ODOR-MEDIATED FORAGING BY YELLOWJACKET WASPS (HYMENOPTERA, VESPIDAE) - PREDATION ON LEKS OF PHEROMONE-CALLING MEDITERRANEAN FRUIT-FLY MALES(DIPTERA, TEPHRITIDAE)

Predation is probably the most important male mortality factor in inse ct species with courtship displays that render males performing them c onspicuous targets of predators. Sexually active Mediterranean fruit f ly males, Ceratitis capitata (Wied.), aggregate in leks, where they pa rticipate in agonistic encounters and engage in visual, acoustic and p heromone-calling displays to attract receptive females. The objective of this study was to assess: a) whether sexually displaying C. capitat a males in leks inside host and non-host foliage are subject to predat ion by the most prominent predators, yellowjacket wasps, Vespula germa nica (F.), and if so, b) whether olfactory, visual or auditive stimuli are used by foraging wasps in locating male C. capitata prey. Studies were carried out in a citrus orchard and surroundings on the island o f Chios, Greece. Observations were conducted using perforated containe rs hung within mulberry, fig or citrus foliage. Living C. capitata fli es of different sex and either mature or immature were placed inside. Our results show that the yellowjacket wasps have learned to associate the presence of sexually active medfly males aggregated in leks with their prey's pheromone (kairomone). Foraging wasps, flying through the crowns of host trees, responded to the odour source of C. capitata ma le pheromone by approaching from downwind. Even inside dense citrus tr ee foliage, wasps keyed in on aggregations of pheromone-calling males using olfactory stimuli. Stimuli of visual and acoustic male signallin g were only used at close range, after having followed the pheromone p lume close to its source. Visual cues played a greater role in directi ng wasp foraging under more open and exposed host foliage conditions. Odour-based foraging of wasps inside host foliage in the mid-morning h ours, when medfly male lekking activities peak, shifted gradually to a more visual-based host fruit patrolling in the afternoons to capture ovipositing and feeding medfly females. On ripe fruit, particularly fi g, V. germanica visual prey hunting also included the capture of feedi ng medfly males, other feeding Diptera, as well as medfly larvae extra cted from wasp-made perforations in the fruit.