Research On Capabilities Of High Temperature Resistance And Cold Tolerance Of Immature Instars In Changsha And Some Laws Of The Body Color Changes Of Beet Armyworm

Beet armyworm, Spodoptera exigua (Hubner), is one kind of worldwide agricultural pests. It has the trend of successive outbreak in recent years in China. Some important factors of outbreak of beet armyworm were analyzed with the actual situation of Changsha, while the capabilities of high temperature resistance, cold tolerance and overwintering of beet armyworm are studied. It considers that Beet armyworm has a strong temperature capability. It can complete the life cycle at 30℃and 35℃and the 1st instar larvae can survive 5 days in the continuous condition of 45℃. while a 5th instar larvae can live in the sustained high temperatures for two days. The supercooling point temperature of Beet armyworm larvae and pupae from low to high as follows:1st instar larvae (-19.12±0.26℃)< 2nd instar larvae (-18.05±0.26℃)< pupae (-16.83±0.26℃)< 3rd instar larvae (-16.09±0.26℃)< 4th instar larvae (-13.73±0.26℃)< 5th instar larvae (-8.70±0.26℃). In 5℃low temperature viability experiments,1 st and 2nd instars larvae survival time less than 30 days, and after 5℃low temperature treating for 30 days the pupae survival rate up to 46.7%. The low-temperature viability of pupa stronger than the larvae, and the beet armyworm pupae is the growth stage that has the strongest cold tolerance. Field overwintering test showed that beet armyworm is not able to overwinter in Changsha where it has a rainy winter. The outbreak of beet armyworm is the result of interaction of the various factors.Beet armyworm larvae have multivariant body colors with a complex body pattern. It is easily confused with other pests from the appearance, thus the effective treatment time is delayed and this result in the outbreak of the beet armyworm finally. Researching on changes of body color timely and accurate provides basis for the identification and prevention to reduce the outbreak of beet armyworm caused by human factors. In this study, through a large number of observation of beet armyworm larvae the body patterns are classified to provide information for Identification in the agricultural production. The dorsal pattern was divided into non-pattern type, light pattern type and heavy pattern type, which was divided into 9 small groups according to the specific shape. By studying the impact of different colors food that is Chinese cabbage, artificial diets and purple cabbage, backgrounds and environment where they live on the body color of beet armywonn larvae found that the background color have little effect; food and small feeding environment dived body color code value (after treatment) gradually approaching the food color code value. The food and small environment is the important factors in decision of beet armyworm larvae body color.