Reasons for the large day-to-day variations in the numbers of nymphs and adults of the Coreid bug, Pseudotheraptus wayi Brown, taken in the crowns of coconut palms in Zanzibar by the searching technique over a period of six years were investigated in 1957–58. Data are given showing the results of searches (each occupying less than 20 minutes) carried out on two young palms at different times of day and night and in different weather conditions. For each successive 2-hour period between 6.0 a.m. and 2.0 p.m. (in the case of nymphs) or 4.0 p.m. (in the case of adults) the proportion of searches in which P. wayi was observed was significantly greater on dull days than on bright, sunny days, but there were no such differences that were significant in respect of any other 2-hour period for which comparisons could be made, except 4.0 to 6.0 p.m., when the proportion of searches disclosing nymphs was greater on bright days. During the hours of bright sunlight, the adults and nymphs hide in crevices and in the debris found in the leaf axils, but both remain in the open from dusk to dawn. During heavy rain they take shelter in dry crevices and niches.

It is pointed out that this behaviour must be taken into consideration if the searching technique is used to assess the result of an application of insecticide.