Shoziro Ishii

GROWTH RESPONSES OF LARVAE OF THE RICE STEM BORER TO RICE PLANTS TREATED WITH 2,4-D

Growth response of rice stem borer larvae to rice plants treated with 2,4‐D was investigated. In greenhouse rearing experiments, growth of the larvae was improved when they fed on 2,4‐D treated plants. In aseptic rearing experiments, the larvae also grew better on stems of rice plants treated during growth with 2,4‐D than on untreated stems. On the other hand, larval growth was not improved by addition of 2,4‐D to a diet of sterilized rice stems. The nitrogen content of the 2,4‐D treated plant is higher than that of the untreated plant. Because of the importance of nitrogenous compounds for larval growth, the improved growth on 2,4‐D treated plants was apparently caused by the increased nitrogen content of the plants, and not as a direct effect of 2,4‐D itself.

UTILIZATION OF DIETARY CARBOHYDRATES AND NITROGEN BY RICE STEM BORER LARVAE, UNDER AXENIC CONDITIONS

Larvae of the rice stem borer utilize simple carbohydrates and protein in their food at rates as high as most other lepidopterous larvae. The larvae also utilize starch at an unexpectedly high rate, in view of early evidences that the starch‐hydrolyzing enzyme of the larval digestive tract is very weak and that the nutritive value of starch in synthetic food is very low. The results indicate that starch contained in the rice stem may be significant in the nutrition of the larvae in the field.