The codling moth Cydia pomonella, a major invasive pest of pome fruit, has spread around the globe in the last half century. We generated a chromosome-level scaffold assembly including the Z chromosome and a portion of the W chromosome. This assembly reveals the duplication of an olfactory receptor gene (OR3), which we demonstrate enhances the ability of C. pomonella to exploit kairomones and pheromones in locating both host plants and mates. Genome-wide association studies contrasting insecticide-resistant and susceptible strains identify hundreds of single nucleotide polymorphisms (SNPs) potentially associated with insecticide resistance, including three SNPs found in the promoter of CYP6B2. RNAi knockdown of CYP6B2 increases C. pomonella sensitivity to two insecticides, deltamethrin and azinphos methyl. The high-quality genome assembly of C. pomonella informs the genetic basis of its invasiveness, suggesting the codling moth has distinctive capabilities and adaptive potential that may explain its worldwide expansion.

The oriental fruit moth Grapholita ( = Cydia) molesta is a key fruit pest globally. Despite its economic importance, little is known about its population genetics in its putative native range that includes China. We used five polymorphic microsatellite loci and two mitochondrial gene sequences to characterize the population genetic diversity and genetic structure of G. molesta from nine sublocations in three regions of a major fruit growing area of China. Larval samples were collected throughout the season from peach, and in late season, after host switch by the moth to pome fruit, also from apple and pear. We found high numbers of microsatellite alleles and mitochondrial DNA haplotypes in all regions, together with a high number of private alleles and of haplotypes at all sublocations, providing strong evidence that the sampled area belongs to the origin of this species. Samples collected from peach at all sublocations were geographically structured, and a significant albeit weak pattern of isolation-by-distance was found among populations, likely reflecting the low flight capacity of this moth. Interestingly, populations sampled from apple and pear in the late season showed a structure differing from that of populations sampled from peach throughout the season, indicating a selective host switch of a certain part of the population only. The recently detected various olfactory genotypes in G. molesta may underly this selective host switch. These genetic data yield, for the first time, an understanding of population dynamics of G. molesta in its native range, and of a selective host switch from peach to pome fruit, which may have a broad applicability to other global fruit production areas for designing suitable pest management strategies.

No abstract

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NADPH–cytochrome P450 reductase (CPR) plays an important role in the cytochrome P450 (CYP)-mediated metabolism of endogenous and exogenous substrates. CPR has been found to be associated with insecticide metabolism and resistance in many insects. However, information regarding CPR in the bird cherry-oat aphid, Rhopalosiphum padi, is unavailable. In the current study, a full-length cDNA (2,476 bp) of CPR (RpCPR) encoding 681 amino acids was cloned from R. padi. Nucleotide sequence and deduced amino acid sequence analysis showed that RpCPR exhibits characteristics of classical CPRs and shares high identities with those of other insects, especially with the pea aphid, Acyrthosiphon pisum. The mRNA of RpCPR was expressed at all developmental stages, with the highest expression level found in the second instar and the lowest in adult. Expression levels of RpCPR in isoprocarb-resistant and imidacloprid-resistant strains were 3.74- and 3.53-fold higher, respectively, than that of a susceptible strain. RpCPR expression could also be induced by low concentrations (LC30) of isoprocarb and imidacloprid. Moreover, we sequenced the open reading frame (ORF) of RpCPR from 167 field samples collected in 11 geographical populations. Three hundred and thirty-four SNPs were detected, of which, 65 were found in more than two individuals. One hundred and ninety-four missense mutations were present in the amino acid sequence, of which, the P484S mutant had an allele frequency of 35.1%. The present results suggest that RpCPR may play an important role in the P450-mediated insecticide resistance of R. padi to isoprocarb and imidacloprid and possibly other insecticides. Meanwhile, RpCPRmaintains high genetic diversity in natural individuals, which provides the possibility of studying potential correlations between variants and certain special physiological characters.