When beetle Aulacophora femoralis chinensis Weise fed on cucumber seedlings, it first chewed a circular trench on their leaves and then nibbled the leaf tissues isolated by the trench, but when it was fed with the detached fresh cotyledons of cucumber, such an interesting trenching behavior did not occur, which indicated that the feeding behavior of the beetle was obviously correlated with the chemical response of the cucumber to the herbivory. Within 60 min after feeding, the level of cucurbitacin C in fed cotyledons of the cucumber seedling increased 10 fold or more.Cucurbitacin I was also detected 15 min after feeding, which reached 75 μg/g within 60 min. The high levels of cucurbitacins C and Ⅰ in fed cotyledons could be maintained for at least 24 h. A. Femoralis chinensis was strongly stimulated to take food by cucurbitacin C at a concentration between 10and 250 μg/g, and the feeding deterrent activity was observed at ＞250 μg/g, while the feeding deterrent threshold of A.femoralis chinensis to cucurbitacin I was 50 μg/g. The mixture of cucurbitacins C and Ⅰ had a much stronger feeding deterrent activity than single cucurbitacin I. The results suggested that cucumber could elicit chemical response to the beetle herbivory, its leaf being induced to produce more kinds of cucurbitacins and make them reach the levels of feeding deterrent activity on the beetle, while the trenching behavior of A. Femoralis chinensis was its strategy to answer the chemical response of cucumber. The trenching behavior of the beetle not only stopped the cucurbitacins biosynthesis in cucumber leaf tissues, but also blocked the translocation of cucurbitacins to the feeding sites. The trenching behavior of the beetle and the chemical response of host cucumber were the mutual adaptive strategies for protecting the host plant and the beetle themselves.