Abstract
Weekly census of nymphs and adults of Leptogrossus australis was conducted over 2 years, from April 1981 to April 1983, in 5 plots grown with a wild host, Diplocyclos palmatus, in a southern locality of Okinawa Is. where the insects were collected. No insects were collected during the period from February to April, but through May to December both nymphs and adult bugs could be recovered. Two peaks of nymphal incidence were recorded in May to June and in October to November, respectively. A long interval with a lower density of nymphs lasted for about 4 months between the two peaks, presumably due to the marked decrease in the number of fruits associated with the drought in the hot summer. The typhoon that struck the area in the early and middle part of fall exerted an effect similar to that of the summer drought resulting in the disappearance of the later (second) peak of nymphal incidence as observed in 1981. Based on the total number of effective day-degrees estimated from the incubation experiments, the period during which the insects could not attack the wild host was approximately 1.8 times longer than that required for the completion of the egg and nymphal stages. This finding suggests that the migration of the adult bugs from the unsuitable wild hosts to cultivated hosts such as bitter cucumber and cucumber is likely to occur and that at least one generation. develops on the cultivated hosts between the two generation peaks on the wild host.
