Miscellaneous : Abstracts of Ph . D . Dissertations Published in 1987 : Biological Studies on the Pine Needle Gall midge , Thecodiplosis japonensis ( Diptera : Cecidomyiidae ) and Its Parasites , Platygaster matsutama and Inostema seoulis ( Hymenoptera :

This paper deals with the fundamental biology of the pine needle gall midge, Thecodiplosis japonensis and its important parasites, Platygaster matsutama and Inostemma seoulis. This study was conducted at Nijino-Matsubara, Saga Prefecture, Japan, for three and a half years in order to establish control measures for the pine needle gall midge, which had been causing serious damage to pine forests in Korea. The results obtained are summarized as follows : 1. The pine needls gall midge, T. japonensis has 1 generation per year. The adults emerge from early May until mid-July, and females lay eggs on the developing needles. Newly hatched larvae immediately move down between the needles to feed at their bases, which subsequently cause the formation of a gall. Mature larvae begin leaving the galls and dropping to the soil in mid -November, and overwinter in the soil or litter. Overwintering larvae begin pupation in late March, and the adult midges emerge about 5 weeks later. 2. Adults are much observed at twilight on sunny days, but are not observed on rainy days. Mating and oviposition take place soon after emergence. Eggs are laid in masses 2 to 3 ㎜ from the tips of the developing needles. Peak oviposition occurs between 17:00 and 20:00. Individual adults survive only 1 to 2 days in the laboratory. 3. The sex ratio obtained from field emergence trap and sweeping samples was 46 : 54 and 28 : 72, respectively. That obtained from laboratory -rearing was 59 : 41. 4. The average number of ovarian eggs per newly -emerged virgin female was 140.16±2.94(186 females), and the average number of eggs laid in the field was 110 (66 females). The average number of eggs per egg-mass was 7.5, and usually only one egg-mass is found on a needle pair. 5. The egg stage lasted 5-7days under the weather conditions of late May in the field, and the hatching percentage was very high. Hatching larvae immediately entered the bases of developing needles. 6. There are 3 larval instars, all of which are spent inside the developing gall. The average body lengths of instars 1, 2, and 3 were 0.49㎜ (August 26), 1.37㎜ (September 20) and 2.30 ㎜ (November 9), respectively. The average number of larvae per gall was 5.50 in July and 4. 96 in November. There was a linear relationship between the number of larvae per gall and the length of a gall, but there was no correlation between the number of larvae per gall and the length of an infested-needle. Larval body length was inversely related to the number of larvae per gall. Full-grown larvae(3rd-instar) leave the galls and drop to the soil from mid-November through January. Larval dropping is greatly intensified following rain. The larvae overwinter beneath the trees from which they drop at depths of 2-5㎝ in the soil or litter, and they begin pupating in late March. The population density of hibernating larvae decreased remarkably after mid-April. 7. Overwintering larvae pupate in their hibernation sites in the soil from late March through mid-June. Pupation occurs in the cocoon formed just prior or in a state of exposure, depending upon soil conditions. The pupal stage lasted 24-31 days at a laboratory temperature of about 20℃. 8. The damage of pine needles by T. japonensis begins with the entrance of the larvae into the base of needles. The elongation of infested needles ceases in July, and in August the bases of they needles begin to enlarge. Thereafter, galls rapidly enlarge, and during September and October the inner tissues of galls are completely destroyed by the feeding of the larvae. In November, the infested needles, which are only about half as only as healthy ones, turn yellow and wither. Most larvae are induced to leave the galls at that time. 9. Both parasites have 1 generation per year. Platygaster matsutama adults emerge from early May to mid-June, whereas those of Inostemma seeulis emerge from late May to mid-July. Soon after emergence the parasites mate and oviposition follows immediately.