Host plant manipulation by fig gall midges (Diptera: Cecidomyiidae) which induce emergence projections on flower galls in the syconia of Ficus microcarpa (Moraceae)

Abstract

AbstractWe observed that unique projections developed from female flower galls induced by three unidentified cecidomyiid species in the syconia of Ficus microcarpa (Moraceae) on Okinawa and Amami Islands, Japan. The three cecidomyiids (sp. 1, 2 and 3) were tentatively distinguished by the differences in the shape of the projections. The projection of sp. 1 started to develop from the bottom of each gall before emergence, broke the skin of the syconium, and developed finally up to 5–6 mm in length within 6–8 h. During this period, the pupa oriented its head towards the bottom of the gall. After the projection fully elongated, the pupa pushed open the bottom of the projection with its head. The projection was easily removed from the gall at the base. The pupa quickly crawled half way out of the gall through the opening at the bottom of the projection and an adult then emerged. The projection did not develop when other hymenopteran gall inhabitants emerged. The projection was derived from plant tissues consisting of a mass of small square cells in the basal and distal portions and regularly arranged long cells in the middle portion. No projection was induced by the application of gibberellin's paste to the bottom of syconia. The gall midge seemed to manipulate the fig plant to develop the projection before emergence, so that the pupa can easily pass through the sticky epidermis of the syconium. The emergence of sp. 2 and 3 could not be intensively observed.