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Morphology of individual labial pit organ (LPO) sensory neurons. (A) Confocal image (maximum intensity projection) of one bilateral LPO neuron. (B) Confocal image (maximum intensity projection) of several co-stained neurons, all projecting to the ipsilateral LPO glomerulus (LPOG). (C,D) Confocal images showing projections of two sub-types of contralateral LPO neurons. The neuron in C, projects along the main fiber bundle on the ipsilateral side of the gnathal ganglion (GNG) before crossing the midline and targeting the contralateral LPOG. The dotted yellow circle represents the LPOG in the antennal lobe (AL). In (D), one fiber (arrowhead) projecting along the thin axon-bundle on the contralateral side terminates in the contralateral LPOG. The additional fibers in the ipsilateral GNG were assumingly originating from sensilla on the outer palp surface. (E) Schematic diagram showing the morphological types of LPO neurons. ES, esophagus; d, dorsal; v, ventral; l, lateral. The neurons in A,C were obtained by retrograde staining from the LPOG whereas the neurons in B,D were obtained by anterograde staining from LPO. Scale bars (A–D) 50 μm.
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Lepidopteran species detect CO2 via a specialized organ located on the peripheral segment of the labial palps, the labial palp pit organ (LPO). Based on tracing of LPO sensory neurons targeting one distinct antennal-lobe glomerulus, Kent and her colleagues described the projections originating from the LPO in the sphinx moth as “an accessory olfact...
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The sense of taste plays a crucial role in herbivorous insects by discriminating nutrients from complex plant metabolic compounds. The peripheral coding of taste has been thoroughly studied in many insect species, but the central gustatory pathways are poorly described. In the present study, we characterized single neurons in the gnathal ganglion o...
Citations
... The discovery of gustation in the labial palps of moths may shed new light on the innervation of the labial palp nerves in the moth brain. Unilateral palp backfills typically reveal bilateral projections ascending to the antennal lobe where they stain a basal glomerulus, equivalent in both males and females, the "labial pit organ glomerulus" (LPOG) 33,59,60 . This glomerulus receives the input from the CO 2 sensory neurons housed in the labial pit organ. ...
... However, palp backfills show additional arborizations in the suboesophageal ganglion (SOG) 33,59 . To clarify this point, Pramod et al. 60 performed selective mass staining from both, the inside of the labial pit organ and the outer surface of the distal labial palp segment of H. armigera and compared their arborizations. LPO sensory neurons projected exclusively to the LPOG, whereas the non-LPO sensory neurons targeted the gnathal ganglion and the ventral nerve cord. ...
In adult Lepidoptera the labial palps are best known for their role in CO2 detection, but they can also bear sensilla chaetica which function is unknown. The number and distribution of sensilla chaetica in labial palps was studied using a bright field microscope. To determine if these sensilla have a gustatory function, we performed single sensillum electrophysiology recordings from palp and antennal sensilla of adult moths of Cydia pomonella (L.), Grapholita molesta (Busck) and Lobesia botrana (Denis and Shieffermüller). Each sensillum was stimulated with 3 doses of one of four test stimulus (sucrose, fructose, KCl and NaCl). Overall, responses (spikes/s⁻¹) increased with dose, and were higher in the palps than in the antennae, and higher to sugars than to salts. With sugars the response increased with concentration in the palp but not in the antenna. With salts there was a drop in response at the intermediate concentration. The number and position of sensilla chaetica on labial palps was variable among individuals. Sensilla were located in the most exposed areas of the palp. Differences in sensilla distribution were detected between species. Such differences among species and between palps and antenna suggest that taste sensilla on the palps have an unforeseen role in adaptation.
... In R. bubo, the sensilla of LPPO are stimulated by carbon dioxide (Bogner et al., 1986;Bogner, 1990). In one case, in addition to 500 club-shaped sensilla, 700 hair-shaped sensilla were found in the LPPO of H. armigera (Zhao et al., 2013;KC et al., 2020). Two sensillum types have been identified in M. separata (Dong et al., 2014) and G. molesta (Song et al., 2016). ...
In this study, investigation of the morphology and distribution of mouthpart sensilla in the adult tomato leafminer moth, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae), using a scanning electron microscope (SEM) is performed. SEM studies examining the mouthparts of Gelechiidae have been noted to be rare; moreover, there have been few investigations on the sensory structures of adult T. absoluta, despite the fact that it is an important pest. In adult T. absoluta, mouthpart structures include the labrum, maxillae comprising two maxillary galeae that form a proboscis, two maxillary palps, and two labial palps. Mandibles were not observed in all studied specimens (30 adults). The proboscis resembles that in other lepidopterous insects and is 1.48 ± 0.08 mm long. Its outer surface is covered with lamellar scales, dense microtrichia, and four sensillum types, that are, aporous sensilla chaetica, uniporous sensilla chaetica, uniporous sensilla styloconica, and aporous sensilla squamiformia. Uniporous sensilla basiconica were also found on the internal face of the proboscis. The labial palps are three-segmented and are known to bear three types of sensilla: squamiformia (present on all three segments), campaniformia, and coeloconica. In this study, we focus on the functional importance of the morphology and distribution of sensilla campaniformia on these labial palps.
