| There are obvious differentiations in host use and migratory capacity of cotton aphid, Aphis gossypii Glover in Nanjing. The cotton aphid can be classified as cotton-and cucurbit-specialized strains in using host plant, and they can also be classified as migratory and sedentary strains in migratory capacity. But the molecular mechanisms of host-specialization and migration are still vague. The behaviour of the copulation, mutation in COⅠ/COⅡand Buchnera genes sequences, and the content of endosymbionts Buchnera in migratory and host-specialized biotypes of Aphis gossypii Glover in Nanjing were studied in this paper, in order to explore the molecular background of the formation of host-specialization and migratory biotypes. The results were showed as follows:(1) The sexual generation of the cotton-(Co), cucurbits-(Cu) specialized, migratory (M) and sedentary (S) strains of cotton aphid were induced under the low temperature (18℃) and short photoperiod (L:D=8:16), and the mating behavior between different strains was also compared. The results showed that migratory strain was prone to give birth to sexual generation. The date generated male and female aphids was earlier about 5 days to the sedentary strain. The durations of finding spouse of M♀×M(?) was significantly shorter than those of the copulation M♀×S(?) and S♀xM(?) but there was not significantly different between M♀×M(?) and S♀×S(?). The durations of mating of M♀×S(?) was significantly longer than that of the M♀×M(?) and S♀×S(?),but there was no significant difference between M♀×S(?) and S♀×M(?).The assortative mating behavior was found between migratory and sedentary strains. The durations of finding spouse and mating were no significant difference between Cu♀×Co(?) and Co♀×Cu(?). The mating behavior of different strains of cotton aphid revealed that mating behavior could happen between host-specialized aphids, and between migratory and sedentary strains, and there was no segregation at sexual generation.(2) Sequence variations in the mtDNA genes COI and COII among different strains of cotton aphid were determined. The results indicated that there was no COI sequence mutation in cotton- and cucurbits-specialized strains even if they had been reared seven years in laboratory on cotton and cucumber plant, respectively, or were collected from natural field of cotton and cucumber, But there were two bases mutations in migratory strains of 2008 and 2010 population, and one base mutation in sedentary strain of 2008. However, the mutation in sedentary strain was not detected again in 2010 population. There were four haplotypes (H1, H2, H3, H4) of cotton aphid in Nanjing at mtDNA level, and all the cotton-and cucurbit-specialized strains, migratory and sedentary strains shared the same haplotype H4. Phylogenetic analysis showed that cotton aphid population in Nanjing could be divided into three clades. Clade 1 was dominant and no any mutation in COⅠand those aphids fed on the hibiscus, cotton and cucurbits host plants in summer. The clade 2 and clade 3 were comprised of migratory strain, and contented some mutations in COⅠgene. Not any mutations in Leu-tRNA/COⅡsequence were found in the above strains. Mutation in COⅠgene sequence did not affect the fecundity and fitness of the aphids.(3) Seven strains of cotton aphid, M-H3 (haplotype H3), M-H4 (haplotype H4), S (sedentary strain), Cuw (just collected from cucumber field), Cow (just collected from cotton field), Co (cotton-specialized) and Cu (cucurbit-specialized) were determined in the differentiation of the endosymbionts Buchnera's leuA gene. The results showed that the two groups of cucurbit-specialized strains (Cu and Cuw) contented one base mutation in leuA gene sequence, while the cotton strain, migration and sedentary strain had no mutation. Phylogenetic analysis showed that the two groups of cucurbit-specialized strains (Cu and Cuw) were in the same branch, and the other strains were in the other branch. Cotton- and cucurbit-specialization of cotton aphid may be related to their endosymbionts.(4) Buchnera trpEG genetic differentiation and Buchnera quantity in the above seven strains of cotton aphid were studied. The results showed that two bases mutations were found in the trpEG sequence of the cucurbit-specialized strain and the cotton aphid collected just from cucumber. No mutation in cotton-specialized strain, migration, sedentary strain was detected. Phylogenetic analysis showed that the aphids living on cucumber were clustered firstly, and the other cluster tree was aphids living on cotton. Quantitative PCR of Buchnera discovered that Buchnera in cucurbit-specialized strains was significantly higher than that of the other strains. The results revealed that the primary symbiots of cotton aphid was close related to the host-specialized biotypes. |
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