ABSTRACT
Sampling is the basic requirement for estimating the numbers of an insect within a crop, varying with weather conditions, cultural practices, the activities of its natural enemies and dispersal and for assessing the effects of various control measures. Sampling may concentrate on adults of Bemisia tabaci or the last two nymphal instars including the so-called 'pupae' or red-eyed nymphs. Adult whiteflies are characteristically attracted to yellow surfaces. Yellow sticky traps have become a major tool in monitoring the adult population of B. tabaci. Various, trapping surfaces such as yellow plastic sheets, plates or Petri dishes have been used, after coating with some sticky substance, either grease, tanglefoot or other diluted adhesive. Sampling the sedentary immature stages gives more reliable estimates of the absolute population density and detailed work has been done by R. von Arx et al. and B. Ohnesorge and G. Rapp.
