Studies On The Population Characteristics Of Tetranychus Urticae Koch And Its Harming To Some Crops

Experiments were conducted to study the population characteristics of T. urticae Koch and its harming to some crops. The researching process included three facets as follows: analysis of the life tables, chlorophyll variation in the leaves of the host plants and competition with T. cinnabarinus (Boisduval).The life table of experimental population of T. urticae Koch was established at constant temperature of 25 C, illumination time of 16 hours one day and humidity of 50%.The result of the experiment indicated that the value of the innate capacity of increase was 0.2634, 0.1788, 0.2098, 0.2280, 0.1538 on kidney bean, cotton, apple, aubergine and capsicum respectively and the quantity of the offspring obviously increased. When the age distribution of experimental population was steady, the amounts of the immature age were 88.3335%, 85.3052%, 85.0386%, 87.3787% and 86.8404% on five host plants respectively and the amounts of the adults 11.6636%, 14.6946%, 15.0635, 12.6218% and 13.1598% correspondingly. The reaction time to the adverse environment causing 99% death rate of T. 'urticae Koch was less than 30 days on all the four host plants.The diversity of decrement of chlorophyll was distinct with the different densities of T. urticae Koch impacting the same host plants, and the leaves of host plants had the capability of compensating chlorophyll while the density of T. urticae Koch was comparatively low. The total decrement of chlorophyll was basically equal with the same density of T. urticae Koch impacting different hostplants with the diversity of everyday decrement of chlorophyll among different host plants being obvious. The diversity of chlorophyll decrement in different host plants impacted by T. urticae Koch of the same density was obviously distinct.T. urticae Koch had different preference for the four host plants. Inferring from the differences of innate capacity of increase and the diversity of decrement of chlorophyll among different host plants infested by T. urticae Koch, the kidney bean was the best food for T. urticae Koch, the aubergine the better and the cotton the worst among these four host plants.The capacity of competition was positive in relation to the the innate capacity of increase. Compared to T. cinnabarinus (Boisduval), The capacity of competition of T. urticae Koch was obviously higher for both single population and mixed population on the kidney bean, apple, aubergine and capsicum. But the result was opposite on the cotton. This indicated that the capacity of competition of T. urticae Koch was correlative to the host plant species.Above all, the experimental population parameters of T. urticae Koch on cotton was lower than other host plants. This predicted it was impossible that T. urticae Koch enter the cotton fields and harm the cotton seriously at present.