Bt棉田边缘杂草带对棉田内叶螨发生的影响

2003～2004年，在冀南棉区系统研究了棉田边缘杂草带对棉田内叶螨发生的影响。试验设3个处理：转Bt基因棉化防田(使用杀螨剂控制棉叶螨且保留棉田边缘杂草)、转Bt基因棉对照田(保留棉田边缘杂草)和转Bt基因棉除草田(去除棉田边缘杂草)。结果表明，2003年6月28日～8月7日，处理间的叶螨发生量和有螨株率差异明显。2003年叶螨发生高峰期(7月28日)，对照田的百株平均螨量达834头，分别是化防田、除草田的9.4倍和11.5倍；对照田的有螨株率的峰值为34.7%，分别高于化防田和除草田6.4%和12%；棉叶螨的总计值，对照田分别是化防田和除草田的5.8倍和5.5倍。2004年7月10日～8月29日，对照田的百株螨量和有螨株率明显高于除草田和化防田。2004年叶螨发生高峰期（8月10日），对照田的百株平均螨量达1 222头，分别是化防田、除草田的4.3倍和23.4倍；对照田的有螨株率的峰值达100%，分别比除草田和化防田多75%和87%；棉叶螨的总计值，对照田分别是化防田和除草田的4.9和9.7倍。两年中，除草田和化防田的百株螨量和有螨株率峰值出现日期有所不同。对照田内，棉田边缘杂草至所调查的棉株距离同螨害指数呈显著(P＜0.05)或极显著(P＜0.01)的负相关。本研究表明，去除棉田边缘杂草的棉田，叶螨发生始期较晚且发生量较少；棉田边缘杂草到取样点的距离与棉叶螨的为害程度呈直线负相关，距离越近，叶螨的发生为害越重。

Influences of weed strips at cotton field edges on population dynamics of cotton spider mites

Systematic investigations were conducted to determine the effect of weed strips at cotton field edges on population dynamics of cotton spider mites (mainly Tetranychus cinnabarinus Boisduval and T. truncatus Ehara) and to evaluate influence of eradicating weeds at cotton field edges on occurrence of cotton spider mites in South Hebei, China in 2003-2004. Three treatments were designed, i.e., Bt cotton field with weed strip retained at cotton field edge (FRW), Bt cotton field with weeds on cotton field edge eradicated (FEW), and Bt cotton field with acaricide applied to control cotton spider mites but with weed strip retained at cotton field edge (FAC). The results showed that there were obvious difference in spider mite densities and the ratio of plants with acarids among the three treatments in both years. Both cotton spider mite densities and the ratio of plants with acarids in FRW were obviously higher than those in FEW and FAC. In 2003, the cumulative value of spider mites in FRW was 5.8 and 5.5 times that recorded in FAC and FEW respectively, and the peak of the ratio of plants with acarids in FRW was 34.7%, 6.4% and 12% higher than that in FAC and FEW. In 2004, the cumulative value of spider mites in FRW was 4.9 and 9.7 times that recorded in FAC and FEW respectively, and the ratio of plants with acarids in FRW was 75% and 87% higher than that in FAC and FEW in peak day. The ratio of plants with acarids and densities of cotton spider mites between FAC and FEW reached peaks at different dates in both years. The results showed that: (1) Eradicating the weeds at cotton field edges proved to be more effective in weakening the damage caused by cotton spider mites than keeping the weeds retained; (2) The distance from weed strip to sampled cotton plants was negatively correlated with the damage index of cotton spider mites.