Population dynamics of mosquito larvae overwintering in southern Japan

Abstract

An ecological study was made on the larval populations of mosquito overwintering in Kagoshima City, southern Japan. The purpose of this report is to show the mode of overwintering habits of several mosquito species from the view point of seasonal change in population size and larval age structure. 1) Larvae of Uranotaenia bimaculata, Aedes japonicus and Tripteroides bambusa survived winter season, and their population size increased during winter months with appearance of the younger larvae and reached to a maximum in January, February and April, respectively. The older larvae and pupae became dominant in spring months, when a considerable number of pupal exuviae was observed. These facts apparently indicate that eggs of these species hatch in the course of overwintering and that the first adult populations of the next year originate mainly from the newly hatched larvae. 2) Population size of Armigeres subalbatus diminished gradually from December to March. Through these months, only the fourth stage larvae were observed except in March, when a number of pupae appeared. The larval population became extinct in April and a small number of pupal exuviae remained. These indicate that the fourth stage larvae survive the coldest months and pupate in March and that adults emerge in spring months. 3) Population size of Culex pipiens s. l. diminished gradually from December to March. During these months, however, a number of the fourth stage larvae grew to pupae and a few pupal exuviae were observed. Early in April, population size reached to a maximum with appearance of the first stage larvae, which hatched from the egg masses newly laid in March. These indicate that most larvae and pupae become extinct during the coldest months, even if a few of the pupae emerge into adults. So, the first adult population must be originated from the newly hatched larvae. 4) None of Aedes albopictus larvae and pupae was observed in the coldest months. The first population of younger larvae started in March and older larvae became dominant in May, when a considerable number of pupae and pupal exuviae were observed. These show that this species can not survive the coldest months as larvae and that the first adult population originates from the newly hatched larvae.