Evaluation Of Jatropha Curcas L. (EUPHORBIACEAE) As A Biopesticide in The Control Of Insect Pests Complex Of Auberine (Solatium melongena L.)

Abstract

The potentials of aqueous seed extract and seed oil of the coral plant, Jatropha curcas L. (Euphorbiaceae) were evaluated as a biopesticide compared with aqueous seed extract of neem (Azadirachta. indica A. Juss) and cymethoate, (a commercially used synthetic insecticide) in the control of insect pests complex of aubergine (black beauty), Solanum melongena L. (Solanaceae) both in the laboratoiy and in the field. Three major insect pests of aubergine namely, Urentius hystericellus Richter (Homoptera: Tingidae) Aphis gossypii Glover (Homoptera, Aphididae) and Selepa docilis Butler (Lepidoptera; Noctuidae) collected from an aubergine field at the University of Ghana Farm, Legon that had not received chemical treatment for eight months were used to determine the levels of jatropha seed oil and aqueous seed extract that could induce 50 % mortality. Choice assays as well as the ovicidal effects of neem and jatropha products on S. docilis were investigated In the laboratory fifty percent mortality was induced in S. docilis, A. gossypii and U. hystericellus when they were exposed to aubergine leaves dipped for 3 sec in 1.5, 2.2 and 3.6 ml/1 seed oil of jatropha, respectively. Also 28.4 and 22.3 g/1 aqueous seed extract of jatropha induced 50 % mortality in A. gossypii and S. docilis, respectively. Higher concentrations of the extract (40-100 g/1) and oil (2-8 ml/1) on treated leaves inhibited feeding by the larvae of S. docilis, which died within 48 hrs. Ninety percent of U. hystericellus and 60 % of the larvae of S. docilis avoided leaf discs or filter paper treated with the seed oil or the aqueous seed extract of jatropha. Jatropha seed oil reduced hatchability by 21 % while aqueous seed extracts of neem and jatropha had no ovicidal effect on S. docilis. In the field, aqueous extract of jatropha (40 g/1), jatropha seed oil (4 ml/1), neem (75 g/1) cymethoate (2 m/1) were sprayed on weekly basis four weeks after transplanting. Results obtained showed that control (non-treated) differed significantly (P < 0.05) from other treatments in number of holes in fruits, marketable fiuit weight, number of fruits and number of thrips per plant. In addition, percentage fruits bored, marketable fruit weight per plant, percent leaf area defoliated by leaf feeders and yield in tonnes/ha differedsignificantly (P< 0.01) from the control. Plant height at flowering and number of flower buds bored showed no significant differences (P = 0.05). Jatropha seed oil treatment gave slightly higher yield indices even though not significantly different (P= 0.05) from the other plant products and cymethoate. A significant (P < 0.01) positive correlation was observed between number of marketable fruits and fruit yield expressed in tonnes/h. Based on this findings jatropha seed extracts are good candidate biopesticide in controlling insect pests of aubergine and should be integrated into an overall management of agricultural pests.