The Wogs Are

Getting Used To It

NSECT resistance to DDT and other insecticides seriously complicates the fight against lalaria, yellow-fever, typhus and ther diseases transmitted by in lets. So far, 50 species of insects -including flies, mosquitoes, roaches, ed-bugs, lice and ticks —are re orted as being resistant in various arts of the world to one or more [ the new insecticides.

The situation has recently been in Geneva by an expert jmmittee of the World Health rganisation (WHO), as the culmin tion of two years of research.

Tests of mosquito resistance that ere developed through the efforts f the Committee are being applied i many parts of the world, with le result that WHO has today a jasonably complete picture of hich malaria mosquitoes, where, re how resistant to what insecti ide.

This knowledge is vital to the suc ess of the world eradication of lalaria undertaken by WHO.

Tests for resistance in other in- Bcts, including bed-bugs and fleas, r ere defined at the session.

The Committee made detailed on insect control lethods in the light of the latest isecticide research and field ex erie n c e. The recommendations over not only mosquitoes but other isects of public-health importance, s well as pests such as rats, mice nd scorpions. Campaigns against

scorpions have been undertaken, notably in Brazil.

The experts have concentrated on two kinds of insect resistance: Physiological resistance, by which populations of insects, over a num ber of generations, acquire increased tolerance for the insecticides; and hehaviouristic resistance, by which insect populations change their habits so as to avoid contact with the insecticide.

Both kinds of resistance are hereditary. Irritability of mosquitoes when resting on surfaces sprayed with, for example, DDT, is one of the points on which the Committee is now arranging further investiga tions. The time mosquitoes spend between alighting and flying off again may, in successive genera tions, become shorter and permit the insects to survive. Mosquitoes that are not irritated sufficiently by

the poison absorb a lethal dose and die, while the others go on breed ing.

The WHO Expert Committee on Insecticides also investigated the efficiency of insect control methods in aircraft. At present, methods vary from country to country, and there is no internationally accepted way of testing their effectiveness.

In the past, this has led to diffi culties and passenger delays.

One of the dangers to be guarded against here, is that of mosquitoes with yellow fever reaching countries in Asia where the disease does not exist, but where mosquitoes that can transmit it, do. Here again, it is insect resistance which complicates matters.

This world brains trust of the insect war was chaired by Dr. J. R.

Busvine, of the London School of Hygiene and Tropical Medicine.