Effect of diflubenzuron on the chitin biosynthesis pathway in Conopomorpha sinensis eggs

Conopomorpha sinensis is the dominant borer pest of Litchi chinensis (litchi) and Euphoria longan (longan) in China. Control of C. sinensis is difficult because of its cryptic life habit; thus, an effective ovicide could be beneficial. The larvicidal effects of diflubenzuron (DFB) have been documented in many insect pest species. Therefore, DFB might be a useful ovicide to control C. sinensis. However, the detailed mode of action of DFB interference with insect molting and egg hatching is unclear. Thus, we studied alterations in expression of all genes potentially affected by DFB treatment using a transcriptome approach in 2-d-old C. sinensis eggs. Clean reads were assembled to generate 203 455 unigenes and 440 558 transcripts. A total of 4625 differently expressed genes, which included 2670 up-regulated and 1955 down-regulated unigenes, were identified. Chitin binding and chitin metabolic processes were among the most significant enriched pathways according to Gene Ontology analyses. Most of the genes that encode enzymes involved in the chitin biosynthesis pathway were unaffected, whereas genes that presumably encode cuticle proteins were up-regulated. Furthermore, altered expression patterns of 10 genes involved in the chitin biosynthesis pathway of C. sinensis embryos were observed in response to DFB treatment at different time points by quantitative reverse transcription polymerase chain reaction. We also observed abnormal development; there was reduced chitin content and modulated chitin distribution of newly hatched larvae, and altered egg hatching. Our findings illustrate an ovicidal effect of DFB on C. sinensis, and reveal more molecular consequences of DFB treatment on insects.