... The AL innervations of the four multiglomerular medial-tract PNs innervating all MGC units varied considerably. To investigate a putative association between MGC innervation and response characteristics, we quantified the dendritic density of each PN by measuring the fluorescence intensities within the separate MGC units ( Figure 5-figure supplement 6), as previously performed (see Chu et al., 2020b;Kc et al., 2020). Most of these PNs having terminal projections in the VLP and Video 2. Confocal stacks of neuron dmp-mALTc. ...
... Preparation of the insect has been described in detail elsewhere (Kc et al., 2020;Kymre et al., 2021). Briefly, the moth was restrained inside a plastic tube with the head exposed and then immobilized with dental wax (Kerr Corporation, Romulus, MI). ...
The pheromone system of heliothine moths is an optimal model for studying principles underlying higher-order olfactory processing. In Helicoverpa armigera, three male-specific glomeruli receive input about three female-produced signals, the primary pheromone component, serving as an attractant, and two minor constituents, serving a dual function, i.e. attraction versus inhibition of attraction. From the antennal-lobe glomeruli, the information is conveyed to higher olfactory centers, including the lateral protocerebrum, via three main paths – of which the medial tract is the most prominent. In this study, we traced physiologically identified medial-tract projection neurons from each of the three male‑specific glomeruli with the aim of mapping their terminal branches in the lateral protocerebrum. Our data suggest that the neurons’ wide-spread projections are organized according to behavioral significance, including a spatial separation of signals representing attraction versus inhibition – however, with a unique capacity of switching behavioral consequence based on the amount of the minor components.
... Preparation of the insect has been described in detail elsewhere 13,25 . Briefly, the moth was restrained inside a plastic tube with the head exposed and then immobilized with dental wax (Kerr Corporation, Romulus, MI, USA). ...
Many insects possess the ability to detect fine fluctuations in the environmental CO2 concentration. In herbivorous species, plant-emitted CO2, in combination with other sensory cues, affect many behaviors including foraging and oviposition. In contrast to the comprehensive knowledge obtained on the insect olfactory pathway in recent years, we still know little about the central CO2 system. By utilizing intracellular labeling and mass staining, we report the neuroanatomy of projection neurons connected with the CO2 sensitive antennal-lobe glomerulus, the labial pit organ glomerulus (LPOG), in the noctuid moth, Helicoverpa armigera. We identified 15 individual LPOG projection neurons passing along different tracts. Most of these uniglomerular neurons terminated in the lateral horn, a previously well-described target area of plant-odor projection neurons originating from the numerous ordinary antennal-lobe glomeruli. The other higher-order processing area for odor information, the calyces, on the other hand, was weakly innervated by the LPOG neurons. The overlapping LPOG terminals in the lateral horn, which is considered important for innate behavior in insects, suggests the biological importance of integrating the CO2 input with plant odor information while the weak innervation of the calyces indicates the insignificance of this ubiquitous cue for learning mechanisms.
... The staining procedure was performed as previously described Ian, Zhao, et al., 2016;KC et al., 2020 ...
The relatively large primary olfactory centre of the insect brain, the antennal lobe (AL), contains several heterogeneous neuronal types. These include projection neurons (PNs), providing olfactory information to higher-order neuropils via parallel pathways, and local interneurons (LNs), which provide lateral processing within the AL. In addition, various types of centrifugal neurons (CNs) offer top-down modulation onto the other AL neurons. By performing iontophoretic intracellular staining, we collected a large number of AL neurons in the moth, Helicoverpa armigera, to examine the distinct morphological features of PNs, LNs, and CNs. We characterize 190 AL neurons. These were allocated to 25 distinct neuronal types or sub-types, which were reconstructed and placed into a reference brain. In addition to six PN types comprising 15 sub-types, three LN and seven CN types were identified. High-resolution confocal images allowed us to analyse AL innervations of the various reported neurons, which demonstrated that all PNs innervating ventroposterior glomeruli contact a protocerebral neuropil that is rarely targeted by other PNs, i.e. the posteriorlateral protocerebrum. We also discuss the functional roles of the distinct CNs, which included several previously uncharacterized types, likely involved in computations spanning from multisensory processing to olfactory feedback signalization into the AL.
The pheromone system of heliothine moths is an optimal model for studying principles underlying higher-order olfactory processing. In Helicoverpa armigera, three male-specific glomeruli receive input about three female-produced signals, the primary pheromone component, serving as an attractant, and two minor constituents, serving a dual function, i.e. attraction versus inhibition of attraction. From the antennal-lobe glomeruli, the information is conveyed to higher olfactory centers, including the lateral protocerebrum, via three main paths - of which the medial tract is the most prominent. In this study, we traced physiologically identified medial-tract projection neurons from each of the three male specific glomeruli with the aim of mapping their terminal branches in the lateral protocerebrum. Our data suggest that the neurons' wide-spread projections are organized according to behavioral significance, including a spatial separation of signals representing attraction versus inhibition - however, with a unique capacity of switching behavioral consequence based on the amount of the minor components.
