Distribution Pattern And Genetic Structure Of Phenacoccus Solenopsis Tinsley And Distribution Pattern Of Its Parasitoid Wasps In China

The cotton mealybug,Phenacoccus solenopsis Tinsley(Hemiptera: Pseudococcidae),is a cosmopolitan invader that damages many host plants of economic important,including cotton,vegetables,fruits,ornamental and tobacco,and thus inflicts significant damage to agricultural and horticultural industries worldwide.We revealed the explicit invasion areas and reconstructed the expansion process of P.solenopsis by field and literature investigations.Then we analysed the relations between expansion process of P.solenopsis with transportation and flower industry.This study also clearly indicated the occurrence and distribution pattern of the parasitoids of P.solenopsis and the relations with host plants.In addition,the influence of geographic isolation and host plants on the genetic diversity and genetic structure of P.solenopsis were analyzed based on mtDNA COI gene and nine microsatellite loci in present study.This work provides theory evidence for further understanding of the basis of outbreaks of the pest and the effective pest-control.The main results are as follows:(1)The invasion pattern of P.solenopsis.We revealed the explicit invasion areas and reconstructed the expansion process of P.solenopsis by field and literature investigations.Here,we describe the first recorded observation of P.solenopsis in Shandong Province and Kunming city of Yunnan Province.P.solenopsis was first detected in Chinese mainland in 2008 in Guangdong,has since invaded areas of 17 other provinces by 2018,and is still expanding its invasion ranges.The transportation and flower industry remarkably promoted the expansion process of P.solenopsis,especially through highways,national roads,provincial roads and the logistics trade centers.The flower industry also made great contributions to the expansion process of P.solenopsis,which incarnated in the high infestation level of P.solenopsis on the host plants that long-term existed in the flower markets or their surrounding.Thus,further monitoring and management strategy is required to limit the spread of this pest species.(2)Genetic diversity and structure of different geographical populations of P.solenopsis.In the present study,we genotyped five loci and sequenced the mtDNA COI derived from 85 populations collected from arcoss the invasion ranges of P.solenopsis in China and seven foreign populations.The results showed that all the populations have lower genetic diversity.However,the populations with high genetic diversity were collected from the transportation hub or flower industry developed areas,which would be the bridgehead for invasion of P.solenopsis.There was a high degree of genetic differentiation among different geographic populations,but no any geographical differentiation pattern.Meanwhile,most of the genetic variation was within populations,variation among geographical populations was next.More importantly,most populations had complicate genetic components,which would be genetic sources for strong adaptability of this pest.Overall,multiple invasions,long distance gene-flow wrought by human activity and the low mobility of this sedentary pest jointly lead to the genetic pattern of P.solenopsis,i.e.complicate genetic structure and a certain degree of genetic differentiation coexist in P.solenopsis.(3)Genetic diversity and structure of P.solenopsis from different host plants.Nine microsatellite loci and COI gene were used to investigate the variation of genetic diversity and genetic structure of P.solenopsis from 13 different host plants belong to five families in Guangdong Province.The results showed that all the populations have lower genetic diversity.However,the populations collected on plants belong to Malvaceae and Asteraceae had the relatively high genetic diversity,whilst the populations collected from Malvaceae were higher than that of Asteraceae.There was a high degree of genetic differentiation among populations from different host plants,especially the populations from Asteraceae,while the populations from Malvaceae,Portulacaceae and Solanaceae were opposite.Meanwhile,most of the genetic variations were within populations,variation among different populations collected from host plants belonging to the same family was next.Populations from Asteraceae showed relatively single genetic component.Instead,the complicate genetic components were found in populations from Malvaceae,Portulacaceae and Solanaceae,which would be genetic sources for host-switching of this pest.(4)The distribution pattern of the parasitoid wasps of P.solenopsis.The occurrence and pattern of parasitoid wasps of P.solenopsis were clarified by national investigation and molecular identification.In the present study,a total of 11 parasitoid wasp species inclusive of hyperparasitoids were identified.Parasitoid wasps are effective natural enemies of P.solenopsis,more than 60% populations of P.solenopsis were parasitized,the parasitism rate ranged from 5% to 70%.Aenasius bambawalei Hayat was found predominantly on P.solenopsis,and occurred in all host plants of P.solenopsis across its invasion ranges.The occurrence of parasitoid wasps was different in various populations of P.solenopsis from different host plant species.The parasitoid wasps of P.solenopsis were infrequently present on Asteraceae and Portulacaceae,while the opposite on Malvaceae.The parasitoid wasps of P.solenopsis were also infrequently present on ornamental bonsais,while the opposite on ornamental plants in the field.