Growth Inhibitors in Host Plant Resistance to Insects: Examples from a wild tomato with Heliothis zea (Lepidoptera: Noctuidae)

Non-lethal, growth inhibiting allelochemicals have potential roles in host plant resistance to insects because they can extend the time the insects are exposed to other mortality factors. Four chemical constituents of the wild tomato, Lycopersicon hirsutum f. glabratum, PI 134417 were evaluated in artificial diet as growth inhibitors to Heliothis zea (Boddie): alpha-tomatine, chlorogenic acid, beta-caryophyllene and alpha-humulene. All caused small increases in developmental time, and, except for chlorogenic acid, small decreases in pupal weight. These changes may be too small to be of biological significance in host plant resistance. Our results suggest that the usual method of evaluating growth inhibitors, which is to weigh the insects after a fixed feeding period, is inadequate to assess the biological significance of any observed growth inhibitory effects. Because differences in weight after fixed feeding periods do not always translate into equivalent changes in developmental time or final weight, measurement of actual developmental time may be more appropriate.