Effect of four powdered spices as repellents against adults of <i>Rhyzopertha dominica</i> (F.), <i>Sitophilus granarius</i> (L.) and <i>Tribolium castaneum</i> (Herbst) in laboratory conditions

Abstract

Studies were conducted to test the repellency of four powdered spices, black pepper (Piper nigrum.), chili pepper (Capsicum annuum), cinnamon (Cinnamomum aromaticum) and turmeric (Curcuma longa), against three stored-product insects, the lesser grain borer, Rhyzopertha dominica, the granary weevil, Sitophilus granarius and the red flour beetle, Tribolium castaneum. The cup bioassay technique was used, to determine the response of insects to potential repellents by measuring their movement from treated grain. The device is made of galvanized screening with 2 mm perforations shaped into a cylinder of 6 cm diameter and 15 cm high, with a mesh bottom, and is placed in the centre portion of plastic container of 15 cm diameter and 15 cm high. The powdered spices were poured into 200 g of wheat mass by a long-stemmed funnel at concentrations of 0, 0.25, 0.75, 1.5 and 2.5% on (w/w) basis. Twenty adults of three species are released into the centre of the grain mass in the container through a long-stemmed funnel. The experiments were conducted at room conditions. The number of trapped insects was determined at 3 different intervals after the introduction of the insects. Results showed that all tested plant powders had repellent activity against the three stored-product insects. Adults of S. granarius repelled faster, followed by T. castaneum and R. dominica. At the highest concentrations and intervals, wheat grains treated with cinnamon powder were the most repellent to adults of S. granarius (up to 92.5% after 1 h), followed by chili pepper treatment for T. castaneum (up to 72.5% after 6 h) and black pepper treatment for R. dominica(up to 58.75% after 24 h).

Keywords: Repellency, Spices, Rhyzopertha dominica, Sitophilus granarius, Tribolium castaneum