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      Multimodal defensive strategies in larvae of two Hemichroa sawfly species

      Journal of Hymenoptera Research

      Pensoft Publishers

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          Abstract

          The two European sawfly species in the genus Hemichroa are a contrast in behaviour and appearance, since H. crocea is gregarious and brightly coloured, whereas H. australis is solitary and cryptic. Here, their defensive strategies are compared by integrating further components. In both species, ventral glands are minute, and no distinctive volatiles were detected by chemical analysis; hence, these exocrine glands are probably irrelevant in defence. Ethanol extracts of body parts were feeding deterrent to ant workers of Myrmica rubra, especially the integument of H. australis which was more deterrent than that of H. crocea. Single, living larvae of H. crocea were also attacked more frequently by ants. In contrast, single larvae of H. crocea are reluctantly taken by the bird Parus major that readily feeds on H. australis. The larvae of both species jerk their abdomen to physically defend themselves and/or to increase their (visual) warning signal (H. crocea). The larvae of H. crocea can scratch the host plant leaf with the tip of their abdomen to produce a sound assumed to convey information in intraspecific communication. However, this behaviour was also elicited from H. australis, when disturbed, which suggests that it may have another function. The defensive strategy is multimodal in both species. The principal differences are the reliance on gregariousness in H. crocea, as opposed to the use of integumental chemicals in H. australis.

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          Most cited references 11

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          World Catalog of Symphyta (Hymenoptera)

          The first complete World Catalog of sawflies (Hymenoptera, suborder Symphyta) for over 100 years is presented. It contains references to the original descriptions and provides brief distributional data for 803 genera, 8353 species (123 with two or more subspecies) and 161 subspecies in addition to the nominal subspecies. 15245 proposed names are treated, including replacement names, infrasubspecific names and nomina nuda, of which only 22 could not be checked in the original publications. Current taxonomic placement of genera and species and occurrence in zoogeographic regions are indicated. The list of names contains 31245 name combinations, variant spellings and family-group names. The authors attempted to consult all publications with taxonomic content referring to Symphyta that have appeared up to 31.12.2009. The 2960 cited references include all those that are known to contain original descriptions of taxa. Short biographical data and portraits of 168 symphytologists as well as images of representatives of extant sawfly taxa are included.
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            Why are warning displays multimodal?

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              Larval habits, host-plant associations, and speciation in nematine sawflies (Hymenoptera: Tenthredinidae).

              Adaptive radiations consist of two intertwined processes, diversification of species and diversification of their ecological niches, but it is unclear whether there is a causal link between the processes. In phytophagous insects, ecological diversification mainly involves shifts in host-plant associations and in larval feeding habits (internal or external) on different plant parts, and several observations indicate that speciation is facilitated by host shifts. Data on host use in individual species suggest that internal feeders are less likely to colonize new hosts than external-feeding taxa and, consequently, increases in collective host ranges and species numbers should be slowed down in endophagous lineages. We tested these related hypotheses by using phylogenetic information to reconstruct the evolutionary history of larval resource use in the sawfly subfamily Nematinae, a group of 1000 plus species with a broad range of niches: the subfamily's combined host range includes over 20 plant families, and larvae may feed externally on leaves or needles, or internally, for example, in buds, fruits, leaves, or galls. The results show that: (1) Most internally feeding groups have evolved independently from external-feeding ancestors, but several distinct internal habits have appeared convergently multiple times; (2) Shifts among host taxa are clearly more common than changes in larval habits; (3) The majority of host switches have occurred among phylogenetically close plant groups, but many shifts are manifest among distantly related, ecologically proximate hosts; (4) Although external feeding characteristic of the common ancestor of Nematinae is associated with relatively high rates of host-shifting, internal feeders are very conservative in their host use; (5) In contrast, the effect of endophagy on speciation probabilities is more variable: net speciation rates are lowered in most internal-feeding groups, but a striking exception is found in species that induce galls on Salicaceae. The loose connection between collective host ranges and species diversity provides empirical support for theoretical models suggesting that speciation rates are a function of a complex interplay between "intrinsic" niche width and resource heterogeneity.
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                Author and article information

                Journal
                Journal of Hymenoptera Research
                JHR
                Pensoft Publishers
                1314-2607
                1070-9428
                November 30 2015
                November 30 2015
                : 46
                : 25-33
                Article
                10.3897/JHR.46.7064
                © 2015
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