Population density of the citrus red mite, P U I I O I~C~I I I Scirri (McGregor), in Japanese pear orchards remained low until mid-August, even after inoculation of pear leaves with a considerable number of adult female P. ciii-i from May onwards. This raised the possibility that pear leaves contain a natural compound that suppresses an increase of P. ciiri populations. The rate of development from larva to adult was significantly lower on leaves collected in July than on leaves collected earlier or later, in several years. The population suppression was caused by molting deterrent activity and ovicidal activity, according to our close observation in the laboratory. To clarify whether a natural pear compound caused this molting deterrence, a methanol crude extract of pear leaves was isolated and added to a newly developed artificial diet, consisting of sodium caseinate, sucrose, levulose, glucose and inositol. The compound extracted from pear leaves resulted in the molting deterrence as observed on pear leaves. Based on infrared and NMR spectral analysis, the compound extracted from pear leaves closely resembled the synthetic acaricide hexythiazox. Furthermore, the LC50 values of the compound extracted from pear leaves for ovicidal activity of P. citri eggs and for deterrence of molting to protonymphs were similar to those of hexythiazox. These results strongly suggest that the molting deterrent extracted from pear leaves was in fact hexythiazox, an acaricide in use on pear trees, rather than a natural product. This suggestion becomes even stronger, considering that the molting deterrence was observed in a hexythiazox-spray year, but not in a non-spray year.

The purpose of this study was to investigate the effects of calcium carbonate and saccharides on the feeding behavior of newly hatched larvae of the silkworm, Bombyx mori L. Japanese strains, "Hi", "KAI", "Ryo" and "Yo", and Chinese strains, "Kai", "Bono", "Kenpaku" and "Tsukuba", were used for the experiments. Calcium carbonate (CaCO 3) and sucrose were added to the basal diet, consisting of cellulose powder, agar and distilled water. This was fed to the larvae immediately after they hatched. It was found that the feeding of any variety of silkworm was improved by the synergetic effects of CaCO 3 and sucrose. The amount of feeding for "Kai" and "Bono", however, were notably less than those of the other varieties. Next, diets containing CaCO 3 and two kinds of saccharides were fed to both the "Kai" and "Bono". The amount of diet consumed by "Kai" and "Bono" remarkably increased when CaCO 3 was used together with sucrose and myo-inositol, and CaCO 3 together with glucose and myo-inositol, respectively. The above results indicated that CaCO 3 combined with sucrose or other saccharides synergistically stimulated larval appetite. Also it was found that CaCO 3 could restrict larval movement to the area immediately surrounding the diet.