Systematics of jumping plant-lice (Hemiptera: Psylloidea) : examples from the west palaearctic and neotropical regions including a revision of the genus Russelliana

Coevolution or cospeciation of phytophagous insects and plants is assumed to be a major driver of evolution leading to the present enormous insect diversity. However, an increasing number of insect–plant studies suggest that speciation is driven by geographical vicariance, and host switching to related plant taxa also occurs frequently in insects. Despite a number of studies on global patterns of insect–plant associations, there are notable gaps in the interpretation of evolutionary processes leading to insect speciation. This thesis consists of four studies in five papers (three published papers and two are to be submitted) conducted to investigate the biodiversity of a poorly known group of insects, the psyllids or jumping plant-lice, and their associations with host-plants. The studies were focused on areas from which few information were available: western Palaearctic (Belarus) and south temperate Neotropical regions. Most psyllids are mono- or oligophagous on a restricted number of plant taxa. The first study examined the plausibility of polyphagy of the Neotropical potato pest Russelliana solanicola Tuthill by means of multivariate analyses of morphological characters. The results showed an unexpectedly high polyphagy of the species on a number of economically important crops and its very likely introduction from the native Andean region into eastern South America. Considering its high potential of a successful invasion into non-native regions, it is extremely important to prevent spread and invasion of R. solanicola in the incipient stages. The second project assessed and predicted the potential occurrence of R. solanicola worldwide using species distribution models (SDMs), based on environmental variables derived from its natural range of distribution. We also investigated the similarities between geographical, environmental and morphological characteristics of R. solanicola and its related Solanaceae-feeders, and their tolerance to a range of environmental conditions by contrast to non-Solanaceae feeding species from the same genus. The third study investigated and described the diversity of Russelliana species in order to understand patterns of psyllid speciation and explain the evolutionary processes leading to the species diversity in the genus. The Neotropical genus Russelliana is an excellent and interesting model group for host-plant and biogeographical studies, considering its high species-richness and wide host associations with species from a number of plant families. The revision of Russelliana included the descriptions of 24 new psyllid species and the redescriptions of 19 previously described ones. A phylogenetic analysis suggested that the psyllid speciation in Russelliana is better explained by geographical vicariance rather than by cospeciation with plants, and host switching has occurred relatively frequently in the genus. The fourth study is reflected in two publications on the fauna of Belarusian psyllids. The psyllid fauna of the west Palaearctic region is relatively well known, with Belarus being a notable exception. Based on the literature records and recently collected material, an updated checklist of psyllids of Belarus is provided. The checklist is supplemented with an illustrated identification key for the psyllid species confirmed from and likely to occur in Belarus. To my knowledge, the results of this thesis provide important taxonomic information on the biodiversity and host-plant associations of a poorly studied group of insects from the western Palaearctic (Belarus) and south temperate Neotropical regions. These findings may contribute to studies on global patterns of insect–plant associations helping to interpret the evolutionary processes leading to insect speciation and its current huge diversity on the planet. Moreover, the studies on the polyphagy and potential distribution of pest species in new regions can predict the establishment of invasive populations and provide the pest management with all necessary information before the species is recognised as a serious threat. In addition, the developed illustrated identification keys for the psyllid species will be of help to applied entomologists dealing with agricultural, forestry and ornamental pests