Experiments conducted in Louisiana during 1961-62 indicate that effective control of the forest tent caterpillar, Malacosoma disstria Hubner, can be obtained by applying phosphamidon or Bidrin®, 3-hydroxy-N-N-dimethyl-cis-croton-amide dimethyl phosphate, at 1 lb and ¼ lb per acre, respectively. These insecticides were effective when applied with aircraft or high gallonage ground sprayers. There was no visible effect on crayfish, fish, or other wildlife species. Crayfish and fish fed caterpillars killed by these insecticides showed no apparent effects of poisoning. Both insecticides killed a wide spectrum of insect species though no sustained residual kill of nonphytophagous insects was observed. No phytotoxicity was observed on any plant in the treated area. Sarcophagid flies parasitized about 41% or the mature larvae and pupae in the vicinity of the experimental area in 1961.