Commercial Fisheries News - April 2002

Lobsters and Insecticides

Many towns in Maine have been wrestling with the issue of whether to participate in aerial spraying of the insecticide diflubenzuron to control browntail moths, which, at certain developmental stages, can cause rashes and respiratory problems for some people.

The spraying question is of particular concern to lobstermen because no poison is so specific that it will kill or impair only its intended victim. In the case of diflubenzuron, a chemical known by the name Dimilin(TM), a registered trademark of Uniroyal Chemical Company Inc., the innocent bystanders include all aquatic, marine, and terrestrial arthropods, including shrimps, crabs, and lobsters.

Diflubenzuron is a "chitin synthesis inhibitor." It works by preventing browntail moth caterpillars from manufacturing a healthy exoskeleton. When the caterpillars emerge from their tents in late April and early May, they feed on new leaves. If the leaves are coated with diflubenzuron, some caterpillars will fail to metamorphose into adults.

For lobsters, diflubenzuron potentially threatens the manufacturing of the new shell. Hard-shelled lobsters exposed to low concentrations of the chemical will probably survive. And lobsters having a new shell underneath the old may molt successfully in spite of exposure. However, the next time an exposed lobster tries to make a new shell, it may run into problems.

Unfortunately, the experiments that would confirm the delayed effects of diflubenzuron have not been carried out. To assess the impacts of diflubenzuron on lobsters, the animals must be followed through at least two molting events. For adult lobsters, such experiments would take years. For juveniles, the experiments could be done in several months.

One could argue that the spraying will be done before the lobsters return to nearshore waters. But there are at least two problems with this argument. First, juvenile lobsters are along shore now. Second, diflubenzuron can persist in the environment for several months.

Browntail moths are not hidden opponents. Their conspicuous tents can be removed from small trees and shrubs by simple pruning. Physical removal of the tents is a much more direct strategy to combat the infestation. This removal strategy focuses on the problem and prevents unintentional killing of harmless and beneficial species.

Ask the Lobster Doc