Abstract
Considerable interest has developed in recent years as to the effects of nutritional changes in host plants agains insect infestation. Some workers reported that fertilizers influence the development of insects which are feeding on plants. In the rice stem borer, Chilo suppressalis WALKER, it has been observed that the greatest damage in the rice plant caused by the borer larva is frequently due to the increase of nitrogenous fertilizers applied to the crop. The more general use of nitrogenous fertilizers in the recent years may be an important factor in the serious damage of the rice plant caused by the larva. But there is seldom any experimental evidence to support such conclusions. Furthermore there is no information on the mode of the effect of the fertilizers on the insect fecundity.
The present experiments were undertaken, with nutritional physiology in our minds, in order to investigate exactly the growth of the larva which fed on the rice plants deficient in nitrogen, as compared with the growth on a diet of plants cultured in soil supplied with sufficient nitrogen. Two experiments were carried out, one of them is on the growth of the larvae fed on growing rice plants cultured in a greenhouse, and the other is on the growth of the larvae reared with sterilized rice stems in flasks under aseptic conditions.
The larvae fed on both rice stems were weighed individually after a rearing period. Some chemical compositions of the rice plant stems used for the rearing experiments were analysed to endorse the growth of the larvae.
The effects of the nitrogenous fertilizer have been found to be basically similar in both experiments. All the diets composed of the rice plant stems grown on low nitrogen soil had a marked effect on the growth of the rice stem borer larvae, significantly reducing larval weights as compared with the high nitrogen series. There is a close correlation between weights of larvae and nitrogen content of the rice stems. The superiority of the growth of the larva is largely due to the significantly high nitrogen content of the rice plants stems grown on high nitrogen soil.In the previous paper (ISHII and HIRANO, 1957), it has been reported that the growth of the larva reared with a synthetic food is faster on a protein rich medium than on a carbohydrate rich one. The results obtained from the present experiments agree with those of the previous experiments and show a rather high requirement of nitrogenous compounds for the larva.
