BIOCONTROL POTENTIAL OF SELECTED PLANT ESSENTIAL OIL CONSTITUENTS AS FUMIGANTS OF INSECT PESTS ATTACKING STORED FOOD COMMODITIES.

Abstract

Laboratory space fumigation studies were conducted to evaluate the fumigant toxicity of selected essential oil terpenoids

against adult Sitophilus oryzae L., Rhyzopertha dominica F., Tribolium castaneum (Herbst), Oryzaephilus surinamensis

1. and Callosobruchus chinensis F. Five essential oil constituents, alpha humulene, caryophyllene oxide, myrcene,

R-(+)-alpha pinene and R-(+)-beta pinene were each evaluated at four rates (0, 1, 5 and 10 µl/L air) in space fumigation

chambers with four replicates per concentration. Results showed strong dose-, insect species- and time-dependent

fumigant toxicity in which caryophyllene oxide, myrcene, α- humulene, R- (+)-α- pinene and R- (+)-β- pinene caused

18- 100, 49- 100, 55- 100, 47- 100 and 33- 100% kill of all test insects, except the most tolerant species, T. castaneum, at

10 µl/L air 168 h after treatment. Except T. castaneum, end-point LC50 values of 0.03- 8.5, 0.03- 7.0, 0.01- 4.82, 0.01-

8.20 and 0.03- 6.5 µl/L air were obtained for the five terpenoids, respectively. The varied toxicities could be explained

by the compound structure-insecticidal activity relationships that influence their degree of penetration into the insect

cuticle and neurotoxicity. These findings provide the scientific basis for using essential oils as fumigants against storage

insects and hence, potential alternative fumigants in both subsistence and commercial agriculture. Further studies are

recommended to evaluate the grain fumigation potency, biosafety and broad spectrum bioactivity of these essential

constituents against insect pests of stored food commodities.