Volatile oil from plantation-grown lemon-scented gum (Corymbia citriodora (Hook.) K.D. Hill and L.A.S. Johnson): its physicochemical properties and efficacy against wood-destroying insects
2014
Palanginan, I.I. | Garcia, C.M.
The volatile leaf oil (VLO) of plantation-grown lemon-scented gum (Corymbia citriodora (Hook) K.D. Hill and L.A.S. Johnson) was characterized and its toxicity against wood-destroying insects evaluated. The light yellow VLO yield amounted to 3.78% based on oven-dry weight after 3 hr at a material to water ratio of 1:4. The efficacy of crude VLO and its methanol and hexane fractions was tested against subterranean termites (Coptotermes vastator Light), drywood termites (Cryptotermes dudleyi Banks) and powder-post beetles (Dinoderus minutes F.). The solutions were topically applied on the insect's thoracic region. Mortality within 24 hr was the basis of determining toxicity. There was a general increase in insect mortality as the doses of crude VLO and its fractions were increased. The methanol fraction was highly toxic to C. vastator (85-95% kill), moderately toxic to C. dudleyi (26.7-40% kill) and slightly to moderately toxic to D. minutus (15-46% kill). The hexane fraction was highly toxic to C. vastator (85-100% mortality) and moderately to highly toxic to D. minutus (28.3-7.3% mortality). Crude VLO at lower levels (50% and 60%) was not toxic to slightly toxic to termites, while higher doses (70% and 80%) were slightly to moderately toxic to termites and powder-pest beetles. The methanol and hexane fractions regardless of dose displayed potentially high toxicity to subterranean termites, with an efficiency similar to the standard chemical.
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