Study on biological and ecological characteristics of Ips subelongatus Motsch.
Ips subelongatus is a major borer pest in larch [Larix] plantations in China, where it has caused serious damage. The biological and ecological characteristics of the pest were studied in the laboratory and at 2 sites in the field (an infested 22-yr-old larch plantation in Lishu County, Jilin Province, and an infested 35-yr-old plantation in Hongxing, Dahailin, Heilongjiang Province) during 1992-94. The life cycle of the pest in Lishu County is described. The study results indicated that temperature was the main factor affecting the development of Ips subelongatus. The initial temperature for development of eggs, larvae, pupae and adults was 6.1, 8.0, 10.3 and 9.8°C, respectively. The completion of one generation needs, respectively, 48 days at a temperature of 18°C, 39 days at 20°C and 33 days at 22°C. The pest has a different number of generations in different areas because of different temperature regimes. In Jilin Province, it generally has 3 generations a year, except that some individuals have 2 generations. Natural enemies of the pest include Thanasimus substriatus, Tomicobia seitneri, Coeliodes sp. etc. The pest is normally a secondary invader of damaged or weakened trees, but can invade healthy trees during an outbreak period.