Interactions, Plant-Insect

Interactions, Plant-Insect

Insect-plant interaction refers to the activities of two types of organisms: insects that seek out and utilize plants for food, shelter, and/or egg-laying sites, and the plants that provide those resources. These interactions are often examined from the plant's perspective, and a principal broad research question is: "How do the activities of the insect affect plant growth and development?"

The interactions can be beneficial to both the plant and the insect, as illustrated by pollination. During pollination, an insect moving within a flower to obtain nectar may transfer pollen either within that flower or among other flowers on that plant. Other relationships between insects and plants can be detrimental to the plant but beneficial to the insect (e.g., herbivory, or feeding upon the plant). Plant-feeding insect species are numerous, constituting more than one-quarter of all macroscopic organisms. Although most plant parts are fed upon by insect herbivores , the majority of insect herbivores are specific in terms of the plant species and the plant part on which they will feed. Some examples of significant insect herbivores worldwide on cultivated crops include: aphids on cereal crops, diamondback moth larvae (immatures) on members of the cabbage family, and larvae of the moth genus Heliothis on a broad range of plants, including cotton. In addition to the direct effects of herbivory, insects can be damaging to plants by acting as vectors (carriers) of pathological microorganisms, transmitting the organisms when the insects feed on the plants.

Interactions in Agricultural Settings

In order to prevent significant losses of agricultural crops to herbivory, both in the field and following harvest, some form of insect population control is often required; some crops may require protection from more than one insect herbivore. Under conventional farming methods in the industrialized world, insecticides are applied to agricultural fields to control insect pests. Often, more than one type of insecticide and/or more than one treatment will be applied in a single crop cycle. The type of control method used for a particular insect/crop combination in part depends upon the understanding of the insect and its use of a particular crop plant. Research into novel aspects of insect-plant interaction may provide improved alternatives for controlling insect pest populations. For instance, recent research examining the effects of moth larvae feeding on corn has demonstrated that after herbivore damage, corn plants release a new complex of odorants into the air, and that some of these molecules are attractive to parasitic wasps. The parasitic wasps then seek out and parasitize the larvae feeding on the corn plants. These odorants have the potential to be used to help control moth damage on corn.

A very different view of insect-plant interaction focuses on the use of insects as biological control agents for weeds and takes advantage of the fact that insects can feed destructively on plants. A well-known example of insect control of weeds occurred in Australia when prickly pear cacti were controlled by the cactus moth from Argentina, Cactoblástis cactòrum (Berg), an insect herbivore imported for that purpose.

Areas of Inquiry

Some insect-plant relationships can be traced through the fossil record, as some fossilized leaves show evidence of ancient herbivory that occurred prior to the fossilization of the plant material. Other insect-plant relationships continue to develop as insect species incorporate novel host plants into their diets and plants evolve new defensive compounds. The dynamic nature and variety of these interactions provides much opportunity to increase our understanding of the physiology of both types of organisms, interactions between them, and ecological and evolutionary processes.

Wendy Mechaber

Bibliography

Bernays, Elizabeth A., and Reginald F. Chapman. Host-Plant Selection by Phytophagous Insects. New York: Chapman & Hall, 1994.

Tumlinson, James H., W. Joe Lewis, and Louise E. M. Vet. "How Parasitic Wasps Find Their Hosts." Scientific American, March 1993.