6: Insects Feeding on Plants Check Access

About half of all the insect species are phytophagous. Some insects are polyphagous, others consume some plants only and are called oligophagous. Monophagous insects feed mostly on one type of plant. The dietary requirements of insects are comparable to those of other animals, with the difference that insects can synthesize fatty acids in their bodies but must have a nutritional source of cholesterol. Most terrestrial insects are highly adapted for water conservation. A common method to learn about the nutritional needs of insects is to feed them artificial diets in a laboratory. Plants are not ideal sources for required nutrients for herbivorous insects because they do not supply cholesterol and contain only low amounts of phytosterols. Plants’ phloem is much more nutritious for insects than the xylem, and many phytophagous insects obtain their nutrients directly from the phloem. Other sources of insect nutrition are pollen and flower nectars. The chemical constituents of a plant, including their olfactory and taste characteristics, ultimately determine if insects will start consuming a plant or avoid it. Electroantennograms are commonly used to detect a positive or negative response of an insect towards a plant and its chemical constituents. Charcoal beetles (Melanophila acuminate) are not only highly sensitive to volatile compounds typical of burning wood but also to infrared radiation from the heat produced by wildfires.