Studies On The Important Natural Enemy Cassida Japana Baly Of The Field Weed Chenopodium Album L.

Chenopodium album L. is the cosmopolitan species. It belongs to a malignant type of weeds, Especially in northern spring wheat field. Chenopodium album grows quickly, and the capacity of absorption on N,P,K is high and powerful. It is the major weeds which impacts wheat growth. Chenopodium album. In nature, Cassida japana Baly only feed Chenopodium album, so it is likely to become important enemies in field weeds bio-control. At present, the study of Cassida japana is still less both at home and abroad. So we have studied the abiogenesis dynamic of the turtleback, biology and ecology, host-specificity, Feeding amount and control effect of Cassida japana Baly The main contents and conclusions are as follows:1. Cassida japana Baly has four generations per year in Yangzhou city of Jiangsu province and overwinters by adult in soil slit, stubble such as weeds or leaves, or withered bark nearby. Generally, the population of C. japana reaches its peak stage both late June and mid August. The standing high temperature and frequent heavy rain could lead to swiftly decline of population and the climate condition is the key factor to influence population dynamic2. We studied the influence of temperature on the development, survival and fecundity of Cassida japana Baly at 19, 22, 25, 28, 31, 34℃, and also built the life tables of experimental population of turtleback were studied at different temperatures. The results showed that fed on Chenopodium album L., the mean development times of the beetle were as follows: eggs, 3.50 days; larvae, 11.59 days; pre-pupae, 1.71 days; pupae, 3.74 days; adult, 11.50 days, and the whole generation, 32.04 days at 28℃in lab. The appropriate temperature range on growth and reproductive of Cassida japana is from 22℃to 31℃. The results showed that the maximal fecundity No. was observed as 546.2 per female at 28℃, the highest survival rate was 47.70% at 28℃, and the shortest duration of the whole generation was 27.43 days at 31℃. By linear regression method and the optimum seeking method to analyze the thermal threshold and the thermal sum, the results showed that the former method was better than the latter, and the thermal threshold for eggs to adults were 9.45, 9.85℃, and the thermal sum were 625.47,609.98 day-degrees, respectively. Ranging from 19℃to 34℃, the adult life of Cassida japana Baly shortened accompanying with the rise of temperature, and had a power relation with the temperature. The population trend index had a clear second-degree parabola relation with the temperature, and reached its peak at 25℃. After treated 72h at -5℃, egg mortality could reach 91.55%, so the egg of Cassida japana had a weak low-temperature characteristics of resistance. After treated 72h at -5℃, adult mortality reached 26.7%, at -11℃, most of the adults were dead after 72h, and at -14℃, all were dead after 24h. Egg and young larvae were not resistant of high temperature. At more than 38℃, the mortality rate increased significantly, and generation development of Cassida japana could not be completed The supper-cooling points of female and male adults in the pre-winter and mid-winter were - 11.57℃, - 10.04℃and - 16.87℃, -16.06℃respectively. The adult of Cassida japana could survive over the winter outside in Yangzhou.3 27 plant species from 16 families were used to test host specificity of Cassida japana. Non-choice and choice experiment showed that adult turtleback addicted to Chenopodium album L., fed a small amount of Amaranthus tricolor, Alternanthera philoxeroides, Alternanthera sessilis, but only completed its life cycle on Chenopodium album L.. Though the experiment of feeding amount and the capacity of hunger resistance, the result showed that the 3rd larvae of Cassida japana entered the age of overeating period, and the feeding amount of 1st,2ed, 3rd, 4th.and 5th instar were that 14.56 mm2,21.6 mm2,60.9 mm2,114.52 mm2,244.19 mm2, respectively. Compared the feeding amount of mated adults to that of no-mating adults, it showed that copulatory behavior stimulated feeding amount of male adults, and the feeding amount of female and male adults of no-mating and mated were that 75.93mm2, 50.24mm2, 69.96mm2 and 24.24mm2, respectively. The starvation resistance of male adults were stronger than female adults.4. At feasible climate condition, 3~7 pairs of Cassida japana Baly could completely defoliate a certain number of Chenopodium album L. within 2-4 weeks.