Toxicity of Peppermint Monoterpenes to the Variegated Cutworm (Lepidoptera: Noctuidae)

Abstract

Toxicity of five monoterpenes to the variegated cutworm, Peridroma saucia Hubner, was evaluated. Larvae fed for 6 d from the beginning of the fifth stadium on semi defined artificial diet fortified with pule gone (0.05%, 0.1%), menthol (0.1%, 0.2%), or menthone (0.2%) weighed less than controls. Reduced growth was the result of feeding inhibition in larvae fed menthone and pule gone and to molting abnormalities in larvae receiving menthol. Menthol completely inhibited pupation at doses approximating those in peppermint (0.05-0.2% wet wt). Limonene (0.2%), menthone (0.1%, 0.2%), and pule gone (0.1%) also inhibited pupation. Growth, feeding, and pupation were not affected when larvae ingested limonene (0.05% or 0.1%) or α-pinene (0.05-0.2%). Growth, maximum weight, and pupal weight of neonate larvae fed artificial diet fortified with menthol, menthone (0.05%), Iimonene (0.05%), α-pinene (0.05%), or pule gone (0.025%) did not differ from those of controls. However, larval mortality was significantly higher in menthone and pule gone treatments than in the controls. The median lethal dose for pule gone applied topically to sixth instars was 1,077 μg/g; for menthone, 2,478 μg/g; and for a-pinene, 7,925 μg/g. Piperonyl butoxide synergized the latter two effects. Suspensions of midgut microsomesfrom sixth instars metabolized all five monoterpenes as indicated by disappearance of NADPH.