Astragalus adsugens depended on different seasons, years and pasture ages in Huanxian, Gansu Province

tanding milkvetch (Astragalus adsurgens) is an important leguminous forage and soil conservation plant. Harmful insect is one of the limiting factors to forage production. Crapholita shadawana (Tortricidae) and Melanagromyza adsurgenis (Agromyzidae) are the stemboring insects of the plant. Occurrences of the two insect species were investigated in four age pastures (established in 2003, 2002, 2000 and 1998) at Huanxian, Gansu province in August or September of 2004, 2005 and 2006, and in May (late regreening), June (branching) and August (early flowering) of 2005. The occurrences were associated with pasture age, year and seasons. The two kind of insects feed A. adsurgens plants that older than 3yearold and younger than 8yearold, percentage of damaged plants was 20.0%-100.0% and 52.0%-100.0%, respectively, in which 100% plants were damaged by the first insect and the second insect in 2005. Amount of each insect varied in different year, in which amount of C. shadawana larvae per 100 plants (ALPP) in both of the oldest (established in 1998) and youngest (established in 2003) pastures in 2006 was significantly (P0.05) higher than each of 2005 and 2004, and in other pastures was fewer (P0.05). The maximum of C. shadawana amount in three years was 65.8 larvae per 100 shoots (i.e., 65.8% shoots were damaged, 2004 data from 1998established pasture). ALPP of M. adsurgenis in the youngest pasture in 2006 was significantly (P0.05) higher than in 2004 and 2005, and in the oldest pasture in 2006 was significantly (P0.05) fewer than in other two years. The maximum of ALPP of M. adsurgenis in three years was 38.8 larvae per 100 shoots (i.e., 38.8% shoots were damaged, 2004 data from 2000established pasture). Based the relationship between pasture ages and ALPP, although it fluctuated in different year, ALPP of both of insect species increased as the age increased, reaching the peak at 7yearold and 8yearold, and then decreased rapidly as the majority of plants died. Among a year, the two kind of insect began fed in June (not found in May), however, C. shadawana was only found in the oldest pasture in June, 2005, and M. adsurgenis in June was found in all pastures and its ALPP reached the maximum. Furthermore, ALPP in June was higher than in August in each of pastures. The two kind of insect had not live in a same shoot even two larvae of same species. Since there were no differences were found between damaged shoots and nodamaged shoots, examination on insect body, boring holes and frass after splitting stems should be a reliable method to diagnose if boring insects in shoots. Gansu province is the new distribution region of the two insects.