1INRA, Unité de Phytopharmacie et des Médiateurs chimiques. Route de St Cyr, 78026 Versailles Cedex, France.
2INH, 2 rue Le Nôtre, 49045 Angers Cedex, France.
Sesamia nonagriodes (Lef.) is pest on maize crop all around the
Mediterranean area. Due to its oligophagous character and to the obvious specialisation on
maize, it was interesting to determine the interactions between the plant and the insect on
two essential points for population dynamic: reproductive behaviour and host selection.
Reproductive behaviour, calling behaviour and mating rate were studied in presence of host
plant versus without host plant. Results showed that presence of host plant amplified both
calling behaviour and mating. In S. nonagrioides host selection for oviposition is
crucial, the young larvae are gregarious with reduced mobility. The selection of host plant
was studied at different levels: host orientation, host contact and host assessment. Gravid
females were submitted to 3 different types of plants: maize, leak and cabbage, in wind
tunnel and in static atmosphere. Long range behaviour was found to be steered by visual
cue and generic plant odours. Physic characteristics of the plants that allowed stereotyped
oviposition behaviour were found to be more important than chemical informations.
Females appeared poorly equipped for chemoreception, not equipped to detect specific
compound of other plants, even of unsuitable plants for larvae survival as leak. In term of
adaptation, it seemed likely that the insect switched from natural hosts to maize and
succeed mainly because the maize crops are cultivated on large area, with reduced crop
rotations. As maize plant increased reproductive behaviour, it seemed likely that this species
mate in the crop and that dispersion will be an occasional phenomenon.