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Peroxiredoxins (Prxs), which scavenge reactive oxygen species (ROS), are cysteine-dependent peroxide reductases that group into six structurally discernable classes: AhpC-Prx1, BCP-PrxQ, Prx5, Prx6, Tpx, and AhpE. A previous study showed that forkhead box protein O (FOXO) in the insulin signaling pathway (ISP) plays a vital role in regulating locust diapause by phosphorylation, which can be promoted by the high level of ROS. Furthermore, the analysis of transcriptome between diapause and non-diapause phenotypes showed that one of the Prxs, LmPrx6, which belongs to the Prx6 class, was involved. We presumed that LmPrx6 might play a critical role in diapause induction of Locusta migratoria and LmPrx6 may therefore provide a useful target of control methods based on RNA interference (RNAi). To verify our hypothesis, LmPrx6 was initially cloned from L. migratoria to make dsLmPrx6 and four important targets were tested, including protein-tyrosine phosphorylase 1B (LmPTP1B), insulin receptor (LmIR), RAC serine/threonine-protein kinase (LmAKT), and LmFOXO in ISP. When LmPrx6 was knocked down, the diapause rate was significantly reduced. The phosphorylation level of LmPTP1B significantly decreased while the phosphorylation levels of LmIR, LmAKT, and LmFOXO were significantly increased. Moreover, we identified the effect on two categories of genes downstream of LmFOXO, including stress tolerance and storage of energy reserves. Results showed that the mRNA levels of catalase and Mn superoxide dismutase (Mn-SOD), which enhanced stress tolerance, were significantly downregulated after silencing of LmPrx6. The mRNA levels of glycogen synthase and phosphoenolpyruvate carboxy kinase (PEPCK) that influence energy storage were also downregulated after knocking down of LmPrx6. The silencing of LmPrx6 indicates that this regulatory protein may probably be an ideal target for RNAi-based diapause control of L. migratoria.

Pieris napi oleracea Harris is a native pierid butterfly whose range in New England has decreased since the 1869 invasion of an exotic congener, Pieris rapae (L.). Populations have disappeared from all but a few locations in western Massachusetts, but persist more widely in northern Vermont. Parasitism by the introduced braconid wasp Cotesia glomerata (L.) has been postulated as responsible for this decline. Field exposures of cohorts of P. napi larvae in 2002 showed that, on the summer host plant Sisymbrium officinale (L.) Scoop., parasitism rates of second generation butterfly larvae were very high (100% in Massachsusetts and 66% in Vermont). Direct observations of host plant and habitat use patterns by P. napi females in northern Vermont in 2000 showed that this species changes habitats between the first and second generation, with over 95% of eggs of the first generation of P. napi being laid in wooded habitats on the crucifer Cardamine (formerly Dentaria) diphylla (Michx.) Wood. Second generation butterflies fly in meadows and oviposit on S. officinale and other crucifers in full-sun habitats. The second flight of P. napi is, however, only a partial generation, with many first generation pupae entering diapause. The proportion of butterflies entering diapause increases if eggs are laid on C. diphylla plants at or past the flower bud stage. Of first instar P. napi reared outdoors on pre-flower-bud C. diphylla, 63% (n=64) entered diapause in Massachusetts, but 86% (n=119) did so in northern Vermont. Higher rates of diapause in early larval groups in northern Vermont, plus lower rates of parasitism of second generation larvae in meadows, as compared to Massachusetts, indicate that the impact of C. glomerata on total population survival is lower in Vermont and is likely the reason P. napi has persisted in northern Vermont, but not in western Massachusetts. This case illustrates how non-target effects of parasitoids may be mediated by habitat and life history features of populations of affected insects, which may differ geographically. [Copyright &y& Elsevier]

Simple Summary: LmPrx6 of the insulin signaling pathway is significantly associated with diapause induction in Locusta migratoria L. as per our pervious transcriptome data. In the current study, we first cloned and sequenced the gene and demonstrated its similarity to other Prxs using phylogenetic analyses. Later on, we knocked down Prx6 using RNAi and showed that phosphorylation of proteins associated with the insulin signaling pathway and responses to oxidative stress were altered. Knockdown of Prx6 also resulted in a reduced ability to enter diapause, and hence, we are of the opinion that this gene could serve as an effective target for RNAi-based control of L. migratoria L. The study has provided some helpful insights into the diversified roles of Prx6 in locusts and will be of interest to other insect pests for examining the relatively unexplored group of proteins as well. Peroxiredoxins (Prxs), which scavenge reactive oxygen species (ROS), are cysteine-dependent peroxide reductases that group into six structurally discernable classes: AhpC-Prx1, BCP-PrxQ, Prx5, Prx6, Tpx, and AhpE. A previous study showed that forkhead box protein O (FOXO) in the insulin signaling pathway (ISP) plays a vital role in regulating locust diapause by phosphorylation, which can be promoted by the high level of ROS. Furthermore, the analysis of transcriptome between diapause and non-diapause phenotypes showed that one of the Prxs, LmPrx6, which belongs to the Prx6 class, was involved. We presumed that LmPrx6 might play a critical role in diapause induction of Locusta migratoria and LmPrx6 may therefore provide a useful target of control methods based on RNA interference (RNAi). To verify our hypothesis, LmPrx6 was initially cloned from L. migratoria to make dsLmPrx6 and four important targets were tested, including protein-tyrosine phosphorylase 1B (LmPTP1B), insulin receptor (LmIR), RAC serine/threonine-protein kinase (LmAKT), and LmFOXO in ISP. When LmPrx6 was knocked down, the diapause rate was significantly reduced. The phosphorylation level of LmPTP1B significantly decreased while the phosphorylation levels of LmIR, LmAKT, and LmFOXO were significantly increased. Moreover, we identified the effect on two categories of genes downstream of LmFOXO, including stress tolerance and storage of energy reserves. Results showed that the mRNA levels of catalase and Mn superoxide dismutase (Mn-SOD), which enhanced stress tolerance, were significantly downregulated after silencing of LmPrx6. The mRNA levels of glycogen synthase and phosphoenolpyruvate carboxy kinase (PEPCK) that influence energy storage were also downregulated after knocking down of LmPrx6. The silencing of LmPrx6 indicates that this regulatory protein may probably be an ideal target for RNAi-based diapause control of L. migratoria. [ABSTRACT FROM AUTHOR]