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Endosymbiotic bacteria can induce parthenogenesis in many haplo-diploid species, but little is known about their role in asexual reproduction in diplodiploids. Bacteria are essential for reproduction in the asexual lineages of springtails and booklice, and possibly some weevils, but whether they are the causative agent of parthenogenesis remains to be proven. This would require comparing unisexual forms and their closely related bisexual species, but such model species are very rare. Empoasca leafhoppers from the Madeira Archipelago provide an excellent case to test whether bacterial infections can cause parthenogenesis. Here we examined the diversity of the sex-distorting bacteria, Wolbachia , Cardinium , Rickettsia, and Arsenophonus , in three apomictic morphotypes (A, B, C) and three bisexual relatives of Empoasca. Wolbachia of group B was present in all unisexual and bisexual species. Rickettsia were the only bacteria restricted to the three unisexual forms, suggesting an association between infection and asexual reproduction. In addition, we found Asaia for the third time in the Cicadellidae, although this may have little to do with the reproductive mode of its host. Adult females of morphotype C reared on plants watered with tetracycline solution did not result in the production of male offspring. To our knowledge, this is the first study to suggest a possible association between bacterial infection and parthenogenesis in apomictic XO/XX diplodiploid bisexual species based on a range of sex ratio-distorting bacteria. [ABSTRACT FROM AUTHOR]

There are controversial opinions on whether asexual reproduction is more common on islands than on the mainland. Although some authors consider that the evidences of geographical parthenogenesis support the view that asexual reproduction is more common on islands, comparative data on the modes of reproduction of insular and continental taxa confirming this statement are very limited. In this work, we report the presence of three unisexual forms and three bisexual species of the genus Empoasca (Cicadelloidea, Hemiptera, Insecta) from Madeira Island. Experimentally, the unisexual forms reproduced in the absence of males for several generations. The chromosome analysis has shown that the bisexual species differ from one another in chromosome number, and unisexual forms are apomictic and also each have different chromosome numbers. Of parthenoforms, one is triploid and two are of obscure level of ploidy, 2n or 3n. The results obtained show that for this genus unisexual forms are more common on Madeira Island than in the nearby continental areas. It is suggested that unisexual forms may be more plentiful on islands than on the mainland because if an asexual reproduction event occurs, the relaxing competition in these underexploited and enemy-free habitats may favor the establishment of new parthenogenetic lineages. [ABSTRACT FROM AUTHOR]