UTILISATION DU PIÉGEAGE SEXUEL POUR L‘ÉTUDE DU DÉPLACEMENT DE L'ALUCITE SITOTROGA CEREALELLA . (LÉPIDOPTÈRE: GELECHIIDAE) VERS LES CULTURES DE MAIS

Après avoir mis en évidence, par une expérience préliminaire, l'efficacité du piégeage sexuel chez S. cerealella , en dehors de sa période normale d'activité, l'auteur a utilisé cette méthode au cours des années 1968, 1969 et 1970 pour préciser le cycle biologique de cette espèce dans le Sud‐Ouest de la France. A cette occasion, l'action de différents facteurs sur le rendement du piégeage sexuel a pu être étudiée. Parmi les facteurs physiques, le plus important paraît être la luminosité: c'est au crépuscule, pendant une heure environ, que se font les captures. Parmi les facteurs biotiques, la présence de la plante‐hôte, le Maïs, et le stade phénologique de celle‐ci ont une action déterminante sur le taux des captures: ces dernières sont plus nombreuses à partir de la floraison mâle jusqu'à l'approche de la maturité des grains. Summary SEX TRAPPING AS A METHOD FOR STUDYING DISPERSAL OF SITOTROGA CEREALELLA TO MAIZE FIELDS In order to determine if sex trapping could be utilised as a method of studying the dispersal of S. cerealella , 120 males reared in the laboratory were released and caught in a sex trap containing 100 virgin females. This first experiment took place in April 1968, outside the normal period of insect activity in nature. During the 10 days following the male release, we caught, at dusk, 40 males in this sex trap (30% of the release). This method was later used to determine the life cycle of the Angoumois grain moth in South‐West France. S. cerealella appears in late May and early June in nature. It appears to produce three generations a year. The first and the second would be passed either on maize in cribs or stores, or on other cultivated or wild Graminaceae; on the other hand, the third generation would be spent on ears of maize in the fields. Among the climatic factors which influence the trapping rates of males, daylight seems the most important. The males are trapped only at dusk and for a period of about one hour. Temperature, aerial‐humidity, and wind are not negligible. The sex attractiveness of virgin females seems such as to draw males from considerable distances: an experiment with several sex traps, each containing 5 virgin females only, has proved that it was possible to trap males at several hundred metres from the release point. Among biotic factors excluding those pertaining to the insect itself, the host‐plant seems to be the principal factor for the number of trapped males. The maize has a double effect by its mere presence and its phenological stage: continuous trapping from June to November by two sex traps on uncultivated fields and two other sex traps on maize fields gave respectively the following results: 393 and 6520 males. The experiment of trapping males after release in uncultivated areas and in corn fields gave the following results (% of males covered), for the three periods studied: July 9–13 whorl stage: 7.3% August 27–31 late tasseling and silking stage: 19.6% October 4–8 milking stage of kernels, maturity: 19.0%