Brazilian Journal of Biological Sciences, 2018, v. 5, No. 11, p. 673-681. ISSN 2358-2731 https://doi.org/10.21472/bjbs.051106 Bioefficacy of Alstonia boonei leaf extract against cowpea beetle Callosobrochus maculatus infesting stored cowpea seeds in storage Kayode David Ileke¹ and Arotolu Temitope Emmanuel¹,² ¹Department of Biology. Federal University of Technology Akure. Nigeria. Email: [email protected]. ²Centre of Conservation Medicine and Ecological safety, Northeast Forestry University, Harbin P.R. China. Email: [email protected]. Abstract. This study was conducted to investigate the efficacy of the oils of Alstonia boonei leaf extracted with n-hexane, Received petroleum ether, methane and acetone as contact insecticides October 5, 2018 against the activities of Callosobrochus maculatus in stored cowpea seed. The oils were incorporated at rates 2.0 mL per Accepted December 23, 2018 20 g of cowpea seeds. The parameters assessed include, mortality of adult insects, oviposition and adult emergence to Released ascertain the control of the beetle. All concentration of the December 31, 2018 extracts used evoked 100% mortality of C. maculatus after 72 h of post treatment. The development of Callosobrochus maculatus Full Text Article was inversely proportional to the concentration of the oil. As the ratio of Alstonia boonei leaf oil extract increased, the mortality of the beetle increased. Therefore, complete protection of seeds and complete inhibition of adult emergence in the oils extracts of Alstonia boonei leaf were effective in controlling cowpea bruchid in stored cowpea seed. Keywords: Alstonia boonei; Leaf oil extracts; Cowpea seed; Callosobrochus maculates; Seed protection. 0000-0002-3106-4328 Kayode David Ileke 0000-0003-1330-0160 Arotolu Temitope Emmanuel Introduction most important producing areas in Nigeria are located in the savanna Cowpea Vigna unguiculata L. (Agboola, 1979). According to Blade et al. (Walp), is an important crop in the (1997), Nigeria accounts for 70% of the tropics especially in West Africa where it world’s production. Cowpea is an is a cheap source of dietary protein extremely valuable crop both as a source (Boeke et al., 2004). Cowpea is widely of revenue and an important source of cultivated and consumed in Nigeria; the cheap dietary protein for the third world ISSN 2358-2731/BJBS-2018-0073/5/11/6/673 Braz. J. Biol. Sci. http://revista.rebibio.net 674 Ileke and Emmanuel where meat is expensive (Ileke and on the use of alternative eco-friendly Olotuah, 2012). High protein and lysine insect pest control methods among contents of cowpea make it a natural which are the use of plant products supplement to staple diets of cereals, (Ileke and Oni, 2011). Lale (1995) roots, tuber and fruits (Bressani, 1985). reported that plants materials and local In Nigeria, the production of cowpea is traditional methods are safer than carried out largely by peasant farmers synthetic insecticides and suggested that and cowpea production is limited by their use needed exploitation. Small scale insect pests which cause serious post- farmers in the tropics have reported the harvest losses to the cowpea grain. The need to protect cowpea against pest value of cowpea lies in its high protein damage during storage (Lale, 1995; content and ability to tolerate drought Golob et al., 1999). The potential of using and also its compatibility as an intercrop plant products such as leaf, bark, root with maize, millet, sorghum, sugarcane powder from certain plants such as and cotton (Caswell, 1984). This makes Capsicum spp, Piper spp, and citrus peels the grain legumes an important have been investigated by Rajapakse and component of traditional intercropping Van Emden (1997) and Ileke and Bolus systems especially in the complex and (2012). elegant subsistence farming systems of Alstonia boonei De wild is a the dry savanna in sub-Saharan Africa. medicinal plant of West and Central Cowpea bruchid, Callosobruchus African origin which is extensively used maculatus depreciates stored cowpea for the treatment of malaria fever, (Jackai and Adalla 1997). The huge post- intestinal helminthes, snake bite, arrow, harvest losses and quality deterioration impotence, toothache and oedema caused by this insect pest are threat to (Terashima, 2003; Akinmoladun et al., food security in a developing nation like 2007). The various ethnomedical, Nigeria (Boeke et al., 2004). chemical, pharmacological and The infestation of cowpea seeds toxicological properties of Alstonia by Callosobrochus maculates (F.) boonei were recently reviewed and the accounted for the major loss of cowpea profile further revealed that it is useful in both in store and at fields (Adedire, the treatment and management of 2001; Udo, 2005). The females of the several illnesses (Adotey et al., 2012). In bruchid lay their eggs on the seed surface spite of its vast acceptability as a which hatch into larvae within 5 days. medicinal plant, the insecticidal potential The larvae bore through the seed coat of A. boonei has not been fully explored into the underlying cotyledons where compared to other botanicals used in development continues until adult storage. The objectives of this study is to emergence; the adults are already investigate the efficacy of A. boonei leaf sexually mature on emergence (Credland extract against the biological activities of and Wright, 1989; Ofuya and Credland, Callosobruchus maculatus in storage. 