Studies on the Toxicity of insecticide Films. II.—Effect of Temperature on the Toxicity of DDT Films

Abstract

1. A series of exploratory experiments on the relationship between temperature and toxicity of DDT films to adults of Tribolium castaneum, and larvae of Plutella maculipennis, are described. The main conclusions with T. castaneum are:—(a) When the insects are continuously kept on the film at different temperatures there is a higher kill at higher temperatures.(b) When the insects are exposed to the film for about 24 hours at the same temperature and then kept away from it at different temperatures there is a higher kill at the lower temperature.(c) When the insects are kept on the film at different temperatures for about 24 hours and then kept away from the film for reaction at the same temperature, there is a higher kill in those kept on the film at the higher temperature.(a) and (b) above apply equally to larvae of P. maculipennis but (c) is reversed. The probable cause of this reversal appears to be the observed fact that at higher temperatures these larvae cover the film with much more silk thread and thus avoid contact to a greater extent than at lower temperatures.2. A review of literature, in the light of the conclusions arrived at, indicate that many of the observations made upon the temperature-toxicity relationship can be accounted for by the following generalisations:—(a) Insect resistance to poisons changes with temperature as do its other vital activities, increasing up to a critical degree and afterwards declining.(b) The amount of poison reaching the site of action in unit time also varies with the temperature, generally but not always, increasing with its rise. Insect activity, especially locomotor and respiratory, may play an important part in these effects.(c) The apparent effects of temperature on insecticidal action is the combination of these two factors, namely, resistance and pick-up.