The seasonal changes in water content and fat content of olive psylla, Euphyllura olivina in the field were investigated in two successive years. The overwintering adults of olive psylla had more fat than spring and summer generation adults. There was a steady increase in % fat contents of females from mid-October to early January. The % fat of both sexes decreased sharply in May, June and July. There was a gradual reduction in % water content from mid-June to early October and then decreased steadily until early November. The % water in the overwintering adults ranged from 57.5 to 45% and became constant around 52.5% of live body weight in February and March. Seasonal changes in % water was positively related to population changes of olive psylla. The % water in olive psylla was negatively related to the fat content.
