Abstract
The beet armyworm, Spodoptera exigua (Hübner), is a serious pest worldwide that causes significant losses in crops. Unfortunately, genetic resources for the beet armyworm is extremely scarce. To improve these resources we sequenced the transcriptome of S. exigua representing all stages including eggs, 1st to 5th instar larvae, pupae, male and female adults using the Illumina Solexa platform. We assembled the transcriptome with Trinity that yielded 31,414 contigs. Of these contigs, 18,592 were annotated as protein coding genes by Blast searches against the NCBI nr database. It has been shown that knockdown of important insect genes by dsRNAs or siRNAs is a feasible mechanism to control insect pests. The first key step towards developing an efficient RNAi-mediated pest control technique is to find suitable target genes. To screen for effective target genes in the beet armyworm, we selected nine candidate genes. The sequences of these genes were amplified using the RACE strategy. Then, siRNAs were designed and chemically synthesized. We injected 2 µl siRNA (2 µg/µl) into the 4th instar larvae to knock down the respective target genes. The mRNA abundance of target genes decreased to different levels (∼20–94.3%) after injection of siRNAs. Knockdown of eight genes including chitinase7, PGCP, chitinase1, ATPase, tubulin1, arf2, tubulin2 and arf1 caused a significantly high level of mortality compared to the negative control (P<0.05). About 80% of the surviving insects in the siRNA-treated group of five genes (PGCP, chitinase1, tubulin1, tubulin2 and helicase) showed retarded development. In chitinase1-siRNA and chitinase7-siRNA administered groups, 12.5% survivors exhibited “half-ecdysis”. In arf1-siRNA and arf2-siRNA groups, the body color of 15% became black 48 h after injections. In summary, the transcriptome could be a valuable genetic resource for identification of genes in S. exigua and this study provided putative targets for RNAi pest control.
Highlights
The beet armyworm, Spodoptera exigua, is one of the most serious agricultural pests of vegetable and flower crops in many agricultural areas all over the world [1]
Since transcriptomes have been reported to be useful genetic resources for high-throughput screening of RNA interference (RNAi) target genes [26], we sequenced the transcriptome of the beet armyworm and selected nine candidate genes to study their potential application in RNAi mediated pest control
The version described in this paper is the first version. This transcriptome provides a useful resource with a large number of genes from the beet armyworm
Summary
The beet armyworm, Spodoptera exigua, is one of the most serious agricultural pests of vegetable and flower crops in many agricultural areas all over the world [1]. In the 1950s, this pest destroyed young citrus trees and nursery stocks in California, leading to substantial economic losses in approximately 500 acres of citrus areas [2]. It is a major pest of tomato in the Southeastern USA. The beet armyworm undergoes complete metamorphosis with a life cycle that consists of four different stages; eggs, five larval instars, pupae and adults Larvae feed on both foliage and fruit of crops. Beet armyworm eats more cabbages than the diamondback moth, Plutella xylostella (Linnaeus), but is less damaging than the cabbage looper, Trichoplusia ni (Hubner) [4] Control of this notorious pest is achieved by chemical pesticides. Since overuse of pesticides leads to environmental and food safety problems it is highly desirable to develop alternate pest control strategies [5]
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