Research On Evaluation Of The Resistance For Mainly Cultivated Rice Varieties To Cnaphaocrocis Medinalis (Guenee) And The Control Action Threshold In Chongqing

Focus on the control of the two main migratory pests, Cnaphalocrocis medinalis (Guenee) in the rice growing areas of Chongqing, following researches were carried out:first, studied the occurrence rules of C. medinalis in fields; second, evaluated the resistance of the eight mainly cultivated rice varieties in Chongqing to C. medinalis and the influence of the eight rice varieties on the growth and reproduction of C. medinalis; third, studied the taxis of C. medinalis to eight rice varieties; the last, evaluated the tolerance and compensation capability of Gangyou3to C. medinalis and studied the control action threshold of C. medinalis’in Chongqing.1. The resistance of the eight mainly cultivated rice varieties to C medinalis and S. furciferaThe occurrence peaks of C. medinalis and in the rice growing areas of Chongqing in2011were booting stage to heading stage in mid to late July. The resistances to C. medinalis were, Lingyou1> Qyou18> Gangyou3. Jinyou18and Hongyou2009were highly susceptible to C. medinalis. Evaluated with yield loss in fields, the Gangyou3and Lingyou1showed high resistance and tolerance to C. medinalis, while Jinyou18and Hongyou2009showed low resistance and tolerance.2. The feeding and oviposition selectivity of C， medinalis to different rice varietiesSignificant differences of the feeding selectivity and oviposition selectivity of C. medinalis to different rice varieties were observed. The results of correlation analysis showed that the damage ratings of different rice varieties were positively related with oviposition selectivity of the female adults (R2=0.7832) and feeding selectivity of primary larvae (R2=0.7082). The oviposition and feeding selectivity were positively related with the chlorophyll content of rice leaf, wile were lowly related with length of the rice leaf. Width of the rice leaf was lowly related with the oviposition selectivity, but was highly related with feeding selectivity of primary larvae (R2=0.7439).3. The influence of different rice varieties on the growth and reproduction of C. medinalisSignificant differences of the larvae survival rate, pupation rate, eclosion rate, developmental duration of different stage, weight of pupa, female-male ratio and oviposition amount per female of C. medinalis feeding on eight different rice varieties were observed. The developmental durations of larvae feeding on TNI and Hongyou1were significantly shorter than that of Lingyou1, Gangyou3and Qyou18, and the developmental duration of Lingyou1was significantly longer than others. The pupa weight of C. medinalis feeding on Qyou18was significantly lower than others, and the weight of pupa feeding on Liyou1and Gangyou3were significantly lower than that of TNI. The pre-oviposition period of female feeding on TNI, Zhunliangyou893, Hongyou2009and Gangyou3were significantly shorter than that of Kyou88, Qyou18and Lingyou1. The oviposition peviod of the C. medinalis feeding on Hongyou2009was2.90d, and was significantly longer than others. The most oviposition amount was94.8per female, feeding on TNI, and the least was27.13per female, feeding on Lingyou1. The damage ratings of rice were significantly positively related with pupation rate, adult longevity, weight of pupa, oviposition period, lowly related with eclosion rate, female-male ratio, significantly negatively related with larvae duration and pupa duration, and partly related with pre-oviposition period.4. The compensation ability of the rice in different growth period for the damage of C medinalis and the control action threshold of C. medinalisThe experiments of cutting leaves for simulating C. medinalis damage did not only influence the growth and yield of the rice in tillering stage, but also increase the yield when the leaves were cut off10%to20%. In jointing stage, implement of cutting leaf increased chlorophyll content significantly contrast to control. When40%leaves was cut off, the chlorophyll content increased significantly contrast to other treatments and the number of full grains per spike of rice decreased significantly. The yield of each treatment was not significantly difference with control in jointing period, and yield of treatment of10%leaves cutting off increased slightly. The ratio of scurf grain increased significantly and yield decreased more than10%under the treatment of30%leaves cutting off in latter booting stage. When50%leaves were cutting off, the number of full grains and weight of per thousand grains decreased significantly, and the damage of yield reached up to16.86%. Model based on ratio of leaves cutting off, damage rating and yield damage per667m2and another model based on population density, ratio of roll leaf were constructed. The control action threshold of C. medinalis was evaluated through last two models, based on damage ratio and damage rating of rice leaves, respectively. The control action threshold based on damage ratio were:8.47,6.71,2.5 individuals per hill in tillering stage, jointing stage and later booting stage, respectively. The control action threshold based on damage rating were:10.7,9.42,3.43in tillering stage, jointing stage and later booting stage, respectively.