Sticky and velvety plants occur within local populations. Velvety plants are less suitable for survival and growth of the tobacco hornworm, flea beetles, a leaf-feeding weevil and are completely resistant to whiteflies. In contrast, sticky plants are more susceptible to Tupiocoris notatus , a small bug that has specific structural adaptations to cope with glandular hairs. Thus, the proportion of sticky and velvety plants in different populations may be, in part, the result of natural selection in opposite directions by different pest species. The production of glandular trichomes for insect resistance is associated with several aspects of plant growth and seed production.
Sticky plants have a greater commitment to vegetative growth than reproduction .
Over time, sticky plants grow larger than velvety plants but they also continue to produce fewer seeds per unit of leaf area. Eventually, the greater vegetative size overcomes the reduced seed production rate so that seed production of sticky plants eventually catches up to that of velvety plants. The relative frequencies of sticky and velvety plants in natural populations are the result of natural selection on all of these characteristics. The variation in different herbivore communities may be responsible for the different frequencies of plants, but our results also suggest that sticky plants may be the superior competitor for light and nutrients when insect herbivores are absent. Currently, we are investigating the relative susceptibility of sticky and velvety plants to controlled levels of insect defoliation.