HOST RACE FORMATION IN THE FLOWER HEAD INFESTING TEPHRITIDS IN LEBANON: EMPHASIS IS ON THE ROLE OF ENDOSYMBIONT

Abstract

Many insects form symbioses with bacteria. In some species, the symbiosis is obligatory and beneficial, while in others it is secondary involving guest microbes which can interfere with host reproduction. Reproductive endosymbionts, such as Wolbachia, are mainly transmitted vertically, and may cause cytoplasmic incompatibility in their insect hosts, consequently restricting gene flow between populations and facilitating host race formation and sympatric speciation. Wolbachia symbionts were commonly found in a number of fruit infesting tephritids; however, it is not known whether they are associated with the non-frugivorous tephritids such as the flower head infesting species. This study aimed at determining the prevalence and status of Wolbachia reproductive symbionts in the flower head infesting tephritids associated with thistles in Lebanon, to check whether the symbionts have a role in the rapid host race formation observed in the generalist tephritids species, Chaestotomella cylindrica and Terellia serratulae, which consist of a complex of host races, and to examine whether the symbionts are also present in the insect parasitoids which might indicate possible horizontal transfer of the endosymbionts. A total of 637 tephritids flies belonging to 17 species and 77 parasitoids belonging to 2 species were reared from 17 thistles species, collected from various sites in Lebanon. The DNA of flies and parasitoids was extracted and screened for the presence of the wsp gene of Wolbachia by PCR. The Wolbachia sequences were compared to Genbank sequences and used to construct a phylogenetic tree using Bayesian Markov Chain Monte Carlo. Results showed that percent Wolbachia infections in tephritids flies and parasitoids were 16.6% and 28.6%, respectively. Our study revealed the prevalence of Wolbachia in different flower head infesting species, but this association was sporadic. The Wolbachia rate of infection was variable ranging from 0 to 50%; it varied significantly with insect species, plant species, and location, but to a lesser extent with elevation. Sequencing of wsp gene demonstrated the existence of 10 different Wolbachia sequences clustering in eight distinct clades. However, the role of Wolbachia in the host race formation in Chaetostomella sp. did not appear to be important as Wolbachia endosymbionts isolated from C. cylindrica and C. lurida populations shared a similar sequence. Because of low sampling, further studies are needed to study the impact of Wolbachia in the host race formation of Terellia serratula. The data was not conclusive for the possibility of horizontal transmission of endosymbionts between tephritids and their parasitoids although similar Wolbachia sequences were found between them. The results also showed that Tephritis cometa collected from Cirsium creticum from one site was infected with multiple (6) sequences of Wolbachia. Future studies should be conducted to check whether this species consists of reproductively isolated populations.