Developmental Control of a Lepidopteran Pest Spodoptera exigua by Ingestion of Bacteria Expressing dsRNA of a Non-Midgut Gene

Background: RNA interference (RNAi) induced through double stranded RNA (dsRNA) has been used widely to study gene function in insects. Recently, it has been reported that gene knockdown in several insects can be induced successfully through feeding with dsRNA. However, it is still unknown whether phenotypic silencing of genes not expressed in the midgut occurs after ingestion of insect dsRNA. Principal Findings: Using chitin synthase gene A (SeCHSA) as the target gene, which is expressed in the cuticle and tracheae of the lepidopteran pest Spodoptera exigua, we showed that the growth and development of S. exigua larvae fed Escherichia coli expressing dsRNA of SeCHSA was disturbed, resulting in lethality. In the 4th and 5th larval instars, prepupae, and pupae, the mean survival rates of insects fed the dsRNA-containing diet were 88.64%, 74.24%, 68.43% and 62.63% respectively. The survival rates in the 5(th) instar larvae, prepupae and pupae stages were significantly lower than those of all controls, and significant lethality differences were also found between dsSeCHSA treatment and dsControl or ddH(2)O control in the 4(th) instar larvae. The effects of ingesting bacterially expressed dsRNA on transcription of the target gene, tissue structure, and survival rates of insects were dose-dependent. Conclusions: Our results suggest that SeCHSA dsRNA may be useful as a means of insect pest control.