Mitochondrial DNA revealed the extent of genetic diversity and invasion origin of populations from two separate invaded areas of a newly invasive pest, Cydia pomonella (L.) (Lepidoptera: Tortricidae) in China

Reads in a haystack: extracting complete mitogenome sequences hidden in baculovirus datasets

Thaumatotibia leucotreta (Lepidoptera, Tortricidae) is one of many economically important insect pests for which no complete mitogenome sequence is available. The complete mitochondrial sequences for this species and other key pests could assist in the development of novel molecular techniques, such as enabling the identification of population-specific markers which could assist in improved monitoring of populations. The objective of this study was to determine whether NGS datasets generated for entomopathogenic viruses contain reads originating from host mitochondrial DNA. A total of 28 NGS datasets generated for the baculovirus Cryptophlebia leucotreta granulovirus (CrleGV) were analysed in this study. Three datasets contained sufficient reads providing adequate coverage for the assembly of complete mitogenomes. All 13 protein-coding genes, 22 tRNAs and both rRNAs present in the mitogenomes of other species within the Grapholitini tribe, were identified. Phylogenetic analysis of the mitogenomes at both an intrafamilial and interspecies level grouped the sequences within the Olethreutinae and T. leucotreta clades, respectively. Analysis of single nucleotide variations (SNVs) between each T. leucotreta sequence indicated up to 75 differences across the mitogenome. The methodology used in this study could be expanded to other baculovirus NGS datasets enabling the generation of novel lepidopteran mitogenome sequences.

Population Genetic Structure of Codling Moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), in Different Localities and Host Plants in Chile

The codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), is a major pest introduced to almost all main pome fruit production regions worldwide. This species was detected in Chile during the last decade of the 19th century, and now has a widespread distribution in all major apple-growing regions. We performed an analysis of the genetic variability and structure of codling moth populations in Chile using five microsatellite markers. We sampled the codling moth along the main distribution area in Chile on all its main host-plant species. Low genetic differentiation among the population samples (F_ST = 0.03) was found, with only slight isolation by distance. According to a Bayesian assignment test (TESS), a group of localities in the coastal mountain range from the Bío-Bío Region formed a distinct genetic cluster. Our results also suggest that the codling moth that invaded the southernmost locality (Aysén Region) had two origins from central Chile and another unknown source. We did not find significant genetic differentiation between codling moth samples from different host-plant species. Our results indicate high genetic exchange among codling moth populations between the different Chilean regions and host plants.

Genetic diversity of Diaphorina citri and its endosymbionts across east and south-east Asia

BACKGROUND

Diaphorina citri is the vector of 'Candidatus Liberibacter asiaticus', the most widespread pathogen associated huanglongbing, the most serious disease of citrus. To enhance our understanding of the distribution and origin of the psyllid, we investigated the genetic diversity and population structures of 24 populations in Asia and one from Florida based on the mtCOI gene. Simultaneously, genetic diversity and population structures of the primary endosymbiont (P-endosymbiont) 'Candidatus Carsonella ruddii' and secondary endosymbiont (S-endosymbiont) 'Candidatus Profftella armatura' of D. citri were determined with the housekeeping genes.

RESULT

AMOVA analysis indicated that populations of D. citri and its endosymbionts in east and south-east Asia were genetically distinct from populations in Pakistan and Florida. Furthermore, P-endosymbiont populations displayed a strong geographical structure across east and south-east Asia, while low genetic diversity indicated the absence of genetic structure among the populations of D. citri and its S-endosymbiont across these regions.

CONCLUSION

The 'Ca. C. ruddii' is more diverse and structured than the D. citri and the 'Ca. P. armatura' across east and south-east Asia. Multiple introductions of the psyllid have occurred in China. Management application for controlling the pest is proposed based on the genetic information of D. citri and its endosymbionts. © 2017 Society of Chemical Industry.

Mitochondrial DNA markers reveal high genetic diversity and strong genetic differentiation in populations of Dendrolimus kikuchii Matsumura (Lepidoptera: Lasiocampidae)

Dendrolimus kikuchii Matsumura, 1927 is a serious forest pest causing great damage to coniferous trees in China. Despite its economic importance, the population genetics of this pest are poorly known. We used three mitochondrial genes (COI, COII and Cytb) to investigate the genetic diversity and genetic differentiation of 15 populations collected from the main distribution regions of D. kikuchii in China. Populations show high haplotype and nucleotide diversity. Haplotype network and phylogenetic analysis divides the populations into three major clades, the central and southeastern China (CC+SEC) clade, the eastern China (EC) clade, and the southwestern China (SWC) clade. Populations collected from adjacent localities share the same clade, which is consistent with the strong relationship of isolation by distance (r = 0.74824, P = 0.00001). AMOVA analysis indicated that the major portion of this molecular genetic variation is found among the three groups of CC+SEC, EC and SWC (61.26%). Of 105 pairwise FST comparisons, 93 show high genetic differentiation. Populations of Puer (PE), Yangshuo (YS) and Leishan (LS) are separated from other populations by a larger genetic distance. Distributions of pairwise differences obtained with single and combined gene data from the overall populations are multimodal, suggesting these populations had no prior population expansion in southern China. The nonsignificant neutral test on the basis of Tajima' D and Fu's Fs, and the lack of a star-shaped haplotype network together with the multiple haplotypes support this hypothesis. Pleistocene climatic fluctuations, combined with the host specificity to Pinus species, made these regions of south China into a refuge for D. kikuchii. The high level of population genetic structuring is related to their weak flight capacity, their variations of life history and the geographic distance among populations.

Diversity of tortricid moths in apple orchards: evidence for a cryptic species of Grapholita (Lepidoptera: Tortricidae) from China

Understanding herbivore diversity both at the species and genetic levels is a key to effective pest management. We examined moth samples from multiple locations from a major apple growing region in China. For specimen collection, we used a pheromone trap designed to attract Grapholita molesta (Busck) (Lepidoptera: Tortricidae). Surprisingly, we found a second species captured at high proportions. Its external morphology (e.g., male genitalia and forewing coloration) was the same as for Grapholita funebrana Treitschke (Lepidoptera: Tortricidae) specimens from Europe. However, the barcode sequence of the mitochondrial gene cytochrome oxidase I (COI) diverged markedly between specimens from China and Europe, and the genetic distance value between the specimens from the two regions as estimated using the Juke-Cantor (JC) model amounted to 0.067. These morphological and molecular findings together point to a cryptic species in G. funebrana from China. Further molecular analyses based on COI and COII genes revealed its extremely high genetic diversity, indicating that the origin of this species includes the sampling region. Moreover, molecular data suggest that this species passed through a recent population expansion. This is the first report on a cryptic species in G. funebrana, as well as the first report on its genetic diversity.

DNA barcodes for bio-surveillance: regulated and economically important arthropod plant pests

Many of the arthropod species that are important pests of agriculture and forestry are impossible to discriminate morphologically throughout all of their life stages. Some cannot be differentiated at any life stage. Over the past decade, DNA barcoding has gained increasing adoption as a tool to both identify known species and to reveal cryptic taxa. Although there has not been a focused effort to develop a barcode library for them, reference sequences are now available for 77% of the 409 species of arthropods documented on major pest databases. Aside from developing the reference library needed to guide specimen identifications, past barcode studies have revealed that a significant fraction of arthropod pests are a complex of allied taxa. Because of their importance as pests and disease vectors impacting global agriculture and forestry, DNA barcode results on these arthropods have significant implications for quarantine detection, regulation, and management. The current review discusses these implications in light of the presence of cryptic species in plant pests exposed by DNA barcoding.