**1.2 Insect pests of rice in West Africa**

312 Pesticides in the Modern World - Risks and Benefits

Rice remains one major crop in which West Africa can easily become self-sufficient given the potentials that abound in the region. The potential land area for rice production in West Africa is between 4.6 million and 4.9 million ha. Out of this, only about 3.7 million ha—or 75 percent of the available land area—is presently cropped for rice. Cultivable land to rice is spread over five ecologies, namely: rainfed upland, rainfed lowland or shallow swamp, irrigated rice, deepwater or floating rice and tidal mangrove swamp. The commonly used

Area Production Current Potential

ecosystems and share of rice area for the rice ecosystems are presented in Table 1.

**Ecology Share (%) Yield (t/ha)** 

**Upland:** area expansion and yield increase may be fulfilled

Table 1. Rice production ecology in West Africa

**1.1 Hypothetical shift in production system** 

**Irrigated lowland:** dam construction is too expensive at current rice price

**Rainfed lowland:** most promising

Source: Sakurai, 2006

Upland 40 37 1.0 1.5-4.5 Rainfed lowland 48 49 1.4 2.5-5.0 Irrigated lowland 6 14 2.8 5.0-7.0

Amongst these, lowland rice has the highest priority, being the ecology that represents the largest share of rice area and rice production. Smallholder farmers with farm holdings of less than 1 ha cultivate most of the rice produced in West Africa. However, rice productivity and production at the farm level are constrained by several factors. These constraints include insufficient appropriate technologies, poor supply of inputs, ineffective farmer organizations and groups, poor quality of rice, poor marketing arrangements, inconsistent agricultural input and rice trade policies, and environmental constraints. These environmental constraints include poor drainage and iron toxicity in undeveloped lowland swamps, poor maintenance of developed lowland swamps, drought, deficiencies of N and P, poor soil management practices, seasonal over-flooding of rice fields, pests and diseases.

With the increasing awareness of the limited potential for intensification of rice production in the uplands, farmers are gradually moving into the lowlands, which are less fragile (permits residual moisture use), more fertile and ecologically robust. The lowland areas are underutilized in West Africa. The lowland areas are expected to meet the growing demand for rice in West Africa because they provide potential for expansion, diversification and intensification of rice production in the region. This change in farming practice has been accompanied by an increase in the use of agrochemicals (pesticides and fertilisers), highyielding varieties and monoculture/continuous cropping, which further disrupt traditional farming and natural ecosystem functioning. Most West African countries are currently undergoing intensification in rice production to cope with the high population pressure. However, these may have adverse consequences on pest outbreaks, if it lacked the vision on the conservation of renewable inputs (biodiversity), and the whole issue of sustainability. This prediction is based on the hypothesis that with the improvement in the irrigation system, farmers will be able to grow high-yielding, photo-insensitive rice crops, and more crops per year on the same field. In such systems, the pest and beneficial cycles will be uninterrupted.

The major insect pests of lowland rice in West Africa include: the African rice gall midge (AfRGM), *Orseolia oryzivora* Harris and Gagné (Diptera: Cecidomyiidae); the rice stem borer complex: the stalk-eyed flies – *Diopsis* spp. (Diptera: Diopsidae); the African white borer – *Maliarpha separatella* Ragonot (Lepidoptera: Pyralidae); the yellow stem borers – *Scirpophaga* spp. (Lepidoptera: Pyralidae). Other important pests of rice include: vectors of rice yellow mottle virus (*Trichispa sericea* Guérin, *Chaetocnema pulla* Chapius, *Chnootriba similis* Thunberg and *Oxya hyla* Serville, etc.). All these pests are indigenous to West Africa except *Maliarpha separatella* that can also be found in Asia.
