THE INFLUENCE OF PLANT CHEMICALS ON THE FEEDING BEHAVIOR, DEVELOPMENT, AND SURVIVAL OF THE TWO-STRIPED GRASSHOPPER, MELANOPLUS BIVITTATUS (SAY), ACRIDIDAE: ORTHOPTERA

Abstract

An investigation of the effects of 20 secondary plant chemicals on the survival, development, and feeding behavior of a polyphagous insect, Melanoplus bivittatus (Say), was made using chemically defined synthetic diets.When added to the basic diet, only one chemical, tigogenin, showed unqualified stimulatory effects on growths. Nornicotine dipicrate, solanine, tomatine, digitonin, and saponin caused all nymphs to die before they attained the adult stage, and santonine, indican, diosgenin, hecogenin, and lupinine produced leas severe toxic effects. Very few of the chemicals which permitted survival affected adult weight.Feeding preference experiments showed that some chemicals reduced feeding but none increased it. If it is assumed that the role of secondary plant chemicals in the feeding behavior of M. bivittatus is to indicate to the insect which diets to discriminate against, anomalies existed in that diets containing innocuous chemicals were sometimes discriminated against, whereas diets containing some chemicals producing lethal effects were accepted.Steroid chemicals exhibited the greatest effects on feeding behavior, survival, and growth, and it is postulated that the distribution of plant steroids may provide an insect – food plant association mechanism.