Diaspididae often have cryptic habits, so you need to examine plant material very closely in good light to find them. Most females settle away from direct sunlight; they are more often found on the undersides of leaves or on shaded twigs and branches (even under the epidermis) or (rarely) on roots. Unlike other scale insects that excrete honeydew, Diaspididae are not associated with sticky honeydew deposits or growths of sooty mould, and very few species are associated with ants.
To take a sample, collect pieces of infested plant material. Do not try to pick individual insects off the plant while they are alive, as you will damage them. Each sample should be labelled clearly with the host identity, locality, collector and date.
Samples should be kept in a well-ventilated, cool place (in paper or large polythene bags or sandwich boxes in an insulated box is ideal) for transport back to the laboratory. Avoid leaving samples in direct sunlight, as the heat may damage the scale covers and kill the insects.