Pyrrolizidine alkaloid content in <Emphasis Type="Italic">Senecio</Emphasis>: ontogeny and developmental constraints

Summary. The ontogeny of pyrrolizidine alkaloid (PA) synthesis and constraints on defence level during the seedling stage were examined in the annual Senecio vulgaris and the monocarpic perennial Senecio jacobaea. In both species, PAs were actively synthesized from the onset of seedling growth so that juvenile stages did not go through an undefended stage. Roots are known to be the exclusive sites where PAs are produced. Root biomass was the single most important biomass parameter explaining variation in total PAs per seedling. All correlation coefficients between—relative growth rate and PA concentration were negative, but none was significant. However, a significant negative—correlation was found between shoot to root ratio and PA concentration in S. jacobaeaseedlings, suggesting a dilution effect of the PAs. Earlier studies have shown that the shoot to root ratio is positively correlated with relative growth—rate of established S. jacobaea plants. It is therefore suggested that young S. jacobaea plants with a high shoot to root ratio and hence a high growth capacity necessarily have lower PA defence levels than plants with a low shoot to root ratio. Received 10 July 2002; accepted 16 November 2002.     

Pyrrolizidine alkaloids and pentacyclic triterpene saponins in the defensive secretions of Platyphora leaf beetles

Summary. Field collected exocrine defensive secretions of nine neotropical Platyphora species were analyzed for the presence of plant acquired pyrrolizidine alkaloids (PAs) and pentacyclic triterpene saponins. All species secrete saponins. In addition, five species feeding on Tournefortia (Boraginaceae), Koanophyllon (Asteraceae, tribe Eupatorieae) and Prestonia (Apocynaceae) were shown to sequester PAs of the lycopsamine type, which are characteristic for species of the three plant families. The PA sequestering species commonly store intermedine, lycopsamine and their O^3′-acetyl or propionyl esters as well as O⁷- and O⁹-hydroxyisovaleryl esters of retronecine. The latter as well as the O^3′-acyl esters were not found in the beetles’ host plants, suggesting the ability of the beetles to esterify plant derived retronecine and intermedine or its stereoisomers. Despite the conformity of the beetles’ PA patterns, considerable inconsistencies exist regarding the PA patterns of the respective host plants. One host plant was devoid of PAs, while another contained only simple necines. Since the previous history of the field collected beetles was unknown this discrepancy remains obscure. In contrast to the Palearctic chrysomeline leaf beetles, e.g. some Oreina species which ingest and store PAs as their non-toxic N-oxides, Platyphora leaf beetles absorb and store PAs as the toxic free base (tertiary PA), but apparently avoid to accumulate PAs in the haemolymph. This suggests that Chrysolina and Platyphora leaf beetles developed different lines of adaptations in their parallel evolution of PA mediated chemical defense. Received 30 November 2000; accepted 5 February 2001     

Lack of sequestration of host plant glucosinolates in <Emphasis Type="Italic">Pieris rapae</Emphasis> and <Emphasis Type="Italic">P. grarricae</Emphasis>

Summary. Sequestration of plant toxins in herbivores is often correlated with aposematic coloration and gregarious behaviour. Larvae of Pieris brassicae show these conspicuous morphological and behavioural characteristics and were thus suggested to sequester glucosinolates that are characteristic secondary metabolites of their host plants. P. rapaeare camouflaged and solitary, and are thus not expected to sequester. To test this hypothesis and to check the repeatabi-lity of a study that did report the presence of the glucosinolate sinigrin in P. brassicae, larvae were reared on three species of Brassicaceae (Sinapis alba, Brassica nigra and Barbarea stricta), and different leaf and insect samples were taken for glucosinolate analysis. The major host plant glucosinolates could only be found in traces or not at all in larval haemolymph, bled or starved larvae, faeces or pupae of both species or P. brassicae regurgitant. Haemolymph of both Pieris spp. was not rejected by the ant Myrmica rubra in dual-choice assays; the regurgitant of P. brassicae was rejected. This suggests the presence of compounds other than glucosinolates that might be sequestered in or produced by P. brassicae only. In faeces of both Pieris spp. a compound which yielded 4-hydroxybenzylcyanide (HBC) upon incubation with sulfatase was detected in high concentrations when larvae had been reared on S. alba. This compound may be derived from hydrolysis of sinalbin, the main glucosinolate of that plant. The unidentified HBC progenitor was apparently not sequestered in the two Pieris spp., and was not detected in faeces of larvae reared on B. nigra or B. stricta. Received 18 July 2002; accepted 11 September 2002.     

