Fumigation toxicity of monoterpenoids to several stored product insects

Twenty naturally occurring monoterpenoids were evaluated in a preliminary fumigation screening test on some important stored-product pest insects, including the rice weevil, Sitophilus oryzae, the red flour beetle, Tribolium castaneum, the sawtoothed grain beetle, Oryzaephilus surinamensis, the house fly, Musca domestica, and the German cockroach, Blattella germanica. Cineole, l-fenchone, and pulegone at 50 μg/ml air caused 100% mortality in all five species tested. Ketone compounds were generally more toxic than other monoterpenoids. Three monoterpenoids, the ketones pulegone, l-fenchone, and the aldehyde perillaldehyde, were selected for further study. They were effective against T. castaneum in the fumigation assay; however the toxicity was relatively low in comparison to dichlorvos. LC₅₀ values of these three monoterpenoids tended to decrease at longer exposure times and higher temperatures. Inclusion of either maize kernels or house fly medium (HFM) increased LC₅₀ values, HFM more so than maize kernels. Monoterpenoids may be suitable as fumigants or vapor-phase insecticides because of their high volatility, fumigation efficacy, and their safety.