Genetic Studies on RPW and Other Coleopterans: Genetic Variation and Invasion History

The Red Palm Weevil (RPW), Rhynchophorus ferrugineus (Olivier, 1790), (Coleoptera, Curculionidae, Rhynchophorinae (Dryophthorinae)), is an invasive species that is originated from Southeast Asia. During the last three decades, multiple introductions of RPW to the Middle East, Europe, Caribbean (Island of Curacao, Netherlands Antilles) and USA have occurred and the RPW is now a serious pest of many palm species. Considering the economic importance of RPW, it is necessary to know the history of its invasion and to understand the relationships between the different geographic populations.  In the recent work the genetic variation, genetic invasion history of different geographic populations of RPW collected from the Middle-East and the Mediterranean basin areas were investigated using different molecular markers such as Cytochrome oxidase c subunit 1 (CO1), Cytochrome b (Cytb), ITS2-rDNA and RAPD.   Genetic variation among the tested populations of RPW was detected using the mitochondrial markers and RAPDs’ markers. On the other hand ITS2-rDNA could not detect any Genetic variation. The spatial pattern of the mitochondrial genetic variation revealed that the tested populations of RPW subdivided into two groups according to their geographic positions: 1) the Multicontinent group represented by one haplotype and contained populations from three different continents such as Africa- Egypt, Asia-KSA, Turkey and Europe-Cyprus, France, Greece, Italy, and Spain and 2) the Asian group represented by several haplotypes and contained populations from Asia- Iran, Japan, Oman, Pakistan, Syria and UAE. The genetic distances estimated between the two groups indicated that they have likely diverged about one to two MYA. The haplotype of the Multicontinent group was not included into the Asian haplotype clad indicating its different source population in the area of origin.  RAPD profiles exhibited bands between 200 to 1400 bp in length. Average genetic distances among populations ranged from 0.3 to 0.8. Genetic distances among the analyzed individuals ranged from 0.241 (between individuals from populations of Egypt and Turkey) to 1(between individuals from populations of Japan and both Egypt, Spain and France). The Unweighted Pair Group Method with Arithmetic mean (UPGMA) categorized the tested populations into twelve clusters.   Based on the obtained results, it is concluded that there are two major routes of RPW invasion, the first is at the origin of all the populations found in Egypt and Mediterranean countries and the second is the origin of the populations found in the Arabic Peninsula, Iran and Pakistan.  Genetic comparison between RPW and other four Rhynchophorus spp. such as R. bilineatus, R. phoenicis, R. cruentatus and R. palmarum was investigated using partial sequences of partial COI gene sequences. The number of polymorphic sites ranged from 79 to 102 while the genetic distances ranged from‎0.058 to 0.095 ‎. The number of polymorphic sites, genetic distances and phylogenetic relationships among R. ferrugineus and the other four tested species revealed that R. ferrugineus was more closely related to R. bilineatus while it was distantly related to R. palmarum. It is possible to rank the five tested Rhynchophorus ‎spp. as follows: ‎ R. ferrugineus, R. ‎bilineatus, R. phoenicis, R. cruentatus and R. ‎palmarum.