Toxicity of Compounds Derived from Limnanthes alba Seed to Fall Armyworm (Lepidoptera: Noctuidae) and European Corn Borer (Lepidoptera: Pyralidae) Larvae

When incorporated into artificial diet at 3% (wet weight), milled seed of Limnanthes alba var. versicolor (Greene) C. T. Mason (Limnanthaceae) caused 100% mortality in newly hatched fall armyworm larvae, Spodoptera frugiperda (J. E. Smith) within 8 d. An ether extract and subsequent ethanol extract of the seed were prepared and tested at doses equivalent to 3% ground meal. The ether extract caused slower growth in larvae (weights were 6% of weights of controls after 8 d) but caused no mortality. The ethanol extract caused 30% mortality and retarded growth in survivors (16% of control weight after 8 d). 3-Methoxybenzyl isothiocyanate (3-MBI) was isolated from the ethanol extract and accounted for its activity; the LC50 in the diet incorporation bioassay was 270 ppm. The glucosinolate from which 3-MBI is derived was similar in activity to an equimolar amount of 3-MBI. Activity of the ether extract was due to triglycerides, but the unusual lipids of L. alba were not more active than triglycerides in corn oil, which contained oleic and linoleic acids. European corn borer larvae, Ostrinia nubilalis (Hübner), were less sensitive to the materials derived from L. alba. The seed meal did not cause significant mortality (at 3% in the artificial diet), although weights of the surviving larvae were only 4% of the weight of control larvae after 8 d. The LC50 for 3-MBI was higher (780 ppm), and the ether extract caused no significant effect. Four aromatic analogs of 3-MBI were tested, but none was significantly more active in either species than the naturally occurring compound.