The midgut gland cell differentiation occurs at Z2, There are 4 types of cells, i. e., embryonic cell (E-cell), fibrillar cell (F-cell), blister cell (B-cell) and resorptive cell(R-cell).

中管上皮在Z2期细胞已有了分化，由4类细胞组成，即胚细胞(E细胞)、纤维细胞(F细胞)、泡状细胞(B细胞)和吸收细胞(R细胞)。

The results of biochemical analysis indicated that the difference of the activity of carboxylesterase and esterase isozymes in the larval midguts were the main mechanism of this selective toxicity.

化分析结果进一步指出,昆虫中羧酸酯酶的活性及酯酶同功酶的差异是这种选择麻醉作用的重要机。