Studies on the biology of lac insect, Laccifer lacca (Kerr) Targ.

The lac insect, Laccifer lacca (Kerr) Targ. , is one of the most valuable beneficial insects of China which occurs in Yunnan, Taiwan and Tibet. This paper deals with the result of biological studies carried out in Yunnan from 1955 to 1963. It may be summaried as follows.1. In the regions of its endemic distribution in Yunnan, lac insect occurs two generations a year. Jingdong is the northern boundary of its distribution and the two generations occurred in May-June and October-November respectively, while at southern regions it would breed earlier.2. The duration of developmental stages of different generation is influenced by the local climate and the condition of host plant. However, the life cycle of this insect in various regions of Yunnan seems consistent in time if it has long been adapted to the climatic changes of these regions as well as to the ecophysiological characteristics of the host plants.3. The larvae have regular habit of swarming. The abundance of swarming larvae, the critical moment and duration of swarming are obviously influenced by the climatic condition, the "ripeness" in development of the insect and the seasonal generation.4. The dispersing capacity of larvae is rather limited, only a distance about 5 metres can be attained by the newly hatched larvae in their cruising. After settling the larvae are unable to move again. The unsettled larvae can live only for 4-6 days in the first generation (summer generation) and for 6-8 days in the second generation (overwintering generation). Therefore, in order to increase lac production, artificial inoculation and care of brood-lac is quite neccessary.5. The larvae display the behavior of crowding and host selection in colonization. They prefer 2-3 years old shoots located in the high position or in the middle of the crown of dominant host plants to settle, where the temperature, light, ventilation and bark surface are suitable. On the whole, the enviromental condition as described above would provide ideal habitat for the young larvae of this insect to settle and develop. Accordingly, in addition to the selection of good host plants, prunning and care in management, we should pay also attention to host plant nursing.6. The lac insect would secret lac, wax and honey dew during its development. They are not only the signals of life process of the insect but also the qualitative criteria of the living condition. In general, the quantity of lac, wax and honey dew secretion indicates whether growth and development are carried out in optimal condition. 7.The amount of lac secretion is greater in the first generation than in the second generation, the total amount of lac secreted by a single female larva on Eriolaena spectabi-lis (DC.) Planchon ex Mast at Jingdong during the first generation is estimated to be 0.54 mg in average and in the second generation 0.28 mg, and the total amount of lac secreted by a single female adult ranges from 16.3 to 25.7 mg in the first generation and from 7.4 to 10.4 mg in the second generation.8. The reproductive potential of lac insect is relatively high, and a female of the first generation lays 224-307 eggs while that of the second generation 160-240 eggs.9. The sex ratio of lac insect is variable in different generations. Generally, females are predominant in both generations, 75-80% in the first generation and 50-78% in the second generation.10. Tn irs endemic regions in Yunnan the lac insect has larger amount of iac secretion and higher reproductive potential as well as more females in sex ratio in the summer generation than in the overwinter generation, Therefore, it will be very beneficial to adopt the experience on lac production from the masses, cultivate and harvest lac twice annually, and to lay more stress upon the summer generation (cutivation in summer and collection in autumn).