Triterpene saponin hemi-biosynthesis of a leaf beetle’s (<Emphasis Type="Italic">Platyphora kollari</Emphasis>) defensive secretion

The adults of the leaf beetle Platyphora kollari (Chrysomelidae) are able to metabolise the oleanane triterpene β-amyrin (1) into the glycoside 3-O-β-d-glucopyranosyl-(1→4)-β-d-glucuronopyranosyl-hederagenin (2) that is stored in their defensive glands. The aim of this study was to test the hypothesis that oleanolic acid (3) is an intermediate in the conversion of 1 into 2 and to check whether the sequestration of pentacyclic triterpenes is selective in favour of β-amyrin (1). To this end, adults of P. kollari were fed with Ipomoea batatas leaf disks painted with a solution of [2,2,3-²H₃]oleanolic acid or [2,2,3-²H₃]α-amyrin and the secretion of their defensive glands analysed by HPLC–ESIMS. The data presented in this work indicated that the first step of the transformation of β-amyrin (1) into the sequestered glycoside 2 is its oxidation into oleanolic acid (3) and that this conversion is selective but not specific in favour of β-amyrin (1).     

Use of native mosses as biomonitors of heavy metals and nitrogen deposition in the surroundings of two steel works

A biomonitoring survey using the moss species Hypnum cupressiforme Hedw. was conducted in the surroundings of two steel plants located in the North of Spain. Levels of V, Cr, Ni, Cu, Zn, As, Cd, Hg, Pb and N were determined. Very high concentrations in the areas of study were detected when compared to nearby unaffected regions. Similar trends were observed for all the elements in the differently orientated transects, showing an appreciable influence of the NW prevailing winds of the region in the dispersion of pollutants, as well as a clear decreasing gradient in the concentrations of metals in mosses within a distance of 1500 meters from the facilities. A differentiation between the elements emitted by the chimney as result of the industrial activity (V, Cr, Ni, Cu and As) and those with a high presence in steel slag deposits (Zn, Cd, Hg and Pb) was observed. The range of contamination was also established by means of the Contamination Factor, indicating a category 4 out of 6 categories, which shows the high levels reported in the areas of study. A different dynamic was registered for nitrogen regarding the rest of the heavy metals analysed except for Hg, probably due to the elevated volatility and mobility of both elements, as well as their high persistence in the atmosphere.     

Larval chemical defence and evolution of host shifts in Chrysomela leaf beetles

Summary. Larvae of Chrysomela leaf beetles release for defence volatile compounds belonging to various chemical families. This study focuses on the defensive strategy based on the esterification of isobutyric acid and 2-methylbutyric acid with a wide variety of alcohols taken up from the host plant. To date, only two species are known to produce these repellents C. interrupta, which is associated with Betulaceae and C. lapponica which occurs either on Betulaceae or Salicaceae.? In order to know if other species have developed this chemical defence and how the food plant influences the secretion of these toxins, we targeted by mass spectrometry the presence of iso- and 2-methylbutyric acids and esters of them in the defensive secretions of Chrysomela larvae exclusively associated with Betulaceae or Salicaceae. ?Screening analyses reveal that the synthesis of these compounds is a common character restricted to all the members belonging to the C. interrupta group sensu Brown (1956) regardless of the host-plant family. These results suggest that the biochemical mechanism leading to the synthesis of these compounds could be considered as a synapomorphy meaning that the group is probably monophyletic. ?Defensive secretions of the members of the interrupta group are quantitatively assayed for iso- and 2-methylbutyric acids and their (Z)-3-hexenyl esters. Results reveal a chemical plasticity developed by Chrysomela species associated with Salicaceae. The amounts of iso- and 2-methylbutyric acids derivatives and of salicylaldehyde in their larval secretions depend on the food plant and on its content in phenolglucosides. Received 5 October 1998; accepted 25 November 1998.     

Replacement of reproductives in Nasutitermes princeps (Desneux) (Isoptera: Termitidae)

Summary The production of replacement reproductives in experimentally orphaned societies was investigated in Nasutitermes princeps (Desneux). From 1 to 180 replacement queens and multiple kings, all adultoids, were found in the 13 nests that were re-collected. Normal imagos, microimagos, or a mixture of the two forms were present, depending on colony composition at the time of orphaning. In colonies with alates, the corresponding forms were found as replacement reproductives. Where only young nymphs were present, microimagos differentiated. Neither the number of queens nor their level of physogastry was correlated with the time elapsed since orphaning, but the total egg-laying rates were. We suggest that competition among queens rather than time determines individual physogastric development. Observations show that the most likely cause of accidental queen death in nature is probably nest fall from the supporting tree. Even in this case, the queen may be able to migrate to a newly rebuilt nest. An experimental simulation of this situation showed that colony migration can occur. The data indicate that the replacement of the primary queen after her accidental death cannot by itself account for the high rate of polygyny (60%) encountered in N. princeps. Two other possible causes are the replacement of the ageing foundress as a normal event of colony life, and colony reproduction by budding off new nests with adultoid reproductives.King Léopold III Biological Station, Laing Island, Papua New Guinea, contribution no. 84Research Assistant of the National Fund for Scientific Research (Belgium)     

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

Summary The 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.     

