Larval species composition and genetic structures of Carposina sasakii, Grapholita dimorpha, and Grapholita molesta from Korea

Rapid determination of the larval species composition and understanding of their genetic structure is important to establish the appropriate management system for multiple species infesting in fruits. We established accurate and rapid diagnostic methods based on multiplex polymerase chain reaction (PCR) diagnostic techniques to discriminate the three major lepidopteran species in orchard, Carposina sasakii, Grapholita dimorpha, and Grapholita molesta. Each species was identified by amplifying species-specific PCR products (375 bp for C. sasakii, 125 and 234 bp for G. dimorpha, and 125 bp for G. molesta). Based on species composition analysis from six types of infested fruits, G. dimorpha constituted the highest proportion (47.8%), followed by 35.2 and 13.5% for G. molesta and C. sasakii, respectively. Interestingly, high prevalence was found in G. dimorpha and G. molesta for plum and peach, respectively. Based on genetic diversity analysis, the three insect species exhibited moderate or high haplotype diversity and low nucleotide diversity, ranging from 0.319 to 0.699 and 0.0006 to 0.0045, respectively. Demographic expansion was not detected according to either a neutrality test or mismatch distribution analysis. Moreover, no significant genetic structure corresponding to province, host plant, fruit type, or collection period was observed. These results suggest that the population of each species would have high dispersal ability following fruit-generating periods via intrinsic host adaptation ability regardless of the spatial and temporal conditions. Determination of larval composition on fruit is valuable for establishing appropriate management systems that take the species into consideration; additionally, population genetic approaches can be utilized to understand the effects of environmental factors (province, host fruit, fruit type, etc.) on population structures.

Comparative transcriptome analysis of sex pheromone glands of two sympatric lepidopteran congener species

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.