Trichomes: The first line of defense against herbivores (Trichoplusia ni)

Pest insects have significant economic, environmental and social impacts. The cabbage looper, Trichoplusia ni, is a pest native to Canada, Mexico, and the United States. They feed on many vegetable plants including all members of the Brassicaceae family, and even cantaloupe and tomatoes. When herbivores initiate feeding on a host plant, they present "cues”, which the plant perceives and uses to help rapidly mobilize its defenses in response to the herbivore’s attack on the plant. This study was designed to determine if T. ni, is able to induce the production of leaf hairs or trichomes on newly forming leaves of tomato plants. In some plant species, herbivores or defoliation triggers the production of increased numbers of trichomes which act as defenses against herbivores. The induction of trichome development has been seen to be under the control of the plant signal jasmonic acid. We will be answering three questions:  The first being, "Does cabbage looper saliva induce trichomes?”. To further investigate this question, we will ablate the spinneret so that the insect is unable to salivate, cage individual loopers on the fourth true leaf of the tomato plant, and allow them to feed on the area of their cage. We will then compare the number of trichomes on plants fed on by the ablated caterpillars with those that were fed on by caterpillars with intact salivation. Our next question addresses, “Does increased trichome density interfere with growth of cabbage loopers?" A methyl jasmonate treatment, which induces higher trichome densities, will be applied to the tomato plants, while control plants receive no treatment. The treatments will be compared to detect changes in trichome density. Furthermore, a bioassay procedure will be used to determine whether feeding and growth rates of T.ni were affected by the trichome density (specifically glandular) on the host plant. The third question is “Does cabbage looper saliva affect the expression of the defense gene, proteinase inhibitor 2 (Pin 2)?” To test this, quantitative real -time PCR will be used to measure the abundance of Pin2 transcripts. These experiments were conducted to better understand the interaction between insects and plants to facilitate the development of new pest control systems.