Improving IPM decisions for the management of diamondback moth on cabbages using sequential sampling plan

A sequential sampling plan, based on the negative binomial distribution of the insect, was developed for use in the IPM of diamondback moth (DBM) (Plutella xylostella L.) in Malaysia. The value of the common k (=1.84) was calculated from weekly sampling of 60 plants selected randomly from cabbages grown without the use of insecticides. Two sets of sequential sampling lines, representing two action thresholds (7 and 14 DBM larvae per plant, respectively) for two different stages of the crop age (< 1 month and > 1 month respectively) were formulated: d0 = 5.26 n 15.14, d1 = 5.26 n + 15.14 and d0 = 10.61n 6.68, d1 = 10.61n + 6.68, respectively, where 0 = no treatment required and 1 = insecticide application required; n= number of samples taken, a and b (both are probabilities of error) = 0.1. An appraisal of the plan using historical data on three treatments (IPM, prophylatic insecticide application and ecological control) indicated that if treatment is required, it could be detected at the 5th sample, thus making a saving up to 75% of the sampling cost and 60% of insecticide and labour costs.