Chemical mimicry of cuticular hydrocarbons – how does Eremostibes opacus gain access to breeding burrows of its host Parastizopus armaticeps (Coleoptera, Tenebrionidae)?

Summary. Breeding burrows of Parastizopus armaticeps armaticeps, a fossorial desert tenebrionid beetle, are cleptoparasitised by the closely related Eremostibes opacus. Gas chromatographic analyses show a high congruity of the cuticular hydrocarbons of both species. We compare these hydrocarbon patterns with those of four other Stizopina species and the Scaurini Herpiscius sommeri. In a bioassay, dummies treated with cuticular hydrocarbon extracts of E. opacus and the P. a. bifidus parasite E. bushmanicus were mostly ignored by P. a. armaticeps, whereas dummies with applied extracts of the remaining species were heavily attacked. We show that there is a correlation between agonistic behaviour of P. a. armaticeps towards the intruder and the chemical similarity of the cuticular hydrocarbons of the two species. Furthermore, we produced quantitatively modified hydrocarbon patterns of E. barbatus by changing the temperature at which this species was kept. The new 30 °C type was chemically similar to E. opacus, and was frequently ignored by P. a. armaticeps, whereas a reduction of the temperature to 20 °C only had minor effects on the hydrocarbon pattern. Furthermore, we show that the addition of one single component, heptacosane, to the cuticular hydrocarbon extract of E. opacus alters the host’s reaction. We discuss the role of cuticular hydrocarbons for the recognition of this host-parasite system and the relevance of quantitative characters in the hydrocarbon pattern for the discrimination of the host.     

Host-plant leaf surface compounds influencing oviposition in Delia antiqua

Summary. Delia antiqua (Diptera: Anthomyiidae) females lay eggs between the leaves of onion plants or in the soil around the base of the plants, then the maggots feed on the onion bulb and roots causing rapid secondary infection by fungi and bacteria. It is well known that the first sensory modality used by the onion fly is vision, therefore the shape (vertical narrow cylinders) and colour (yellow) of the plant play a crucial role in the recognition of a potential host plant. In the past it has been shown that n-dipropyl disulfide (Pr₂S₂), a typical component of onion volatiles, is an important chemical host plant cue. We extracted host leaf surface to verify if Pr₂S₂ is the major chemical oviposition stimulant and to determine if other as yet unknown substances may play a role in host-plant selection. We confirmed that the females laid more eggs around onion plants with leaves than when only the onion bulb was present and that the odour of chopped onion stimulates oviposition. Extraction of the surface of onion leaves revealed that only the apolar fraction contained substances that stimulate egg-laying in D. antiqua. GC-EAD analysis indicated that a minor constituent, Pr₂S₂, is perceived by the olfactory receptor on the antennae of the onion fly females. This confirmed the importance of Pr₂S₂ as oviposition stimulant. Contact with the polar fraction did not stimulate egg-laying behaviour in this Delia species. We discuss the oviposition strategy of D. antiqua in comparison with its closely related species, D. radicum, in which the oviposition behaviour is stimulated mainly through contact with the cabbage leaf surface and only partially by the host volatiles.     

Daphne gnidium, a possible native host plant of the European grapevine moth Lobesia botrana, stimulates its oviposition. Is a host shift relevant?

Summary. We tested the hypothesis that Daphne gnidium is an ancestral host plant of Lobesia botrana. To this end, we studied the oviposition response of this moth to various aerial organs of this plant. Our results show that females prefer to lay eggs on daphne berries rather than on grapes (cv. chasselas) and that polar surface extracts of daphne berries and leaves strongly stimulate oviposition in a dosedependant way, whereas flower extracts are weakly stimulant and branch extracts are inactive or deterrent for oviposition. Furthermore, a total extract of daphne berries stimulates oviposition in semi-natural conditions when applied onto fresh grapes. Oviposition stimulants from berries were isolated by HPLC coupled with a dual-choice oviposition bioassay. The ecological value of D. gnidium for L. botrana is discussed and the possible use of oviposition stimulants from daphne, contrasting with the oviposition signal of the cultivated host plant, is proposed in the perspective of developing behavioural manipulation methods such as stimulo-deterrent diversionary strategies compatible with IPM programs.     

Oviposition stimulants for the pipevine swallowtail butterfly,Battus philenor (Papilionidae), from anAristolochia host plant: Synergism between inositols,aristolochic acids and a monogalactosyl diglyceride

Aristolochia macrophylla (Lam.) is a major host of the pipevine swallowtail butterfly,Battus philenor (L.), in the eastern United States. The female butterflies use a synergistic mixture of inositols, acids and a lipid as oviposition cues in recognizing this plant on contact. The acids and lipid, all isolated from the Et₂O-CHCl₃ fraction of an alcoholic extract of fresh foliage, were identified as aristolochic acid I (1), aristolochic acid II (2) and 1,2-[di(9Z,12Z,15Z)-octadeca-9, 12, 15-trienoyl]-3-galactosyl-sn-glycerol (3). Identifications were facilitated by UV, MS (EI and FAB) and NMR (1D and 2D) spectral techniques and by analysis of the hydrolysis products of 3. The active inositols were identified as D-(+)-pinitol, reported previously, and sequoyitol. Though this is apparently the first report of oviposition responses to a diacyl glycerol glycoside by a phytophagous insect, responses to aristolochic acids and sequoyitol have been reported previously for anAristolochia-feeding swallowtail of a different genus in Japan. This indicates substantial evolutionary conservatism in chemical oviposition cues within the tribe Troidini.     

