Susceptibilities of the Green Rice Leafhopper and the Smaller Brown Planthopper to Insecticides Determined by Means of Micro-topical Application

Abstract

The susceptibilities to insecticides of the green rice leafhopper (Nephotettix cincticeps UHLER) and the smaller brown planthopper (Delphacodes striatella FALLEN) were determined by the microtopical application method. The method used here was modified from that of KERR described on the microdevice for application of toxicants by microburett. The main modifications were as follows. a) The solution of toxicants was driven out by means of low pressure of air supplied from a pulsating type pump connected with the microburett, b) ethyl alcohol was used as the solvent, and c) the volume of toxicants applied to each insect was measured by the scale engraved on the microburett, therefore all operations were carried out without using the darkroom.
Though there are some problems to be improved such as the measurement of variation in the volume of toxicants applied to each insect and the manipulation of test insects especially of the male of the smaller brown planthopper, this method was useful for the authors' purpose.
The seasonal fluctuations of susceptibility of the green rice leafhopper to malathion, DDT and carbaryl were determined and it seemed that any difference was not recognized in the susceptibilities among the hibernated, first and fourth generations.
Distinct differences were recognized between the green rice leafhopper and the smaller brown planthopper, in both the order of eight insecticides tested and their lethal doses.
With both species, the susceptibility of female adult was lower than that of male adult even in lethal dose of toxicant per body weight.
In comparison with the data reported by KOJIMA et al., it was considered that the green rice leafhopper collected in Chikugo city might be different in the susceptibilities to some of the tested insecticides from that of collected in Odawara city.