Insecticidal activity of bis(methylthio)methane based volatile extract of Olax zeylanica (L.) against Sitophilus zeamais (L.) and Corcyra cephalonica (Stainton)

摘要

Sri Lankan natives traditionally introduce pungently odorized Olax zeylanica (L.) leaves into their grain storages aiming at the efficient control of insect pests associated with stored grains. The headspace components of O. zeylanica leaves were analyzed by GC-MS, subsequently isolated the major compound being responsible for the plant's protective effect and laboratory bioassays were conducted to test its lethal activities against Sitophilus zeamais (L.) (Coleoptera: Curculionidae) and Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae). A total of 2 headspace sulfur-containing constituents were found consisting the volatilome of O. zeylanica leaves wherein bis(methylthio)methane (BMTM) was identified as the major organosulfur constituent (75.3 %). BMTM provided strong and immediate control against 3-7 days old S. zeamais adults, 1 day old eggs, 15-17 days old larvae and 1 day old adults of C. cephalonica within 24 h of post treatment. In contact and fumigation assays, S. zeamais (LC50 (contact) = 0.16 v/v% and LC50(fumigation) = 0.17 v/v%) was more susceptible to BMTM than C. cephalonica (LC50 (contact) = 0.19 v/v% and LC50(fumigation) = 0.22 v/v%) in their adult stages. In contact grain assays, adulticidal effects persisted for 84 h. The degree of susceptibility of different C. cephalonica life stages to BMTM was arranged in the order of eggs (LC50 = 0.18 v/v%) > adults (LC50 = 0.19 v/v%) > larvae (LC50 = 0.29 v/v%) producing > 95 % lethal effects at the respective time points of 9, 12, and 24 h. Additionally, it was evidenced that the grain viability and germination were not affected by the uptake of BMTM. BMTM caused substantial toxicities in S. zeamais and C. cephalonica inferring the favorable use of natural BMTM in the successful control of stored grain insect pests, thereby obviating the necessity in sole relying on conventional synthetic insecticides in storage systems.