Japanese beetle trap.
A pheromone trap is an insect trap that gives off pheromones (chemical substances similar to hormones) used to attract the insect being controlled. Pheromones can mimic the smell of an insect’s favorite food (fruit, flower, etc.), but more often the pheromones used in traps are a bit more libidinous than that: they imitate insect sex pheromones, normally that of the female pest. Thus, the males travel from afar, attracted by the smell of what they think is an attractive young virgin. Once they enter the trap, though, the males can’t get out and therefore can’t impregnate any females, leading to, at least in theory, a drop in the local insect population.
To make the trap even more effective, it is usually colored yellow, blue, green, or purple, depending on the favorite color of the insect.
A Trap for Each Pest
Pheromone traps are very specific: each is designed to attract a particular type of pest. There is therefore no danger they will trap beneficial insects. You therefore have to purchase a different trap for each insect you’re trying to control.
The possibilities for pheromone traps are almost limitless, but for the moment, only one is widely available in most areas in North America: the Japanese beetle trap. It is, of course, designed to repress Japanese beetles (Popillia japonica). It actually contains two pheromones: a sex pheromone that mimics the smell of the female Japanese beetle, which therefore attracts male beetles, and another that gives off a floral scent that attracts both sexes.
Because of the floral pheromone, the Japanese beetle trap can also be used to catch rose chafers (Macrodactylus subspinosus), a Japanese beetle relative. However, there is also a specific trap for rose chafers that only gives off the floral scent. It seems to be more difficult to find in local stores.
Also on the market are apple maggot traps, usually shaped like a red ball that resembles a mature apple. Some models include contain a pheromone: a fruit essence that attracts the apple maggot (Rhagoletis pomonella).
Trap for emerald ash beetles.
While the home gardener has only a limited choice of traps, farmers and foresters have access to a wide range of pheromone traps for just as wide a range of crop pests. You may, for example notice, traps placed in ash trees (Fraxinus spp.) In a park in your municipality. With this trap, authorities try to determine whether the dreaded emerald ash borer (Agrilus planipennis) is lurking in the area.
The Downside of Pheromone Traps
When the trap is too full, the insects can’t enter.
But there is one major flaw with pheromone traps. While they do indeed attract insect pests to the area, but the latter don’t all enter the trap! Sometimes they simply miss the trap because the scent is carried elsewhere by the wind. Or the trap may already be full.
Whatever the reason, the result is that pheromone traps often actually don’t reduce insect damage. The insects that didn’t enter the trap, now starving, flock to the nearest available food plant and start to chow down. This is sadly the situation with Japanese beetle traps: they do catch beetles and lots of them, but they also draw more beetles into the sector, so instead of the damage being reduced, it is often worse.
The joke usually proffered is to buy traps and offer them to your neighbors so the beetles will go to their garden instead of yours! That really would work, but I suspect your neighbours would be a bit upset when they find out!
Effective Use of a Japanese Beetle Trap
You can however use the trap effectively if you follow three simple rules:
- Place Japanese beetle traps well away from the plants they eat (at least 50 feet/15 m). For example, on a pole in the middle of a lawn.
- Empty the traps regularly. Sometimes you have do it every day, otherwise they fill up and new insects can’t get in. Just dump the pests into a bucket of soapy water.
- Collect beetles daily from nearby vegetation, preferably early in the morning when they are not very active, using a hand vacuum (empty the vacuum afterwards over a bucket of soapy water). Children, especially, seem to find collecting beetles with a vacuum a lot of fun.
If you start using this combined method of insect control at the beginning of the season, you can make serious inroads into reducing the infestation.