Repellent effects of powdered leaf mixtures of four plant species, Piper nigrum (black pepper), Ocimum gratissimum (maha maduruthala), Cinnamomum verum (cinnamon) and Mentha viridis (mint) were evaluated against the adult rice weevil, Sitophilus oryzae under laboratory conditions (29 �200 C and 84�2 % relative humidity). The evaluation was made with the view of finding plant materials that effectively protect stored produce and are less poisonous and less detrimental to the environment. A modified cup-bioassay was used for repellency tests. Leaf powders of the plants were tested separately and in different mixtures against S. oryzae. Four combinations of leaf powders were made using two plants at a time (15g altogether) at 1:1 ratio, and added to hundred grams of clean and un-infested rice grains separately. Similarly, another bioassay was set by mixing powdered leaves of all four plants together at a ratio of 1:1. Twenty rice weevils each were introduced into bioassay chambers. When compared with the control, all combinations of plant leaves caused significantly higher repellency (p < 0.05) in adult weevils. Repellent effect of the mixture of M. viridis and O. gratissimum was the most striking as it elicited an extremely high repellency (95.0%) in the weevils just after 2 hours of exposure. Conversely, the weevils demonstrated considerably high rates of repellency to the combinations of, P. nigrum + M. viridis, and P. nigrum + O. gratissimum which were 88.0% and 87.0% respectively. In contrast, a significantly low rate of weevil repellency (46.0%) was observed with the combination of C. verum and P. nigrum after 2 hours. Moreover, a very much high repellent activity (85.0%) was also obtained when weevils were exposed to the combination of leaf powders of all four plants mixed together. Furthermore, when tested separately, only M. viridis elicited a high repellent activity (90.0%) in the weevils. Also, the highest rate of repellency with single plants was observed only after 6 hours of exposure where as all the plant combinations showed their highest repellent effects shortly after 2 hours of exposure. These observations clearly indicate a rapid and great increase in weevil repellency when different mixtures of plant powders were used. The results of the present investigation highly signify the potential of using mixtures of the four plant materials, especially the combination of M. viridis and O. gratissimum as eco-friendly pest control agents in reducing infestation of rice caused by S. oryzae.

Topics: Resource Management, sympoisum 2009 | No Comments »

Comments