Suppresion attempts to reduce the numbers of insects below the economic damage level, the density at which they cause economically significant damage to the forest.
The most commonly used suppression methods against bark beetles involve felling infested trees and either removing them from the forest (salvage), burning infested trees or their bark (pile-and-burn or cut-peel-and-burn), or spraying the bark with chemical pesticides (slide). The practical problem is to treat enough trees in a short enough period of time to have a significant impact on the dynamics of the beetle population.
More recently, a combination of sanitation-salvage, the removal of infested and susceptible trees and/or stands combined with pheromone traps has become popular in Europe. During the last spruce beetle (Ips typographus) outbreak in Scandinavia, thousands of "pipe traps" were placed in sanitation-salvage clearcuts, earning them the name "plastic forests" (slide). Millions of beetles were captured in these pipe traps (slide) and this probably reduced the amount of spruce mortality and may have hastened the collapse of the outbreak.
During bark beetle outbreaks it is sometimes necessary to protect particularly valuable trees, for instance in seed orchards or around campgrounds. This can be achieved by spraying them with chemical pesticides or repellents (slide).
The most common tactic in the past to suppress defoliator outbreaks was broadcast spraying of forests with chemical pesticides (slide). Unfortunately, spraying broad-spectrum chemical pesticides over large areas can have serious side-effects on other components of the ecosystem, particularly fish and wildlife populations, as well as on human health (slide). Nowadays, the tendency is to use biological pesticides containing microorganisms or chemicals that mimic insect growth-regulating hormones. These are often called "soft pesticides" or "biorational" pesticides.
EXAMPLES
Gypsy Moth. At least two microbial formulations are available for suppression of gypsy moth populations or eradication of small spot infestations; Bt, a formulation of Bacillus thuringiensis and Gypchek, a formulation of the gypsy moth virus. Tests with both biological pesticides have shown them to be effective at suppressing gypsy moth populations (slide). In addition, a growth regulator called Dimilin is registered for use against the caterpillars and others are being tested. For more information on gypsy moth suppression, read Issue #36 of Gypsy Moth News (click here).
Douglas-fir tussock moth. Click on the University of British Columbia's Fetch21 project to obtain information on suppression of tussock moth populations with virus sprays. http://www.forestry.ubc.ca/fetch21/DFTM/dftmtot.html
<Use BACK key to return to Sessions>