Characteristics of morphology, electrophysiology, and central projections of two sensilla styloconica in Helicoverpa assulta larvae

Abstract

The medial and lateral styloconic sensilla, constituting the main taste organs of lepidopterous caterpillars, were investigated in the oligophagous species, Helicoverpa assulta (Guenée) (Lepidoptera: Noctuidae). In this paper, the two sensilla were morphologically and physiologically characterized by scanning electron microscopy and tip recordings, respectively. The central projections of their respective sensory neurons were mapped by anterograde staining experiments combined with confocal laser scanning microscopy. The results showed that the two sensilla are in general morphologically similar. However, the size of the peg on the medial sensillum is significantly greater than that of the lateral. Tobacco leaf saps, sinigrin, and nicotine elicited strong responses from neurons housed by the medial sensillum, whereas sucrose activated primarily the lateral sensillum. All stained neurons in either sensillum showed a projection pattern involving axons entering the subesophageal ganglion through the ipsilateral maxillary and passing further on through the ipsilateral circumesophageal connective to the tritocerebrum of the brain. In the subesophageal ganglion, the axons targeted two areas: the ventrolateral section and the region near the neuromere midline. One distinction between the staining patterns originating from the two sensilla, however, is that axons arising from the medial sensillum, and not the lateral, give off some additional neural branches in the subesophageal ganglion including a few arborizations surrounding a tract, plus a long process extending posteriorly along the midline. Differences in the central projections derived from the two sensilla styloconica have not been reported previously.

Higher plasticity in feeding preference of a generalist than a specialist: experiments with two closely related Helicoverpa species

“…The plasticity of feeding behavior induced by dietary exposure could be mediated by peripheral taste sensitivity, gustatory transduction pathways, centrifugal control by the central gustatory system or post-ingestive mechanisms 31 , 33 , 55 , 56 . The central projections of gustatory neurons in the sensilla styloconica displayed similar patterns in caterpillars of the two Helicoverpa species but differed in the distributions of neural branches in the subesophageal ganglion 57 , 58 . Molecular study using cDNA microarrays showed that the specialist Manduca sexta regulated transcripts in a diet-specific manner, while the generalist Heliothis virescens regulated a similar suite of transcripts across all diet types, suggesting that specialists are better adapted than generalist herbivores 59 .…”

Identification and Expression Patterns of Putative Diversified Carboxylesterases in the Tea Geometrid Ectropis obliqua Prout

“…These results suggested that EolbCXE7 and EoblCXE13 might function in the E. obliqua olfactory system; however, whether the functions of EolbCXE7 and EoblCXE13 resemble those of their orthologs SlittCXE7 and SexiCXE13 as candidate ODEs in the degradation of ( Z )-3-hexenyl acetate remains to be further confirmed. Additionally, EoblCXE7 and EoblCXE13 were highly expressed at Sst, a putative gustatory sensillum in lepidopteran species (Zenker et al, 2011 ; Tang et al, 2015 ), and we therefore cannot rule out the possibility that both of these EoblCXEs might function in the gustatory system.…”

Structure and development of the subesophageal zone of the Drosophila brain. II. Sensory compartments

“…Outside Drosophila , gustatory projections of insect larvae have been described for several species of Lepidoptera ( Manduca : Kent & Hildebrand, ; Antheraea : Asaoka, ; Helicoverpa : Tang, Hong, Cao, Yan, & Zhao, ; Tang et al, ). Similar to dipteran larvae, head appendages are much smaller in lepidopteran larvae than in adults.…”