By Drew Carleton, Entomologist, Forest Management Branch, Department of Natural Resources, Government of New Brunswick
If you have been following the Healthy Forest Partnership website and our efforts to develop, test and monitor the effectiveness of an Early Intervention Strategy for spruce budworm, then you have likely heard our bloggers refer to pheromones. With all our chatter, you might be wondering what exactly a pheromone is and how we are using them. The answer to that is actually pretty straightforward, the real question is how and why we use them – that is what really takes some expertise!
Pheromones are chemicals produced and emitted by organisms (in this case the adult female budworm moth) that generate a response from other organisms of the same species. There are lots of different kinds of pheromones, some trigger attraction, other tell individuals to stay away, some can be used to warn of danger. The pheromone we are interested in for spruce budworm is used for mating attraction. These chemicals are produced by the female and stored in a special gland in her abdomen. When she is ready to mate, she releases the pheromone in the air as a signal to help potential mates in the area find her. The males detect this signal using their antennae and follow it to the source. Once mated, the female is ready to lay fertilized eggs, which will hatch and create the next generation of budworm.
The use of pheromones by insects has been well known for a long time. However, it takes highly specialized chemical ecologists to identify and then replicate the chemical make-up, configuration and concentrations found in the native pheromone. The goal is to create a synthesized version that can be used to generate the same response in the target insect. This process often takes many years, many thousands of insects, some very expensive sophisticated equipment and a fine tuned knowledge of what to look for in the chemical structure to create the right blend. When all the structures are identified properly and reconstructed through complex lab bioassays, the results speak for themselves, as the insects are drawn to the pheromone created in the lab.
Once a pheromone has been successfully reproduced in the lab, one of the first things we can do with it is create a lure. Lures come in numerous shapes and sizes (see image below) but across the board their function is to slowly release the pheromone into the surrounding air over a period of time.
The release rate and amount of time are dependent on a number of factors including temperature, humidity, volume of pheromone in the lure and the stability of the compounds that make up the pheromone.
Lures placed in traps and used in monitoring programs provide a release rate and the volume of pheromone needed to last the duration of the spruce budworm moth flight season. Collecting a number of moths from traps provides an indication of a population within a forested area.
In some situations pheromones can also be used for mass trapping. For this use, a stronger dose or a larger network of lures might be deployed. The third and most common use of pheromones in our Early Intervention Strategy project is to test their potential to cause mating disruption this reduces the size of the population by making it difficult for male spruce budworm moths to locate female moths during mating season. To do this, an entire region is treated with pheromone, drowning out the female’s pheromone signal. For this use, we do not use lures, instead we place the pheromone between small (1/32” X 3/32”) dry flakes that are dispersed form the air over forests using aircraft.
Please visit Dr. Peter Silk’s report to see how pheromones are being used in the early intervention strategy research project.