Ecological versus phylogenetic determinants of trophic associations in a plant-leafminer-parasitoid food web.

Specialized trophic interactions in plant-herbivore-parasitoid food webs can spur "bottom-up" diversification if speciation in plants leads to host-shift driven divergence in insect herbivores, and if the effect then cascades up to the third trophic level. Conversely, parasitoids that search for victims on certain plant taxa may trigger "top-down" diversification by pushing herbivores into "enemy-free space" on novel hosts. We used phylogenetic regression methods to compare the relative importance of ecology versus phylogeny on associations between Heterarthrinae leafmining sawflies and their parasitoids. We found that: (1) the origin of leafmining led to escape from most parasitoids attacking external-feeding sawflies; (2) the current enemies mainly consist of generalists that are shared with other leafmining taxa, and of more specialized lineages that may have diversified by shifting among heterarthrines; and (3) parasitoid-leafminer associations are influenced more by the phylogeny of the miners' host plants than by relationships among miner species. Our results suggest that vertical diversifying forces have a significant-but not ubiquitous-role in speciation: many of the parasitoids have remained polyphagous despite niche diversification in the miners, and heterarthrine host shifts also seem to be strongly affected by host availability.

The Eurasian species of Xyela (Hymenoptera, Xyelidae): taxonomy, host plants and distribution.

The 28 Eurasian species of Xyela Dalman, 1819 are revised based on material of ca 7,500 imagines including about 10 % reared specimens. Larvae of Eurasian Xyela usually are monophagous and feed inside the staminate cones of pines (Pinus spp., Pinaceae). Based on the reared material, on identification by barcoding and on additional collection observations, the larval host associations for the Xyela species are summarized and additional biological observations are noted. An illustrated key to the species and distribution maps are presented. Eight species are described as new: X. altenhoferi Blank, sp. nov. (Croatia), X. heldreichii Blank, sp. nov. (Albania, Greece), X. koraiensis Blank & Shinohara, sp. nov. (Russia, South Korea), X. peuce Blank, sp. nov. (Bulgaria), X. pumilae Blank & Shinohara, sp. nov. (Japan), X. rasnitsyni Blank & Shinohara, sp. nov. (China, Russia, South Korea), X. sibiricae Blank, sp. nov. (Mongolia, Russia), and X. uncinatae Blank, sp. nov. (Andorra, France, Spain, Switzerland). For the other species redescriptions are given. A lectotype is designated for X. longula Dalman, 1819, and neotypes are designated for X. graeca J.P.E.F. Stein, 1876 and Pinicola julii Brébisson, 1818. The following new synonymies are proposed: X. lii Xiao, 1988, syn. nov. of X. sinicola Maa, 1947; X. nigroabscondita Haris & Gyurkovics, 2011, syn. nov. of X. lugdunensis (Berland, 1943); and X. suwonae Ryu & Lee, 1992, syn. nov. of X. ussuriensis Rasnitsyn, 1965.

Phylogenetics and evolution of host-plant use in leaf-mining sawflies (Hymenoptera: Tenthredinidae: Heterarthrinae).

The habit of mining within leaves has evolved convergently in numerous plant-feeding insect taxa. Many leaf-mining groups contain a large number of species with distinct feeding preferences, which makes them highly suitable for studies on the evolutionary history of host-plant use and on the role of niche shifts in speciation. We aimed to clarify the origin, classification, and ecological evolution of the tenthredinid sawfly subfamily Heterarthrinae, which contains c. 150 leaf-mining species that collectively feed on over 20 plant genera around the world. For this, we reconstructed the phylogeny of representative heterarthrine species and diverse outgroups from the superfamily Tenthredinoidea on the basis of DNA sequence data collected from two mitochondrial (CoI and Cytb) and two nuclear (EF-1α and NaK) genes. Thereafter, we inferred the history of niche diversification within Heterarthrinae by plotting larval host-plant associations on the trees, and by contrasting a time-calibrated leaf-miner phylogeny with the phylogeny of their host plants. The results show that: (1) heterarthrine leaf-miners constitute a monophyletic group that arose from external-feeding blennocampine lineages within the Tenthredinidae c. 110-80 million years ago; (2) heterarthrines generally radiated well after their host taxa, and extant host-plant associations therefore result from a combination of host conservatism and occasional shifts among available plant taxa; and (3) diversification in Heterarthrinae apparently occurs by multiple mechanisms, including sympatric or allopatric ecological speciation, non-ecological allopatric speciation, and possibly allochronic speciation. Overall, both present and historical host-use patterns within the Heterarthrinae exhibit striking similarities to patterns found in co-occurring herbivore taxa.

Defense by volatiles in leaf-mining insect larvae.

The defense strategy of an insect toward natural enemies can include a trait that appears at first sight to contradict its defensive function. We explored phylogeny, chemistry, and defense efficiency of a peculiar group of hymenopteran sawfly larvae where this contradiction is obvious. Pseudodineurini larvae live in leaf mines that protect them from some enemies. Disturbed larvae also emit a clearly perceptible lemon-like odor produced by ventral glands, although the mine hampers the evaporation of the secretion. The mine could also lead to autointoxication of a larva by its own emitted volatiles. Citral was the major component in all Pseudodineurini species, and it efficiently repels ants. We conclude that full-grown larvae that leave their mine to pupate in the soil benefit from citral by avoiding attacks from ground-dwelling arthropods such as ants. In some species, we also detected biosynthetically related compounds, two 8-oxocitral diastereomers (i.e., (2E,6E)- and (2E,6Z)-2,6-dimethylocta-2,6-dienedial). Synthetic 8-oxocitral proved to be a potent fungicide, but not an ant repellent. The discrete distribution of 8-oxocitral was unrelated to species grouping in the phylogenetic tree. In contrast, we discovered that its presence was associated with species from humid and cold zones but absent in species favoring warm and dry environments. The former should be protected by 8-oxocitral when faced with a fungal infestation while crawling into the soil. Our work shows the importance of integrating knowledge about behavior, morphology, and life history stages for understanding the complex evolution of insects and especially their defense strategies.