| The paper discussed on biotypes of Bemisia tabaci in Xinjiang and resistance of B biotype to insect growth regulator pyriproxyfen, the cross-resistance to other insecticides, the possible reasons and resistance risk were analysed and evaluated. Key points are as the following:1. In comparison of COI sequence with Morocco Casablan-Q, France Gironde-Q, USA California-Q, Jiangsu-Q,Wuhan-Q, the population HH-1 collected in Urumqi Flower Market together with populations of LJ,XHS,QZ collected from Turpan greenhouses share 100% high identity. However, the COI sequence of YC population collected from Turpan on tabacco showed three bases difference comapred with the above 5 documented Q biotype, and they are the 3rd locus of Tâ†'G, the 7th locus of Câ†'T, and the 57th locus of Gâ†'C, respectively, the homology was 99.6%; In comparison with Yangzhou-Q,Jingzhou-Q, there are two different bases were detected, and they are the 3rd locus of Tâ†'G, the 7th locus of Câ†'T, the homology was 99.7%;There are 5 bases different in comparison with Morocco Nador-Q, and they are the 3rd locus of Tâ†'G, the 7th locus of Câ†'T, the 57th locus of Gâ†'C, the 266th locus of Gâ†'A, the 294th locus of Aâ†'G, respectively, the two population share 99.3% identity.Therefore, the Q biotype of Bemisia tabaci in Xinjiang was possibly transported from two or more sources, and the closest genetic relationship are populations of Jiangsu-Q and Wuhan-Q.Populations of JK-S,HH-2,ZH-O,TC-1,TC-2,TC-3 collected from wild flowers in Urumqi, vegetables and cotton in Turpan was still confirmed as B biotype, the homology is 100%compared with documented B biotype of Bejing-B,Guangdong-B,Hubei-B,USA Florida-B.2. The susceptibility of Bemisia tabaci B biotype to different insecticides in Xinjiang by the methods of leaf-dip bioassay and egg loading leaf-dip bioassay. Results suggests that the susceptibility of Bemisia tabaci B biotype collected from different areas and hosts in Xinjiang to different insecticides has been differentiated since the long term application of insecticides. The susceptibility of tested populations to Chlorpyrifos, Thiamethoxan and nature pyrethrin are quite low, values of LC50 are 71.662-330.855 mg-L"',223.028-242.420 mg-L-1 and 107.117-164.639 mg-L-1, respectively, and they belongs to the key products for the resistance management. Values of LC50 to imidacloprid, decamethrin and fipronil are 43.47-67.496 mg-L-1,27.881-61.688 mg·L-1 and 21.808-43.768 mg-L-1, respectively. These insecticides beared high risk of resistance and the development of resistance should be monitored carely. The susceptibility to acetamiprid and alkali·nicotine are still high, they belongs to key products for the protection, and could be served as main compounds for the management of Bemisia tabaci. Furthermore, despite the population of ZH-O collected from a greenhouse exposed with high doeses and frequences of insecticides showed over 3000-fold resistance, other populations are still susceptible to pyriproxyfen, and it is still could be acted as an important compound for the management of Bemisia tabaci.3. In this study, we analyzed the realized heritability of resistance to pyriproxyfen in Bemisia tabaci B-biotype in Xinjiang with the method described by Tabashnik. Selection pressure was given by exposing plants bearing eggs laid within 24h at the dosages sufficient to give 50-70% mortalities. After 4 generation uninterrupted selection, F4 population has built high resistance to pyriproxyfen rapidly at Rf=18.50-fold (LC50=187.336 mg-L-1,95% CL) comparing with the original unselected strain F1(LC50=10.129 mg-L-1,95 % CL; a resistant strain to pyriproxyfen collected from greenhouse in 2008), but at over Rf=60000-fold comparing with the local susceptible reference strain JK-S (LC50=0.003 mg-L-1,95% CL). The realized heritability (h2) of resistance to pyriproxyfen in Bemisia tabaci B biotype was estimate to be 0.3892, and was assumed as 0.1946 in field population (a half value of indoor estimation). The risk predicting of resistance to pyriproxyfen for field population showed that it takes 6～8 generations to achieve 10-fold resistance at the selection pressure of 50-60%, and takes 3-5 generations only at the selection pressure of 70-90%. Results indicated a very high level of risk in the development of resistance to pyriproxyfen both in field and laboratory condition.4. The cross-resistance to different insecticides were monitored on Bemisia tabaci B biotype selected with pyriproxyfen obtained high level resistance in populations of ZH-pyri F2 and ZH-pyri F3 in Xinjiang by the methods of leaf-dip bioassay and egg loading leaf-dip bioassay. Results suggested that there are high level cross-resistance being detected after two generations selection. The Rf value reached to 248.04-fold and 173.87-fold to acetamiprid,60.15-fold and 27.50-fold to imidacloprid, and 17.94-fold and 68.32-fold to chlorpyrifos, respectively. Medium level resistance to Methomyl and Fipronil were assayed, The Rf value reached to 6.94-fold and 33.22-fold to imidacloprid, and 30.90-fold and 39.22-fold to chlorpyrifos, respectively. There were low level cross-resistance to thiamethoxam, deltamethrin, abamectins, alkali-nicotine and nature pyrethrin. |
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