This editorial monograph explores the advances and pitfalls of the common forms of purposeful sampling. Purposeful sampling is a common research design in qualitative research.

The population of coffee stemborers (Coleoptera: Cerambycidae) was estimated at six sites in south-west China using two capture-recapture models. Two sampling methods (simple and systematic random sampling), each at three sampling intensities (10, 20 and 30%) were employed for two-time capture attempts from which the capture-recapture estimates were calculated. Estimates from the models were compared with that of census data from the fields. When sampling intensity was 20%, satisfactory levels of accuracy were obtained using the two models. The level of accuracy of the estimates increased as damage rate and mean density of the insect increased. Accuracy was also increased with increasing the sampling intensity, when damage rate and density of stemborers in the plots were low.

Glossina pallidipes was sampled using biconical traps with stationary and revolving attachments in the form of blue and white flat screens. A modified biconical trap with attachment of four black strips captured the highest number of both female and male G. pallidipes Austen. However, all the stationary traps under-sampled teneral and young tsetse in post-teneral category. Biconical trap attached to a revolving component making 20 rev/min gave the best representative sample with regard to age category of females. Screens making faster revolutions resulted in larger proportions of males and hardly any old females. Flies that visited the trap with revolving screens were non-hungry, and probably mate-seeking. Those in stationary traps were mostly hungry and probably seeking blood meal.

Assessments were made of the applicability of various methods of monitoring tsetse populations for control projects in Niger and Mozambique. Biconical traps proved most effective for sampling G. tachinoides in riparian habitats of Niger, and vehicle patrols for G. morsitans morsitans in savannah woodland of Mozambique. Comparisons are drawn between the various methods in terms of species, sex and physiological composition of catch, patterns of diel activity, and detection of fly concentrations.