Laboratory and field studies were made to investigate the toxicity, mode of action, and persistence of technical DDT and y BHC when applied to the cashew in Sri Lanka to control the mirid bug, Helopehis antonii Sign. The insecticides were tested at concentrations previously used in field trials.
Mirid nymphs were placed on the nuts and the rate of knockdown and mortality after exposure for a test period was recorded. These tests showed that BHC had a higher toxicity and acted more quickly than DDT. BHC had a powerful and transient fumigant action over DDT, which had no fumigant effect at all. Persistence was studied by treating cashew leaves and nuts growing under natural conditions and then testing the residual deposit at intervals.
It was concluded that BHC would be more effective than DDT when treating mature cashews because, in addition to its higher toxicity and quicker action, its fumigant action would compensate for incomplete coverage by low-volume spraying.
