T. I. OFUYA and I. E. OKUKU: Insecticidal effect of some plant extracts on the cowpea aphid Aphis cracdvora Koch 127 Anz. Sch/idlingskde., Pflanzenschutz, Umweltschutz 67, 127-129 (1994) 9 1994, Blackwell Wissenschafts-Verlag, Berlin ISSN 0340-7330 The Federal University of Technology, P.M.B., 704, Akure, Nigeria Insecticidal effect of some plant extracts on the cowpea aphid Aphis craccivora Koch (Homoptera: Aphididae) By T. I. OFUYA and I. E. OKUKU With 3 tables Abstract The insecticidal activity of acetone extracts of Cyra- bopogon eitratus (DC) Stapf., Momordiea ebarantia L., Zingiber officinMe (Ros.), Xylopia ae~iopiea (Dunal) A. Rich., Ocimum gmtissimum L. and Afmmomum me- legueta (Ros.) K. Schum against the cowpea aphid, Aphis cmccivom Koch was investigated. Z. officir~le and A. melegueta extracts had the greatest effect in causing mortality ofA. cmccivora and inhibiting its re- production. Extract from M. cbamntia caused high nymphal mortality whilst extract from C. eitmtus also caused significant nymphal mortality, reduction of life span of adult aphids and inhibition of aphid reproduc- tiOno 1 Introduction Chemical controls involving the use of synthetic insec- ticides constitute the major means of insect pests control in crop production world wide. Use of these convention- al insecticides have over the years manifested a number of disadvantages, the most important of which are the risks involved for human heakh and for the environment. Ear- lier botanical insecticides such as pyrethrum and rote- none have proven to be non-persistent in the environ- ment, of low mammalian toxicity, and relatively safe to other non-target organisms. Thus, in recent years there has been renewed efforts internationally, at developing new sources from the vast store of chemical substances in plants, of non-toxic, safe and biodegradable alternatives to contemporary synthetic insecticides (OLAIFA et al., 1987). The insecticidal activities of extracts from many tropical plants such as Dennetria tripetala G. Baker (IWUALA et al. 1981); Lippia adoensis Hoschst, Monodora tenuifolia Benth. and Piper guineense Schum. and Thonn (OL/dFA et al., ibid.), Azadirachta indica (A. Juss) (NICOL and SCHMUTrERER 1991) and some other mem- bers of tropical Meliaceae (AL-SHAROOK et al. 1991) have been reported. The paper also reports on the insecticidal activities of acetone extracts of six indigenous Nigerian plants against the cowpea aphid, Aphis cracdvora Koch, an important pest of food legumes in the tropics and sub- tropics. 2 Materials and methods The source of A. craccivora were colonies derived from field- collected individuals, established and maintained on cowpea seedlings (Ife Brown variety) planted in pasteurized soil in 0.79 litre plastic cups in screened cages (60 x 60 x 90 cm) in an open laboratory. Ire Brown eowpea seedlings were continuously raised in a screenhouse to provide replacements for ageing seed- lings in the laboratory aphid cultures. The source of the plant extracts are given in table 1. The plant materials were collected from various locations in southern Ni- geria. They were dried and milled into powder. The powders were then separately extracted using acetone in a soxhlet appa- ratus. The extracts were concentrated by exposure to the open air in Petri plates, after which they were stored in a refrigerator at about 80 C until used. The same concentration was used for all the extracts: 0.2 g of each was dissolved in 10 ml of acetone and used to treat cowpea seedlings. The Ire Brown cowpea seed- lings were used when they were 14 days old. The entire exposed surface of each seedling was treated with each extract soaked in cotton wool. The control in this experiment were seedlings treat- ed with only acetone. The effect of the treatments on aphid mortality was deter- mined. Fifty first-instar nymphs of A. cracdvora were placed on a cowpea seedling freshly treated with extract or acetone alone (control). Mortality was taken daily for six days (when the insect would normally have metamorphosed into adult). This proce- dure was replicated 10 times for each extract and the control. The effects of the treatments on aphid reproduction was also determined. For each treatment, including the control, 20 seed- lings were inoculated with one pre-reproductive apterae of A. craccivora using a damp camel brush. The number of nymphs produced on each seedlings daily for seven consecutive days was recorded. The longevity of the reproducing aphid was also not- ed. Data on mortality, fecundity and longevity of the aphid under the various treatments were subjected to analysis of variance. Duncan's multiple range tests were used to separate means. 3 Results Percentage mortality in nymphs of A. cracdvora feed- ing on the plants treated with the various extracts differed significantly (P < 0.05). After 1 day of inoculation, nymphal mortality was recorded only on plants treated with X. aetbiopica extract. Aphids in this treatment suf- fered no further mortality (tab. 2). After 2 days, no nymphal mortalities were still recorded in treatments in- volving use of C. citratus, M. charantia and O. gratissi- mum extracts, and the control, while slight mortality was recorded with A. melegueta extract. However, all nymphs were killed in the treatment with Z. officinale ex- tract. After 3 and 4 days, 100% nymphal mortality was also recorded in treatments with M. eharanda and A. me- legueta extracts respectively. The C. citratus extract t I.S. C .... ieht Clearance Center Code Statement: 0340--7330/94/6706--0127510.50/0