Pyriproxyfen Resistance Of Biotype B And Interactions Between B And Q Biotypes Of Bemisia Tabaci

Juvenile hormone(JH) analogue insecticides are relatively nontoxic to vertebrates and provide efficient control of key arthropod pests.One JH analog,pyriproxyfen,has provided over a decade of exceptional management of whiteflies in cotton of the southwestern US.Thwarting resistance to pyriproxyfen in Bemisia tabaci(Gannadius) (a.k.a.Bemisia argentifolii Bellows and Perring) has been the focus of an integrated resistance management program since this insecticide was first registered for use in Arizona cotton in 1996.Resistance levels have increased slowly in field populations in recent years but have not demonstrably impacted field performance of pyriproxyfen. Resistant strains have been isolated and studied in the laboratory to determine the mechanism of resistance and identify optimal strategies for controlling resistant whiteflies. Synergism bioassays showed that resistance in a laboratory-selected strain QC-02,was partially suppressible with piperonyl butoxid(PBO) and diethyl maleate(DEM) but not with S,S,S - tributyl phosphorotrithioate(DEF).Consistent with the synergism bioassay results,enzymatic assays revealed that the enzyme activities of cytochrome P450 monooxygenases(P450) and glutathione S-transferases(GST) but not esterases were significantly higher in the pyriproxyfen-resistant QC-02 strain than in the susceptible strain.These results indicate that both P450 and GST are involved in whitefly resistance to pyriproxyfen.The results of degenerate,specific PCR and real-time PCR approach showed that the one of the CYP4G gene over expressed in the pyriproxyfen-resistant strain when compared with susceptible strain.Full sequence of the cDNA and DNA of the CYP4G gene was got via the method of RACE and Genome Walking,alignments between the cDNA and DNA of resistant and susceptible strains indicated that the transposable element which inserted into the intron might lead to the over expression of CYP4G gene in resistant strain.The whitefly biotype B is almost displaced by Q biotype in Spain,just like it did on biotype A in 1990’s in US.It was a problem whether the displacement of B biotype by Q biotype will happen in the near future of US.In this study,the whole process of the B and Q biotypes succession within a lab population was observed and the results showed that even in a very low initial percentage,the biotype B could displace biotype Q completely on cotton seedlings under laboratory conditions;the insecticide pressure could hardly affect the biotype succession process. The invasive,insecticide-resistant,Q whitefly biotype,has gradually spread to other countries including the U.S.via human-mediated movement of plant materials.We assessed the utility of the VspI-based mtCOI(mitochondrion cytochrome oxidase I) PCR-RFLP(Polymerase Chain Reaction-Restriction Fragment Length Polymorphisms) technique as a rapid,cost-effective,and reliable alternative for differentiating the Q from the dominant B biotype in Arizona.Using the standard mtCOI gene sequencing and mtCOI PCR-RFLP techniques,we biotyped eight whitefly strains of 5 individuals each collected from poinsettia and cotton at different locations in Arizona.Complete concordance was observed between the two methods,with three strains being identified as the Q biotype and five samples as the B biotype.We also scanned the mtCOI gene sequences for VspI polymorphisms in the B and Q biotype whiteflies currently available in the GenBank database.This global screening revealed the existence of three and four VspI polymorphic types for the Q and B biotypes,respectively.Nevertheless,all three VspI polymorphic Q biotype whiteflies shared a common and unique VspI site that can be used to differentiate Q biotype from the four VspI polymorphic B biotype whiteflies identified.These results demonstrate that the VspI-based mtCOI gene PCR-RFLP provides a reliable diagnostic for differentiating the Q and B biotype whiteflies in the U.S and elsewhere.