Time course of pyrrolizidine alkaloid sequestration in <Emphasis Type="Italic">Longitarsus</Emphasis> flea beetles (Coleoptera,Chrysomelidae)

Summary. Several species of Longitarsus take up, metabolize and store pyrrolizidine alkaloids (PAs) from their host plants. In feeding experiments using radioactively labeled PAs of different types we examined the time course of the sequestration process in L. jacobaeae and L. aeruginosus. We found that adapted species efficiently store PAs for at least two weeks without major losses. During that time, there is virtually no change in the ratio of tertiary alkaloids to stored non-toxic N-oxides, regardless of chemical form fed to the beetles. This implies a transient N-oxidation process where the alkaloids are only temporarily accessible to the enzyme. A dissection experiment with L. aeruginosus six days after uptake of labeled PAs showed that the tertiary alkaloids are not found in the hemolymph but are stored in the elytra and other body compartments. This conforms with earlier experiments that localized the enzymes site of action in the hemolymph. Furthermore we show that different total alkaloid doses in the diet of L. jacobaeae and the potentially less adapted L. succineus do not affect the ratio of recovered N-oxides to tertiary molecules. Thus, the efficiency of the N-oxidizing enzyme is not dependent on the concentration of alkaloids offered.     

<Emphasis Type="Italic">Ceroplastes albolineatus</Emphasis>, the first scale insect shown to sequester pyrrolizidine alkaloids from its host-plant <Emphasis Type="Italic">Pittocaulon praecox</Emphasis>

Summary. The occurrence of pyrrolizidine alkaloids (PAs) in Pittocaulon (ex Senecio) praecox (Asteraceae) a species endemic to Mexico was established. The aboveground plant organs contain the 1,2-saturated monoester 7-angeloyl-dihydroxyheliotridane together with a small proportion of its 9-angeloyl isomer as major alkaloid. The monoesters are accompanied by the macrocyclic otonecine derivative senkirkine. Roots contain only related macrocyclic PAs with senecionine, senkirkine and platyphylline as major components; monoesters are absent. The broom-like succulent stems of P. praecox are infested by the scale insect Ceroplastes albolineatus conspicuously visible by its huge wax cover. All life-history stages, i.e. females, eggs, first instar nymphs (crawlers) and the wax cover were found associated with PAs. The measured PA concentrations clearly indicate sequestration. The highest PA concentrations (mg / g dry weight) reached are: mature females, 0.44; eggs, 0.58; crawlers, 0.37; wax cover, 0.08. The host plant as well as in the infesting scale insect contain the PAs exclusively as free bases. As a phloem-feeder C. albolineatus must acquire the PAs with the ingested phloem sap. This appears plausible since in Senecio species PA are transmitted and circulated through the phloem path. It is suggested that PAs may protect particularly the crawlers as the most endangered stage in the life-cycle of the scale insect.     

Phenological fate of plant-acquired pyrrolizidine alkaloids in the polyphagous arctiid Estigmene acrea

Summary. The alkaloid profiles of the life history stages of the highly polyphagous arctiid Estigmene acrea were established. As larvae individuals had free choice between a plain diet (alkaloid-free) and a diet that was supplemented with Crotalaria-pumila powder with a known content and composition of pyrrolizidine alkaloids (PAs). Idiosyncratic retronecine esters (insect PAs) accounted for approximately half of the PAs recovered from the larvae. These alkaloids were synthesized by the larvae through esterification of dietary supinidine yielding the estigmines, and esterification of retronecine yielding the creatonotines. The retronecine is derived from insect-mediated degradation of the sequestered pumilines (macrocyclic PAs of the monocrotaline type). With one exception, the PA profiles established for larvae were found almost unaltered in all life-stages as well as larval exuviae and pupal cocoons. The exception is the males, which in comparison to pupae and adult females, showed a significantly decreased quantity of the creatonotines and pumilines. These data support the idea that the creatonotines are direct precursors of the PA-derived male courtship pheromone, hydroxydanaidal. Crosses of PA-free males with PA-containing females and vice versa confirmed an efficient trans-mission of PAs from males to females and then from females to eggs. In single cases a male bestowed almost his total PA load to the female, and a female her total load to the eggs. The results are discussed with respect to pheromone formation, PA transmission between life-stages, and the defensive role of PAs against predators and parasitoids     

