German cockroaches have become a large problem in the Shenzhen area because of their pesticide resistance, especially to pyrethroid. A pyrethroid called “Jia Chong Qing” to prevent pests for a long time were found to be resistant to “Jia Chong Qing” with resistance index of 3.88 measured using RT-PCR and immunohistochemistry analysis showed that both CYP4G19 mRNA and CYP4G19 protein expression levels in the wild strain were substantially higher than that of a sensitive strain. dsRNA segments derived from the target gene CYP4G19 were prepared using in vitro transcription and were microinjected into abdomens of the wild strain. Two to eight days after injection, the result showed that CYP4G19 mRNA expressions were significantly reduced in the groups injected with dsRNAs. 1. Introduction The German cockroach (Blattella germanica) is common house pest that can spread diseases by carrying bacteria and viruses, and it can cause allergic responses in human such as asthma [1]. German cockroaches have a good adaptability to different environments and can propagate rapidly. They can become resistant to chemical pesticides easily and are one of the major obstacles for the control of urban pests. It was indicated that the mechanism of pyrethroid resistance involves the metabolic enzyme cytochrome P450 [2]. CYP450 is a hemoprotein that acts as the terminal oxidase in monooxygenase system. In vivo, it catalyzes oxidizing reaction of endogenous and exogenous material, and plays an important role in pesticide detoxification [3]. RNA interference (RNAi) is a technology that can be used to down-regulate the expression of a gene by the addition of a gene-specific double-stranded RNA (dsRNA). It was originally characterized in Caenorhabditis elegans [4] and has since been applied to a wide variety of organisms to study gene function, including protozoa, insects, and mammals [5–7]. The molecular processes and components necessary for a functional RNAi pathway have been extensively investigated in C. elegans [8]. B. germanica has been used as a model to study nuclear receptor families participating in the 20-hydroxyecdysone (20E)-triggered genetic hierarchy [9]. B. germanica E75 is a member of the 20E-triggered genetic hierarchy, and RNAi experiments in vivo during the penultimate and last nymphal instars of B. germanica reveal that BgE75 is required for successfully completing nymphal-nymphal and nymphal-adult transitions. Injection of dsRNA into the haemocoel of nymphs and adults of the cockroach B. germanica was used to silence gene function in vivo and to halt the
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