Sprays, nets and candles: how a treated surface compares

Mosquitoes on a summer evening, ants in the kitchen, bed bugs after a trip. People have tried a long list of answers: sprays, traps, nets, candles and coils. Each works up to a point, and each comes with a catch.

Insecticide sprays

Sprays based on pyrethroids and similar insecticides act on the insect's nervous system. They work on what they reach, on the day. The catches are well known.

• Repetition: a spray deals with today's insects, so it has to be repeated.
• Resistance: insects exposed to the same insecticides again and again become less sensitive to them. Resistance to permethrin and other pyrethroids is documented in several mosquito species.
• Side effects: many insecticides also affect insects you want to keep, such as bees, and permethrin is dangerous for cats and for aquatic life.
• Smell and residue: many sprays leave an odour or a film on surfaces.

Nets, screens and covering up

Physical barriers are among the oldest methods, and good ones. Their limits are practical. A net only helps while you are under it, screens and nets tear, long sleeves are uncomfortable in the heat, and none of them does anything about insects that crawl into furniture, luggage and bedding.

Candles and coils

Citronella candles and coils work in a small circle around them, while they burn, when there is no wind. They need watching, and the smoke can irritate eyes and airways, especially indoors or around people with asthma.

A treated surface

Repeltec works on a different principle.

It goes on the places insects travel and rest, such as frames, edges, furniture and textiles, rather than into the air or onto skin. It needs no flame and gives off no smoke, and the formulation is water-based.

Using them together

This is not one method replacing all the others. Screens on the windows, a net over the bed where it is needed, standing water emptied, gaps sealed, and a treated edge where insects come in: the combination is what works.