Study on the Distribution of Olfactory Antennal Sensilla of Sitophilus zeamais Motsch (Coleoptera: Curculionidae) and their Response to Some Botanical Extracts

Abstract

The repellency potential of Euphorbia balsamifera Aiton, Lawsonia inermis L. and Mitracarpus hirtus (L.) DC against Sitophilus zeamais was assessed at 30±2 °C and 70±5% R.H. The botanicals were applied as chloroform extracts at the rate of 6.25, 12.50, 25.00, 50.00 and 100.00 mg ml -1 per 20 g sorghum grains. Percent repellency of the botanicals against S. zeamais was taken at 1 and 24 hour after exposure (HAE). Scanning electron microscopy (SEM) was conducted for examination and identification of olfactory antennal sensilla of the weevil. This was enhanced by the aforementioned repellency test with antennal distal flagellomere of the weevils excised. The SEM showed that sensilla chaetica (SC), sensilla trichoidea (ST) and sensilla basiconica (SB) were the types of antennal sensilla of S. zeamais identified. Results from repellency tests conducted revealed that ST and SB were the olfactory sensilla located on the last distal flagellomere of the weevils. It was also found that the botanicals had promising repellent activity against S. zeamais and might be used in the protection of stored sorghum grains.