EFFICIENCY OF VARIABLE-INTENSITY AND SEQUENTIAL SAMPLING FOR INSECT CONTROL DECISIONS IN COLE CROPS IN THE NETHERLANDS

A total of 24 commercial fields of cabbages and Brussels sprouts were sampled in a grid fashion with 20-25 equally spaced cells with four pl ants per cell. Using this data base of 80-100 plants, we conducted com puter stimulations to compare the treatment decisions that would be ma de for the major insect pests using published sequential sampling prog rams and a newly developed variable-intensity sampling program. Additi onally, we compared the number of samples required to make the decisio n. At low thresholds (10-20%) for both Lepidoptera and cabbage aphids, variable intensity-sampling required a smaller sample size and provid ed more reliable decisions, while at high thresholds (40-50%) sequenti al sampling provided more reliable decisions. In both procedures, the occurrence of incorrect decisions was minimal. The number of cases in which a decision would not be reached after a 40-plant sample was lowe r for variable-intensity sampling. Considering the number of samples r equired to make a correct decision and the greater need for reliable d ecisions at lower thresholds, variable-intensity sampling was superior to sequential sampling. Additionally, variable-intensity sampling has the advantage of requiring samples to be taken in a greater area of t he field and thus increases the probability of detecting localized inf estations. Although variable-intensity sampling was not designed to cl assify pest populations for treatment decisions but rather to achieve sampling precision around the population mean, our present studies ind icate that it can also be an effective method to aid in treatment deci sions.