A new approach to the physiological host plant-parasite relationship — A technique in the field of applied entomology

Less than ten years ago research on the feeding physiology of mites and aphids was hardly developed. Since then there have been a number of investigations about the influence of changes in the chemical composition of the leaves on the population development of insects and mites. It has nevertheless not yet been possible to acquire a useful understanding of this particular problem. This is parry due to the great diversity of the methods applied and parry to the fact that the special food requirements of the majority of parasites are as yet unknown and those known vary greatly. A comparison of the results is therefore extremely difficult and hampers an evalution of the data obtained. Within the framework of the Dutch Study Group on Integrated Control of Pests, the authors have studied the influence of the host plant's physiological condition 2 on the population development of phytophagous insects and mites. By changing the ion-ratio of the nutrient solution on which the plants are grown, chemical changes in the leaves are induced and differences in population development of the parasites can be evaluated. The experiments were set up as balance studies, that is to say, the whole of nutrient solution together with the plants and parasites was arranged as a closed system for certain nutrient elements. The distribution of a certain element over the three components, viz. nutrient solution, plant and phytophagous organism, is influenced by the composition of the solution, the ion uptake capacity of the plant and the food uptake and population density of the parasite. As a closed system was being considered, the initial quantity of the testelement had to equal the sum of the quantities recovered from the three corn