Odour and feeding preference of noctuid moth larvae conditioned to vanillin diet and non-vanillin diet

It is largely accepted that larval experience influence host-plant preference of larvae. In general, larval experience with a host plant induces both an odour and feeding preference for that plant. In a previous study, exposure of three noctuid stem borer species, i.e. Sesamia nonagrioides, Busseola fusca and B. nairobica, to a vanillin-enriched medium induced an olfactory preference for the odours of this medium in the larvae of these species. Here, we checked if the exposure to a vanillin-enriched medium also induced a feeding preference for this diet. Different life stages (i.e. neonate larvae to adults) of the three species were conditioned to an artificial diet enriched with vanillin over two generations. Thereafter, two-choice tests on third-generation larvae were done using a Y-tube olfactometer for odour preferences and diet choice experiments. Larvae of all three-species conditioned to the vanillin diet oriented significantly towards the odour of this diet, whereas the non-conditioned larvae did not. Still, apart for B. fusca, the conditioned larvae did not exhibit a feeding preference for this diet, thus odour preference did not match the feeding choice of the conditioned larvae. The implication of this result on insect's adaptability to a new host plant in a changing environment is discussed.