A systems model and computer simulation of the green rice leafhopper populations in control programmes

Summary A simulation model of the green rice leafhopper-spiders system was presented. The validity of this model for simulation purpose was tested by comparing the calculated values with observed ones (Fig. 4). The effectiveness of various control measures against leafhoppers was evaluated by computer simulations. The computer simulation demonstrated that the wrong use of selective insecticide, contrary to expectation, brought an increase in the pest density, i. e., that the egg densities of leafhoppers in the 2nd and 3rd generations are increased by the insecticidal application in February, while they are decreased by the July application (Table 2). To obtain satisfactory control by sterile-male release, 320,000 sterile-male per square kilometer should be released even in the combined use with insecticides (Fig. 5). The escape of leafhoppers from predation by spiders was demonstrated by the simulation. It is suggested that spiders are able to suppress the leafhopper populations at a low density when there is a very favorable balance between spiders and leafhoppers, and this condition may be realized by sophisticated use of selective insecticides (Fig. 6). Factors and/or processes which have to be involved in a more improved systems model are discussed. A part of this research was supported by science research fund from the Ministry of Education.