Sequential Sampling for Thrips tabaci on Onions

Abstract

A binomial sequential sampling procedure based on the presence of 5 or more individuals of Thrips tabaci/onion was as precise as Iwao's sequential sampling method requiring counting of all thrips present. Acceptance boundaries were calculated for economic thresholds of 0.9 and 2.2 thrips/leaf and validated in the field in Quebec with 0.01 to 32.33 thrips/leaf. For both procedures, the correct decision was reached >83% of the time by sampling 12-14 onions. Error rates were 4%, which is below the theoretical error levels of 10% used for the Iwao procedure and 5% for the binomial procedure. Binomial sampling was more time efficient than the Iwao method. Thrips in onion fields exhibited a contagious distribution.