Chemical Repels Insects

close up photograph of green plant leaves

Biological Strategy

Catnip

AskNature Team

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Protect From Animals

Animals–organisms that range from microscopic to larger than a bus–embody a wide variety of harms to living systems, including other animals. They threaten through predation, herbivory, defense, and parasitism, and they compete for resources such as water, nutrients, and space. Any given living organism commonly faces threats from a variety of animals, requiring strategies that effectively defend from each. Trout and other bony fish, for example, escape predators by having scales made of very thin, flake-like pieces of bone covered with slippery mucus. They also have behavioral strategies such as camouflage, fast swimming, and twisting and turning to achieve release from a predator’s grip.

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Send Chemical Signals (Odor, Taste, Etc.)

Tastes, odors, and hormones are all chemical signals that can float through the air or water, or be applied to solid surfaces. Chemicals are important for signaling and communication; even humans, with our underdeveloped sense of smell, are influenced by chemicals more than we realize. Chemical signals are often specific to the living system intended to receive them, and are often relatively weak, dispersing upon moving through liquids or gases. To ensure that chemical signals reach their target, living systems create unique chemical signals and methods of dispersal. One example is an orchid that is pollinated by dung beetles, and therefore distributes a dung-smelling aroma to attract them.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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The chemical defense system of catnip may repel insects with the chemical nepetalactone.

Image: KENPEI / Wikimedia Commons /

Image: Penarc / Wikimedia Commons /

<a href=http://commons.wikimedia.org/wiki/Nepeta_cataria title=Nepeta cataria>Nepeta cataria</a>, pot plant

“Anisomorphal [a chemical named for insect, Anisomorpha, a walking-stick that uses it as a defensive spray] bore a chemical resemblance to, of all things, catnip. Formally known as nepetalactone, and produced by a plant of the mint family (Nepeta cataria), catnip derived its reputation from its peculiar ability to excite cats. That property, surely, had nothing to do with whatever the compound did for the plant that produced it. It occurred to me that I was now in a position to propose a natural function for nepetalactone. Could the compound not be defensive like anisomorphal, and serve to protect the plant itself? I got some pure nepetalactone from Jerry–by coincidence it was he who had determined the structure of the compound–and did some simple tests, in which I showed the chemical to be a potent insect repellent. I found that insects would quickly fly off or walk away if I pointed at them a capillary tube filled with nepetalactone, and that ants would shy away from insect baits that I had laced with the compound. It was clear that plant and insect had hit upon a common defensive strategy here, in the sense that they had both evolved the capacity to produce similar substances for a similar purpose…Interestingly, anisomorphal is now known also to be produced by a plant. Not surprisingly, that plant, cat thyme (Teucrium marum), is also a member of the mint family (Labiatae). And nepetalactone itself has been shown to be produced by a species of walking-stick.” (Eisner 2003:89-91)