Relationship between deterrence and toxicity of plant secondary compounds for the grasshopperSchistocerca americana

A variety of plant secondary compounds, several of which are quite widespread in nature were tested for their deterrence to the generalist grasshopperSchistocerca americana in short-term behavioral assays. The compounds were coumarin, salicin, tannic acid, gramine, nicotine, quinine, carvone, geraniol, abietic acid, umbelliferone, and ursolic acid. These were then tested for their post-ingestional effects over the whole of the last larval instar. Different methods were employed to mask the taste of compounds that were deterrent in order to ensure that any effects were not due to reduced feeding. In no case was there any indication of a detrimental effect or any trend suggesting one. In two cases, there was a significant increase in growth rate with the addition of the secondary compound to the diet. The evolutionary implications of these findings are discussed.