Comparative Study of the Morphology of the Ovipositor ofPlatygaster diplosisae(Hymenoptera: Platygasteridae) andAprostocetus procerae(Hymenoptera: Eulophidae) Two Parasitoids Associated with the African Rice Gall Midge,Orseolia oryzivora(Diptera: Cecidomyiidae)

We studied the morphology of the ovipositor ofPlatygaster diplosisae(Hymenoptera: Platygasteridae) andAprostocetus procerae(=Tetrastichus pachydiplosisae) (Hymenoptera: Eulophidae), two parasitoids associated with the African rice gall midge (AFRGM), andOrseolia oryzivora(Diptera: Cecidomyiidae). Scanning electron microscope techniques were used for this study. The ovipositor ofP. diplosisaewas short (40 μm), and most of the sensillae found on it were mechanoreceptors and located on the distal portion of the 3rd valvulae. These sensillae may be involved in selection of an egg or larval host. The shortness of this ovipositor may be an adaptation to a host whose egg envelope thickness is not more than 0.7 μm. The ovipositor ofA. proceraewas 30 times (1.2 mm) the length of theP. diplosisaeovipositor. It was not only well equipped with mechanoreceptive sensillae, but these sensillae were very diverse and distributed along the length of the valvulae. The 10 denticulations of the lancet of this ovipositor allow this parasitoid to exploit hosts that are not otherwise readily accesible. These two parasitoids share the same resource by infesting different life stages of the host. The ovipositor of each species of parasitoid enhanced resource sharing, due to its length and its sensillae type and distribution.

Description of a new species of Orseolia (Diptera: Cecidomyiidae) from Paspalum in West Africa, with notes on its parasitoids, ecology and relevance to natural biological control of the African rice gall midge, O. oryzivora

Field sampling of grasses growing in and near rice fields at 12 sites in Nigeria during April/May 1994 recorded the presence of galls on Paspalum scrobiculatumat densities of up to 10.9 galls per m2. These galls were induced by Orseolia bonzii Harris, sp. n., which is described. This species is morphologically close to, but distinct from, the African rice gall midge, Orseolia oryzivora Harris & Gagné, with which it has been confused in earlier studies of that pest species. In host-transfer experiments O. bonzii did not transfer to rice, Oryza sativa. Six hymenopterous parasitoids were reared from galls of O. bonzii and the most abundant of these were Platygaster diplosisae Risbec, Aprostocetus nr. procerae (Risbec) and Neanastatusnr. cinctiventris Girault. Host-transfer experiments with the Platygasterand Aprostocetus species from O. bonzii on Paspalum indicated that the Platygaster may not transfer onto O. oryzivora on rice whereas the Aprostocetus does. The overlap between the parasitoid faunas of the two species of Orseolia is potentially useful as it may be possible to enhance the natural biological control of O. oryzivora by manipulating parasitoid populations on Paspalum.