Other Interactions Between Carnivorous Plants And Insects

Thus far, plant—insect interactions have been presented in the context of insects serving as prey. But the associations can be much more varied and complex, as seen in the instance of the assassin bug and Roridula. Entomologists are now only beginning to appreciate the many other ways in which carnivorous plants and insects/animals interact. Some of the more fascinating examples are found in the pitcher plants, where other animals turn the traps to their own advantage. Spiders often can be found prowling about the mouth of pitchers, then lowering themselves on silken strands to retrieve prey from the pitcher well. In Nepenthes, spiders also use the pitcher for protection from predators. If a predator is detected, the spider will lower itself on a silk thread to the pool and, if necessary, will even hide under the water until danger passes.

Other insects spend part or most of their lives in the wells of pitchers. For example, the pitcherplant mosquito (Wyeomyia smithii) lays its eggs on the moist inner surface of the leaf, or more often, in the pool of liquid. The larvae hatch and feed on detritus from trapped insects, bacteria, and protozoans. As winter approaches, the larvae go into a dormant state and overwinter in the pitcher, exiting the pitcher in the spring as adult mosquitoes. In climates where water freezes, the larvae spend winter frozen in the ice of the pitcher. Interestingly, the liquid that digests the trapped insects seems to have no detrimental effects on the larvae. Fish fly larvae also live in pitchers and, like the mosquito larvae, are not injured by the pitcher's digestive enzymes because, it is speculated, their bodies produce a protective substance.

One of the most fascinating examples of an association between plant and insect, benefiting the insect, is seen in species of Exyra moths (Noctuidae) that exploit the pitcher leaf to shelter their young. The cycle begins with the female moth entering an open leaf and laying its eggs on the inner wall of the pitcher leaf. When the larvae hatch, they move about on silken strands, feeding on the inner wall. As they grow, hence becoming more visible to predators, the larvae move to the top of the pitcher, severing vascular strands carrying water to the upper regions of the pitcher leaf, which causes the top of the pitcher leaf to dry, collapse, and fold over the opening. The developing larvae are now shielded from predators. Just before a larva prepares to pupate, it chews a hole in the wall of the leaf. Through this hole, the moth exits the leaf.

Yet another example of an insect exploiting its association with carnivorous plants is the solitary sarracenia wasp (Chlorion harrisi). This insect uses the pitcher as an incubator for its eggs. In preparation for the laying of eggs, the wasp packs into the bottom of the pitcher tube a layer of grass, which is then overlayered with freshly killed grasshoppers or crickets. This process may be repeated several times, resulting in alternating layers of insects and plant materials. Eggs are then laid among the dead insects and the whole construction covered by another layer of grass. The eggs can now develop protected, and when the young hatch, they have a food supply.

The last example represents what may come closest to a commensal, or symbiotic, association between plant and insect. Certain species of Nepenthes (e.g., N. bicalarate) have enlarged, hollow petioles in which ants take up residence. In return for this "home" (domatia), the ants, it is suggested, protect the plant from predators.

See Also the Following Article

Plant—Insect Interactions

Further Reading

D'amato, P. (1998). "The Savage Garden." Ten Speed Press, Berkeley, CA. Darwin, C. (1875). "Insectivorous Plants." Appleton, New York. Juniper, B. E., Robins, R. J. and Joel, D. M. (1989). "The Carnivorous

Plants." Academic Press, London. Lerner, C. (1983). "Pitcher Plants: The Elegant Insect Traps." Morrow, New York.

Lloyd, F. E. (1942). "The Carnivorous Plants." Chronica Botanica, Waltham, MA.

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