Behavioural evidence for hygro- and mechanoreception by ovipositor sensilla of Dacus tryoni (Diptera: Tephritidae)

ABSTRACT. Gravid female Queensland fruit flies Dacus tryoni (Froggatt) readily oviposit when the ovipositor sensilla are stimulated either by a relatively thick (≥2 mm) surface layer, or by moisture under a relatively thin (<0.5 mm) or thick surface layer. A single layer of Parafilm over dry air elicits almost no oviposition; significantly more oviposition occurs when the underside of the Parafilm is coated with a 2 mm thick layer of petroleum jelly; even more oviposition occurs when the Parafilm is floated on liquid paraffin; greatest oviposition is elicited when moist media (agar gel, water or moist air) are presented under the Parafilm. Hollowed-out domes of apple skin elicit significant oviposition only when sealed basally, to give high internal concentrations of water vapour. The previously identified groove sensilla on the tephritid ovipositor are inferred as being a source of mechanical and chemical information used by the fly in such ovipositional decisions. The ovipositor also has two other types of tactile sensilla. The three types of ovipositor sensilla of tephritids are considered to play roles analogous to those of certain labial receptors of flies with piercing mouthparts.