Inferring native range and invasion scenarios with mitochondrial DNA: the case of T. solanivora successive north–south step-wise introductions across Central and South America

Trade-off and adaptive cost in a multiple-resistant strain of the invasive potato tuber moth Tecia solanivora

BACKGROUND

Resistance to pesticides is an evolutionary process that entails, in most cases, substantial consequences to the biology of the resistant populations. In this study we focus on the life history traits of the potato tuber moth Tecia solanivora, an invasive and voracious pest for which resistance to pyrethroid insecticides was recently reported. Marginally resistant and multiple-resistant populations were selected from eight sampled localities in Colombia; the use of a fully susceptible population was not possible since none was recognized in the laboratory or field. The multiple-resistant Siachoque population exhibited a 42-fold resistance to the carbamate insecticide carbofuran, and low levels of resistance to chlorpyrifos, a trend observed in six of the eight tested populations. This population also exhibits 24-fold resistance to permethrin. The marginally resistant population of Gualmatán showed 4-fold resistance to chlorpyrifos.

RESULTS

The multiple-resistant population exhibited a 3.8-day shorter developmental time than the susceptible population, but with higher larval mortality. The peak of egg-laying was delayed in the resistant population in 9 days and the population growth rate was lower than that of the susceptible population.

CONCLUSION

We hypothesize that the short developmental time of the multiple-resistant population may be an adaptation to minimize exposure to insecticides, which are applied to the soil. This adaptation is likely to require the surviving adults to compensate for the smaller nutrient amounts accumulated by the larvae in investing part of its adult life in securing the necessary resources for late-life egg production. © 2018 Society of Chemical Industry.

Pest categorisation of Tecia solanivora

The Panel on Plant Health performed a pest categorisation of Tecia solanivora (Lepidoptera: Gelechiidae) the Guatemalan potato tuber moth, for the EU. T. solanivora is a well-defined species which feeds exclusively on Solanum tuberosum. It was first described from Costa Rica in 1973 and has spread through Central America and into northern South America via trade of seed potatoes. It has also spread to Mexico and the Canary Islands and most recently to mainland Spain where it is under official control in Galicia and Asturias. Potatoes in the field and storage can be attacked. Some authors regard T. solanivora as the most important insect pest of potatoes globally. T. solanivora is currently regulated by Council Directive 2000/29/EC, listed in Annex II/AI as Scrobipalpopsis solanivora. Larvae feed and develop within potato tubers; infested tubers therefore provide a pathway for pest introduction and spread, as does the soil accompanying potato tubers if it is infested with eggs or pupae. As evidenced by the ongoing outbreaks in Spain, the EU has suitable conditions for the development and potential establishment of T. solanivora. The pest could spread within the EU via movement of infested tubers; adults can fly and disperse locally. Larval feeding destroys tubers in the field and in storage. In the warmer southern EU, where the development would be fastest, yield losses would be expected in potatoes. Measures are available to inhibit entry via traded commodities (e.g. prohibition on the introduction of S. tuberosum). T. solanivora satisfies all of the criteria assessed by EFSA to satisfy the definition of a Union quarantine pest. It does not satisfy EU regulated non-quarantine pest (RNQP) status because it is under official control. There are uncertainties over the effectiveness of preventing illegal imports via passenger baggage and the magnitude of potential impacts in the cool EU climate.

Mitochondrial genome characterization of Tecia solanivora (Lepidoptera: Gelechiidae) and its phylogenetic relationship with other lepidopteran insects

The complete mitogenome of the potato tuber moth Tecia solanivora (Lepidoptera: Gelechiidae) was sequenced, annotated, characterized and compared with 140 species of the order Lepidoptera. The circular genome is 15,251 bp, containing 37 genes (13 protein-coding genes (PCGs), two rRNA genes, 22 tRNA genes and an A+T-rich region). The gene arrangement was identical to other lepidopteran mitogenomes but different from the ancestral arrangement found in most insects for the tRNA-Met gene (A+T-region, tRNA-I, tRNA-Q, tRNA-M). The mitogenome of T. solanivora is highly A+T-biased (78.2%) and exhibits negative AT- and GC-skews. All PCGs are initiated by canonical ATN start codons, except for Cytochrome Oxidase subunit 1 (COI), which is initiated by CGA. Most PCGs have a complete typical stop codon (TAA). Only NAD1 has a TAG stop codon and the COII and NAD5 genes have an incomplete stop codon consisting of just a T. The A+T-rich region is 332 bp long and contains common features found in lepidopteran mitogenomes, including the 'ATAGA' motif, a 17 bp poly (T) stretch and a (AT)8 element preceded by the 'ATTTA' motif. Other tandem repeats like (TAA)4 and (TAT)7 were found, as well as (T)6 and (A)10 mononucleotide repeat elements. Finally, this mitogenome has 20 intergenic spacer regions. The phylogenetic relationship of T. solanivora with 28 other lepidopteran families (12 superfamilies) showed that taxonomic classification by morphological features coincides with the inferred phylogeny. Thus, the Gelechiidae family represents a monophyletic group, suggesting that T. solanivora and Pectinophora gossypiella have a recent common ancestor.

Molecular genetics and genomics generate new insights into invertebrate pest invasions

Invertebrate pest invasions and outbreaks are associated with high social, economic, and ecological costs, and their significance will intensify with an increasing pressure on agricultural productivity as a result of human population growth and climate change. New molecular genetic and genomic techniques are available and accessible, but have been grossly underutilized in studies of invertebrate pest invasions, despite that they are useful tools for applied pest management and for understanding fundamental features of pest invasions including pest population demographics and adaptation of pests to novel and/or changing environments. Here, we review current applications of molecular genetics and genomics in the study of invertebrate pest invasions and outbreaks, and we highlight shortcomings from the current body of research. We then discuss recent conceptual and methodological advances in the areas of molecular genetics/genomics and data analysis, and we highlight how these advances will further our understanding of the demographic, ecological, and evolutionary features of invertebrate pest invasions. We are now well equipped to use molecular data to understand invertebrate dispersal and adaptation, and this knowledge has valuable applications in agriculture at a time when these are critically required.