Abstract 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.
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One of the earliest basal carnivoraforms, Miacis latouri, previously known by only two teeth from the earliest Eocene of Dormaal, Belgium, is here described based on about 280 new specimens from Dormaal, allowing illustration of almost the entire deciduous and permanent dentition and thus giving information on the dentition of an early basal carnivoraform species and its variability. Based on the dental features, we refer the species to a new genus, Dormaalocyon. We identify possible sexual dimorphism in D. latouri that is less pronounced than in Uintacyon rudis. We also describe for the first time the tarsal bones (calcaneum and astragalus) of D. latouri; these indicate arboreal capabilities for this species. In order to ascertain the position of Dormaalocyon among basal carnivoraforms, we performed a phylogenetic analysis of the carnivoramorphans. Among basal carnivoraforms, three groups are recovered: the Uintacyon group, Oodectes group, and the Vulpavus group. Dormalocyon is one of the most primitive carnivoraforms and is closely related to North American Vulpavus and Miacis species. We propose that the two latter genera are North American with an ancestry that involves the European Dormaalocyon; this implies a dispersal of carnivoraforms from Europe to North America near the Paleocene-Eocene boundary. Finally, the topology of the phylogenetic tree supports a Paleocene radiation of the carnivoraforms, which is presently unknown.
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