Genetic Diversity in Invasive Populations of Argentine Stem Weevil Associated with Adaptation to Biocontrol.

Thomas W R Harrop,Sarah N Inwood,Siva Ganesh,Marissa F Le Lec,Rachael L Ashby,Tracey Van Stijn,John Skelly,Peter K Dearden,Hannah Henry,Jeanne M E Jacobs,Ruy Jauregui,Stephen L Goldson,Shannon E Taylor

doi:10.3390/insects11070441

Thomas W R Harrop, Sarah N Inwood + Show 11 more

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https://doi.org/10.3390/insects11070441

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Journal: Insects	Publication Date: Jul 14, 2020
Citations: 13	License type: CC BY 4.0

Affiliation: University of Otago, AgResearch, Lincoln University

Abstract

Modified, agricultural landscapes are susceptible to damage by insect pests. Biological control of pests is typically successful once a control agent has established, but this depends on the agent’s capacity to co-evolve with the host. Theoretical studies have shown that different levels of genetic variation between the host and the control agent will lead to rapid evolution of resistance in the host. Although this has been reported in one instance, the underlying genetics have not been studied. To address this, we measured the genetic variation in New Zealand populations of the pasture pest, Argentine stem weevil (Listronotus bonariensis), which is controlled with declining effectiveness by a parasitoid wasp, Microctonus hyperodae. We constructed a draft reference genome of the weevil, collected samples from a geographical survey of 10 sites around New Zealand, and genotyped them using a modified genotyping-by-sequencing approach. New Zealand populations of Argentine stem weevil have high levels of heterozygosity and low population structure, consistent with a large effective population size and frequent gene flow. This implies that Argentine stem weevils were able to evolve more rapidly than their biocontrol agent, which reproduces asexually. These findings show that monitoring genetic diversity in biocontrol agents and their targets is critical for long-term success of biological control.

Highlights

Biological control of pests via the release of specialist natural predators can provide continued, self-sustaining, non-polluting and inexpensive management
Genetic variation was found along a latitudinal cline, and was associated with signatures of selection in regions of the genome, indicating a level of local adaptation within populations, but at the resolution of this study we found no evidence of genetic adaptation in parasitised weevils compared to parasitoid-free weevils
Our results showed that the amount of genetic variation in New Zealand populations of Argentine stem weevil (ASW) is far greater than detected by traditional molecular markers [21,22], implying that ASW populations have evolved resistance via weak selection acting on variants of minor effect that existed before the introduction of M. hyperodae

Summary

Introduction

Biological control of pests via the release of specialist natural predators can provide continued, self-sustaining, non-polluting and inexpensive management. A biocontrol system has been in use since the 1990s to manage a destructive, invasive pest of. New Zealand pastures, the Argentine stem weevil (ASW; Listronotus bonariensis Kuschel) (Coleoptera: Curculionidae). New Zealand pastures are highly modified, based on a very low number of introduced. Palearctic plant species, and are particularity susceptible to pest impacts [5]. This susceptibility is due to low plant and animal diversity, resulting in low biotic resistance to invasive species [5]. In New Zealand, adult ASW populations can reach densities of 700 adults m-2 and cause economic impacts of up to

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