This bioassay of five vegetable oils: Palm oil, groundnut oil, coconut oil, sheanut oil, and palm kernel oil on sitophilus seamais were collected from pure insect culture maintained in the laboratory and introduced into each of eleven jars containing 40g each of five white varieties, five yellow varieties and one control. Each maize sample was treated separately with each of the vegetable oils at the dosage of 7.0m/kg and 15.0m/kg, while the control jar was not treated. Following the treatment the grain were poured out for sun drying for 5hours before packing them individually into the appropriate jar. The mixing of the grains with the oil was performed manually by continuous shaking rotating for 10minutes, to enhance even distribution of the oils among the Zeamays grains with the oil was performed for 10 minutes, to enhance even distribution of the oils among the Zeamays grains. The mortality of the weevils was studied over a 3-week period and was recorded. All the 5 vegetable oils used showed some killing effect on the weevils. Coconut oil which represents the most effective had a mortality rate of 64 (25%) followed by groundnut 44 (20.8%), palm oil 53 (20.4%), sheanut oil 44 (17.3%) and palm kernel oil 42 (16.5%). It is obvious that coconut oil is the most effective of all the vegetable oils investigated in this work and may indicate its possession of insecticidal properties especially against sitophilus Zeamays.

CHAPTER ONE

INTRODUCTION

Background of the Study

According to (Acknerman and Jannifer, 2002), maize or corn is a large, annual monoecious grass of the small tribe may deals. It is one of the oldest and most widely cultivated world’s cereals, which provides food for man and feed for livestock.

In many part of West Africa, this is a staple food and is sometimes grown on a garden scale where it cannot be grown as a farm crop. It is an important source of carbohydrates and if eaten in the immature state, it provides useful quantities of vitamin C. The yellow grain varieties also contain vitamin A. There are several types of maize grown for various purposes. The varieties are distinguished by the type of endosperm/pericarp, crown appearance and the grain colour. About six varieties of maize are known; these are pop corn, flict maize, dent maize, semi flint, floury (flour) maize and sweet corn.

Popcorn Objective of Study

This variety of maize possesses the characteristics of popping when it is heated. The pericap is very thick with thick and hard starchy endosperm. The crown when matured appears pointed or rounded.

Flint corn:

This maize variety has small hard starchy endosperm but with a very thick corneous starch layer. The pericarp is thick and the maize generally hard this makes it resistant to weevil attack. It is usually rounded.

Semi-Flint:

This is a milder form of the flint maize. Here, the corneous layer less in thickness. It has hard corneous pericarp and a relatively larger amount of starchy endosperm.

Dent Maize

This is characterized by a depression of the top due to the presence of soft starch which is able to dry and shrink around the crown. As such, the crown is usually dented. The corneous layer is to the sides and the starchy layer protrudes to the crown with only a small layer or pericarp.

Floury Maize

This variety is soft due to the presence of starchy endosperm. It has a very thin, stretched pericarp and a large amount of white starchy endosperm, which is usually soft. This type of maize is very susceptible to weevil attach (Kochhar, 2001).

Sweet Corn

Here, the starchy endosperm is sugar because in conjunction with starch granules, there are many sugary granules in the endosperm. However, when immature the grains are transparent and usually wrinkle on drying. The pericarp is mediumly thick and endosperm glassy.

Maize originated from Mexico and it has become a particular important cereal crop.

In North America and Africa, maize was introduced into Africa by the Portuguese between the 16^th and 18^th centuries and is now the continent’s premier cereal crop. Kenya and South Africa grow the most in Africa because of its sensitivity to drought conditions. It cultivation in semi arid zones can cause problems (Purseglove, 2002).

Cultivation of Maize

Maize is grown extensively throughout the world on a wide range of soil types and under a variety of climatic conditions. (Brenneman and Dale 2001), it requires a wide range of well-drained soils. Sandy or gravely soils. It requires a generous supply of moisture during the growing season with high temperature. It requires a minimum temperature of 10⁰C and a maximum of about 40⁰C.

The good performance of maize does not depend much on the amount of rainfall but on the distribution. The annual rainfall should not be below 500mm and it is essential for a moisture supply to be maintained throughout the growing period of four months. Drought leads to very poor yield and the most critical period of maize is between about fifteen days before tasseling and fifteen days after tasseling, maize grows well in soils within the pH range of 5.0 – 7.0

Harvesting of Maize

Maize can be harvested dry or green. Majority of maize in West Africa is harvested for immediate in West Africa is harvested. For immediate consumption. The green maize is harvested when the silks have just brown.

In many parts of the world, maize is harvested green for silage. Dry maize is harvested when the silks are completely dried up and the leaves and husks are also dry which is about thirty days after tasseling. It there is risk of bird attach, itcan be harvested earlics and then sun dried or tied over a fireplace. The maize co is traditionally harvested by hand by simply breaking of the cobs (Onyenuchega, 2000).