Abstract: 【Aim】The molecular mechanism of the wing morph regulation of rice planthopper is clear, but the change rules of wing morph and expression levels of wing development genes during the continuous selection for the long- and short-winged strains remain obscure. This study aims to explore the responses of wing length, wing weight and wing development genes of the long- and short-winged strains of the small brown planthopper, Laodelphax striatellus to the directional selection, so as to clarify the genetic rule and evolution of its wing morph. 【Methods】The long- and short-winged morphs of L. striatellus were successively selected for 14 and 13 generations, respectively, under the constant conditions, and the long and short-winged strains were established. The rates of long- and short-winged individuals, wing length and wing weight of the two strains were measured in each selection generation, and the relative expression levels of the wing development genes InR1, InR2 and FoxO were examined using the qPCR method. The selection responses of the wing morph and wing development genes were characterized by comparing the differences in the wing morph indicators and gene expression levels between the long- and short-winged strains in each selection generation. 【Results】 Through the directional selection of long- and short-winged strains of L. striatellus for 14 and 13 consecutive generations, respectively, the rate of long-winged individuals in the longwinged strain and the rate of shortwinged individuals in the shortwinged strain significantly increased, and both could remain about 95%. With the increase of the selection generations, the wing length of the longwinged strain became longer whereas that of the short-winged strain became shorter, and both the wing weights of the long- and short-winged strains became lighter. The relative expression levels of InR1 and InR2 in the 3rd instar nymphs of the long-winged strain decreased with the increase of selection generations, whereas that of FoxO had no change. However, the relative expression levels of InR1, InR2 and FoxO in the 3rd instar nymphs of the short-winged strain increased with the increase of selection generations. The expression levels of these three genes in adults had no obvious responses to the selection for the long- and short-winged morphs. 【Conclusion】L. striatellus has obvious responses to the directional selection for wing morphs, and the rate of the selected wing morph increases significantly and remains a high level. The wings of the long-winged strain become longer and thinner whereas the wings of the short-winged strain become shorter and lighter after directional selection. The multi-generational directional selection inhibits the expression of two wing development genes InR1 and InR2 of the longwinged strain, while activates the expression of them of the short-winged strain, thereby promoting the formation and maintenance of the pure-bred lineages of long- and short-winged morphs. These results indicate that the L. striatellus population may evolve towards the pure-bred lineages of long-winged and short-winged morphs.

Key words:  Laodelphax striatellus, wing polymorphism, directional selection, wing length, wing weight, insulin receptor, gene expression level