Sub-Lethal Effects of Fenvalerate on the Development, Fecundity, and Juvenile Hormone Esterase Activity of Diamondback Moth, Plutella xylostella (L.)

The toxicities of fenvalerate （20% EC） to the 3rd instar larvae of diamondback moth （DBM）, Plutella xylostella （L.）, reared on three host plants viz., radish, oilseed rape, and cabbage were tested. The LC50 values of fenvalerate to the 3rd instar larvae of DBM varied with host plants, however, there wasn＇t any significant difference among them （P〉 0.05）. Similarly, DBM fed on three host plants had same pupal weight, pupal period, pupation rate, adult emergence rate, female ratio, and fecundity. The activity of juvenile hormone esterase （JHE, EC 3.1.1.1） in the 3rd instar larvae of DMB did not significantly vary with host plants, either. These suggested that DBM had similar fitness on the three host plant species. When fed on the host plants pretreated with fenvalerate at the concentrations equivalent to LC20, LC50 and LC50, the pupation rate, pupal weight, adult emergence rate, female ratio, fecundity, and JHE activity of the tested insects were declined as compared with insects in control treatments fed on the same host plant species. Furthermore, the pupal period of the tested insects was extended after fenvalerate treatment. The decrease in JHE activity after fenvalerate treatment in the tested insects could partly explain the changes in the mentioned growth parameters. Whether the role of fenvalerate in the inhibition of JHE activity could serve as a new way to control DBM needs further investigation.

Incidence and prevalence levels of three aphid-transmitted viruses in crucifer crops in China

Poleroviruses,which are distributed worldwide,infect many crops of economic importance and cause severe plant diseases.Brassica yellows virus(Br YV),which has three genotypes,A,B,and C,is a newly identified polerovirus infecting crucifer crops in China,but its distribution is still unclear.Here,we report the distribution and prevalence levels of the three Br YV genotypes in crucifer crops in China.A total of 570 crucifer leaf samples randomly collected from 22 provinces,four ethnic minority autonomous regions,and three municipalities in China were tested for Br YV.RT-PCR detection showed that 97 of the field samples were positive for Br YV,and the average incidence of Br YV was 17.0%.The virus was detected in 22 provinces,with high incidences in north,northwest,and northeast China.The multiplex RT-PCR amplification of the three Br YV genotypes revealed that both single and mixed infections occurred.Among the Br YV infections,38.1% were mixinfected by more than two viral genotypes,and 8.2% samples were mix-infected by three viral genotypes.Our findings indicated a widespread prevalence of Br YV in China,and Br YV mixed infections with Turnip mosaic virus and Cucumber mosaic virus in crucifer crops are common.This study is the first large-scale survey of Br YV in crucifer crops in China.The information generated in this investigation will contribute to the national prevention and control of viral diseases.