THE BIOLOGY OF THYSANOPTERA WITH REFERENCE TO THE COTTON PLANT

Investigations were made of the degree of infestation of plants grown in light soil and in clay soil sown at different dates. The plants sown late in the season in light soil were more affected by the thrips, the infestation being relatively high almost from the germination of the plant and causing death before the flowering stage was reached. On the blocks of plants in light soil sown earlier in the year the infestation was relatively low for a considerable period, and although, at the end of the season, the thrips became very numerous on these plants it was not until after the bolls had been formed, and in this case the practical damage was small.
The plants sown in clay soil at different dates did not show such a marked difference in the degree of infestation, and all were less infested by the insects than the corresponding blocks of plants in light soil. This corroborates the findings of previous experiments, namely, that plants grown in light soil are found to be more heavily infested by T. tabaci than plants grown under similar conditions in clay soil.
I should like to take this opportunity of thanking Prof. Dunkerly for his helpful criticism, Miss R. M. Smith and Mr I. Thomas for their assistance in making the counts, and Mr R. Stewart for his analysis of the soils used.