Laboratory Evaluation of Ethanolic Extracts of Garlic (Allium Sativum) Cloves and Aloe Vera Leaves as Protectants Against the Maize Weevil, Sitophilus Zeamais.
ABSTRACT
This study evaluated the efficacy of ethanolic extracts of Allium sativum (Woodwill) cloves, Aloe vera (Miller) leaves and their mixture against Sitophilus zeamais (Motschulsky) under laboratory conditions. Experiments were carried out to check the toxicity, adult mortality, oviposition inhibition, repellent and anti-feedant effects of these plant extracts against S. zeamais. The experiments were laid out in a completely randomized design of ten treatments replicated three times.
The adult weevils were exposed to maize grains treated with three concentrations (200, 250 and 300mg/ml) of A. sativum and A. vera and equal proportion (50:50) of their mixture while the control was treated with only the solvent. Probit analysis revealed A. sativum had lower LC50 than A. vera and therefore was more toxic than it. All treatments recorded higher significant (p<0.05) mortality than the experimental control.
Most mortality occurred within 24hr of treatments showing that the extracts had no residual toxicity. Among the extracts used, the mixture recorded highest adult mortality (43.3%) followed by A. sativum (35%) and A. vera (30%). The plant extracts showed varying levels of repellency to the weevils with the highest repellency (66.7%) recorded by the mixture followed by A. sativum (44.4%) and A. vera (26.7%).
The extracts were able to lower progeny production with the mixture having the highest percentage inhibition rate (61.5%) while the control recorded the lowest (19.1%). Percentage grains weight losses was significantly higher in the untreated check than in the treated grains and are recorded as follows: mixture (3.5 %), A. sativum (6.1%), A. vera (14.1%) and control (29.3%). The overall results show that the mixture of the two plant extracts performed better in all bioassays than individual plant extracts.
TABLE OF CONTENTS
Title Page – – – – – – – – – – – i
Certification – – – – – – – – – – – ii
Dedication – – – – – – – – – – – iii
Acknowledgements – – – – – – – – – – iv
Table of Contents – – – – – – – – – – v
List of Tables – – – – – – – – – – – vi
List of Figures- – – – – – – – – – – vii
List of Plates – – – – – – – – – – – viii
Abstract – – – – – – – – – – – ix
CHAPTER ONE: INTRODUCTION AND LITERATURE REVIEW
1.1 Introduction – – – – – – – – – – 1
1.1.1 Justification of the study – – – – – – – – 3
1.1.2 Objectives of the study – – – – – – – – 4
1.2 Literature Review – – – – – – – – – 5
1.2.1 Origin of maize production – – – – – – – – 5
1.2.2 Varieties of maize – – – – – – – – – 6
1.2.3 Economic importance of maize – – – – – – – 6
1.2.4 Insect pest problems in maize storage – – – – – – 8
1.2.5 Life history of maize weevil – – – – – – – – 9
1.2.6 Conditions favouring insect pest attack – – – – – – 13
1.2.7 Damage caused by stored maize pests – – – – – – 13
1.2.8 Pesticides application and their side effects – – – – – – 14
1.2.9 Botanicals as alternatives to synthetic pesticides in stored grain protection – – 15
1.2.10 Classification and mode of action of pesticidal plants – – – – 17
1.2.11 Importance of pesticidal plants in IPM – – – – – – 20
1.2.12 Description of research plants – – – – – – – – 20
CHAPTER TWO: MATERIALS AND METHODS
2.1 Collection and Preparation of Plant Materials – – – – – – 25
2.2 Preparation of Plant Extracts – – – – – – – – 25
2.3 Collection and Preparation of Maize Grains – – – – – – 28
2.4 Culturing of Sitophilus zeamais- – – – – – – – 28
2.5 Experimental Design – – – – – – – – – 28
2.5.1 Acute toxicity test – – – – – – – – – 28
2.5.2 Adult mortality test – – – – – – – – – 29
2.5.3 Repellency test – – – – – – – – – – 30
2.5.4 Oviposition inhibition test – – – – – – – – 30
2.5.5 Damage assessment test- – – – – – – – – 31
2.6 Statistical Analysis – – – – – – – – – 32
CHAPTER THREE: RESULTS
3.1 Acute Toxicity Test of Ethanolic Extracts of Allium sativum and Aloe vera – – 35
3.2 Adult Mortality Effects of Ethanolic Extracts of Allium sativum, Aloe vera and
their Mixture – – – – – – – – – – 37
3.3 Repellency Effects of Ethanolic Extracts of Allium sativum, Aloe vera and their Mixture – 39
3.4 Oviposition Inhibition Effects of Ethanolic Extracts of Allium sativum, Aloe vera and
their Mixture – – – – – – – – – – 43
3.5 Damage Assessment Test Results- – – – – – – – 45
CHAPTER FOUR: DISCUSSION
4.1 Conclusion – – – – – – – – – – 51
4.2 Recommendations- – – – – – – – – – 51
References
INTRODUCTION
Insects are a problem in stored grain throughout the world because they reduce the quantity and quality of grain. Grains constitute the most important staple foodstuff for the ever-growing population in the tropics. Grains are small, hard, dry seeds (with or without hull or fruit layers attached) harvested for human food or animal feed (Babcock, 1976). Agronomists also call the plants producing such seeds ‘grains’ or ‘grain crops’.
Grains include cereals such as maize, rice, wheat, oats, barley, sorghum, millet etc; legumes or pulses such as soybean, cowpea, pigeon pea, peanut etc and oilseeds such as mustard seeds, canola, sunflower seeds etc. Cereal grains are all members of the grass family and they contain much starch, a carbohydrate that provides dietary energy. Legumes have higher protein than most other plant foods.
They also contain starch or oil (Vaughan et al., 1997). Harvested, dry grain has advantages over other staple foods such as the starchy fruits (e.g., plantain, breadfruit) and roots/tubers (e.g., sweet potato, cassava, yam) in being easy to store, handle and transport. In particular, these qualities have allowed mechanical harvesting, transporting by rail or ship, long-term storage in grain silos, large-scale milling or pressing and industrial agriculture in general.
Thus, major commodity exchanges deal with soybean, rice, wheat, maize and other grains but not in vegetables, tubers, or many other crops. Grain storage has often resulted in quantitative and qualitative losses due to physical, chemical, and most importantly biological factors such as pests which may be birds, rodents, fungi, or insects (Oke and Muniru, 2001).
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