Female sex pheromone gland of the boxwood leafminer, Monarthropalpus buxi (Diptera: Cecidomyiidae): Morphological and behavioural evidence

Morphological studies were carried out to determine whether females of the boxwood leafminer, Monarthropalpus buxi (Laboulbène) (Diptera: Cecidomyiidae) have a pheromone gland, its position and ultra-structure. In addition, the reproductive behaviour of this gall midge was studied in the laboratory in a wind-tunnel. The source of the sex pheromone was identified as the epidermis of the inter-segmental membrane between the 8th and 9th abdominal segments of females. The epidermis there was hypertrophied and consisted of a unicellular layer of secretory cells with ultra-structural features that include a well developed smooth endoplasmic reticulum and Golgi complexes that are typical of pheromone-producing glands. At adult emergence the sex ratio was 1 : 1. The virgin females extruded their ovipositor and moved it slowly (visible using a video-camera at high magnification), which was followed by mating. The females were monogamous, while the males usually mated several times with different females. Wind-tunnel bioassays using virgin females, ovipositor-ectomised virgins and mated females provided further evidence that virgin females produce a sex pheromone.