Apportionment of nuptial alkaloidal gifts by a multiply-mated female moth (Utetheisa ornatrix): eggs individually receive alkaloid from more than one male source

Summary. In the moth Utetheisa ornatrix the female is promiscuous and receives a nuptial gift of pyrrolizidine alkaloid (PA) by seminal infusion from each mate. The alkaloidal gifts are transmitted by the female to the eggs, which are protected as a result. We here show that individual eggs may receive PAs from more than one male source and that individual males have no assurance that the PA they themselves contribute to the female will find its way exclusively to eggs of their siring. Received 28 June 2002; accepted 28 August 2002.     

Variation of pyrrolizidine alkaloids in Ithomiinae: A comparative study between species feeding on Apocynaceae and Solanaceae

Summary The primitive, Apocynaceae-feeding Ithomiine,Tithorea harmonia, incorporates dehydropyrrolizidine alkaloids (PAs) from its larval foodplant (Prestonia acutifolia), rarely visiting PA sources pharmacophagously in the adult; females show higher concentrations of PAs than males, with similar variance. The close relativeAeria olena (feeding onP. coalita, without PAs) shows similar PA concentrations in both sexes and greater variation in males, like more advanced Solanaceae-feeding Ithomiine such asMechanitis polymnia, which likeA. olena obtain PAs by pharmacophagy in the adult (mainly males). This difference is due to the dynamics of PA incorporation in these species. Little variation in PA content was found among allopatric populations of the same species, but variation in available PA sources in different months was correlated with different average storage levels in the butterflies.     

The roles of nicotine and natural enemies in determining larval feeding site distributions of Manduca sexta L. and Manduca quinquemaculata (Haworth) on tobacco

Summary. Field observations indicated that hornworms select feeding sites non-randomly on tobacco. We tested the hypotheses that differences in feeding site locations of larvae of Manduca sexta L. and Manduca quinquemaculata (Haworth) (Lepidoptera: Sphingidae) on tobacco could be explained by differential nicotine concentrations within plants and leaves, species-specific responses to nicotine, or pressure exerted by natural enemies. Results showed that third-instar larvae of M. sexta fed more proximally and centrally on the leaf, whereas M. quinquemaculata fed more distally. Within-plant selection of leaves did not differ; both species selected leaves in the middle region of the plant. Nicotine concentrations in a high nicotine genotype, NC95, varied within each leaf, increasing 2—3 fold from the basal to apical portion of the leaf, and within each plant, increasing 7—10 fold from the first fully expanded leaf to the twelfth (lowest) leaf. In laboratory bioassays, both Manduca species responded to nicotine as a feeding deterrent. Electrophysiological studies demonstrated that gustatory organs of both species responded to nicotine at concentrations found in tobacco leaves and that M. quinquemaculata generally showed a less vigorous response to nicotine than M. sexta. Field mortality of M. sexta due to parasitism by Cotesia congregata (Say) and to parasitism and predation combined differed among feeding sites; predation alone did not. Results suggest that although nicotine concentration and species specific responses to nicotine play a role in determining feeding site locations, pressure exerted by natural enemies, especially parasitism by C. congregata, is more important. Received 22 February 2000; accepted 20 July 2001.     