1995). Effective and efficient controls of Materials and method storage insect pests are centered mainly on synthetic insecticides. The use of Insect cultures these synthetic chemicals is hampered by The starter culture of many attendant problems like Callosobruchus maculatus was obtained development of resistance insect strain, from an infested cowpea seeds at toxic residues in foods and humans; Environmental Biology and Fisheries workers safety and high cost of laboratory, Adekunle Ajasin University, procurements (Adedire and Lajide 2001, Akungba Akoko, Nigeria. The cowpea Ileke and Oni, 2011, Ileke and Olotuah, were first sorted to eliminate stones, 2012). These have necessitated research chaff and other unwanted material, and Braz. J. Biol. Sci., 2018, v. 5, No. 11, p. 673-681. Bioefficacy of Alstonia boonei leaf extract against cowpea beetle 675 were later disinfected by keeping them in Toxicity of A. boonei leaf oil extract on a freezer at -5 °C for 7 days. The mortality, oviposition, adult disinfected seeds were then air dried in emergence of Callosobruchus the laboratory to prevent mouldiness maculatus, weight loss, damage and before the introduction of insects from weevil perforation index of cowpea infected ones (Adedire et al., 2011). They seed were placed in kilner jars and covered The toxic effect of plants oil on with muslin cloth. The jars were placed adult C. maculatus was accomplished in insect rearing cages at ambient using 250 mL plastic containers temperature of 30±3 °C and 70%±5% containing 20 g of cowpea seeds with relative humidity. concentration of 2 mL of solvent extract of Alstonia boonei leaf. The oil and seeds Plant collection were thoroughly mixed with the aid of a Fresh leaves of Alstonia boonei glass rod and agitated for 5-10 min to were collected once from Ijiro, Ilasa Ekiti, ensure uniform coating. The containers Ekiti State. The plant leaves were air were left open for 30 min so as to allow dried in an open laboratory and ground trace of solvent to evaporate off. Ten into very fine powder using an electric copulating pairs of C. maculatus were blender (Supermaster, Model SMB 2977, introduced into the container and Japan). The powders were further sieved mortality was observed daily for 4 days. to pass through 1 mm² perforations prior Cowpea seeds that were solvent treated to storage in a plastic with tight lids in a served as the control experiment refrigerator at 4 °C before use (Ileke and (Arannilewa et al., 2006). Similar Oni, 2011). preparation was set up for Alstonia boonei leaf extracted with N-hexane, Oil extract petroleum ether and methanol. Three Extracts of Alstonia boonei was replicates per treatment were prepared. carried out using cold extraction method. The adult mortality was assessed every About 250 g of A. boonei powders were 24 h for 96 h. Adult insects were soaked separately in an extraction bottle considered dead where no response was containing absolute acetone, petroleum observed after probing them with ether, methanol and N-hexane. The forcepts. After 96 h, all insects both dead mixture was stirred occasionally with a and alive were then removed. Number of glass rod and extraction was terminated eggs laid in each container was counted after 72 h. Filteration was carried out and recorded. using a double layer of Whatman No. 1 Progeny emergence (F1) was filter paper and solvent evaporated using then recorded at 6 weeks. The containers a rotary evaporator at 30 °C to 40 °C with were sieved out and newly emerged rotary speed of 3 to 6 rpm for 8 h (Ileke adult bruchid were counted with an and Olotuah, 2012). The resulting extract aspirator. The percentage adult was air dried in order to remove traces emergence was calculated according to of solvents. the method described by Odeyemi and Daramola (2000): % Adult emergence = No of adults emerged x 100 No of eggs laid Braz. J. Biol. Sci., 2018, v. 5, No. 11, p. 673-681. 676 Ileke and Emmanuel The cowpea were re-weighed by determined as described by Odeyemi and using Metler weighing balance and Daramola (2000): percentege loss in weight was % Weight