Caterpillars have been called "eating machines", and eat leaves voraciously. Most species shed their skin four or five times as their bodies grow, and they eventually pupate into an adult form. Caterpillars grow very quickly; for instance, a tobacco hornworm will increase its weight ten-thousand fold in less than twenty days. An adaptation that enables them to eat so much is a mechanism in a specialized midget that quickly transports ions to the lumen (midget cavity), to keep the potassium level higher in the midget cavity than in the blood.
A Gypsy Moth caterpilars
Most caterpillars are solely herbivorous. Many are restricted to one species of plant, while others are polyphagous. A few, including the clothes moth, feed on detritus. Most predatory caterpillars feed on eggs of other insects, aphids, scale insects, or ant larvae. Some are cannibals, and others prey on caterpillars of other species (e.g. Hawai'ian Eupithecia ). A few are parasitic on cicadas or leaf hoppers. Some Hawai'ian caterpillars (Hyposmocoma molluscivora) use silk traps to capture snails
Hypsipyla grandela damages mahogany in Brazil
Caterpillars cause much damage, mainly by eating leaves. The propensity for damage is enhanced by monoculture farming practices, especially where the caterpillar is specifically adapted to the host plant under cultivation. The cotton bollworm causes enormous losses. Other species eat food crops. Caterpillars have been the target of pest control through the use of pesticides, biological control and agronomic practices. Many species have become resistant to pesticides. Bacterial toxins such as those from Bacillus thuringiensis which are evolved to affect the gut of Lepidoptera have been used in sprays of bacterial spores, toxin extracts and also by incorporating genes to produce them within the host plants. These approaches are defeated over time by the evolution of resistance mechanisms in the insects.
Plants evolve mechanisms of resistance to being eaten by caterpillars, including the evolution of chemical toxins and physical barriers such as hairs. Incorporating host plant resistance (HPR) through plant breeding is another approach used in reducing the impact of caterpillars on crop plants
No comments:
Post a Comment