关键词: Bt棉田, 杂草带, 棉叶螨, 种群动态, 螨害指数

Abstract:

Systematic investigations were conducted to determine the effect of weed stripsat 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.

Key words: Bt cotton field, weed strip, cotton spider mites, population dynamics, damage index of spider mites