Abstract:

Profile sampling method，macro-group classification method，and statistical method were used to study the community structure and dynamics of soil insects in ragweeds Ambrosia artemisiifolia and A．trifida habitats．Forty-six families of soil insects （adults and larvae were separately counted）belonging to 12 orders were collected．On the level of order，the individual number of Collembola was absolutely dominant（amounting to 80.879% of the total individual number of soil insects），followed by Hymenoptera （8.765%），Coleoptera larvae（3.951%），and Diptera larvae （3.093%），while the rest orders together amounted to 3.312% of the total．Among the 46 families，three families, i.e., Onychiuridae（amounting to 32.756% of the total individual number of soil insects），Tomoceridae（18.869%），and Isotomidae （18.178%）, were dominant．The number of individuals and groups of soil insects increased with the proceeding of growth season and attained the maximum value in August．Ragweeds reduced the individual number and community diversity of soil insects. According to the results of monthly ANOVA and LSD，in August and September the individual number and diversity indices of soil insects in the control plot without ragweeds were significantly higher than those in ragweed plots．Ragweeds showed expellant effects on some groups of soil insects，and in the whole growth season of ragweeds, Carabidae adults，Dasytidae larvae，Jassidae， Histeridae，and Phloeothripidae were never found in ragweed habitats．The restrictive impacts of ragweeds on soil insects were more remarkable in pure ragweed community and in the bloom of plant growth．Vertically, soil insects aggregated mainly in surface soil profile．

Key words: Soil insects, ragweeds, ragweed habitat, community structure, community dynamics, diversity, vertical distribution