Jean Claude Braekman

Salicin from host plant as precursor of salicylaldehyde in defensive secretion of chrysomeline larvae

ABSTRACT. Phratora vitellinae L. and Chrysomela tremulae F. (Chrysomelinae, Coleoptera) feed on Salix or Populus spp. (Salicaceae). Their larvae, as well as the larvae of other chrysomelines feeding on Salicaceae, secrete salicylaldehyde. In this study, we demonstrate that salicylaldehyde is derived from salicin, a phenylglucoside present in the leaves of the host plant. The concentration of salicylaldehyde in the secretion is positively correlated with the amount of salicin in the food of the larvae. The transformation of salicin into salicylaldehyde occurs in the defence glands since the β‐glucosidase activity is 4 times higher in their glands than in the gut. The larvae recover most of the glucose that results from the hydrolysis of salicin. For generalist predators, such as ants, salicylaldehyde is a more potent deterrent than saligenin or salicin.

Chemical defence in chrysomelid larvae and adults

Abstract The defensive secreation of several species of chrosomelid larvae and adults have been analyzed. Salicyaldehyde and some already known methylcyclopentanoid monoterpenes have been identified in the larvae. In the adults of the tribe Phaedonini, two isoxazolin-5-one derivatives (8 and 9) were isolate and their structures determined. The chemical defence of chrysomelid beetles is briefly reviewed with emphasis on chemataxonomy and ecological significance.

Distribution et activités des alcaloïdes défensifs des Coccinellidae

Abstract From a survey of 30 species and varieties of ladybugs the presence of alkaloids appears to be correlated with the existence of aposematic colour and not with being carnivorous or phytophagous. The alkaloids described until now all belong to the Coccinellini and are closely related, but other types of bases have been detected in some genera. The observed distributions are in agreement with the modern taxonomy of the family. Ladybug alkaloids constitute an effective defence against ants, Myrmica rubra, and quails, Coturnix coturnix, but all the beetles containing alkaloids do not possess the same degree of protection. Individual quail react differently towards moderately protected species. The bioassay used for the first isolation of coccinelin is described. The repulsive activities of aqueous solutions of coccinellin and convergin towards ants have been compared.

Chemical defences in leaf beetles and their larvae: The ecological, evolutionary and taxonomic significance

Abstract The chemical defences of the Chrysomelinae are reviewed. Defensive glandular secretions have evolved independently in larvae and adults, and faster than the morphology of the glands. Both characters are used in a phylogenetic study of the Chrysomelini, disclosing suprageneric affinities. First, a close relationship between the Chrysomelina and Phratora is proposed. Secondly, Leptinotarsa and Gonioctena are probably more closely related to the Chrysolinina than to the Chrysomelina and Phratora . The qualitative and quantitative composition of larval and adult secretions sometimes differs between geographically isolated populations of the same species, which are therefore probably genetically distinct. The host plant shows an influence which explains discrepancies between the current classification and the chemical nature of the secretions. Some beetles sequester secondary plant metabolites or use them as precursors for their own defences. The original biosynthetic pathway has been lost in these species. Other factors which could affect the chemical diversity of the secretions are discussed: random events such as neutral mutations and genetic drift, conditioning or adaptation of predators to specific defensive mixtures, and the diversity of potential predators. The latter could help to explain the divergence in the chemical nature of the larval and adult secretions. The volatile irritants produced by the larvae are well suited to repel small arthropods, such as ants, whereas poisons associated with aposematic coloration in the adults could be directed against small vertebrates, such as birds.

The Chemistry of Pheromones and Other Semiochemicals II

W.S. Leal: Pheromone Reception .- J. G. Millar: Pheromones of True Bugs .- W. Francke, K. Dettner: Chemical Signalling in Beetles .- P. Laurent, J.-C. Braekman, D. Daloze: Insect Chemical Defense .- B.V. Burger: Mammalian Semiochemicals .- S.R. Chhabra, B. Philipp, L. Eberl, M. Givskov, P. Williams, M. Camara: Extracelluar Communication in Bacteria

Chemical defense in the Chrysomelidae

Antipredation mechanisms exist in nearly all animals, but are of course better developed in those which appear to be most vulnerable. Among them are phytophagous insects and above all phyllophagous insects such as leaf beetles. Due to their low food conversion efficiency (Southwood 1973), phytophagous insects spend much time feeding, during which they are little mobile and poorly hidden. Leaf damage to and feces left on the foliage could give additional cues to predators, including parasitoids (Weselok 1981). Many chrysomelids are food specialists and pass all or most of their life cycle on their food plant. The patchy distribution of the food plants and the low dispersion rate of larvae and gravid females are such that leaf beetles tend to form conspicuous aggregates.

Chemotaxonomy of Agelas (Porifera : Demospongiae)

The secondary metabolite content of four different species of Agelas (Porifera) from the West Indies has been studied. All the compounds isolated are already known metabolites whose identification was confirmed by comparison of their spectral properties with those reported in the literature. They pertain to two different classes of compounds: terpenoids and pyrrole-2-carboxylic acid derivatives. The chemotaxonomic value of these secondary metabolites has been evaluated. Their distribution amongst the Porifera, as well as that of isocyanide derivatives, suggests a close relationship between the Agelasidae, the Axinellidae and the Halichondriidae.

Ladybird defence alkaloids: Structural, chemotaxonomic and biosynthetic aspects (Col.: Coccinellidae)

SummaryThe defensive mechanisms which protect ladybird beetles (Coccinellidae) against predators are reviewed. Besides behavioural mechanisms, such as thanatosis and reflex bleeding, chemical defence mechanisms are playing a prevalent role. Indeed, ladybirds are protected not only by their smell, but also by repulsive alkaloids, most of which are considered to be of autogenous origin. In a few cases, dietarily-acquired substances are also involved. Particular emphasis is laid on the repellent alkaloids which are contained in the haemolymph of many species. The structures of 34 nitrogen-containing compounds isolated so far are presented, and their distribution within the family is discussed in the light of the most widely accepted classification of these beetles. To conclude, the mode of release of the alkaloids, their variation through the life cycle and their repellent and toxic properties are discussed, as well as the few biosynthetic data yet available.

Two new guanidine alkaloids from the Mediterranean sponge Crambe crambe

Crambine A (1) and B (2) were isolated from the Mediterranean sponge Crambe crambe. Their structures were determined mainly by extensive NMR 2D experiments at 600 MHz.

Absolute configuration of the solenopsins, venom alkaloids of the fire ants

Abstract An effective and practical procedure has been developed that allows the assignment of the absolute configuration of solenopsins from diverse origins us