European corn borer (ECB) feeding on maize (Zea mais), mugwort (Artemisia vulgaris), and hop (Humulus lupulus) are genetically different in France and referred to as host-plant races. Here, we investigated sex pheromone composition as a possible trait linked to the host plant. ECB host races were sampled from 13 different sites in France. GC-MS analysis of female pheromone showed that 175 out of 176 maize females belonged to the Z type with one hybrid. In contrast, mugwort and hop females belonged almost exclusively to the E type. No Z females were found on these plants and only 2 females out of 169 were hybrids. In the three sites of sympatry, the hybrid proportion was far from Hardy-Weinberg expectations. Wind tunnel experiments showed that 76-79% of maize males from three populations were attracted by Z females, whereas neither mugwort nor hop males were. Mugwort males from Toussus-le-Noble were attracted by E females originating from an American maize strain. These data showed that maize, mugwort, and hop host races of O. nubilalis differ not only in their host plant but also in the sex pheromone they use. Because mugwort and hop are putative ancestral host plants, these results are discussed from the point of view of evolutionary scenarios for the emergence of Z and E strains.

Abstract. Sexual behaviour in most of the noctuid Lepidoptera follows a diel periodicity and is limited to a precise period of either the day or the night. The periodicity and the maturation periods are specifi c as well as the onset of oviposition behaviour. The knowledge of these traits of biology is an essential prerequisite for all the studies in chemical ecology. The periodicity of adult emergence, calling behaviour and oviposition of Busseola fusca (Fuller) was studied under laboratory conditions. Most males emerged before onset of the scotophase whereas most females did so one hour later. The virgin females started to exhibit calling behaviour few hours after emergence and there is no sexual maturation time. The calling behaviour starts the fourth hour after the onset of the scotophase but is lightly delayed for females having emerged the same night as compared to older females. Sexual and oviposition behaviours occur during the dark period. Oviposition started the fi rst night after the mating night, peaked during the second night and then gradually decreased until the fi fth night. The fi rst night of oviposition, females laid eggs during the fi rst three hours and after the 5 th hour of the scotophase with a maximum during the 8 th and 9 th hour. During the second night, oviposition peaked during the second hour and tended to decrease thereafter. Résumé. Chronologie de l'émergence, du comportement d'appel et de l'oviposition chez la mineuse du maïs Busseola fusca (Fuller) (Lepidoptera : Noctuidae). Le comportement sexuel de la plupart des lépidoptères Noctuidae est cyclique et limité à une période bien précise du jour ou de la nuit. Les rythmes et les délais de maturation sexuelle sont propres à chaque espèce. L'initiation du comportement de ponte est aussi une des composantes de l'espèce. La connaissance de ces points de biologie est un préalable indispensable à toutes études d'écologie chimique qui traitent de la reconnaissance du partenaire sexuel et de la plante-hôte. Les périodes d'émergence, du comportement d'appel et de ponte de Busseola fusca (Fuller) ont été étudiées dans des conditions de laboratoire. La plupart des mâles émergent avant le début de nuit et les femelles lors des premières heures. Le comportement d'appel des femelles vierges débute quelques heures après l'émergence et il n'y pas chez B. fusca de délai de maturation sexuelle. La période d'appel commence quatre heures après le début de nuit, et est un peu plus tardive pour les femelles qui viennent d'émerger. L'insecte présente une activité nocturne tant pour l'accouplement que pour la ponte. L'oviposition débute la nuit qui suit celle de l'accouplement et la quantité d'oeufs déposés augmente la deuxième nuit de ponte pour ensuite décroître progressivement jusqu'à la cinquième nuit. La ponte se répartit sur toute la durée de la scotophase avec deux pics : l'un se situe en début de nuit et l'autre dans la seconde moitié de la scotophase.

The African stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), is an important pest of maize and sorghum in sub‐Saharan Africa. As in many other lepidopteran insects, the ability of B. fusca to recognize and colonize a variety of plants is based on the interaction between its sensory systems and the physical and chemical characteristics of its immediate environment. In this study, we tried to identify the behavioural steps of B. fusca leading to host selection and oviposition. Three Poaceae species commonly cultivated in Kenya for human consumption and animal forage were used in this study: the two most preferred hosts, maize (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench], and one non‐preferred host, Napier grass (Pennisetum purpureum Schumach). Wind tunnel observations revealed that volatiles produced by the different plant species did not appear to strongly influence the general orientation of B. fusca towards the plant, as similar behavioural steps were exhibited by the female moth regardless of the plant species involved. This indicated that the females were not able to recognize their preferred hosts from a distance. After landing, the female typically swept her ovipositor on the plant surface, simultaneously touching it with the tips of her antennae, and then oviposited. This behaviour was more frequently observed on maize and sorghum than on Napier grass, and indicated that both antennal and ovipositor receptors are used by the female moths to evaluate the plant surface before deciding to oviposit. As a result, the females laid more eggs on the two crops than on Napier grass. We conclude therefore that females recognized their preferred hosts only after landing. Tactile and contact‐chemoreception stimuli from the plants seemed to play a major role in oviposition decisions of B. fusca.

Abstract. Busseola fusca (Fuller) (Lepidoptera: Noctuidae) is the most important African stem borer damaging maize and sorghum. Chemical mediators play an essential role in all life cycle of this moth, especially for mating recognition and host plant choice. The female sex pheromone, courtship and mating behaviours act on the reproductive isolation within insect populations. B. fusca courtship behaviour was studied to decipher each step that could account as a process for reproductive isolation. B. fusca males and females presented a very simple and fast courtship behaviour, without any particular events or male pheromone emission.Résumé. Comportement de cour du foreur africain de graminées : Busseola fusca (Fuller) (Lepidoptera: Noctuidae) en conditions de laboratoire. Busseola fusca (Fuller) (Lepidoptera : Noctuidae) est le plus important ravageur des cultures de maïs et de sorgho en Afrique. L'écologie chimique est essentielle pendant toute la vie de ces Lépidoptères nocturnes et intervient pour la rencontre des partenaires sexuels et le choix de la plante hôte. La phéromone sexuelle produite par la femelle et le comportement précopulatoire sont des facteurs importants du maintien de l'isolement reproducteur au sein des populations de cet insecte. Le comportement de cour de B. fusca a été étudié pour préciser chaque événement comportemental, qui pourrait avoir un rôle dans l'isolement reproducteur. Le comportement de cour s'avère être très simple et rapide, sans événement particulier ni émission d'une phéromone mâle.