Abstract
In Akita, three kinds of insect were recognized to be the dominant pest on water shield. Polypedilumtigrinum injured young leaves of the plant, causing the quality of the goods to decline. Elophila interruptalis and Galerucella nipponensis might have a negative influence on the growth of the plant by injuring its floating leaves. The damage to the floating leaves of the plant by P. tigrinum was observed frequently from late May until the end of July, and the severe damage caused by the E. interruptalis and G. nipponensis from the beginning of June until the end of September.
