Pest risk assessment of light brown apple moth, Epiphyas postvittana (Lepidoptera: Tortricidae) using climate models and fitness-related genetic variation

Abstract

Light brown apple moth (LBAM), Epiphyas postvittana, is a leafroller pest native to Australia and currently has limited distribution around the world. The moth is an extremely polyphagous species which can feed on more than 250 host plants, including many important economic crops such as fruit, vegetable and ornamental species. Epiphas postvittana is also well-known for its polymorphism with respect to its morphology. Its physiology and biology have been well studied compared with many other pest species. For the past 10 years, however, this moth has been gradually expanding its territory around the world. This has resulted in increasing calls for targeted risk assessment so that appropriate quarantine measurements can be put in place to prevent its entry and spread into new regions. Three important aspects related to risk of establishment by E. postvittana were investigated in this study, 1) E. postvittana potential global distribution based on climate, 2) the genetic variation of a target gene for its potential to assess population fitness and invasibility, and 3) the potential use of barcoding as molecular tool for E. postvittana identification at the border. By comparing the climatic conditions of its native (Australia) and long-established (New Zealand) ranges to the rest of the world using CLIMEX, it is suggested that E. postvittana has potential to establish in countries in Central and South America, southern Africa, west Europe and South-east Asia. However, the predicted global distribution of E. postvittana using a range of other types of species distribution models suggested that there are additional climatically suitable areas around the world where this species could potentially survive and establish. Morphological identification of E. postvittana has been problematic which increased the risk of it esacaping detection at the border of countries that wish to regulate this pest. In this study, we sequenced the COI gene from 26 samples of E. postvittana from four populations in New Zealand. We found that the intraspecies variation of E. postvittana is less than 3%, while interspecies variation between E. postvittana and other tortricid species available in the barcode of life database (BOLD) system is much greater than 3%. This result confirms that using barcodes for identification of E. postvittana for biosecurity purposes is practical. The COI gene sequences have been submitted to GenBank as reference sequences. Genetic analysis of the phosphoglucose-isomerase (Pgi) gene in E. postvittana was investigated based on its association with various characteristics of fitness in other Lepidoptera. Using novel PCR primers developed in this study, a comparison of 957 bp of the Pgi coding region amongst four E. postvittana populations revealed 70 segregating sites including 61 synonymous and nine non-synonymous sites. Introns of Pgi gene also show a great variation in length among populations and between alleles within the same locus. The significant variation of Pgi gene in E. postvittana populations indicates the Pgi gene as a useful target gene to assess fitness factors associated with invasibility of E. postvittana. Modeling species distributions and pest identification are both key components in pest risk assessment. The study of fitness-associated genetic variation is currently a novel approach additional approach to risk assessment of invasive species but has much potential in this area. Our study provides basic but important information for further assessment of the establishment capacity of this species in new habitats. Further research in these areas will provide the knowledge required to make science-based decisions in biosecurity.