Search publications of the members of the Royal Belgian institute of natural Sciences
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L’occupation romaine du territoire de la commune de La Bruyère (province de Namur).
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The secretion of the ventral glands in Hoplocampa sawfly larvae
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Checkliste der Pflanzenwespen Deutschlands (Hymenoptera: Symphyta)
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Chemical ecology of the European apple sawfly, Hoplocampa testudinea
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The secretion of the ventral glands in Cladius, Priophorus and Trichiocampus sawfly larvae
- The volatile secretion from ventral glands of the larvae of Cladius pectinicornis, Priophorus morio, P. pallipes and Trichiocampus grandis was found to be principally composed of long-chain acetogenins, in majority of the esters and hydrocarbons, with more than 15 carbon atoms. The scarcity of more volatile compounds may be considered as plesiomorphic for the tribe Cladiini to which the four species belong. Further chemotaxonomic significance and chemical ecological implications of the glandular secretions are discussed. Moreover, the function of the well-developed pubescence covering the body of Cladiini larvae is discussed as a part of their defensive mechanism.
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Sequestration of host plant glucosinolates in the defensive hemolymph of the sawfly Athalia rosae
- Interactions between insects and glucosinolate-containing plant species have been investigated for a long time. Although the glucosinolate-myrosinase system is believed to act as a defense mechanism against generalist herbivores and fungi, several specialist insects use these secondary metabolites for host plant finding and acceptance and can handle them physiologically. However, sequestration of glucosinolates in specialist herbivores has been less well studied. Larvae of the tumip sawfly Athalia rosae feed on several glucosinolate-containing plant species. When larvae are disturbed by antagonists, they release one or more small droplets of hemolymph from their integument. This "reflex bleeding" is used as a defense mechanism. Specific glucosinolate analysis, by conversion to desulfoglucosinolates and analysis of these by high-performance liquid chromatography coupled to diode array UV spectroscopy and mass spectrometry, revealed that larvae incorporate and concentrate the plant's characteristic glucosinolates from their hosts. Extracts of larvae that were reared on Sinapis alba contained sinalbin, even when the larvae were first starved for 22 hr and, thus, had empty guts. Hemolymph was analyzed from larvae that were reared on either S. alba, Brassica nigra, or Barbarea stricta. Leaves were analyzed from the same plants the larvae had fed on. Sinalbin (from S. alba), sinigrin (B. nigra), or glucobarbarin and glucobrassicin (B. stricta) were present in leaves in concentrations less than 1 micromol/g fresh weight, while the same glucosinolates could be detected in the larvae's hemolymph in concentrations between 10 and 31 micromol/g fresh weight, except that glucobrassicin was present only as a trace. In larval feces, only trace amounts of glucosinolates (sinalbin and sinigrin) could be detected. The glucosinolates were likewise found in freshly emerged adults, showing that the sequestered phytochemicals were transferred through the pupal stage.
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Host specificity and host recognition in a chemically-defended herbivore, the tenthredinid sawfly Rhadinoceraea nodicornis
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Host plant derived feeding deterrence towards ants in the turnip sawfly Athalia rosae
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Why does the larval integument of some sawfly species disrupt so easily? The harmful hemolymph hypothesis
- The larvae of several sawfly species belonging to the Tenthredinidae (Hymenoptera) have such a low mechanical resistance in the integument that slight mechanical damage to the integument is enough to provoke the release of hemolymph at a given spot. We quantified this phenomenon, which we call "easy bleeding", by measuring the pressure needed to pierce dissected sawfly integument. We also investigated the feeding deterrance of ethanolic extracts of the hemolymph by laboratory bioassays using Myrmica rubra ant workers. These traits, integument resistance and hemolymph deterrence, were inversely related, considering 22 tenthredinid species. A negative correlation was obtained by only taking into account the species of one tenthredinid tribe, namely the Phymatocerini (nine species studied). Our results support the "harmful hemolymph hypothesis" that we present here and that assumes a functional link between these morphological and chemical traits, jointly acting as a chemical defense strategy. We suspect hemolymph deterrence to be often due to sequestration of plant secondary metabolites. We discuss the role of easy bleeding, considering the fact that sawfly larvae are frequently the prey of invertebrate and vertebrate predators. It is suggested that invertebrates such as ants were more important than vertebrates in the evolution of easy bleeding.
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Gustatory perception and metabolic utilization of sugars by Myrmica rubra ant workers
- The suitability of various nectar and honeydew sugars as a food source for the polyphagous ant species M. rubra (L.) was studied. The sugars used included monosaccharides (fructose, glucose, galactose, mannose, rhamnose), disaccharides (sucrose, maltose, trehalose, melibiose, lactose) and trisaccharides (melizitose, raffinose, erlose). Single-sugar solutions were tested on ant workers in a long-term laboratory bioassay in which acceptance of the solutions and ant survival were recorded. The acceptance of the sugars was confirmed in a second bioassay in which feeding time was established. Enzymatic hydrolysis of sucrose, maltose and melibiose was investigated through HPLC analyses of workers fed these disaccharides. Sugar acceptance and feeding time were related to ant survival. Considering the monosaccharide units of which the sugars are composed, fructose seems especially suitable as a short-term energy source, while glucose appears to be used both directly and for storage. The presence of a galactose unit appears to reduce sugar suitability. It is suggested that the workers possess invertase and maltase and to a lesser degree also galactosidase. The gustatory perception is correlated with the profitability of sugars in further metabolic processes.
