F.J. MULLER, D. TAUBAN, M. RENOU, S. DERRIDJ
INRA, Unité de Phytopharmacie et
des Médiateurs Chimiques, Route de St Cyr, 78 026 Versailles, France
The contact of insects with the plant surface is a behavioral step during which the host can be recognized and thus induce acceptance for egg laying. The chemical analyses of water-soluble maize surface leaches show that both growth stages and organs of the maize plant can be discriminated by their primary metabolite composition. We have shown that the maize leaf surface water-soluble leaches stimulate egg laying of Diabrotica virgifera virgifera (D.v.v.) on artificial substrates.
The question is how can the bio-chemicals influence the egg laying behavior and where they are perceived.
Morphology of the ovipositor was observed under microscope. Scanning electron microscopy was used to search for sensilla on legs and on the ovipositor. Laboratory observations were carried out to determine the different steps of D.v.v. egg laying behavior on an artificial substrate. Distribution of the insects in a maize field was investigated in Hungary at different times of the day and at two growth stages.
Before laying eggs on artificial substrate, females extrude their ovipositor, which is used for scanning back and forth. preliminary observations show the presence of sensilla on the tarsae and on the upper side of the ovipositor, which are likely to be gustatory sensilla. both were found to be put in contact with the substrate during the “pre-egg laying” event.
Walking and resting on the leaves and then husks were the main behaviors observed in the fields. Abundance of females on the maize plants varied with the maize growth stage.
We can hypothesize that insect morphology and egg laying behavior are adapted to the use of bio-chemical information given by the plant surface which provides the decision making of egg laying at the plant bottom into the soil.
Acknowledgements to U. Kuhlman and S. Toepfer from CABI Bioscience Centre in Switzerland and to co-workers of the European project present in Hungary.