Study On Selection Response Of Wing Form And Its Laws Of Heredity In Three Rice Planthoppers

Rice planthoppers are the main pests of rice including Nilaparvata lugens (Stal), Sogatella furcifera (Horvath) and Laodelphax striatellus (Fallen), which cause large losses of rice yield. The migration and spread of rice planthoppers via producing marcropterous form can lead to the expansion of the damage area and bring about great economic losses. Wing dimorphism of rice planthoppers is always an important topic of the study on population ecology of planthoppers. Clarifying the genetic law and regulation mechanism of wing dimorphism will contribute to forecasting of occurrence and development of rice planthopper population, and to guide the prevention and control. Moreover, it will provide the important theoretical support for the study on the evolution of wing form in planthoppers.In order to reveal the selection response and genetic law of wing form in three rice planthoppers, the wing form screenings of N. lugens, S. furcifera and L. striatellus were carried out to attain the long-and short-winged lines in a constant condition (25±1℃,80%RH, L:D=14:10), and the hybrid experiments between the long-and short-winged pure or nearly pure lines were executed. The responses of wing form pure or nearly pure lines to photoperiods, developmental stages of rice and the larva density were also studied in this paper. The preliminary results are list as follow.(1) Under the constant conditions (25±1℃,80%RH, L:D=14:10), the continuous generation screenings of wing forms in four types of copulation lines in N. lugens: long-winged male×long-winged females (M(?)×M♀), long-winged male x short-winged females (M(?)×B♀), short-winged male×short-winged females (B(?)×B♀) and short-winged male×long-winged female (B(?)×M♀), and two types of copulation lines in S. furcifera and L. striatellus:M(?)×M♀and M(?)×B♀, were carried out in the standardized rice seedlings. During the screening, the female and male offspring were selected to copulation which wings were wholly like their mother and father in all the selection generations. The results showed that the wing form of the three rice planthoppers had a strong selection response. Ratio of the long-winged form in males was more than97%and the long-winged form ratio in females increased up to80%while the M♂×M♀of N. lugens were selected for16generations. Short-winged form ratio in males and females increased to about80%and100%, respectively while the B♂×B♀were selected for16generations. The wing form of the M♂×B♀and B♂×M♀had no response to selection, and the long-winged form ratio of the former was basically stable around50%in all the15selected generations, and long-winged in female and short-winged in male from the latter were still very lower after selected12generations. In the S. furcifera, long-winged form ratio became100%while the M♂×M♀were selected for3generations and the long-winged pure line was attained. The long-winged rate was around50%in the M♂×B♀during the8-15selected generations. In the L. striatellus, long-winged form ratio was kept stably at95%while the M♂×M♀were selected for6-15generations, and it fluctuated around50%while the M♂×B♀were selected9-15generations. The obvious differences of selection response in wing form among the three rice planthoppers were found, and the long-winged pure line in S. furcifera was easiest to select, followed by L. striatellus, and the long-winged pure line in N. lugens was most difficult to attain.The results of wing form selections showed that wing form of N. lugens female offspring was controlled not only by the maternal but only by the paternal. When the wing form of mother was long-winged, the long-winged form in female offspring was higher for the long-winged paternal than for the short-winged paternal. When the mother’s wings were short, more than90%of the female offspring were short-winged whether the paternal was long-winged or short-winged. Wing form of male offspring in N. lugens was also affected strongly by the maternal and paternal. When the paternal was short-winged, male offspring was more short-winged in the short-winged maternal than in the long-winged maternal. But when the paternal was long-winged, the male offspring’s wings form were affected little by the maternal wing form, and90-100%males were long-winged whether the maternal was long-winged or short-winged.(2) Hybridization inheritance between wing forms pure or nearly pure lines was studied. The preliminary results showed that the wing forms of N. lugens basically accorded to the genetic law of a sex-influenced trait which was controlled by a pair of alleles. Dominance or recessive was different in male and female. In males the long-winged was dominance, and in females, the short-winged was dominance. Coincidence rates of offspring wing form according to this rule among different selected generations in the M(?)×M♀,B(?)×B♀and M(?)×B♀of N lugens were higher, but it was low in the B(?)×B♀There existed the significant mismatch between phenotype and genotype of wing form in N. lugens wings. The wing form rate of offspring from B(?)×B♀was the same as the offspring from M(?)×M♀when the B(?), B♀, M(?), M♀came from the same parents.To a certain extent, the genetics of wing form of S. furcifera and L. striatellus could be explained by two pairs of alleles which one located in a euchromosome controlled the female’s wing form and the other located in a sex chromosome controlled the male’s wing form. The short-winged was dominance in females and the long-winged was dominance in males. The wing form accorded to this genetic rule very well in all the selection generations for S. furcifera and L. striatellus.(3) The responses of wing form pure or nearly pure lines in the three planthoppers to the photoperiods, the growth stages of rice and the density of larvae were measured. The results show that the long-and short-winged pure or nearly pure lines in the three rice planthoppers were relatively insensitive to these factors, the photoperiods, growth stages of rice and larvae density. If the genetic background was the same, wing form determination of the three planthoppers was mainly controlled by genetic factor and the external factors only played a very small role.