Foraging responses in the butterflies <Emphasis Type="Italic">Inachis io</Emphasis>, <Emphasis Type="Italic">Aglais urticae</Emphasis> (Nymphalidae), and <Emphasis Type="Italic">Gonepteryx rhamni</Emphasis> (Pieridae) to floral scents

Summary. For butterflies to be efficient foragers, they need to be able to recognize rewarding flowers. Flower signals such as colours and scents assist this recognition process. For plant species to attract and keep butterflies as pollinators, species-specific floral signals are crucial. The aim of this study is to investigate foraging responses to floral scents in three temperate butterfly species, Inachis io L. (Nymphalidae), Aglais urticae L. (Nymphalidae), and Gonepteryx rhamni L. (Pieridae), in behavioural choice bioassays. The butterflies were allowed to choose bet-ween flower models varying in scent and colour (mauve or green). Flowers or vegetative parts from the plants Centaurea scabiosa L. (Asteraceae), Cirsium arvense (L.) (Asteraceae), Knautia arvensis (L.) (Dipsacaceae), Buddleja davidii Franchet (Loganicaeae), Origanum vulgareL. (Lamiaceae), Achillea millefolium L. (Asteraceae), and Philadelphus coronarius L. (Hydrangiaceae) were used as scent sources. All visits to the models — those that included probing and those that did not — were counted, as was the duration of these behaviours. Both flower-naive and flower-experienced (conditioned to sugar-water rewards, the colour mauve, and specific floral scents) butterflies were tested for their preference for floral versus vegetative scents, and to floral scent versus colour. The butterflies were also tested for their ability to switch floral scent preferences in response to rewards. Flower-naive butterflies demonstrated a preference for the floral scent of the butterfly-favourable plants C. arvense and K. arvensis over the floral scent of the non-favourable plants Achillea millefolium (Asteraceae), and Philadelphus coronarius cv. (Hydrangiaceae). Most of the butterflies that were conditioned to floral scents of either C. arvense, K. arvensis, or B. davidii readily switched theirfloral scent preferences to the one most recently associated with reward, thus demonstrating that floral scent constancy is a result from learning. These findings suggest that these butterflies use floral scent as an important cue signal to initially identify and subsequently recognize and distinguish among rewarding plants. Received 2 September 2001; accepted 9 September 2002.     

Detoxification of pyrrolizidine alkaloids by the harvestman <Emphasis Type="Italic">Mitopus morio</Emphasis> (Phalangidae) a predator of alkaloid defended leaf beetles

Summary. The harvestman Mitopus morio (Phalangidae) is a generalist predator. It is known to prey on larvae of the chrysomelid leaf beetle Oreina cacaliae defended by plant acquired pyrrolizidine alkaloids (PAs). Tracer feeding experiments were performed to determine how harvestmen tolerate protoxic PAs. Minced meat containing either [¹⁴C]senecionine or [¹⁴C]senecionine N-oxide was fed to M. morio and subsequently feces and bodies were analyzed. Labeled alkaloid N-oxide remained stable and was eliminated almost unaltered with the feces; only 10% was recovered as tertiary PA. In contrast, approximately 80% of labeled tertiary alkaloid (senecionine) ingested with the diet was N-oxidized and eliminated; the remaining 20% consisted of unchanged senecionine and a polar metabolite of unknown structure. Harvestmen process their diet by excreting digestive juice, indicated by bleaching of the meat color. Analysis of the processed diet revealed some N-oxidation of [¹⁴C]senecionine, suggesting the gut as the site of Noxidation. Analysis of the bodies of harvestmen 80 hours after the tracer feeding pulse revealed only trace amounts of the polar metabolite. Neither senecionine nor its N-oxide could be detected in the body extracts. The results are discussed in relation to the strategies of PA adapted insects to avoid accumulation of tertiary PAs in living tissues.     

