The refreshing scent of pines and cedars often repels insects.
Conifers feature simple, evergreen leaves, often referred to as needles, and naked seeds housed in cones. Pines, junipers, yews, cedars and redwoods are all classified as conifers. The fragrant wood from conifers features qualities that give make it insect repellent. Understanding how conifers are insect repellent helps in making proper insect management decisions. Does this Spark an idea?
Insect Defenses
Insect repelling works as a form of defense against insect infestation. One of the greatest threats to conifers are pest insects and the pathogens they carry, according to Christopher Keeling, a researcher in conifer plant defense. As conifers have evolved to protect themselves against insects by using chemicals to repel them, insects have also evolved and developed resistance to the chemicals. Conifers produce chemical compounds to repel, kill and reduce invading insects.
Attracting and Repelling
Plants with insect-repellent qualities feature chemical substances that repel certain insects, but not all insects. The same chemicals, known as terpenoids, that attract beneficial insects work to repel pest insects. Conifers, in fact, use odors and pheromones to attract predators and insects that prey upon damaging insects. Chemicals released by conifers under attack from an insect pest actually work to attract parasitoid wasps, predatory mites, clerid beetles and predator beetles, according to Sheryl Costello of Colorado State University. Other insect defense mechanisms of conifers work without chemical means. For example, conifers provide shelter for birds, which in return eat insects.
Resin Production
Conifers produce oleoresin, also called resin, as a response to wounding or disturbance. This sticky, strongly scented substance consists of monoterpenoid, sesquiterpenoid and diterpenoid compounds. When an insect bores into the tree, the resin pitches out of the tree. Insects become stuck in the resin, which cleans and seals the wound. It also acts as a repellent to deter insects with a toxicity based in both the resin and the vapors.
Adaptation of Conifers
Conifers in areas of high-insect infestation feature higher levels of monterpene than other trees in less stressful areas of growth. For example, the ponderosa pine creates limonene, a toxic chemical to pine beetles. Limonene, myrcene and beta-pinene in pines are all found at higher concentrations in areas with higher levels of pine beetle predation, according to . This may be due to environmental stresses, such as drought, which both raises the levels of terpenoids in trees and draws in insect predators.
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