Evaluation of presence-absence sampling plans for the diamondback moth (Plutella xylostella) (Lepidoptera: Plutellidae).

Two sets of sequential presence-absence sampling plans for the management of diamondback moth (DBM) were developed and evaluated, one for the classification of levels of the proportions of plants infested with larvae and the other for the classification of levels of larval density. The action thresholds investigated were 0.15, 0.25, 0.35 and 0.45 for proportion-based sampling plans and 0.2, 0.4, 0.6 and 0.8 larvae/plant for density-based sampling plans. Under the proportion-based sampling plans, the expected correct decision rates were i 95% for 86-87% of all possible population levels and the expected average sample size was i 50 plants for 73-87% of all possible population levels. Re-sampling analyses showed average sample sizes of <40 plants in reaching the i 95% accuracy. For density-based sampling plans, an empirical proportiondensity model was first established. The resulting model was highly significant (P<0.001) and explained 97% of the total variation in the independent variable. Satisfactory performance (i 95% accuracy at i 50 plants sample size) of the density-based sampling plans can be expected when the true population density does not lie in the vicinity of the action threshold. In conclusion, the sequential binomial sampling plans presented here can be used effectively in the monitoring of DBM populations for decision making.