus, a clear “receptor-neuron” relationship in H. assulta was demonstrated here, suggesting that HassOR40/HassOrco are expressed in neuron B of short trichoid sensilla. The active tobacco volatile nerolidol, recognized by this receptor-neuron line, elicits significant behavioral attraction of both sexes in H. assulta adults. The results indicate that we identified a receptor-neuron route for the peripheral coding of a behaviorally relevant host volatile in H. assulta.

Narrow tuning of an odorant receptor to plant volatiles in Spodoptera exigua (Hübner).

Olfaction plays an important role in insects in recognizing volatile compounds, which are used to find food and mates, as well as avoid danger, predators and pathogens. The key players in the detection of volatile compounds are olfactory receptor (OR) proteins, which are located within the dendritic membrane of sensory neurons and extend into the lymph of sensilla on insect antennae. In the present study, we identify an OR gene, named SexiOR3, which is expressed in adult antenna in both sexes, but with female bias, in the beet armyworm moth Spodoptera exigua. Further in situ hybridization analysis revealed that SexiOR3 was mainly located in short trichoid sensilla. In in vitro heterologous expression experiments, SexiOR3 was narrowly tuned to E-β-farnesene and several compounds of related structure, among 62 different compounds tested in this study. Furthermore, SexiOR3 responds to E-β-farnesene at a low concentration of 10(-9) M, comparable to that of pheromone receptors (PRs) responding to the pheromones. This is a very interesting finding for a general OR, indicating that high specificity is a feature of at least one general OR and not only the PRs. The results suggest that the OR3 gene may play an important role in the moth olfactory system, and underpins important insect behaviour.

The Ultrastructure of Sensilla Associated with Mouthparts and Antennae of Lucilia Cuprina

Antennal and maxillary palps of Lucilia cuprina male and female (family: Calliphoridae) were studied using scanning electron microscopy. Five types of sensilla were observed namely: trichoid, basiconic, coeloconic, styloconic and sensory pit. Trichoid sensilla (one subtype: short trichoid sensilla) was found on the scape of the antenna, while both trichoid (two subtypes: short and long trichoid sensilla) and styloconic sensilla were observed on the antennal pedicel. Basiconic sensilla (two subtypes: small and large basiconic sensilla), coeloconic sensilla and sensory pits were detected on the flagellum of antenna. Cheatica (two subtypes: small and large Cheatica) and small basicinic sensilla were located on the maxillary palps. Microtrachia were observed on all joints of antenna and maxillary palps. No marked differences were observed in the morphological structure of any of the sensilla among the two sexes studied. The suggested function of each antennal sensillum was based on comparison with results of other investigations on similar sensilla.

Spatial Organization of Antennal Olfactory Sensory Neurons in the Female Spodoptera littoralis Moth: Differences in Sensitivity and Temporal Characteristics

Single-cell recordings from olfactory sensory neurons (OSNs), housed in sensilla located at the base and at the tip of the antenna, showed selective responses to plant odors and female sex pheromone in this polyphagous moth. A spatial variation existed in sensitivity: OSNs present on the more proximal segment (P) were more sensitive than those on the more distal segment (D). OSNs of the 2 locations also differed in temporal characteristics: OSNs on P had shorter latency and displayed more phasic responses, whereas those on D had more tonic responses, especially at low stimulus concentrations. The 196 OSNs responding to our 35 monomolecular stimuli in the screening were housed in 32 functional sensillum types: 27 in basiconic, 3 in long-trichoid, 2 in coeloconic, and 3 in auricillic sensilla. The OSNs in basiconic, coeloconic, and auricillic sensilla responded to plant-associated odorants, whereas OSNs in long-trichoid sensilla responded to female-produced sex pheromone components. Short-trichoid sensilla showed spontaneous activity, but no responses to any odorant tested. OSN specificity to plant stimuli ranged from highly specific to broadly tuned, but it did not differ clearly from females in more specialized moths. OSN response diversity is discussed in terms of olfactory coding, behavior, and ecological specialization.

Cuticular and sensory structures on the copulatory apparatus of Rhithrogena semicolorata (Ephemeroptera: Heptageniidae)

The male copulatory apparatus of Rhithrogena semicolorata shows paired penis lobes, armed with teeth laterally projected and equipped with ventral titillators. As revealed by observations under scanning and transmission electron microscopy (SEM, TEM), the titillators are unarticulated appendages that lack sensory structures. The presence of two depressions, located inside the female genital apparatus, is coherent with a possible function of the titillators in stabilising the couple at mating. Sensory structures are located ventrally in the distal portion of each penis lobe and consist of two kinds of sensilla: campaniform sensilla and short trichoid sensilla. Both sensilla show an organisation consistent with a mechanosensory function, particularly related to pressure stimulations. The presence of mechanoreceptors in the penis lobes is coherent with the need of the male to receive mechanosensory information about the female position during mating.

