Protect and Enhance the Nations Natural Resource Base and Environment

Turning Forest Pest Against Themselves: Can Insect Odors Be Used As A Natural Pesticide?

Issue (Who cares and why?)
      Bark beetles are the most destructive pests of saw timber and pulpwood in the United States and are responsible for the loss of billions of cubic feet of coniferous timber each year. Their depredations were particularly severe in western Nevada and California, where the normally high biotic stress on conifers due to bark beetle colonization had been exacerbated by an extended drought. If the current nine year drought is extended by a few more dry years, outbreak conditions could return. Bark beetles cause direct economic losses, alter timber management strategies, and create excessively high fuel loads, thereby increasing the chances for catastrophic forest fires.
      With increasing public concern about the use of toxic pesticides to control insects and other pestiferous organisms and the lack of effective control techniques for bark beetles, resource managers are turning toward other techniques of integrated pest management. Some of these techniques are "hi-tech", such as the use of odors called “semiochemicals,” and in particular, pheromones, to manipulate the behavior of insect pests. Bark beetles rely on ‘aggregation pheromones’ to successfully colonize and kill trees, so understanding how the pheromones are produced may lead to better control strategies.

What has been done?
      University of Nevada researchers are working on understanding the regulation of pheromone production in bark beetles. When this work was initiated at UNR in the early 1990s, it was thought that bark beetles used the turpentine chemicals from the pine tree, the chemicals that give the pleasant odor to pine trees, and made them into pheromones. UNR researches discovered that this is not the case, and that bark beetles make the pheromones from scratch. A hormone that is usually used to control development and reproduction in insects, called ‘juvenile hormone’ has been recruited to regulate pheromone production in adult bark beetles. UNR scientists have determined a number of biosynthetic pathways used by bark beetles to make pheromones and discovered that the key enzyme regulating pheromone production is the same enzyme that regulates cholesterol production in humans. They have also isolated, cloned, and modeled another key enzyme in pheromone production.
      In contrast to most other insects, UNR scientists have determined that bark beetles use mid-gut tissue to produce pheromones. The normal course of events is that feeding on a new host tree triggers juvenile hormone production which then increases pheromone production in the mid-gut. The pheromone molecules then enter the gut tract and are literally pooped out to attract other beetles.
      Two new approaches, genomics and proteomics, have been successfully helping understand the myriad of other mid-gut enzymes affected by juvenile hormone to induce pheromone production. A technique that has great potential in disrupting specific enzymes is RNA interference, and this approach is now being used in attempts to interfere with pheromone production.

Impact
      Thus far, researchers at the University of Nevada have fashioned weak congregating pheromone cocktails that attract hungry bark beetles. These cocktails are now being explored in mass trapping experiments with pine bark beetles and have resulted in millions of insects attracted specifically into traps and away from trees. Another promising project is attempting to synthetically produce pheromones that attract males away from females that are willing to mate, causing a reduction in mating. Nevada Division of Forestry Pete Anderson stated that, “investing into this line of research will only save dollars for both California and Nevada in the long run.”

Contact
JGary Blomquist
Dept. of Biochemistry/330
University of Nevada
Reno, Nevada 89557
Blomquis@unr.edu