甘肃环县两种沙打旺蛀秆害虫数量随季节、年份和草地年龄的变化动态

沙打旺是我国北方主要的豆科牧草和水土保持植物，害虫是其生产的限制因素之一，其中沙打旺小食心虫（Crapholita shadawana）（卷蛾科）和沙打旺黑潜蝇（Melanagromyza adsurgenis）（潜蝇科）为重要的蛀秆害虫。本研究于2004年、2005年和2006年8月或9月以及在2005年5月（返青后期）、6月（拔节期）和8月（开花初期）调查了甘肃环县4个年份（1998年、2000年、2002年和2003年）建植的沙打旺草地上此两虫的发生规律，发现其发生与年份、草地年龄和季节有关，两虫分别为害3龄以上（含3龄）和8龄以下（含8龄）沙打旺，植株被害率分别为20.0%~100.0%和52.0%~100.0%，其中2005年发生最普遍，植株被害率均为100%。虫口数量随年份变化，其中在年龄最大（1998年建植）和最小（2003年建植）的草地上，沙打旺小食心虫在2006年时的百枝虫量均显著（P<0.05）低于其他两年，而在其他年龄的草地上则均显著（P<0.05）高于其他两年，3年中最高达65.8头·百枝-1（即65.8%的枝条受害，1998年建植2004年数据）；沙打旺黑潜蝇在2006年时在年龄最小草地上显著（P<0.05）高于其他年份，在年龄最大草地上则显著低于（P<0.05）其他年份，3年中最高达38.8头·百枝-1（即38.8%的枝条受害，2000年建植2004年数据）。基于4个年度建植的草地在调查年份中年龄与百枝虫量的关系可知，总体上，两虫的虫口数量均随着草地年龄的增加而增加（年度有波动），分别于7龄和8龄时达到高峰，此后随着草地的衰退而急剧下降。在同一年份的不同生长季节，两虫均于6月开始为害（5月时未见发生），但沙打旺小食心在6月时仅出现在年龄最大草地，在各龄草地上8月的百枝虫量显著（P<0.05）高于6月，而沙打旺黑潜蝇6月时百枝虫量已达最大值，除年龄最小草地外均显著（P<0.05）高于8月。在同一枝中未发现2种害虫，也未发现2头或2头以上的同一害虫。受害枝条外观与未危害枝条无明显差异，故剖茎观察虫体、虫洞和虫粪是判别枝条是否受害的主要方法。甘肃省为此两虫的新分布省份。

Study on the quantitive dynamics of two stem-boring Astragalus adsugens depended on different years and pasture ages in Huanxian, Gansu species insects of seasons, 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 (P<0.05) higher than each of 2005 and 2004, and in other pastures was fewer (P<0.05). 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 (P<0.05) higher than in 2004 and 2005, and in the oldest pasture in 2006 was significantly (P<0.05) 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.