Population Dynamics of Spider Mites Influenced by DDT2

Abstract

Tetranychus urticae Koeh and T. telarius (L.) exhibit a decided tendency to disperse from crowded colonies. If dense colonies are confined, longevity and oviposition by adults are reduced, and young have less success in maturing. Crowding does not affect hatchability of eggs. Treatment with DDT does not enhance dispersion except at high levels of dosage, and the high levels are toxic, especially to emhryonated eggs and larvae. Emulsified DDT is more toxic than DDT in wettable powder suspension. It is postulated that the outbreaks of spider mites resulting from DDT treatment of crops are the result mainly of: DDT causing dispersion indirectly through the removal of natural enemies, which in turn allows dense local populations to develop. This results in dispersion as a result of crowding, and with dispersion to predator-free surfaces, there follows an increase in the population to economically harmful levels. The terminology used for the species of Tetranychus follows that of Boudreaux and Dosse (1963).