Abstract

Host plant affinity and geographic distance can play critical roles in the genetic divergence of insect herbivores and evolution of insect biotypes, but their relative importance in the divergence of insect populations is still poorly understood. We used microsatellite markers to test the effects of host plant species and geographic distance on divergence of two biotypes of the English grain aphid, Sitobion avenae (Fabricius). We found that clones of S. avenae from western provinces (i.e., Xinjiang, Gansu, Qinghai and Shaanxi) had significantly higher genetic diversity than those from eastern provinces (i.e., Anhui, Henan, Hubei, Zhejiang and Jiangsu), suggesting their differentiation between both areas. Based on genetic diversity and distance estimates, biotype 1 clones of eastern provinces showed high genetic divergence from those of western provinces in many cases. Western clones of S. avenae also showed higher genetic divergence among themselves than eastern clones. The Mantel test identified a significant isolation-by-distance (IBD) effect among different geographic populations of S. avenae, providing additional evidence for a critical role of geography in the genetic structure of both S. avenae biotypes. Genetic differentiation (i.e., FST) between the two biotypes was low in all provinces except Shaanxi. Surprisingly, in our analyses of molecular variance, non-significant genetic differentiation between both biotypes or between barley and wheat clones of S. avenae was identified, showing little contribution of host-plant associated differentiation to the divergence of both biotypes in this aphid. Thus, it is highly likely that the divergence of the two S. avenae biotypes involved more geographic isolation and selection of some form than host plant affinity. Our study can provide insights into understanding of genetic structure of insect populations and the divergence of insect biotypes.

Highlights

  • Many insect species are serious pests on various horticultural plants and agricultural crops.In order to develop ecologically based management programs, it is of great importance to understand the genetic diversity and population structure of insect pests

  • Our results indicate that geographic distance can play a significant role in the genetic structure of both S. avenae biotypes

  • Host plant use and geographic distance are some of the factors that can influence the genetic divergence of insect herbivores and development of insect biotypes

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Summary

Introduction

Many insect species are serious pests on various horticultural plants and agricultural crops.In order to develop ecologically based management programs, it is of great importance to understand the genetic diversity and population structure of insect pests. Genetic diversity and divergence among populations are essential in enabling insect species to respond rapidly to evolutionary challenges, having significant impacts on the adaptability of insects under constantly changing environmental conditions [1,2,3]. Insects 2020, 11, 117 genetic differentiation and diversification from combined effects of mutation, selection, gene flow, and genetic drift [4,5,6,7]. In this process, gene flow among populations could have been prevented by some environmental barriers, and local selection could be in turn accelerated, promoting changes in genetic structure of populations [6,7,8]. Various biotypes (usu. host plant associated populations) have been constantly discovered in many pest insects like the pea aphid (Acyrthosiphon pisum), Hessian fly (Mayetiola destructor), black currant leaf midge (Dasineura tetensi), and soybean aphid (Aphis glycines) [17,18,19,20]

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