1.1 Background of the Study
Rice (Oryzae sativa L.) is one of the world's most important crops providing a staple food for nearly half of the Global population (FAO, 2004), and for 2.7 billion people in developing countries (FAO, 1995). Nigeria is the largest producer of rice in West Africa with average of 3.2 million tons of paddy rice (USDA, 2002, Nwilene et al., 2008). Although rice is grown virtually in all agro ecological zones of Nigeria, rice production is still far below the potentials and domestic needs. One of the major reasons for the low yield of rice in Nigeria is depredation by insect pests (Imolehin and Ukwungwu, 1992). Rice plant is an ideal host for a large number of insect pests in West Africa (Heinrichs and Barrion, 2004). Of all the insect pests of rice, stem borers are the most important insect pests of rice especially to small-scale farmers.
They are about 20 species of stem borers identified damaging rice plant worldwide. However, only four species are of economic importance in Nigeria. These include Chilo zacconius Bles, Diopsis macropathalman Daman, Maliarpha separatalla Rog, and Sesamia calamistis (Heinrichs ang Barrion, 2004). The distribution and abundance of these species vary among rice ecosystem within a given location. For example, Maliarpha separatella and Chilo spp occurs in all climatic zones in West Africa but they are more abundant in the rain fed lowland and irrigated ecosystems than in the uplands and is the most abundant stem borer species in the mangrove swamps while Sesamia spp predominated the uplands (Heinrichs and Barrion 2004). These borers attack rice plant at different growth stages from vegetables stages to grain development. Feeding during the vegetable growth stage causes death of the central shoot ‘dead heart' (DH). Damaged shoot do not produce a panicle and thus produce no grain. Feeding of stem borers during the reproductive stage
(panicle initiation to milk grain) causes a severing of the developing panicle at its base. As a result, the panicle is unfilled and whitish in colour; rather than filled with grain and brownish colour ‘whitehead' (WH), (Mahmood-ur-Rehman, et al., 2007). Rice stem borers have been reported to cause yield losses ranging from 30 to 80 % and 100 % loss has been recorded in worst affected fields in Nigeria (Imolehin and Ukwungwu 1992). In many parts of Africa the borers destroy to 30% -50% of plant tillers during the wet cropping season thereby compromising the whole harvest (Daouo et al., 1991).
Biopesticides are a good alternative to the synthetic pesticide. Neem is one of the most reliable botanical sources of biopesticides. Neem plant has been known for three decades for its potential against insect pests. Leaves and seed extract of Neem plant have been observed for their deleterious effects on insects. The principle component that has insecticidal activity in Neem extracts is a limonoid, azadirachtin.Azadirachtin is non-toxic to mammals, rat, oral acute LD50 is more than 5000 mg/kg. A 90 day oral feeding of rats with 10,000ppm of azadirachtin did not show chronic toxicity (Mehlhorn et al., 2011). Neem products were neither mutagenic nor carcinogenic and they did not produce any skin irritation or organic alteration in mice and rats even in high concentration. From ecological and environmental stand points, azadirachtin is non-toxic to fish. Azadirachtin induce no accumulation in plants and no adverse effect in water and ground water. (Mehlhorn et al., 2011).
Synthetic pesticides are of increasing concern as they accumulate in the environment so much of attention has been divided towards the natural compound that could replace the synthetic ones. Addressing this problem call for a wide range of intervention that include the use of Neem seed kernel extract as the most reliable botanical sources of biopesticide, the plant can alleviate land degradation, reduce environmental pollution and increase farm land fertility among others.
1.4 Aim and Objectives
The overall aim of this study is to assess the use of Neem as biopesticide in management of stem borers of rice.
To evaluate the used Neem seed Kernel extracts as biopesticide in the management of stem borer of rice
1.3 Justification of the Study
Consequence upon the geometrically rising world population and the increasing pressure on food items, it has become increasingly necessary to increase food production from the present level. The possibility of achieving this is not only to increase production but also to protect the crop cultivated. Crop production can be achieved through several means one of such is the use of pesticide. It is therefore important that we encourage the use of biological pesticide which are safe to human and non-target organism. As they are easily biodegradable and environmentally friendly. It should be encouraged as an option in African countries especially Nigeria in agricultural practice.
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