Comparative sensitivity to and consumption of methyl eugenol in three <Emphasis Type="Italic">Bactrocera dorsalis</Emphasis> (Diptera: Tephritidae) complex sibling species

Summary. Sensitivities to methyl eugenol of three sibling species in the Bactrocera dorsalis complex were compared. The degree of species sensitivity to methyl eugenol, i.e. B. dorsalis > B. papayae > B. carambolae (in decreasing order), was concomitant with the species age-related response to methyl eugenol as previously reported. The ability to consume methyl eugenol by the three sibling species showed similar trend - the average ME consumption per male was 0.70 ml for B. dorsalis, 0.58 ml B. papayae and 0.18 μl B. carambolae. Results obtained were discussed in relation to area-wide control of fruit fly. Received 21 April 2002; accepted 9 July 2002     

Antennal responses to floral scents in the butterflies <Emphasis Type="Italic">Inachis io</Emphasis>, <Emphasis Type="Italic">Aglais urticae</Emphasis> (Nymphalidae), and <Emphasis Type="Italic">Gonepteryx rhamni</Emphasis> (Pieridae)

Summary. To better understand the biological role of floral scents for butterflies, electrophysiological responses to floral scents were investigated using combined gas chromatography and electroantennographic detection (GC-EAD). The antennal responses of three butterfly species, Aglais urticae L. (Nymphalidae), Inachis io L. (Nymphalidae), and Gonepteryx rhamni L. (Pieridae) to floral scent compounds from both natural and synthetic mixtures were examined. Floral scents were collected from the butterfly nectar plants Cirsium arvense (L.) (Asteraceae), and Buddleja davidii Franchet cv. (Loganicaeae) with dynamic head-space methods on Tenax-GR and eluted with pentane. These eluates, composed of natural floral scent blends, represent an array of compounds in their natural state. In the GC-EAD analyses eleven compounds were identified from C. arvense with the benzenoid compound phenylacetaldehyde in highest abundance. Seventeen compounds were identified from B. davidii with the irregular terpene oxoisophorone in highest abundance. Thirty-nine synthetic floral scent compounds were mixed in pentane, in equal amounts; about 35 ng were allowed to reach the antennae. The butterflies showed antennal responses to most of the floral scent compounds from both natural and synthetic blends except to the highly volatile monoterpene alkenes. Certain benzenoid compounds such as phenylacetaldehyde, monoterpenes such as linalool, and irregular terpenes such as oxoisophorone, were emitted in relatively large amounts from C. arvense and B. davidii, and elicited the strongest antennal responses. These compounds also elicited strong antennal responses when present in the synthetic scent blends. Thus, the butterflies seem to have many and /or sensitive antennal receptors for these compounds, which points to their biological importance. Moreover, these compounds are exclusively of floral scent origin. For B. davidii, which depends highly on butterflies for pollination, the exclusive floral scent compounds emitted in high abundance could be the result of an adaptive pressure to attract butterflies. Received 2 Septemter 2001; accepted 9 September 2002.     

Systemically-induced response of cabbage plants against a specialist herbivore, Pieris brassicae

Summary. Plant responses to herbivory might directly affect the herbivore (“direct” defences) or might benefit the plant by promoting the effectiveness of natural antagonists of the herbivores (“indirect” defences). Brussels sprouts attacked by Pieris brassicae larvae release volatiles that attract a natural antagonist of the herbivores, the parasitoid Cotesia glomerata, to the damaged plant. In a previous study, we observed that feeding by caterpillars on the lower leaves of the plant triggers the systemic release of volatiles detectable by the parasitoids from upper leaves of the same plant.?The role of these systemically induced volatiles as indirect defence and the dynamics of their emission were investigated in wind-tunnel dual choice tests with C. glomerata. The systemically induced emission of volatiles varied depending on leaf age and on plant age. Systemic induction affected parasitoid effectiveness, as induced plants could be more easily located by parasitoids than non-induced ones.?The role of the systemic induction as a direct defence was investigated through behavioural and feeding tests with P. brassicae. In dual choice assays, 1st instar larvae preferred to feed and fed more on systemically induced than on non-induced leaves. In single choice assays, the leaf area consumed by caterpillars was larger on systemically induced leaves than on non-induced control leaves. However, caterpillars fed on systemically induced leaves attained the same weight as those feeding on non-induced controls. In addition, P. brassicae pupae whose larvae were fed on systemically induced leaves had longer developmental times than those of larvae fed on non-induced leaves. Adult oviposition behavior was not influenced by systemic induction.?We conclude that systemically induced responses in cabbage might reduce P. brassicae fitness both directly, by affecting their development and feeding behavior and indirectly by making caterpillars and pupae more vulnerable to attack by carnivores. The occurrence of a possible relationship between direct and indirect defence is discussed. Received 24 January 2001; accepted 3 May 2001.     

