INVESTIGATION ON THE LOCUS OF ACTION OF DDT IN FLIES (DROSOPHILA)

¹ Medical Division, Entomology Section, Edgewood Arsenal, Maryland

1. The larvae and adults of Drosophilla virilis were fatally poisoned by injecting a one per cent DDT emulsion into the abdominal cavity. The poison produced a typical pattern of symptoms.

2. The neuromuscular system of the wings and legs was apparently very sensitive to the poison, for they went into spasm long before the muscles of the abdominal wall. There was also a difference in sensitivity to the poison between the larva and adult, the larva being more resistant to the DDT emulsion.

3. Phenobarbital was found to affect the nervous system. Paralysis by phenobarbital was also produced in the absence of the central ganglia. This shows that the drug also affected the peripheral nerves. Muscles of larvae treated with phenobarbital responded to mechanical stimulation.

4. Since DDT produced no symptoms in animals treated with phenobarbital and since animals treated with DDT lost their DDT symptoms when injected with phenobarbital, it was shown that DDT acted on the nervous system. Moreover, body parts which had been isolated from the central nervous system and then treated with DDT stopped convulsing after phenobarbital administration. This shows that DDT affected the peripheral nerves.

5. The methods used do not allow one to determine what part of the peripheral nervous system might be affected. There are three possibilities. The poison might affect (1) the motor nerves leading to the periphery; (2) the myoneural junctions; (3) the peripheral nerve net. It is however still questionable whether such a nerve net exists in Drosophila.

6. The antagonistic effect of phenobarbital on DDT was clearly indicated by the fact that the spasm of the legs and wings in DDT-treated flies was partly relieved by treatment with phenobarbital.

7. The conception that only the nervous system is affected by DDT has been strengthened by the fact that larval organs (imaginal discs) which had been exposed to DDT for twenty hours grew and differentiated normally when transplanted into untreated larvae.