THE BIOLOGY OF THYSANOPTERA, WITH REFERENCE TO THE COTTON PLANT

Abstract

Summary In several previous papers on Thysanoptera it has been shown that the condition or type of soil may have some influence on the infestation of a plant by thrips. Experiments were carried out to determine the effect of different types of soil on the infestation of the cotton plant by Thrips tabaci. The types of soil used in the experiments were a heavy clay soil and a light soil with less than 15 per cent, of clay, about fifty pots being filled with each type. Each block of fifty plants was divided into two and the soil in one half was tilled while in the other it was left undisturbed. It was found that the plants in the block with unfilled clay soil were least infested by T. tabaci, while the plants in the block with light, tilled soil were the most highly infested. The average infestation of the two blocks with light soil was slightly higher than the average infestation of the clay soil blocks, in spite of the fact that at the beginning of the season the former blocks of plants and the thrips on them suffered severely from a sudden great rise in temperature. In both types of soil the block with tilled soil was more highly infested than the other block. It appears from these experiments that light soil is more favourable to the multiplication of soil pupating species of thrips than an easily eaking, clay soil and that tilling the soil increases the infestation by these insects.