Evaluation of the potential of some local spices as stored grain protectants against the maize weevil Sitophilus zeamais Mots (Coleoptera: Curculionidae) UDO,

Five local spices (Piper guineense, Allium sativum, Afromomum melequata, Xylopia aethiopica and Tetrapleura tetraptera) were evaluated in the laboratory for their ability to protect stored maize against infestation by S. zeamais. Ground products of the spices were applied as direct admixtures at two concentration levels of 1% and 5% to assess for mortality, progeny emergence, damage and repellency. At 1% and 5% concentration, P. guineense caused significant (P<0.05) mortality of weevils. A. melequata and P. guineense were strongly repellent to the weevils while the other three spices showed moderate repellent activity. There was a significant (P<0.05) reduction in damage caused by the weevils with less damage recorded on grains treated with P. guineense, A. sativum and T. tetrptera. Progeny production was also significantly (P<0.05) influenced by P. guineense than the other four spices and the control. The possible protectant potentials of the five spices are discussed. @JASEM In developing countries, food grain production and consumption often fall below demand as a result of post harvest loses caused by pests and other spoilage agents. Insect pest damage to stored grains results in major economic losses and in Africa where subsistence grain production supports the livelihood of majority of the population, grain loss caused by storage pests such as the maize weevil, Sitphilus zeamais (Mots.) threatens food security. Reduction of insect damage in stored grains is a serious problem in developing countries in the tropics due to favourable climatic conditions and poor storage structures (Bekele et al., 1997). Insect pest control in stored food products relies heavily on the use of gaseous fumigants and residual contact insecticides. The implications of these are serious problems of toxic residues, health and environmental hazards, development of insect strains resistant to insecticides, increasing cost of application and erratic supply in developing countries due to foreign exchange constraints (Obeng-ofori et al., 1997). The need to find materials that effectively protect stored produce, that are readily available, affordable, relatively less poisonous and less detrimental to the environment had stimulated interest in the development of alternative control strategies and the re-evaluation of traditional botanical pest control agents (Niber, 1994; Talukder and Howse, 1995). Resource poor farmers in developing countries use different plant materials to protect stored grains against pest infestation by mixing grains with protectants made up of plant products. This study describes laboratory bioassays to evaluate the efficacies of five local spices; Piper guineense Schum and Thonn, Allium sativum (L.), Afromomum melequata K. Schum., Xylopia aethiopica (Dunal) A. Rich. and Tetrapleura tetraptera (L.) as possible stored grain protectants against the maize weevil, Sitophilus zeamais (Mots.) (Coleoptera: Curculionidae) in the tropics. MATERIALS AND METHOD Culturing of insects: S. zeamais were obtained from infested stock of maize at Uyo main market, Nigeria. The insects were reared on whole maize in 500 l glass jars after being treated for mites (Udo, 2000). The glass jars and grains were sterilized at an oven temperature of 40C for 4 hours (Santhoy and Rejesus, 1975). After three weeks of oviposition, the parent insects were removed and discarded by freezing while the emerging generation of same age insects were re-cultured at 28 C, 70% relative humidity (r.h.) and used for the different bioassays. Collection and preparation of spices: The five spices were purchased from Uyo main market, Nigeria and washed in distilled water and air dried at 25 – 30 C and 65 – 70 % r.h. in the laboratory for 3 days. Prior to application, the spices were ground using a laboratory mill in order to avoid having to store the ground material, thus guarding against possible volatilization of active ingredients. The ground materials were added as direct admixtures to the grains at concentrations of 1% and 5% (Niber, 1994). Mortality, progeny and damage assessment assays: The spices were added separately to 100 g of maize in 2 l glass jars at 1% and 5% concentrations, while JASEM ISSN 1119-8362 All rights reserved J. Appl. Sci. Environ. Mgt. 2005 Vol. 9 (1) 165 168 Full-text Available Online at www.bioline.org.br/ja Evaluation of the potential... Udo, I. O 166 the control treatment had no spices added. Twenty adult S. zeamais of 3 – 5 days old of mixed sexes were introduced into the jars containing the various treatments. The jars were covered with white muslin cloth held with rubber bands. Dead insects in each treatment were counted after 24 hours and up to 96 hours. Insects were considered dead on failure to respond to three probings with a blunt probe. Data were corrected for mortalities in the control by using Abbott’s formula (1925) {[(Sc – St) / Sc] where Sc = % survival in control while St = % survival in treated} and transformed before ANOVA. In another experiment, 20 adult S. zeamais of 3 – 5 days old were introduced into treated and untreated jars replicated five times and left to stand undisturbed for five weeks in order to determine progeny production. At the end of the period, total number of insects present in both treated and untreated glass jars were counted. Damage assessment was carried out on treated and untreated grains by taking samples of 100 grains from each jar. The numbers of damaged (grains with characteristic holes) and undamaged grains were counted and weighed with percent weight loss calculated following the method of FAO (1985) as: % Weight loss = 100 . ) (