Pyrrolizidine alkaloids on three trophic levels – evidence for toxic and deterrent effects on phytophages and predators

Summary. Pyrrolizidine alkaloids (PAs) present a model system in the investigation of tritrophic interactions mediated by plant secondary compounds. However, their toxicity for insect herbivores has never been experimentally proven. Here, we demonstrate the toxic effects of a PA on growth and survival of the eri silk moth Philosamia ricini. In a feeding experiment, larvae of this generalist herbivore fed with an artificial PA diet gained weight significantly slower than control animals, and died as pupae. We suggest that derivatives of the ingested PA N-oxide damage developmental functions during metamorphosis. A tracer test with [¹⁴C]senecionine N-oxide revealed that the caterpillars lack adaptations that would prevent conversion of the chemical into the pro-toxic free base. In contrast, the PA adapted leaf beetle Longitarsus anchusae accumulates PAs as N-oxides. We tested the purpose of sequestration in this species as defence against predators. Through a series of prey choice experiments with three carabid predator species, chemically non-protected bark beetle pupae were chosen almost uniformly over L. anchusae pupae. In a following choice test with one of these predators, artificially PA-treated mealworm segments deterred the predator from feeding. Overall the study corroborates the immediate toxic effect of PAs on non-adapted herbivores and the protective effect that adapted insects may gain by sequestering them. It thereby underlines the potential for PAs to play a central role in multitrophic interactions between plants, phytophages and their predators.     

Sequestration of pyrrolizidine alkaloids by larvae ofTellervo zoilus (Lepidoptera: Ithomiinae) and their role in the chemical protection of adults against the spiderNephila maculata (Araneidae)

Summary Life stages of the primitive Australian ithomiine butterflyTellervo zoilus and its larval hostplant, the apocynaceous vineParsonsia straminea, were quantitatively assayed for pyrrolizidine alkaloids (PAs). PAs were found in all stages, mainly as N-oxides, being most concentrated in larvae and freshly-emerged adults. Although adults feed at various confirmed PA sources this probably does not compensate for losses, as wild-caught adults had considerably lower concentrations of PAs. The main alkaloid present in both freshly-emerged adults and in leaves of the host-plant was lycopsamine (1b), stored by butterflies in the N-oxide form. Its presence in higher proportion, in relation to intermedine (1a), in larvae, pupae and adults ofTellervo in relation to the host-plants suggests the inversion of intermedine to lycopsamine by the insects. No 14-member ring macrocyclic PAs were detected in either food-plant or butterflies. Several other PAs were found in wild-caught adults reflecting visits to other PA sources. PAs were also found in high concentrations in freshly-emerged individuals of the danaineEuploea core bred onParsonsia straminea. Wild-caughtDanaus affinis had high PA levels acquired from adult feeding. Freshly emergedEuploea raised onIschnocarpus frutescens andDanaus raised onIschnostemma carnosum (both PA-free) were preyed on by the orb weaving spiderNephila maculata, and showed no PAs. In all cases where PAs were present, most butterflies were liberated, usually cut out of the web unharmed, byNephila. The spider's response was not closely linked to PA concentration, however, and may also depend on hunger levels and previous experience with PA-containing butterflies. All control and other non-PA containing butterflies were consumed although rejection of some body parts of freshly-emergedDanaus affinis suggests that compounds other than PAs may be involved.     

