REPELLENCY AND CONTACT TOXICITY OF CRUDE EXTRACTS FROM THREE THAI PLANTS (ZINGIBERACEAE) AGAINST MAIZE GRAIN WEEVIL, SITOPHILUS ZEAMAIS (MOTSCHLUSKY) (COLEOPTERA: CURCULIONIDAE)

Abstract

In the present study, plant crude extracts extracted from the rhizomes of three medicinal plants, Curcuma longa L. (turmeric), Zingiber cassumunar Roxb. (cassumunar ginger), and Kaempferia pulchra (Ridl.) Ridl. (peacock ginger) were investigated for their biological activities, repellent and contact toxicity, against maize weevils, Sitophilus zeamais Motsch. The repellent activity was evaluated using the area preferences method whereas the contact toxicity was determined using the micro-applicator to drop onto the thorax of tested insects. For repellency test, cassumunar ginger with solvent hexane scored the highest repellency up to 99% at concentration 1,415 µg/cm2 at 8 hours after application. The methanol extract of turmeric plant exhibited the highest repellency of 87% at 1,415 µg/cm2 7 hours after exposure compared to other two solvents, hexane and methylene chloride with same plant. Peacock ginger plant with solvent hexane revealed the maximum repellency of 79% at 1,415 µg/cm2 5 hours after exposure. On the other hand, for contact toxicity, turmeric plant was found to be the most effective in inducing mortality after one week of treatments. The turmeric crude extract with solvent hexane achieved 13% of mortality of adults S. zeamais at 45 µg/insect. The highest mortality that caused by plant cassumunar ginger was observed by this crude extract with solvent methylene chloride (8%) at 45 µg/insect at seven days after application. Methanol extract of peacock ginger has the lowest mortality (6%) compared to 2 other plants mentioned above. Thus, these results demonstrated that hexane extracts of C. longa and Z. cassumunar were one of the alternative extracts that were possible to use as insecticidal for S. zeamais control.