The insecticidal potential of Jatropha curcas seed oil against Callosobruchus maculatus on stored cowpea was evaluated under laboratory condition. The seed oil was applied at concentrations of 0.2, 0.3, 0.5, and 1.0ml/50g of cowpea seeds. An untreated control and solvent (petroleum spirit)-containing treatment were also included. Jatropha seed oil was highly toxic to cowpea bruchids at all selected dosages compared to the untreated control and solvent treatment. Results showed that adult mortality of bruchids at the highest concentration of 1.0ml/50g seeds gave 100%while the lowest concentration gave 93% mortality. The oil was also significantly (p<0.05) repellent to C. maculatus but its persistency to cause mortality to C. maculatus generally declined in storage from 15 to 30 days. Jatropha curcas seed oil offers an opportunity to develop them as alternatives to pesticides which have been recognised to be detrimental socially, economically, and ecologically.
TABLE OF CONTENTS
Title page i
Table of Content v
List of Tables viii
1.0 Introduction 1
1.1 Objectives of the study 2
2.0 Literature review 3
2.1 Cowpea beetle 3
2.2 Methods of controlling insect pests in storage 4
2.2.1 Biological control method 5
2.2.2 Cultural control method 5
2.2.3 Chemical control method 6
2.2.4 Integrated pest management 6
2.3 The need for alternative insect pest control 7
2.4 Jatropha curcas plant 8
2.4.1 Description of plant 8
2.4.2 Uses of Jatropha plant 9
2.4.3 Physicochemical properties of Jatropha plant seed oil 9
2.4.4 Toxic components of Jatropha 10
2.4.5 Insecticidal properties of Jatropha seed oil 11
3.0 Materials and methods 12
3.1 Insect culture 12
3.2 Preparation of cowpea seeds 12
3.3 Extraction of Jatropha seed oil 13
3.4 Experimental procedure 13
3.5 Repellency bioassay of C. maculatus 14
3.6 Persistence of the Jatropha curcas seed oil extracts 15
3.7 Statistical analysis 16
4.0 Results and discussion 17
4.1 Effect of Jatropha curcas seed oil on adult mortality of Callosobruchus maculatus in stored cowpea
4.2 Persistence of Jatropha curcas seed oil extract and its effect against Callosobruchus maculatus
4.3 Repellent effect of Jatropha curcas seed oil on Callosobruchus maculatus in stored cowpea
5.0 Conclusion and recommendation 28
LIST OF TABLES
TABLE 1: Cumulative effect of Jatropha curcas seed oil on adult mortality of Callosobruchus maculatus in stored cowpea. 18
TABLE 2: Mean mortality percentage of Callosobruchus maculatus after exposure to Jatropha seed oil.
TABLE 3: Persistence of Jatropha curcas seed oil extract for 15 days and its effect against Callosobruchus maculatus.
TABLE 4: Mean mortality percentage of Callosobruchus maculatus after exposure to Jatropha seed oil.
TABLE 5: Persistence of Jatropha curcas seed oil extract for 30 days and its effect against Callosobruchus maculatus.
TABLE 6: Mean mortality percentage of Callosobruchus maculatus after exposure to Jatropha seed oil.
TABLE 7: Repellent effect of Jatropha curcas seed oil on Callosobruchus maculatus in stored cowpea.
The cowpea plant, Vigna unguiculata Linnaeus (Walp) is an important legume in the diet of the people of tropical and subtropical countries (Musa, 2007). Apart from the dry seeds which are made into various food products, the young leaves, pods and mature seeds are eaten and the husks fed to livestock in Africa and India. The production of cowpea is restricted by a number of biotic and abiotic factors both in the field and in storage. Among the constraining biotic factors are insect pests (Swella and Mushobozy, 2007).
The cowpea beetle, Callosobruchus maculatus (Fabricius) belongs to the Order Coleoptera and family Bruchidea which is why it is also known as cowpea bruchid. It is a field-to-store pest as infestation often begins in the field as the mature pods dry (Boateng and Kusi, 2008). Their activities cause loss of weight, nutritional value, and viability of stored grains. Larvae developing within the grain do the largest damage. According to IITA, Callosobruchus maculatus consumes 50-90% of cowpea in storage annually throughout tropical Africa.
Several methods have been used over the years to protect cowpea grains in storage, but the use of synthetic products such as organophosphate and carbamates, has been very dominant, effective and commendable. However, these are usually imported chemicals and are not generally available and accessible to the small-scale, subsistence farmers. Also, the attendant exorbitant cost is not justified by small-scale farmer’s income.