Frank Koch

Host Shifts from Lamiales to Brassicaceae in the Sawfly Genus Athalia

Plant chemistry can be a key driver of host shifts in herbivores. Several species in the sawfly genus Athalia are important economic pests on Brassicaceae, whereas other Athalia species are specialized on Lamiales. These host plants have glucosides in common, which are sequestered by larvae. To disentangle the possible direction of host shifts in this genus, we examined the sequestration specificity and feeding deterrence of iridoid glucosides (IGs) and glucosinolates (GSs) in larvae of five species which either naturally sequester IGs from their hosts within the Plantaginaceae (Lamiales) or GSs from Brassicaceae, respectively. Furthermore, adults were tested for feeding stimulation by a neo-clerodane diterpenoid which occurs in Lamiales. Larvae of the Plantaginaceae-feeders did not sequester artificially administered p-hydroxybenzylGS and were more deterred by GSs than Brassicaceae-feeders were by IGs. In contrast, larvae of Brassicaceae-feeders were able to sequester artificially administered catalpol (IG), which points to an ancestral association with Lamiales. In line with this finding, adults of all tested species were stimulated by the neo-clerodane diterpenoid. Finally, in a phylogenetic tree inferred from genetic marker sequences of 21 Athalia species, the sister species of all remaining 20 Athalia species also turned out to be a Lamiales-feeder. Fundamental physiological pre-adaptations, such as the establishment of a glucoside transporter, and mechanisms to circumvent activation of glucosides by glucosidases are therefore necessary prerequisites for successful host shifts between Lamiales and Brassicaceae.

Biogeography, Diversity and Ecology of Sawflies in the Afromontane Region (Insecta: Symphyta)

In the Afrotropical region the sawfly fauna is, in comparison with other biogeographical regions, except Australia, very poor both in number of species and number of individuals. The Afromontane region is composed of a series of archipelago-like disjunctions. This is especially true for eastern and south-eastern Africa, where these consist of regional mountain systems with specific abiotic factors, and it seems that the mountain-specific sawfly diversity, with its many endemic species, is unique and dependent on the mountain systems’ genesis. Species of the Athalia vollenhoveni-group are known only from the Afrotropical region. The species of this group seem to prefer the montane and sub-montane region and have more narrow ranges than previously thought. The sawfly diversities of different habitats of four mountain systems in the Drakensberg district, South Africa, were investigated over a two-year period. In total 27 species were recognized, including at least 13 species new to science. Furthermore, a minimum of seven species are endemic to vegetational types of the Drakensberg. Only very few species are widely distributed and can be regarded as eurytopic, because these species occur from the lowlands up to the mountains.