Intensive and widespread use of certain organic insecticides for cotton pest control resulted in the rapid development of resistance to these chemicals. By 1958, 12 species of insects and spider mites were known to he resistant and 1 others were strongly suspected. Resistant boll weevils, Anthonomus grandis Boh., were more widespread than any other species and were found in 7 of the 11 states in which it occurs.

In most cases, resistance has developed only to the chlorinated hydrocarbons, but three species of spider mites are resistant to organophosphorus compounds and one other is strongly suspected.

Boll weevil resistance to chlorinated hydrocarbons was first recognized in Louisiana in l955, and is more widespread in that State than any other. Sixty-five percent or more of the total cotton acreage in the state is now infested with weevils showing varying levels of resistance. Annual reports of insecticides sold in Louisiana show that, in 1954, 98% of all insecticides used for boll weevil control were chlorinated hydrocarbons, but by 1958 they had dropped to 34% of the total. Organophosphorus insecticides were not available for boll weevil control until 1956, but accounted for 20% of the total that year and 55% each of the next 2 years.

On a short-range basis, cotton pest resistance is being handled satisfactorily by changing to alternate chemicals with different modes of action. However, if cotton pests develop resistance to alternate chemicals, then this cannot be the answer to the long-range problem.