Effects on Wildlife of DDT Used for Control of Dutch Elm Disease

Abstract

Dutch elm disease, the causal agent of which is a fungus, Ceratostomella ulmi, is spread from tree to tree by certain bark beetles of the family Scolytidae. In eastern United States two important carriers are the native elm bark beetle (Hylurgopinus rufipes) and the smaller European elm bark beetle (Scolytus multistriatus). In the area of this study the latter is of greater importance. Control of the disease involves control of the beetle vectors which introduce spores of the fungus at the time of feeding. Spraying programs are based on the application of sufficient DDT to elm trees to kill the bark beetles before feeding takes place. Since adult beetles emerge and fly to new trees during several spring and summer months, it is necessary to make two applications of spray in order to provide residual amounts during this period. The first is put on before the leaves are developed in the spring and the residual DDT is presumed to remain effective until the time of the second application in July. Preliminary investigations by the Bureau of Entomology and Plant Quarantine indicated that this procedure was an effective means of safeguarding valuable shade elms. However, frequent reports of bird mortality were received and it appeared advisable to review the program in terms of its effect on songbirds and other wildlife. This report summarizes results of the first summer's work on the problem. While the information was obtained from investigations in Princeton, New Jersey, the results would appear to be applicable to the Dutch elm disease problem as it exists elsewhere in the nation and