| Whitefly Bemicia tabaci and wheat aphids were important homopterous pests worldwide. The B and Q biotypes of B. tabaci has been concerned because quick invasion and resistance. The Q biotype whitefly, which has stronger resistance to insecticide than other biotypes, was found in Yunnan provice in China and Arizona in the USA in 2003 and 2004 resepictively. Untill now, the Q biotype was only found in greenhouses in the US, but it has replaced the B biotype in Yangtze Valley and North in China, which has more competitive in fecundity.A resistant wheat variety always has resistance to one wheat aphid species, but it always has two or more aphids species disserve in the wheat field. In this study, the host adaptabilities of whitefly and 3 species of wheat aphids Sitobion avenae, Schizaphis graminum and Rhopalosiphum padi were studied using ecological and molecular techniques. The cDNA and promoter sequences of CYP4G and GST genes, which are probably responsible for pyriproxyfen resistance in B. tabaci, were cloned and functionally analyzed. The feeding behaviour of wheat aphids was also investigated. These studies will lay a solid theoretical foundation for fighting against the invasion of the Q biotype whitefly, reducing the application of chemical insecticide and effectively managing these pests.A total of 93 individuals of 17 populations collected in Arizona during 2004-2008 were identified as the Q biotype. All the 17 Q biotype populations were detected from poinsettias in retail stores or greenhouses. No Q biotype individuals were found in open fields in Arizona. Based on their mitochondrial cytochrome oxidase I gene (mtCOI) sequences, the Q biotype whiteflies found in Arizona were divided into 5 haplotypes, designated as AZhap1, AZhap2, AZhap3,AZhap4, and AZhap5. AZhap1 belongs to the Q2 group originated from the countries surrounding the Mediterranean Sea. In contrast, the other four haplotypes belong to the Q1 group originated from Africa or Europe continents. Relatively, the AZhap1 haplotype of the Q2 group found in Arizona was easier to establish a stable laboratory population than did the haplotypes of the Q2 group. The Q1 group has already invaded the entire world, including China and the USA. The Q1 group is the dominant biotype in the Yangtze valley and Shandong provice in China. In contrast, the Q2 group was only found in its origion regions and the USA (California, Arizona and Florida).When transferred to field crops from it original host poinsettia, P06, a Q1 population (AZhap1) collected in 2006, laid eggs and developed to adulthood on the open field crops cotton, melon, tomato, cowpea, alfalfa and cabbage. However, the F1 females developed on the six field crops lived much shorter and laid about 10-fold less eggs than did the F1 females developed on poinsettia. Nontheless, P’06 established stable sub-populations on the field crops cotton, cowpea and melon (we called them as P06Mt, P06Cp and P06Ml, respectively) and these three sub-populations have maintained on the field crops for more than 3 years. The population net reproduction rates (R0) of these four host sub-populations were 0.92-2.82 when the food was sufficent. So P06 have great risk to break out when the condition of being suitable as the condition is suitable.The experiment of transfer hosts showed that hosts could not impede the P06 host sub-populations expansion beside cotton. All P06 host sub-populations rapidly got accustomed to it host with its great adaptability. But the Q biotype could not disperse to open fields in Arizona in the past 5 years. One reason was the main crop planting in Arizona was cotton, and all P06 host sub-population have short lifespan and extremely low fecundity of its F1 adults on cotton.Sequence analysis showed that the CYP4G gene has an open reading frame (ORF) of 1749 nucleotides encoding a protein of 583 amino acids. The deduced amino acids sequence has CYP conserved domains of helix K(ETLRMYP),heme-binding region (PFSAGPRSCV G) , CYP4 specific region (EQVDTIMFEGHDTTN), N–terminal membrane anchor hydrophobic sequence and a similar oxygen bonded structure helix I. The promoter sequence of this CYP4G gene has the antioxidant response element (ARE) and xenobiotic response element (XRE). The ARE core sequence in the 5’UTR of the B biotype whitefly CYP4G gene is ATGATATGC, whereas it is ATGATACGC in the 5’UTR of the Q biotype whitefly CYP4G gene. The deduced amino acid of the whitefly GST gene we cloned has a GSH binding site (G-site) and a substrate binding site.RT-PCR showed that the expression levels of the CYP4G and GST genes were higher in Qcr02R population than were in Yuma04s population. This suggests that these two genes are probably responsible for pyriproxyfen resistance in B. tabaci. The first luciferase reporter gene expression analyses showed that both genes promoter sequences have promoter activities. The promoter activities of CYP4G gene from Qcr02R in both Sf9 cell and Helicoverpa zea fatbody cells were higher than those of other B biotype populations. The promoter activity of the Q biotype whitefly P06 CYP4G promoter was equal to (in Sf9 cells) or higher (in H. zea fatbody cells) than that of the Qcr02R CYP4G promoter. The promoter activity of the GST gene promoter from the pyriproxyfen-resistant Qcr02R strain was higher than those of the GST gene promoters from pyriproxyfen–suscepitable B biotype strain and the multiply-resistant Q biotype strain P06. These data suggest that pyriproxyfen resistance is at least partially due to overexpression of the CYP4G and GST gene in the pyriproxyfen resistant B biotype strain Qcr02R. The overexpression of CYP4G, but not GST, also contributes to pyriproxyfen resistance in the multiple resistant Q biotype strain P’06.The adaptability of 3 species oligophagous wheat aphids was different on 10 wheat varieties. Only 186tm has good adaptability to 3 species aphids. And only Amigo has bad adaptability (good resistance) to 3 species aphids. If they have good resistance to 1 or 2 species of wheat aphids for other 8 varieties, they must have bad resistance to the rest aphids species. If a wheat variety is good for Si. avenae, it always good for R. padi, but bad for Sc. grammnim, and vice versa.The host exchange tests show that wheat aphid adaptability was didderent among wheat varieties. After feeding 5-6 generations on one wheat variety, Si. avenae and Sc. grammnium were adapting to they host plant, but R. padi (especially the wingless aphids). Si. avenae could more quickly adapt on the stronger resistant wheat varieties than on the weaker resistant wheat varieties. But for R. padi, the least resistant wheat variety Batis was the worst for the aphids when they feed continuously. The adaptability mechanism of Sc. grammnium to Batis was same as Ww2730, but different with Xiaoyan22. |
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