Recycling plant wax constituents for chemical defense: hemi-biosynthesis of triterpene saponins from β-amyrin in a leaf beetle

Several species of Doryphorina leaf beetles from Central- and South America produce oleanane triterpene glycosides in their defensive glands. The presence of pentacyclic triterpenes in insects is intriguing since they lack the key enzymes necessary to synthesize these compounds. Since -amyrin is a common constituent of leaf waxes, we hypothesized that these leaf beetles use this compound as a precursor to their oleanane glycosides. To test this hypothesis we first confirmed the presence of -amyrin in Ipomoea batatas, the food plant of Platyphora kollari. Next, adults of P. kollari were fed for 10 days with I. batatas leaf disks painted with a solution of [2,2,3-²H₃]-amyrin ([2,2,3-²H₃]-1). The secretion from their defensive glands was collected and analyzed by HPLC-ESIMS. The results demonstrated that the secretion of beetles fed with an amount of [2,2,3-²H₃]-amyrin corresponding to the quantity of unlabeled (natural) -amyrin present in the leaf disks contained on average 5.1% of [2,2,3-²H₃]-3-O--d-glucopyranosyl-(1-->4)--d-glucuronopyranosyl-hederagenin ([2,2,3-²H₃]-2), whereas the secretions of beetles fed with 10 times this amount of [2,2,3-²H₃]-amyrin contained on average 23.9% of [2,2,3-²H₃]-2. In both series of experiments, the percentage of labeled versus unlabeled triterpene glycoside in the secretion was positively correlated with the amount of deuterated -amyrin ingested. These results demonstrate for the first time that some leaf beetles are able to metabolize a widespread triterpenic constituent of leaf wax into more complex glycosides that are stored in their defensive glands.     

Uptake and metabolism of [<Superscript>14</Superscript>C]rinderine and [<Superscript>14</Superscript>C]retronecine in leaf-beetles of the genus <Emphasis Type="Italic"> Platyphora</Emphasis> and alkaloid accumulation in the exocrine defensive secretions

Summary. Sequestration and processing of pyrrolizidine alkaloids (PAs) by leaf beetles of the genus Platyphora were investigated. Tracer experiments with labeled alkaloids were performed with P. eucosma feeding on Koanophyllon panamense (Asteraceae, tribe Eupatorieae). P. eucosma catalyzes the same reactions previously demonstrated for P. boucardi specialized to Prestonia portobellensis (Apocynaceae): (i) epimerization of rinderine to intermedine; (ii) esterification of retronecine yielding insect-specific PAs; (iii) efficient transport of the PAs as free bases into the defensive secretions. P. bella feeding on Tournefortia cuspidata (Boraginaceae) shows the same sequestration behavior and ability to synthesize the specific retronecine esters. P. ligata, a species phylogenetically closely related to the PA adapted species and clustering in the same clade, but feeding on a host plant devoid of PAs, feeds easily on PA treated host-plant leaves, but does not sequester or metabolize PAs. P. kollari a species clustering outside the PA clade refused to feed on its food-plant leaves painted with PAs. The results are discussed in relation to host-plant selection of the PA adapted species and the role of PAs in chemical defense. Received 20 September 2002; accepted 18 November 2002.     

Self-organized shortcuts in the Argentine ant

This work is supported in part by the Belgian program on interuniversity attraction poles, Les Instituts Internationaux de Physique et de Chimie, and the Belgian IRSIA grant # 860004.     

De novo biosynthesis of Δ3-Isoxazolin-5-one and 3-Nitropropanoic acid derivatives inChrysomela tremulae

The nature of the cosmic redshift is one of the most fundamental questions in modern science. Hubble's discovery of the apparent Expansion of the Universe is derived from obsevations on a small number of galaxies at very low redshifts. Today, quasar redshits have a range more than 1000 times greater than those in Hubble's sample, and represent more than 100 times as many objects. A recent comprehensive compilation of published measurements provides the basis for a study indicating that quasar observations are not in good agreement with the original predictions of the Expanding Universe theory, but are well fit by the predictions of an alternative theory having fewer adjustable parameters.