The host range, annual cycle and parasitoids of the African rice gall midge Orseolia oryzivora (Diptera: Cecidomyiidae) in central and southeast Nigeria

Abstract

Host range experiments and field sampling in Nigeria produced no evidence that African rice gall midge, Orseolia oryzivora Harris & Gagné, can develop on plants other than Oryza species. Sampling in three outbreak areas during 1994 showed that the insect's annual cycle varied according to the agroecological zone and rice cropping pattern. In the humid forest zone, Orseolia oryzivora persisted through the short dry season on ratoons of cultivated rice Oryza sativa at a rainfed site and on dry season rice crops at an irrigated one. In contrast, at rainfed sites in the moist savannah zone the pest survived the longer dry season on the perennial wild rice O. longistaminata, while ratoons and volunteers of O. sativa provided 'bridges' between the wild host and wet season rice crops. Early in the wet season at rainfed sites, galls of Orseolia oryzivora were not found at high density on wild rice, ratoons or volunteers. The heavy infestations which developed by October resulted primarily from rapid multiplication on rice crops themselves during the wet season. At all 13 sites sampled, the large majority of galls were found on fallow or cropped rice fields, rather than in ditches, bunds or uncultivated wetland, irrespective of the time of year or the hosts involved. From gall dissections, the parasitoids Aprostocetus procerae (Risbec) and Platygaster diplosisae Risbec caused over 30% mortality at some sites by October but generally increased too late to prevent crop damage. Implications of the results for the management of Orseolia oryzivora are discussed.

Population dynamics of the African rice gall midge Orseolia oryzivora (Diptera: Cecidomyiidae) and its parasitoids in the forest and southern Guinea savanna zones of Nigeria

“…During these months, the mean relative humidity and temperature averaged 75% and 25 8C, respectively, and this has been reported as favourable for AfRGM development and reproduction (Umeh and Joshi, 1993). Previous studies have established a link between the weather, especially rainfall during the wet season, and AfRGM rate of infestation and development (Umeh and Joshi, 1993;Williams et al, 1999). Umeh and Joshi (1993) observed that the peaks in AfRGM populations were positively correlated with increase in relative humidity and regular rainfall.…”

“…The African rice gall midge (AfRGM) Orseolia oryzivora Harris and Gagné (Diptera: Cecidomyiidae) is an important insect pest of rainfed and irrigated lowland rice in Africa (Williams et al, 1999;Nwilene et al, 2006). It has also been reported in the rainfed upland ecology in Burkina Faso (Dakouo et al, 1988).…”

“…Chemical control has several drawbacks such as the financial costs, risks to human health and the possible destruction of natural enemies (Nacro, 1984), which could result in new pest outbreaks. Most of these lines are traditional varieties, which, although potentially useful as sources of resistance in a breeding programme, are unsuitable for direct release to farmers because of their low yield (Williams et al, 1999). However, a number of lines with moderate AfRGM resistance when compared with currently released varieties have been identified (Ukwungwu and Alam, 1991;Ukwungwu and Joshi, 1992b).…”

“…Some egg predators have been reported (Williams et al, 2002), which include tiny predatory mites, Neoseiulus spp. Parasitism caused by these two parasitoids can reach as high as 77% of the immature populations of the pest (Marshall, 1906;Hidaka, 1988;Williams et al, 1999;Ba, 2003). Two common parasitoids of the AfRGM include Platygaster diplosisae Risbec (Hymenoptera: Platygastridae), a gregarious egg/larval endoparasitoid, and Aprostocetus procerae (¼ Tetrastichus pachydiplosisae) Risbec (Hymenoptera: Eulophidae), a solitary pupal ectoparasitoid (Dakouo et al, 1988).…”

Seasonal abundance of lepidopteran stemborers and diopsid flies in irrigated fields of cultivated (Oryza sativa) and wild rice (Oryza longistaminata) in western Burkina Faso

“…Wild rice appears to play an important role in the survival of stemborers and diopsid flies between the rice-cropping seasons. (Williams et al, 1999). However, O. longistaminata is not the only alternate host plant of lepidopteran stemborers and diopsid flies.…”