Mémoire
| Résumé : | Euploea core, Danaus petilia and D. plexippus are Lepidopterans from the Nymphalidae occurring in Australia. These three species use plants almost exclusively from the Apocynaceae as host plants. The latex the plants produce is toxic due to the presence of cardenolides. To be able to feed on them, caterpillars have shown genetic and behavioural adaptations making them specialist herbivores. In this study, our aim was to test their specialisation by comparing their survival and weight gain on several Apocynaceae species recorded and not recorded as host plants. We also wanted to see if the instar stage of a caterpillar would influence their ability to survive on a host plant when neonates did not survive. The last part of the experiment was dedicated to test if the plant states (cut stem or intact plant) could impact the caterpillars. We found a highly variable survival rate and weight gain for neonates, suggesting that not all the host plants are equivalent. Only one fourth instar caterpillar succeeded to pupate successfully on a plant not recorded as host plant, which suggests that a switch in host plants might be possible for D. plexippus. Finally, the plant state is a very important factor. Indeed, neonates have a better survival and growth rate on cut materials than on intact plants. This is probably due to the decrease in latex flow. We conclude that a caterpillar’s survival depends on various host plant factors like latex and food quality. The specialization allowing them to feed on their host plant seems to prevent them from feeding on other plants but the possibility of a host plant shift might be possible. |
