The cumulative damage index method: a new method for evaluating the effectiveness of control measures for Plutella xylostella (Lepidoptera: Plutellidae)

Abstract

All previously and currently used methods for effectiveness evaluation of control measures for the diamondback moth (DBM) do not simultaneously take the actual damage and population size into consideration. Here, we propose a new method, the cumulative damage index method, in which the number of larvae and their amount of food consumption are simultaneously included in the calculation of the theoretical cumulative damage index (T) and actual cumulative damage index (A). Evaluation was based on the reduced degree of damage calculated according to indexes T and A. Based on the new method, the corrected effectiveness of the combined use of biological measures, chemical insecticides, Bacillus thuringiensis (Bt) and P. xylostella granulosis virus (PxGV) on DBM was 35.85, 2.37, 12.50 and 11.77% respectively. Under the action of natural factors, the Population Developmental Index (I) of DBM was 5.1 ± 1.4; under the integrated actions of natural factors and these four types of measure, index I of DBM was 0.34 ± 0.1, 6.1 ± 1.5, 2.1 ± 0.5 and 1.1 ± 0.3 respectively. The sole effectiveness of Trichogramma spp. when integrated with other natural factors, integrated biological measures and chemical insecticides was 21.43 ± 1.69%, 45.27 ± 4.09% and 20.68 ± 2.60% respectively. There was some difference between the effectiveness evaluated by the new method and index I, and the actual damage caused by DBM could be reflected well by index A. The new method is more scientifically appropriate and practical for effectiveness evaluation than existing methods. © 2014 Society of Chemical Industry.