Temporal changes in the egglaying behaviour of the Hessian fly

Responses of mated female Hessian flies were investigated by analysing the behaviour of individual flies in wheat and oats. The behavioural repertoire of such females included: flying, alighting on leaves, arching of the body so that the tip of the abdomen touched the leaf surface, antennation, movements of the tip of the abdomen across the leaf at right angles to leaf veins, sitting with the ovipositor straight but still extended, and sitting with the ovipositor telescoped into the body. After alighting, females on wheat showed a higher frequency of transitions from arching to antennation and a lower frequency of transitions from arching to abdomen straight than females on oats. During the first 5 min of observations, individuals released into arenas with wheat arched and antennated 2–3 times more frequently than females released into oats. Time allotted to behaviours also differed; during the first 5 min, females in wheat spent 50 percent more time arching, whereas females in oats spent 50 percent more time sitting. Females in wheat also stayed longer and laid 4 times more eggs than females in oats. Temporal changes in egglaying were monitored by quantifying hourly rates of egglaying in no-choice assays for several hours following mating at 9:00 am. During the first and second hours post-mating, egglaying occurred infrequently. However, during the third hour post-mating (11:00 am to noon) females on wheat laid 5 times more eggs than females on oats. Rates of egglaying decreased on wheat but increased on oats during the fourth hour, and then during the fifth hour, decreased on both wheat and oats. Changes in egglaying responses were also evident when behaviours of individual females were measured 1–3 h vs. 3–7 h post-mating. Females deprived of host plants and released into wheat or oats later in the day showed higher frequencies of arching and antennation and laid more eggs before leaving the arena. Resume Analyse quantitative du comportement de ponte de Mayetiola destructor, ephemere insecte herbivore Les reactions de femelles prealablement accouplees de Mouches de Hesse ont ete examinees en analysant le comportement de femelles isolees sur ble et sur avoine. Le repertoire comportemental de ces femelles comprenait: le vol, l'atterrissage sur feuille, la flexion du corps de sorte que l'extremite de l'abdomen touchât la surface de la feuille, l'antennation, les mouvements de l'extremite de l'abdomen sur la feuille a angle droit des nervures, le repos avec la tariere droite et encore devaginee, le repos avec la tariere telescopee a l'interieur du corps. Sur ble plus que sur avoine, les femelles apres atterrissage ont presente une frequence plus elevee de passage de la flexion a l'antennation que de la flexion a l'abdomen droit. Durant les 5 premieres minutes d'observation, les individus liberes dans des enceintes avec ble flechirent et ‘antennerent’ 2 a 3 fois plus que ceux liberes sur avoine. Les durees des differentes sequences differaient aussi: sur ble, pendant les 5 premieres minutes, les femelles passerent plus de 50% du temps a flechir, tandis que sur avoine elles passerent plus de 50% du temps en repos. Les femelles resterent aussi plus longtemps sur les feuilles de ble et y pondirent 4 fois plus d'œufs que sur avoine. Les femelles de M. destructor ont montre une plasticite du seuil d'acceptation. Pendant les premieres heures de ponte, elles ont ete tres selectives et refuserent, ou ne pondirent que quelques œufs sur avoine, mais accepterent volontiers le ble. La discrimination s'est poursuivie tant que les femelles ont eu acces au ble en meme temps qu'a l'avoine. Cependant, quand les femelles ont ete privees de ble pendant plusieures heures, l'acceptation de l'avoine a augmente. Cet accroissement de l'acceptation a eu lieu a peu pres au moment ou les femelles sur ble pondaient leurs derniers œufs.