Thelytokous Reproduction of Onion Thrips, Thrips tabaci Lindeman 1889, Infesting Welsh Onion and Genetic Variation among Their Subpopulations.

Yonggyun Kim,Falguni Khan,Miltan Chandra Roy

doi:10.3390/insects13010078

Abstract

Simple SummaryParthenogenesis is an asexual type of reproduction that usually occurs in thrips. Thelytokous parthenogenesis is a kind of reproduction that produces female progeny without mating. This study reports a thelytokous reproduction of the onion thrips, Thrips tabaci Lindeman 1889, host strain infesting Welsh onion. Cytochrome oxidase I (COI) sequences of the populations exhibited specific residues at conserved positions of thelytokous biotype (called ‘L2’). Phylogenetic tree analysis revealed that COI sequences of the onion thrips collected from different local populations infesting Welsh onion were clustered with L2 biotype populations. In the laboratory, the thelytokous reproduction was demonstrated because each single thrips produced only female progeny. Interestingly, these thelytokous populations collected from different localities showed a certain level of genetic diversity. However, the genetic distance was independent of the actual distance among different local populations. Results of this study indicate that T. tabaci infesting Welsh onion is a thelytokous biotype with genetic variation among local populations.Parthenogenesis is not uncommon in thrips. This asexual reproduction produces males (arrhenotokous) or female (thelytokous). Only females are found in the onion thrips (Thrips tabaci Lindeman 1889) infesting Welsh onion (Allium fistulosum) in several areas of Korea. To determine the reproduction mode of T. tabaci, thrips infesting Welsh onion were collected from different localities in Korea. Cytochrome oxidase I (COI) sequences were then assessed. Results showed that all test local populations had signature motif specific to a thelytokous type. These COI sequences were clustered with other thelytokous populations separated from arrhenotokous T. tabaci populations. In a laboratory test, individual rearing produced female progeny without any males. These results support that Korean onion thrips infesting Welsh onion have the thelytokous type of parthenogenesis. Local thrips populations exhibited significant variations in susceptibility to chemical and biological insecticides. Random amplified polymorphic DNA (RAPD) analysis indicated genetic variations of local populations. However, the genetic distance estimated from RAPD was independent of the actual distance among different local populations. These results suggest that genetic variations of T. tabaci are arisen from population subdivision due to asexual thelytokous reproductive mode.

Highlights

The onion thrips (Thrips tabaci Lindeman 1889) (Thysanoptera: Thripidae) is an important insect pest of onions including Welsh onion (Allium fistulosum L.)
To control the thrips, foliar spray of chemical insecticides including spinetoram resulted in both regional and temporal variations in its efficacy in USA [7]. This suggests a genetic heterogeneity among the onion thrips populations they can produce progeny in a parthenogenetic mode from a single parent
All biotypes are parthenogenous, T and L1 biotypes reproduce through arrhenotoky while L2 biotype reproduces through thelytoky [11]

Summary

Introduction

The onion thrips (Thrips tabaci Lindeman 1889) (Thysanoptera: Thripidae) is an important insect pest of onions including Welsh onion (Allium fistulosum L.). In addition to directly feeding on plant tissues, the onion thrips play an important role in the transmission of several onion pathogens such as Pantoea agglomerans and P. ananatis known to cause bacterial stalk and leaf necrosis [2,3]. To control the thrips, foliar spray of chemical insecticides including spinetoram resulted in both regional and temporal variations in its efficacy in USA [7]. This suggests a genetic heterogeneity among the onion thrips populations they can produce progeny in a parthenogenetic mode from a single parent. All biotypes are parthenogenous, T and L1 biotypes reproduce through arrhenotoky (unfertilized eggs develop to males) while L2 biotype reproduces through thelytoky (unfertilized eggs develop into females) [11]

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