Mitochondrial genome sequences have been used in diverse fields of biology. In this study, we sequenced the complete mitochondrial genomes (mitogenome) of two pear pests: Cacopsylla jukyungi, the most damaging insect pest to commercial pears in South Korea, and Cacopsylla burckhardti (Hemiptera: Psyllidae). The two mitogenomes were compared to confamilial species to accumulate genetic information and understand evolutionary characteristics of the family Psyllidae. The 15,438 bp-and 14,799 bp-long complete mitogenomes of C. jukyungi and C. burckhardti, respectively, had many features typical of insect mitogenomes; however, at 1283 bp, the C. jukyungi mitogenome had an unusually long A+T-rich region, which was composed of two identical 540-bp repeat sequences. Among the intergenic spacer regions, the one located at the ND1 and trnS₂ junction was relatively well conserved in length (mostly within 23–36 bp). This region had a high sequence identity in all Psyllidae, possessing a 5-bp consensus sequence (CGGTA), which is speculated to have a functional role. Though the A+T-rich region in available Psyllidae mitogenomes varied substantially in length (662–1430 bp) and sequence divergence, all species had a conserved sequence stretch at the 3′-end of srRNA, which is also speculated to have a functional role. Genetic divergence among genes indicated the lowest variability in srRNA, lrRNA, and COI, whereas ATP8 and ND6 showed the highest variability at both family and genus (Cacopsylla) levels. Our data provide evidence that the family Psyllidae, including current C. jukyungi and C. burckhardti, have evolutionary unique features that were previously undetected, along with the unique A+T-rich region structure in C. jukyungi.

The pear pest, Cacopsylla jukyungi (Hemiptera: Psyllidae), is the most damaging insect to commercial pears in South Korea. An assessment of the population genetic characteristics of the species will raise the potential of effective control. In the present study, we developed eight microsatellite markers specific to C. jukyungi and genotyped 132 individuals collected from 11 localities throughout South Korea. Populations showed lower observed heterozygosity than expected heterozygosity and slightly or highly positive values of inbreeding coefficients, suggesting that C. jukyungi is subjected to inbreeding. A strong dependence on commercial pear trees throughout the whole life cycle, even during overwintering, and a nationwide targeting of the overwintered adults are likely contributors to such heterozygosity deficiency. On the other hand, population analyses consistently indicated strong gene flow among populations, implying the presence of persistent factors that have facilitated this process. The nationwide expansion of pear orchards and the replacement with a popular new cultivar during the last 50 years, which may have accompanied the spread of C. jukyungi-bearing pear grafts and scions, are likely causes of such facilitated dispersal. Thus, a management strategy against unintended anthropogenic dispersal of the pear psyllid will be required for better control of C. jukyungi.

Drought stress and insecticide exposure are two significant environmental factors that can impact the physiology and behaviour of aphids, a major agricultural pest. An understanding of the mechanisms of green peach aphids’ response to insecticides under drought stress is a critical area of research that needs urgent attention. In view of this, we conducted this study to determine the impact of drought and insecticides on the activity of detoxification enzymes in green peach aphid. A 2 × 2 × 3 factorial experiment involving two levels of water treatments (drought and no drought), two levels of aphids infestation (aphids and no aphids), and three levels of pesticides applications (thiacloprid, flonicamid and no pesticide) was conducted. The treatments were arranged in a randomized complete block design with three replications. The results showed that there was a significant (p < 0.01) interaction effect of drought × insecticides on the green peach aphid performance under drought or no drought conditions. Generally, the highest aphids host acceptance, survival rate, colonization success, and average daily reproduction under drought and well-watered conditions occurred on flonicamid-treated plants, whereas thiacloprid-treated plants had the least. However, the thiacloprid-treated plants had higher photosynthetic rate, water use efficiency, lower stomatal conductance, and decreased transpiration rate. Moreover, flonicamid treatment increased the accumulation of glutathione–S-transferase, acetylcholinesterase, butyrylcholinesterase, 1-napthyle acetate, and 1-napthyle butyrate activities in aphids, compared to the thiacloprid treatments. The thiacloprid pesticide, which demonstrated higher efficacy against green peach aphid, can be used in areas where green peach aphids and drought stress are major concerns.