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.

Diapause Regulation in the Moth Sesamia nonagrioides （Lepidoptera： Noctuidae）

Insects enter in diapause in response to diverse environmental cues. During diapause, insects arrest their development and many genes are down-regulated while a small number of genes uniquely expressed at this time. This review aims to present available data regarding the regulation of diapause in the moth Sesamia nonagrioides （Lepidoptera： Noctuidae）. Studying the transcriptional regulation of several genes （five heat shock proteins, two storage proteins and one juvenile hormone esterase） showed that these genes may play various roles in the diapause programming. The results show that SnoHsp19.5 gene was consistently expressed, while SnoHsp20.8 was down-regulated in deep diapause and was up-regulated at the termination of diapause. SnoHsc70 may play important roles in assisting protein conformation during specific stages of diapause. SnoHsp83 displays a similar pattern to SnoHsc70 under diapause conditions, when extra larval moults occur, indicating that could be involved in the developmental process that occurs between two moults. Expression of two SnoSP1 and SnoSP2 hexamerin genes was also observed throughout diapause. And the results lead us to the conclusion that larval diapause of S. nonagrioides is associated with continuous synthesis and accumulation of storage proteins. In addition, the transcript level of the carboxylesterase SnoJHER was higher in non-diapausing larvae than in diapausing ones. During the fifth instar of the non-diapausing and the ninth instar of the diapausing larvae, SnoJHER mRNAs reached higher expression levels on the days close to each larval molt.