Fumigant and Contact Toxicities of Monoterpenes to Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) and their Inhibitory Effects on Acetylcholinesterase Activity

• Published in: Journal of chemical ecology 2009-05, Vol.35 (5), p.518-525
• Main Authors: Abdelgaleil, Samir A. M, Mohamed, Magdy I. E, Badawy, Mohamed E. I, El-arami, Sailan A. A
• Format: Article
• Language: English
• Subjects: Acetylcholinesterase; Acetylcholinesterase - metabolism; Agriculture; Animals; Bioassays; Biochemistry; Biological and medical sciences; Biological control; Biological Microscopy; Biomedical and Life Sciences; Chemical ecology; Cholinesterase Inhibitors - chemistry; Cholinesterase Inhibitors - pharmacology; Cholinesterase Inhibitors - toxicity; Comparative studies; contact toxicity; Control; Ecology; Entomology; Enzymatic activity; enzyme activity; enzyme inhibition; fumigant toxicity; Fumigation; Fundamental and applied biological sciences. Psychology; Insects; Larvae; lethal dose 50; Life Sciences; mechanism of action; Monoterpenes; Monoterpenes - chemistry; Monoterpenes - pharmacology; Monoterpenes - toxicity; monoterpenoids; mortality; Odors; Oils & fats; Oryza sativa; Phytopathology. Animal pests. Plant and forest protection; Protozoa. Invertebrates; Sitophilus oryzae; storage insects; structure-activity relationships; Toxicity; Tribolium - drug effects; Tribolium - metabolism; Tribolium castaneum; Weevils - drug effects; Weevils - metabolism
• ISSN: 0098-0331; 1573-1561
• DOI: 10.1007/s10886-009-9635-3

A comparative study was conducted to assess the contact and fumigant toxicities of eleven monoterpenes on two important stored products insects--, Sitophilus oryzae, the rice weevil, and Tribolium castaneum, the rust red flour beetle. The monoterpenes included: camphene, (+)-camphor, (-)-carvone, 1-8-cineole, cuminaldehyde, (l)-fenchone, geraniol, (-)-limonene, (-)-linalool, (-)-menthol, and myrcene. The inhibitory effect of these compounds on acetylcholinesterase (AChE) activity also was examined to explore their possible mode(s) of toxic action. Although most of the compounds were toxic to S. oryzae and T. castaneum, their toxicity varied with insect species and with the bioassay test. In contact toxicity assays, (-)-carvone, geraniol, and cuminaldehyde showed the highest toxicity against S. oryzae with LC₅₀ values of 28.17, 28.76, and 42.08 μg/cm², respectively. (-)-Carvone (LC₅₀ = 19.80 μg/cm²) was the most effective compound against T. castaneum, followed by cuminaldehyde (LC₅₀ = 32.59 μg/cm²). In contrast, camphene, (+)-camphor, 1-8-cineole, and myrcene had weak activity against both insects (i.e., LC₅₀ values above 500 μg/cm²). In fumigant toxicity assays, 1-8-cineole was the most effective against S. oryzae and T. castaneum (LC₅₀ = 14.19 and 17.16 mg/l, respectively). Structure-toxicity investigations revealed that (-)-carvone--, a ketone--, had the highest contact toxicity against the both insects. 1-8-Cineole--, an ether--, was the most potent fumigant against both insects. In vitro inhibition studies of AChE from adults of S. oryzae showed that cuminaldehyde most effectively inhibited enzyme activity at the two tested concentrations (0.01 and 0.05 M) followed by 1-8-cineole, (-)-limonene, and (l)-fenchone. 1-8-Cineole was the most potent inhibitor of AChE activity from T. castaneum larvae followed by (-)-carvone and (-)-limonene. The results of the present study indicate that (-)-carvone, 1,8-cineole, cuminaldehyde, (l)-fenchone, and (-)-limonene could be effective biocontrol agents against S. oryzae and T. castaneum.