Insect Management

Pheromones

Monitoring with Pheromones

Insects send out chemical signals or pheromones that enable them to communicate with other members of their species. Usually the adult female produces these chemicals to attract males. Thus a particular pheromone attracts only adult males of one particular species. Synthetic pheromone lures are available for the adult moth stages of the black cutworm, tomato pinworm, beet armyworm, cabbage looper, diamond-back moth, variegated cutworm, potato tuberworm, corn earworm, and fall armyworm.

While pheromones can be sensed by adult males at low concentrations, the effectiveness of a trap can be lowered by rainfall, cool temperatures, and wind speed and direction. Lures are generally packaged in dispensers which contain a membrane to control the rate of release. Since they are damaged by heat, lures should not be exposed to sunlight or kept in vehicles or hot storage buildings. Pheromone lures are usually used to monitor rather than to control insect populations in vegetable crops. The presence or absence of a particular type of pest might indicate a need for additional sampling or the beginning or ending of spraying for the season. Determining whether a pest has reached an economic threshold depends on scouting for the damaging stages.

Control with Pheromones

Pheromone traps have been used with limited success to trap out certain pests in fruit trees. Traps must be placed over a wide area to be effective. Trapping out is most likely to succeed when the pest density is low initially and immigration into the pheromone treated area is minimal. Japanese beetle traps are often promoted as controlling adult populations but may actually increase damage to the plants closest to the traps. Beetles are attracted to the area but are not necessarily trapped because they can distinguish between the synthetic pheromone and prefer pheromone released by living insects.

Mating disruption with synthetic sex pheromones has been used for tomato pinworm and some pests of fruit and forest trees. As with pheromone trapping, to be effective, mating disruption requires large isolated treatment areas and low to medium pest populations. Another potential application for pheromones is to attract predators.

A new method of insect control now in the experimental stage is to attract adults to a trap where they are infected with a pathogen before exiting. Researchers in England have developed special traps that allow diamondback moths to enter the trap, pick up the fungal pathogen Zoophthora radicans and then exit the trap. The moth then carries the pathogen to the crop where it can infect both moth larvae and other adults.

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