Abstract
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.
Highlights
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
Some studies documented that the sensitivity of the deterrent neuron in the sensilla styloconica decreased significantly but not completely after a chronic dietary exposure to the deterrent substance from neonates to the final instar[27,28]
The sugar concentrations investigated here are within the range of reported levels in different plants and plant organs on which H. armigera is known to feed
Summary
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. The sensitivity was completely restored in the ninth generation after neonate larvae were exposed to low-sucrose diet. 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. Some studies documented that the sensitivity of the deterrent neuron in the sensilla styloconica decreased significantly but not completely after a chronic dietary exposure to the deterrent substance from neonates to the final instar[27,28]. Such desensitization of peripheral gustatory neurons to feeding deterrent substances could be mediated by gustatory transduction pathways, centrifugal control by the central gustatory system or post-ingestive mechanisms[21,29,36]
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