DISSERTATION RESEARCH: Influence of Herbivory and Plant Age on Induced Resistance of the Black Mustard, Brassica nigra

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This proposal explores how plants respond to injury by leaf-feeding insects by increasing defenses in new tissue. The black mustard, Brassica nigra, has two principal leaf-damaging insects in nature: the mustard flea beetle and caterpillar of the cabbage white butterfly. A preliminary study showed that feeding by the caterpillar caused the black mustard to double the density of protective hairs on new leaves, whereas feeding by flea beetles did not. The new experiments test whether this doubling of leaf hair density protects new leaves from subsequent damage by either herbivore and will show whether greater initial damage stimulates even greater protection of new leaves by the plant. The experiments will also test whether a plant's ability to protect itself declines with age. There are three significant aspects to this research. First, researchers have primarily concentrated on responses of plant chemistry to insect damage and often ignored leaf hairs. Second, little is known about whether there is competition among leaf-damaging insects in nature. This research may demonstrate that competition between insects occurs indirectly through their effects on plant resistance. Third, the research may indicate how crop scientists can manipulate intrinsic defenses of agricultural crops to more effectively combat insect pests.