The Research On The Geographical Parthenogenesis Of Rice Water Weevil, Lissorhoptrus Oryzophilus Kuschel

The rice water weevil (RWW) Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), was native to the Mississippi basin in north American. The RWW in south American was produced by sex, but the populations in California, Japan, Korea, and China undergone parthenogenetic reproduction. Parthenogenesis was important to the geographical distribution and population expansion. To understand the formation and mechanism of geographical parthenogenesis in RWW, death-feigning behavior, chromosome analysis, ovary section observation, polymorphism analysis of geographical populations and SSH library were carried by using squash technique, electron microscope, AFLP and SSH. The primary results were as follows:1) Effect of adult density on death-feigning behavior and body weight of RWWOriginal density of adult weevil significantly influenced duration of death-feigning (DDF) and number of stimuli needed for death-feigning (NSDF). The higher of the density, the longer of DDF, and the fewer of NSDF. Age of adult weevil has no effect on DDF, but the NSDF of the three densitis decreased with the increase of age of adults. Density of adult weevil also influenced the body weight of adult weevil. The body weight increased with the increase of age in the lowest density 1, but decreased in the high density 5 and 10. These results showed that adult weevils in high density were prone to death-feigning, and the date of emigration certainly would be postponed and shape the second generation.2) Chromosomal karyotypeResearches on the chromosomes of parthenogenetic females and sexual males showed that, sexual males was diploid with 22 chromosomes, chromosomal sex determination mechanism could be as XY♂/XX♀. Parthenogenetic female was triploid with 33 chromosomes. The basic chromosome number was 11 in both sexual males and parthenogenetic females.3) Structure of ovary and the meiosis of oocytesConfocal Laser Scanning Microscope (LSM) observations were carried by using the parthenogenetic ovaries. The results showed that egg become mature and were before embryo development in the bottom of telotrophic ovary. Transmiting electron microscope (TEM) research showed that, there were microorganisms in the trophocyte and follicle cells, but no in the oocyte. The oocyte undergone single maturation division. These results indicate that parthenogenesis of RWW was under genetic control.4) Genetic polymorphism analysis of the RWW of two types of reproductionAmplified fragment length polymorphism (AFLP) analysis of different geographical populations showed that sexual and parthenogenetic populations clustered together separately. RWW populations of Italy belonged to Asia RWW populations, indicated that the RWW in Italy may originated from Asia. The low coefficient between sexual and parthenogenetic populations indicated the distant relative relationship. The sequence of co-segregation fragments of parthenogenetic female that different from sexual female were identical in some degree to periplasmic trehalase precursor, FRAS1-related extracellular matrix protein 3 precursor and phosphoinositide 4-kinase. These fragments may be contributed to the molecular mechanism of parthenogenesis.5) Construction of subtracted cDNA library and the sequence analysiscDNA of parthenogenetic female ovary was tester and subtracted by sexual female ovary cDNA (driver), subtracted cDNA library was constructed between parthenogenetic female ovary and sexual female ovary. The sequence analysis showed that SSH4, 12, 98 and 108 were identical in some degree to cDNA sequences encoding tubulin, GTP-binding protein, MAPKKK3 and cyclin. The functions of these fragments were assumed to be involved in parthenogenesis process.