Luring Pests to Protect Trees
SourDough News | July 14, 2013
Alex Vaisvil, a student intern from Xavier University in Cincinnati Ohio, lowers a Lindgren multi-funnel trap from the mid-canopy. Traps were located in the Tongass National Forest as part of a study to refine woodborer trapping methods in Southeast Alaska.
Kat Pratt (left, biological technician with Forest Health Protection) and Alex Vaisvil (right, student intern with Xavier University in Cincinnati, OH) checking clear panel traps for woodboring beetles.
Longhorned beetles are a type of woodboring beetle named for their characteristic long antennae. They often garner attention as pest species; however they do play a critical role in our forested ecosystem. Adult beetles select weakened and dying trees, which serve as a host for their young.
In many species, male beetles will land on a potential host and “call” females by emitting an attractive pheromone. They can then be seen scurrying up and down the tree, waving their long antennae around in the hope of contacting a female. Upon mating, the female will find or chew a niche in the bark to lay her eggs. The larvae will then hatch and bore into the tree, feeding on the woody tissue.
Typically, a healthy tree has defense mechanisms to protect itself from beetle attack such as sap or resin which oozes out and smothers the beetle. Therefore, longhorned beetles prefer to attack trees that are already weakened and dying and incapable of defending themselves. In a way, the beetles begin the decomposition process and aid in forest succession.
Under the right circumstances, longhorned beetles can become a major forest pest. An abundance of stressed trees, such as following a disturbance and/or under certain climate conditions, can provide enough breeding material for beetle populations to reach outbreak level. At that point, healthy trees may be attacked as well. However, the most threatening insects to a healthy forest are non-native species introduced into a new area.
Non-native longhorned beetles are easily transported around the world in solid wood packing material, arriving in a new location with no natural enemies to control their populations. The Asian longhorned beetle is an example of a non-native species that has become established in the U.S., and as a result, tens of thousands of hardwood trees have been lost in Illinois, New York, New Jersey, Massachusetts, and Ohio. Hundreds of millions of dollars has been spent trying to eradicate this beetle, however success has only been achieved in areas where the beetles were detected early and swift action was taken. This is why detection and monitoring for forest pests is crucial to maintaining a healthy forest and preventing the spread of invasive species.
The most effective traps for woodboring beetles are designed to mimic the silhouette of a tree. The traps are baited with an attractive component, such as host volatiles and/or pheromones, which lure the beetles to the trap and collected in the container below. Research on pheromones of longhorned beetles has demonstrated they can be effectively used to monitor and survey beetles; however these pheromones have not been thoroughly tested in the wet environment of Southeast Alaska. In order to determine the best trap/pheromone emitter for Southeast Alaska, a collaborative study was established between professionals with Xavier University and USFS’s Forest Health Protection staff. The study compared the efficacy of different type of pheromone emitters in Year 1 and different trap design and height of traps in Year 2.
Three different trap types were compared: Lindgren multi-funnel traps, panel intercept traps, and clear panel intercept traps. The traps were located in Juneau, Alaska at two sites in the Tongass National Forest and a third site at the Jensen-Olsen Arboretum. Traps were placed at the understory and canopy level to compare the effect of trap height on beetle collections. Traps placed in the canopy were installed using a “Big Shot” line launcher, which launches a weighted bag, tied to a rope, over a branch. The trap is then tied to the rope and suspended in the canopy. Understory traps were hung from low hanging branches.
The traps are regularly checked and the beetles identified to species. No non-native species have been collected in this study, thus far. The results of this study will help guide forest health specialist in detecting non-native beetles and monitoring native populations of longhorned beetles in a coastal rainforest.
Find more photos and information on the Longhorned beetles collected in Juneau, AK by visiting our Alaska Region Flickr page.
By Elizabeth E. Graham, Ph.D., Entomologist, Alaska Region State & Private Forestry, Forest Health Protection