Q. About a year ago, I began having trouble with silverfish in my upstairs condominium. Someone suggests they came in with the insulation. I hired an exterminator, who sprayed around the pipes and elsewhere in the apartment and attic, but in three weeks the silverfish were back. What would you do? A reader
A. Silverfish are often brought in with insulation and this is one reason why they are difficult to control. The insects feed on starches, wallpaper paste, book bindings, and sometimes even linen. Their population is cyclic and generally reaches a high number and consequent visibility in the summer months.
''Silverfish are most effectively treated by using an insecticide dust,'' says Dr. George Rambo of the National Pest Control Association in Dunn Loring, Va. ''The dust has to be applied in the attic, on walls, and at the baseboards.''
Dr. Rambo recommends having a reliable, experienced pest-control firm inspect the premises and discuss with you its control recommendations.
If you want to obtain more information on silverfish, get in touch with the nearest office of the cooperative extension service. New Jersey has an excellent staff at Rutgers University.
As in every business and profession, there are amateur as well as seasoned pest-control operators, not to mention varying degrees of integrity. Before finally choosing a pest-control firm, check it out with the Better Business Bureau, your bank, or local credit agency.
Assure yourself of the firm's competency before hiring it to do the work. Avoid oral contracts. One reasonable assurance of competency is to select a pest-control firm that is a member of the National Pest Control Association. The telephone number is (703) 573-8330.