The Web of Life (79-7) Self-Protection continued


Several plants plant a time bomb for pests. Armyworms, the caterpillar of a phalaenid moth, are fond of daisies. As a countermeasure, daisy leaves are laced with polyacetylenes: highly electrically conducting compounds that become toxic when exposed to sunlight.

Once a worm has digested laced leaves, the polyacetylene within travels to the worm’s surface tissues, catches some UV rays, and turns lethal. The armyworm quickly shrivels up and dies.

While the armyworm lacks armor to protect itself from the daisy bomb, “leaf-rollers” blanket themselves from poisoning. Leaf-rollers is a colloquial name for various moth caterpillars, weevils, and wasps that have a strategic counterplan to photosensitive plant bombs. They shape a leaf into a shelter, letting them munch in the shade of their protective pocket, out of the Sun, and out of sight from potential predators.

Insects have adapted various ways around plant defenses. Sucking insects, such as cicadas and leafhoppers, tap directly into the cells conducting succulent water and sugary sap. Aphids punch past leaf epidermis laden with secondary compounds, and so precisely dine on the fine juices within.

Other insects feed exclusively on nutrient-rich seeds: a source of proteins and fats, and a luxurious diet for many insect larvae.

While some insects feed on a variety of plants, many specialize, identifying favorites by their individual chemistry. The secondary compounds designed to act as a deterrent instead provide an olfactory signal of specificity.

Polyphagous feeders must adapt to digest various compounds from the different plants they eat, while picky oligophagous eaters have adaptively adjusted only to their selected species. Insects adaptively handle the toxins by either disarming them or becoming tolerant to their effects. As with hornworms, some insects employ plant secondary compounds for their own defense, themselves becoming toxic to their predators simply by eating well.