Preferences of six leaf beetle species among qualitatively different leaf age classes of three Salicaceous host species

Summary. As Salicaceous plants produce new leaves for a prolonged period of time, they expose a wide range of differentially aged leaves to herbivores during the growing season. In this work, I show that young leaves of three Salicaceous species, Populus tremula L., Salix phylicifolia L. and S. pentandra L., contain more nitrogen than conspecific old leaves. In P. tremula and S. pentandra young leaves also contained more low-molecular weight secondary compounds, phenolic glucosides. Leaves of S. phylicifolia did not contain phenolic glucosides in detectable amounts. Furthermore, in P. tremula and S. pentandra young leaves contained less polymeric digestability-reducing phenolics, condensed tannins, than old leaves. In S. phylicifolia, higher concentrations of condensed tannins were found in young leaves. In laboratory feeding trials with six leaf beetle species, young leaves of the studied plants were invariably preferred in all tested herbivore × host species combinations. In particular, it is remarkable that three leaf beetle species with known different overall relationships to phenolic glucosides equally preferred more glucoside-containing young S. pentandra leaves over conspecific old ones. Four beetle species were found to prefer young leaves of S. phylicifolia despite the higher content of condensed tannins in young leaves. These results indicate that the general preference of leaf beetles for young leaves of Salicaceous plants probably does not primarily result from variable distribution of secondary compounds. Apparently, the preference for young leaves is fundamentally due to variation in leaf nutritive traits, such as nitrogen content. Received 9 February 2001.     

Evidence for two genetically and chemically defined host races of Tyria jacobaeae (Arctiidae, Lepidoptera)

Summary. A widely distributed host race of Tyria jacobaeae lives on Senecio jacobaea and related species and accumulates pyrrolizidine alkaloids (“PA race”), another race, which is restricted to the Alps and found on Petasites paradoxus, sequesters sesquiterpenes, such as petasol and isopetasol. Nucleotide sequences of the mitochondrial 16S rDNA gene show 1% sequence divergence, indicating that genetical differences exist between the PA exploiting and the terpene-sequestering host races of T. jacobaeae. This finding suggests that both host races of T. jacobaeae must have been separated for some time already, possibly since the Pleistocene. Received 2 May 2001; accepted 1 June 2001.     

Pheromone-based aggregation behaviour of the firebrat, <Emphasis Type="Italic">Thermobia domestica</Emphasis> (Packard) (Thysanura: Lepismatidae)

Summary. We tested the hypothesis that aggregation behaviour of the firebrat, Thermobia domestica (Packard) (Thysanura: Lepismatidae), an inhabitant of enclosed microhabitats, is mediated, at least in part, by a pheromone. Individual insects were released into the central chamber of a 3-chambered olfactometer and test stimuli were placed in lateral chambers. Paper discs previously exposed for 3 days to 10 female, male, or juvenile T. domestica were all preferred by female, male, or juvenile T. domestica over unexposed paper discs, indicating the presence of an aggregation/arrestment pheromone. In additional experiments, frass and scales from female T. domestica, tested singly and in combination, proved not to be the source of the pheromone. Physical contact was required for pheromone recognition, indicating that the pheromone arrests rather than attracts conspecifics. Arrestment by the long-tailed silverfish, Ctenolepisma longicaudata Escherich (Thysanura: Lepismatidae), but not by the common silverfish, Lepisma saccharina L. (Thysanura: Lepismatidae), to T. domestica exposed paper discs suggests closer phylogenetic relatedness between C. longicaudata and T. domestica, than between C. longicaudata and L. saccharina. Whether C. longicaudata or L. saccharina produce an aggregation signal, and whether T. domestica respond to this signal is unknown. Received 10 June 2002; accepted 30 September 2002.     

Tropane and pyrrolizidine alkaloids in the ithomiinesPlacidula euryanassa andMiraleria cymothoe (Lepidoptera: Nymphalidae)

Summary Larvae of the ithomiine butterflyPlacidula euryanassa sequester tropane alkaloids (TAs) from the host plantBrugmansia suaveolens and pass them through the pupae to freshly emerged adults. Wild caught adults also show in their tissues, variable amounts of pyrrolidizine alkaloids (PAs), probably sequestered from variable plant sources and subject to dynamics of incorporation, accumulation and utilization of PAs by ithomiine butterflies. The ratio TAs/PAs is also variable between different populations.Miraleria cymothoe, another ithomiine that feeds onB. suaveolens as larvae, does not sequester TAs from the host-plant, but sequesters PAs from plant sources visited by the adult butterflies. The main alkaloid found in both butterflies is lycopsamine, which also is the principal PA found in all genera of Ithomiinae.