Physiology and antennal lobe projections of olfactory receptor neurons from sexually isomorphic sensilla on male Heliothis virescens

The neurophysiology and antennal lobe projections of olfactory receptor neurons (ORNs) within sexually isomorphic short trichoid sensilla of male Heliothis virescens (Noctuidae: Lepidoptera) were investigated using cut-sensillum recording and cobalt-lysine staining. A total of 202 sensilla were sorted into 14 possible sensillar categories based on odor responses and physiology of ORNs within. Seventy-two percent of the sensilla identified contained ORNs stimulated by conspecific odors. In addition, a large number of ORNs were specifically sensitive to ss-caryophyllene, a plant-derived volatile (N = 41). Axons originating from ORNs associated with individual sensilla were stained with cobalt lysine (N = 67) and traced to individual glomeruli in the antennal lobe. ORNs with responses to female sex pheromone components exhibited similar axonal projections as those previously described from ORNs in long sensilla trichodea in male H. virescens. Antennal lobe axonal arborizations of ORNs sensitive to hairpencil components were also located in glomeruli near the base of the antennal nerve, whilst those sensitive to plant odorants projected to more medial glomeruli. Comparisons with ORNs described from female H. virescens supports the notion that glomeruli at the base of the antennal nerve are associated with conspecific and interspecific odorants, whereas those located medially are associated with plant volatiles.

Variation in antennal sensory system in different phenotypes of large fruit-tree tortrix Archips podana scop. (Lepidoptera: Tortricidae)

Quantitative composition of antennal sensilla was studied in different phenotypes of large fruit-tree tortrix imago. Changes in the number of sensilla were observed in individuals reared on lilac: male phenotypes AB and B differed by the number of chaetoid, coeloconic, auriculate, and basiconic sensilla; female offspring of males with AB and B phenotypes differed by the number of short trichoid sensilla and auriculate sensilla of the first type. The relationship between male phenotype and the number of sensilla as well as the impact of parental male genotype on the variation in antennal sensory system in female offspring are discussed.

Physiology and glomerular projections of olfactory receptor neurons on the antenna of female Heliothis virescens (Lepidoptera: Noctuidae) responsive to behaviorally relevant odors

The neurophysiology and antennal lobe projections of olfactory receptor neurons housed within short trichoid sensilla of female Heliothis virescens F. (Noctuidae: Lepidoptera) were investigated using a combination of cut-sensillum recording and cobalt-lysine staining techniques. Behaviorally relevant odorants, including intra- and inter-sexual pheromonal compounds, plant and floral volatiles were selected for testing sensillar responses. A total of 184 sensilla were categorized into 25 possible sensillar types based on odor responses and sensitivity. Sensilla exhibited both narrow (responding to few odors) and broad (responding to many odors) response spectra. Sixty-six percent of the sensilla identified were stimulated by conspecific odors; in particular, major components of the male H. virescens hairpencil pheromone (hexadecanyl acetate and octadecanyl acetate) and a minor component of the female sex pheromone, (Z)-9-tetradecenal. Following characterization of the responses, olfactory receptor neurons within individual sensilla were stained with cobalt lysine (N=39) and traced to individual glomeruli in the antennal lobe. Olfactory receptor neurons with specific responses to (Z)-9-tetradecenal, a female H. virescens sex pheromone component, projected to the female-specific central large female glomerulus (cLFG) and other glomeruli. Terminal arborizations from sensillar types containing olfactory receptor neurons sensitive to male hairpencil components and plant volatiles were also localized to distinct glomerular locations. This information provides insight into the representation of behaviorally relevant odorants in the female moth olfactory system.

Structure of the Ovipositor of Hylotrupes bajulus (Coleoptera: Cerambycidae)

The female of Hylotrupes bajulus (L.) has an elongated ovipositor comprising modified abdominal segments 8 and 9, intersegmental membrane 8/9, and a pair of distal gonostyli. When not in use, the ovipositor is retracted within abdominal segment 7. An internal apodeme attached to the base of the 8th sternite allows for extension and retraction of the ovipositor. Intersegmental membrane 8/9 makes up half the length of the ovipositor. The 9th sternum is split along the midline to form a pair of hemisternites. The gonostyli comprise basal coxites and apical styli. Segment 8 has long tactile hairs and short trichoid sensilla; intersegmental membrane 8/9 has no visible sensory receptors; segment 9 has campaniform sensilla and short trichoid sensilla. Gonostyli have several types of sensory receptors, including long tactile hairs, medium trichoid sensilla, short trichoid sensilla, and basiconic sensilla. Long tactile hairs and campaniform sensilla are innervated by a single dendrite, thus functioning as mechanoreceptors. Medium trichoid sensilla are innervated by three dendrites, two of which extend into the lumen of the receptor. Short trichoid sensilla are innervated by five sensory neurons. Basiconic sensilla are innervated by 1–3 dendrites, depending on type and location of the receptor. All three types of sensilla function as contact chemoreceptors, and may provide information on suitability of the oviposition substrate.

External morphology and distribution of the antennal sensilla of the stonefly, Paragnetina media (Walker) (Plecoptera : Perlidae)

The distribution and external morphology of sensilla on the antennae of nymphal and adult stonefly, Paragnetina media (Plecoptera : Perlidae) were studied with light and scanning electron microscopy. A peculiar arrangement of 3 types of sensilla was observed on the antennae of the nymphs. Thick- and thin-walled sensilla basiconica and coniform sensillar complexes occur in a group, and 6 to 7 such groups are located around the distal margin on the segments in the mid-region of the flagellum. Campaniform sensilla are concentrated in a ring around a crown of thick- and thin-walled sensilla basiconica on the distal end of the pedicel. Two types of trichoid sensilla, long wavy, and stout straight, are present on the flagellum of the nymph. Adult stoneflies have an antennal surface profusely covered only with long and short trichoid sensilla; all other nymphal type sensilla are absent. The lack of nymphal type sensilla on their antennae may be related to the adult's brief, non-feeding terrestrial life.