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Sawflies (Hymenoptera: Tenthredinidae)
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Surface structure, model and mechanism of an insect integument adapted to be damaged easily
- BACKGROUND: Several sawfly larvae of the Tenthredinidae (Hymenoptera) are called easy bleeders because their whole body integument, except the head capsule, disrupts very easily at a given spot, under a slight mechanical stress at this spot. The exuding haemolymph droplet acts as a feeding deterrent towards invertebrate predators. The present study aimed to describe the cuticle surface, to consider it from a mechanistic point of view, and to discuss potential consequences of the integument surface in the predator-prey relationships. RESULTS: The integument surface of sawfly larvae was investigated by light microscopy (LM) and scanning electron microscopy (SEM) which revealed that the cuticle of easy bleeders was densely covered by what we call "spider-like" microstructures. Such microstructures were not detected in non-easy bleeders. A model by finite elements of the cuticle layer was developed to get an insight into the potential function of the microstructures during easy bleeding. Cuticle parameters (i.e., size of the microstructures and thickness of the epi-versus procuticle) were measured on integument sections and used in the model. A shear force applied on the modelled cuticle surface led to higher stress values when microstructures were present, as compared to a plan surface. Furthermore, by measuring the diameter of a water droplet deposited on sawfly larvae, the integument of several sawfly species was determined as hydrophobic (e.g., more than Teflon(R)), which was related to the sawfly larvae's ability to bleed easily. CONCLUSION: Easy bleeders show spider-like microstructures on their cuticle surface. It is suggested that these microstructures may facilitate integument disruption as well as render the integument hydrophobic. This latter property would allow the exuding haemolymph to be maintained as a droplet at the integument surface.
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Phylogeography of two parthenogenetic sawfly species (Hymenoptera: Tenthredinidae): relationship of population genetic differentiation to host plant distribution
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Defence effectiveness of easy bleeding sawfly larvae towards invertebrate and avian predators
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Structure and mechanical strength of larval cuticle of sawflies capable of "easy bleeding" a defence strategy against predators evolved in Tenthredinidae (Hymenoptera)
- The cuticle of Tenthredinidae (Hymenoptera) larvae is ruptured after a very mild mechanical stress and hemolymph is released. This phenomenon, called "easy bleeding" is considered as a defence strategy against predators. We investigated the cuticle structure of some selected species capable of "easy bleeding" by light-, transmission- and scanning microscopy and compared it with phylogenetically-related sawfly species without this defense strategy (control). Cuticle thickness has no major influence on mechanical stability, but pronounced local differences in thickness seem to be inversely correlated with mechanical strength. The density of chitin fibrils is considerably reduced in animals capable of easy bleeding and the fibres form a loose 3D network in contrast to the densely packed layers seen in related "non easy bleeding" species like Strongylogaster multifasciata, where a pressure of 2584 kPa is needed to pierce the integument, and which served as a control. Efficient bleeders like Phymatocera aterrima (203 kPa) and Rhadinoceraea nodicornis (219 kPa) are devoid of any defined layers or other structural elements. In Athalia rosae (Allantinae) (539 kPa), and Aglaostigma discolor (Tenthredininae) (1494 kPa)–bleeders with medium efficiency–a reduced number of layers are observed by LM and TEM and a loose network of chitin fibres is visible after treatment with KOH.
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Differing patterns of chemically-mediated defence strategies in Nematinae versus Phymatocerini larvae (Hymenoptera: Tenthredinidae)
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Sequestration of furostanol saponins by Monophadnus sawfly larvae.
- Sawfly larvae of the tribe Phymatocerini (Hymenoptera: Tenthredinidae), which are specialized on toxic plants in the orders Liliales and Ranunculales, exude a droplet of deterrent hemolymph upon attack by a predator. We investigated whether secondary plant metabolites from Ranunculaceae leaves are sequestered by phymatocerine Monophadnus species, i.e., Monophadnus alpicola feeding upon Pulsatilla alpina and Monophadnus monticola feeding upon Ranunculus lanuginosus. Moreover, two undescribed Monophadnus species were studied: species A collected from Helleborusfoetidus and species B collected from Helleborus viridis. Comparative high-performance liquid chromatographicphotodiode array detection-electrospray ionization-mass spectrometric analyses of plant leaf and insect hemolymph extracts revealed the presence of furostanol saponins in all samples. Larvae of species A and B actively sequestered (25R)-26-[(alpha-L-rhamnopyranosyl) oxy]-22alpha-methoxyfurost-5-en-3beta-yl O-beta-D-glucopyranosyl-(1–3)-O-[6-acetyl-beta-D-glucopyranosyl-(1–3)]-O-beta-D-glucopyranoside (compound 1). This compound occurred at a 65- to 200-fold higher concentration in the hemolymph of the two species (1.6 and 17.5 micromol/g FW, respectively) than in their host plant (0.008 and 0.268 micromol/g FW, respectively). In M. monticola, compound 1 was found at a concentration (1.2 micromol/g FW) similar to that in the host plant (1.36 micromol/g FW). The compound could not be detected consistently in M. alpicola larvae where, however, a related saponin may be present. Additional furostanol saponins were found in H. foetidus and H. viridis, but not in the two Monophadnus species feeding on them, indicating that sequestration of compound 1 is a highly specific process. In laboratory bioassays, crude hemolymph of three Monophadnus species showed a significant feeding deterrent activity against a potential predator, Myrmica rubra ant workers. Isolated furostanol saponins were also active against the ants, at a concentration range similar to that found in the hemolymph. Thus, these compounds seem to play a major role for chemical defense of Monophadnus larvae, although other plant secondary metabolites (glycosylated ecdysteroids) were also detected in their hemolymph. Physiological and ecological implications of the sequestered furostanol saponins are discussed.
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Sawflies (Hymenoptera: Tenthredinidae)
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Easily damaged integument of some sawflies (Hymenoptera) is part of a defence strategy against predators
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Secretion of the ventral glands in Craesus sawfly larvae
