Comparative study on the responses of maxillary sensilla styloconica of cotton bollwormHelicoverpa armigera and Oriental tobacco budwormH. assulta larvae to phytochemicals

Hong²,

Cao³

et al. 2015

NeuroReport

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.

Section: Electrophysiological Responsementioning

confidence: 64%

Section: Introductionmentioning

confidence: 99%

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

Hong²,

Cao³

et al. 2015

NeuroReport

“…As a control for the specificity of effects of diets on the sensitivity of the sucrose-best neuron, we also tested whether diets containing different contents of sucrose have effects on the sensitivity of another phagostimulant neuron and a deterrent neuron, i.e. the independent phagostimulant neuron to myo -inositol and the deterrent neuron to sinigrin in the medial sensillum of H. armigera caterpillars37. Concentration of both chemicals was 1 mM, a concentration often used in lepidopteran taste studies6478.…”

Section: Methodsmentioning

confidence: 99%

“…It is known that the maxillary sensilla styloconica of caterpillars of all lepidopteran species studied contain a “sucrose-best”neuron, the activation of which leads to stimulation of feeding behavior373839404142. Compared to the number of reports on the plasticity of gustatory neurons in response to exposure to feeding deterrents, the effects of exposure to varying levels of phagostimulants on the gustatory sensitivity of plant-feeding insects have received little attention.…”

mentioning

confidence: 99%

“…Taste neurons sensitive to sucrose and the deterrent azadirachtin are located in the lateral sensillum, whereas neurons responding to the sugar alcohol myo -inositol and the deterrents strychnine and strophanthin-K reside in the medial sensillum2737484950. Deterrent-sensitive neurons in the maxillary sensilla of H. armigera caterpillars reared on artificial diets containing either strychnine or strophanthin-K from neonate to the 5 th instar exhibited reduced sensitivity to the two chemicals compared with the caterpillars reared on normal diets27.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Trans-generational desensitization and within-generational resensitization of a sucrose-best neuron in the polyphagous herbivore Helicoverpa armigera (Lepidoptera: Noctuidae)

et al. 2016

Sci Rep

Dietary exposure of insects to a feeding deterrent substance for hours to days can induce habituation and concomitant desensitization of the response of peripheral gustatory neurons to such a substance. In the present study, larvae of the herbivore Helicoverpa armigera were fed on diets containing either a high, medium or low concentration of sucrose, a major feeding stimulant. The responsiveness of the sucrose-best neuron in the lateral sensilla styloconica on the galea was quantified. Results showed the response of the sucrose-best neuron exposed to high-sucrose diets decreased gradually over successive generations, resulting in complete desensitization in the 5th and subsequent generations. However, the sensitivity was completely restored in the ninth generation after neonate larvae were exposed to low-sucrose diet. These findings demonstrate phenotypic plasticity and exclude inadvertent artificial selection for low sensitivity to sucrose. No significant changes were found in the sensitivity of caterpillars which experienced low- or medium-sucrose diets over the same generations. Such desensitization versus re-sensitization did not generalise to the phagosimulant myo-inositol-sensitive neuron or the feeding deterrent-sensitive neuron. Our results demonstrate that under conditions of high sucrose availability trans-generational desensitization of a neuron sensitive to this feeding stimulant becomes more pronounced whereas re-sensitization occurs within one generation.

INHERITANCE OF ELECTROPHYSIOLOGICAL RESPONSES TO LEAF SAPS OF HOST‐ AND NONHOST PLANTS IN TWO Helicoverpa SPECIES AND THEIR HYBRIDS

Arch Insect Biochem Physiol

Huang

Wang

et al. 2014

The polyphagous cotton bollworm Helicoverpa armigera (Hübner) and the oligophagous oriental tobacco budworm Helicoverpa assulta (Guenée) (Lepidoptera: Noctuidae) display contrasting heritable feeding preferences for cotton and pepper leaves. In this study, electrophysiological response patterns to cotton and pepper leaf saps in gustatory sensilla styloconica on the maxillae of these two species, their reciprocal F1 hybrids, and backcrossed lines were investigated using the tip recording technique. The identity of the neurons responding to the two leaf saps has been established using action potential waveform analysis. The two plant leaf saps elicited neural activity in at least six of the eight taste neurons innervating the lateral and medial sensilla styloconica of the parental species and crosses. Discriminant analysis of this multineural input predicted that correct classification occurred in 87 - 92% of the cases. Differences in taste neuron responses between insect lines to the two plant saps were consistent with differences in feeding preference behaviors. Comparisons of taste neuron response patterns of parental species, F1 hybrids and backcrosses indicate that autosomal loci contributed to the difference in gustatory response patterns between the two Helicoverpa species with the H. armigera derived alleles being partly dominant to those carried by H. assulta. These findings contribute to the understanding of gustatory codes for preference and provide insight into taste evolution of lepidopteran insects.