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Two internal apple feeders of Grapholita molesta and Grapholita dimorpha share two major sex pheromone components (stereoisomers) and exhibit a similar circadian rhythm of mating behavior. This study aimed to determine the genetic factors diversifying these two congeners with respect to sex pheromone biosynthetic machinery. Transcriptomes of sex pheromone glands in both species were analyzed with a deep sequencing technology. To find out the gene(s) responsible for the stereoisomer ratios of G. molesta and G. dimorpha, a hypothetic sex pheromone biosynthetic pathway was predicted based on the transcriptomes of their sex pheromone glands. Some orthologs of Δ10 desaturase and FARs in the synthetic pathway were specifically expressed in sex pheromone glands. The relatively high variation in DNA sequence and expression levels between G. molesta and G. dimorpha suggest their crucial roles in generating differential ratios of the sex pheromone stereoisomers in these two sympatric congeners.

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The occurrence of plum fruit moth, Grapholita dimorpha, has been recently reported in apple orchards in Korea. It has been suspected that G. dimorpha and its related species, G. molesta, may occur simultaneously in other host plants. This study reports the occurrence of G. dimorpha in pear orchards of different localities in Korea. The identification of G. dimorpha was determined by morphological characters and the DNA marker. The cross-trapping of both species may be possible because the major sex pheromone (SP) compositions for the two species are similar. From the monitoring data, G. dimorpha and G. molesta were caught in SP lure traps of G. dimorpha and both species were also caught in SP lure traps of G. molesta. This cross-trapping of G. molesta to a SP lure of G. dimorpha varied significantly among pear orchards in different geographical localities. Furthermore, the occurrence peaks of the two species were not coincidental in all monitored orchards. These suggest that monitoring data obtained from each SP trap of both species in pear orchards may be mixed with two species, which would result in the over-estimation of population density and peak frequency on both species in pear orchards.