Rhizosphere microbial communities play important roles in facilitating or inhibiting the establishment of exotic species.  Since some invasive plants interact with soil microbial communities such as rhizosphere bacteria, changes triggered by rhizosphere bacteria may alter competitive interactions between exotic and native plants.  This study compared the Bacillus cereus content in soils with different degrees of Ageratina adenophora invasion, and investigated the effects of A. adenophora allelochemicals on B. cereus growth and soil characteristics and the feedback effects of B. cereus on A. adenophora growth.  Bacillus cereus content in the rhizosphere of A. adenophora increased with intensification of the invasion process, and newly invaded soil contained almost twice as much bacteria as noninvaded soil.  When rhizosphere soil was added to the root exudates of A. adenophora, the contents of B. cereus were twice as much as the control, except on the first day.  Certain soil parameters increased significantly, such as ammonium nitrogen (NH₄⁺-N) and available phosphorus (AP), which were increased by 41 and 27%, respectively.  Soil treatment with B. cereus promoted the degradation of two allelochemicals from the rhizosphere of A. adenophora, amorpha-4,7(11)-dien-8-one and 6-hydroxy-5-isopropy1-3,8-dimethyl-4a,5,6,7,8,8a-hexahydraphthalen-2(1H)-one, to varying degrees; and increased the germination rate by 50%, root length by 117%, shoot length by 48% and fresh weight by 81% for A. adenophora compared to those of untreated soil.  Our results confirmed that the invasion of A. adenophora will promote an increase of B. cereus, a beneficial rhizosphere bacterium, which in turn induces a positive feedback effect on A. adenophora.

The potato tuber moth (PTM), Phthorimaea operculella (Zeller), is one of the most economically significant insect pests for potato in both field and storage worldwide.  To evaluate the infestation, reduction of potato yield and the control efficacy for PTM, field tests were conducted in two seasons by intercropping of potato as the host plant with maize as a non-host plant of PTM.  Three intercropping patterns were tested, which were 2 rows of potatoes with either 2, 3, or 4 rows of maize (abbreviated 2P:2M, 2P:3M, and 2P:4M), and the monocropped potato as the control, 2 rows of potatoes, without maize,  (abbreviated 2P:0M).  Results showed that the population and infestation of PTM in the 2P:3M intercropping pattern was significantly lower than those in 2P:2M, 2P:4M and the monocropping pattern of 2P:0M, due to the enhancement of natural enemies.  Cumulative mines and tunneling in potato leaves in 2P:3M intercropping were significantly lower than those in 2P:2M and 2P:4M patterns.  The population of parasitoids and the parasitism rate of PTM in intercropping pattern of 2P:3M were significantly higher than that in intercropping pattern of 2P:2M, 2P:4M and monocropping pattern of 2P:0M.  We conclude that the potato intercropped with maize reduced the adult and larva populations, and reduced the damage from PTM by enhancing the number of parasitoids and the level of parasitism.  The greatest population density of parasitoids and parasitism rate were in the intercropping pattern of 2 rows of potatoes with 3 rows of maize.  These data indicate that the host/non-host intercropping patterns can be used as a biological control tactic against PTM by enhancing the density of natural enemies in the agro-ecosystems.