Eggs of cabbage root fly stimulate conspecific oviposition: Evaluation of the activity and determination of an egg-associated compound

Summary. Previous studies indicated the presence of antennally-active compounds in extracts of eggs laid by female cabbage root flies, Delia radicum, that stimulated oviposition by conspecific females. We confirmed that previously laid D. radicum eggs stimulated oviposition by other D. radicum females, in a dose-dependent manner. Methanol extracts of conspecific eggs stimulated oviposition by females D. radicum, whereas egg extracts of D. antiqua and Psila rosae had no effect. Electrophysiological recordings from the tarsal sensilla of D. radicum females indicated that neurones of the C₅ sensillum responded to the egg extracts from both D. radicum and D. antiqua, but not P. rosae. Chemical analysis revealed that the extract of eggs from D. radicum contained the thia-triaza-fluorene compound, 1,2-dihydro-3-thia-4,10,10b-triaza-cyclopenta[.a.]fluorene-1-carboxylic acid (CIF-1), an oviposition stimulant found previously only in cruciferous plants. Another potentially active component has yet to be identified.     

Volatiles of the honey bee larva initiate oogenesis in the parasitic mite Varroa destructor

Summary. Varroa reproduction is closely synchronized to the development of its host. In this study we present a new bioassay for field and laboratory tests to evaluate host factors triggering Varroa oogenesis. Female mites deprived of feeding activated oogenesis when perceiving larval volatiles. In laboratory assays the living L5-larva and pentane extracts of the larval cuticle had a clear activating effect. Wax and larval food did not elicit Varroa oogenesis. The activating components apparently are in the polar fraction of the cuticular volatiles. The consequences of this regulative mechanism for the host parasite relationship and prospects for further research are discussed.     

Cleptoparasitism increases the host finding ability of a polyphagous parasitoid species,<Emphasis Type="Italic"> Rhopalicus tutela</Emphasis> (Hymenoptera: Pteromalidae)

Host finding abilities were investigated in the braconid Coeloides bostrichorum and the pteromalid Rhopalicus tutela, two ectoparasitoid wasps attacking the late instar of the bark beetle Ips typographus. Under laboratory conditions, important differences in the host-searching behaviour of these species were found, R. tutela being highly mobile as compared to C. bostrichorum. In the presence of C. bostrichorum, R. tutela behaved as a cleptoparasitoid, displacing the females from their oviposition sites and stealing the hosts previously located by the braconid. This behaviour facilitated host finding in R. tutela and could partly explain the relative success of the polyphagous R. tutela when occurring with the more specialised C. bostrichorum.Communicated by R.F.A. Moritz     

Profiles of cuticular hydrocarbons mediate male mate choice and sexual isolation between hybridising <Emphasis Type="Italic">Chrysochus</Emphasis> (Coleoptera: Chrysomelidae)

Summary. Chemical signals frequently underlie sexual isolation between insect species. Our understanding of the evolutionary forces influencing these signaling systems is known for very few systems, challenging both our efforts to understand insect speciation, and our ability to predict long-term changes in the chemical communication systems of insects. Thus, we are in need of more systems in which both the chemical signals causing sexual isolation and the evolutionary forces driving sexual isolation are understood. Sexual isolation in the hybrid zone between Chrysochus cobaltinus and C. auratus has apparently increased in response to natural selection against hybridisation (i.e. reinforcement). Previous experiments suggested that this isolation was due, at least in part, to male preferences for conspecific females. Here, we confirm this role of male choice, and document that male mate choice in this system is influenced by cuticular hydrocarbon (CHC) profiles. Specifically, male C. cobaltinus responses to control cadavers and conspecific female cadavers painted with different cuticular hexane extracts, together with analyses of the composition of those extracts, revealed that male mate choice is governed by CHC profiles. Multivariate analyses of GC profiles demonstrated that those profiles are indeed both sex- and species-specific. Although GC-MS enabled identification and quantification of the specific cuticular hydrocarbons, we have not yet determined which individual compounds govern mate choice. Having established that CHCs influence sexual isolation in this system, we can now assess the evolutionary lability of these cues, which will inform both our understanding of speciation, and of the conditions under which the chemical signaling systems that influence mate choice in insects can evolve.     

Trail discrimination signal of Lasius japonicus (Hymenoptera: Formicidae)

Summary. Trail-following behavior of Lasius japonicus was colony-specific in the field, while trail pheromone activity was not. We found that the footprint substance caused colony-specific trail-following behavior only when working in conjunction with the trail pheromone. The footprint substance alone did not lead the workers to follow trails. The substance consisted mainly of hydrocarbons with composition almost identical to that of cuticular hydrocarbons, except for the absence of n-alkanes. Nestmate workers shared footprint hydrocarbon profiles as well as cuticular hydrocarbons, but the profiles differed among colonies. We therefore consider that the footprint hydrocarbon profiles serve as the trail discrimination signal in L. japonicus.     

Mother’s choice of the oviposition site: balancing risk of egg parasitism and need of food supply for the progeny with an infochemical shelter?

Summary. Oviposition site selection of herbivorous insects depends primarily on host plant presence which is essential for offspring survival. However, parasitoids can exploit host plant cues for host location. In this study, we hypothesised that herbivores can solve this dilemma by ovipositing within high plant diversity. A diverse plant species composition might represent an ‘infochemical shelter’, as a potentially complex volatile blend can negatively affect the host location ability of parasitoids. We examined this exemplarily for the egg-laying response of the generalist leaf beetle, Galeruca tanaceti, in relation to (1) host plant availability and (2) plant species diversity in the field. Further, we investigated the effect of odours from mixed plant species compositions on (3) leaf beetle oviposition site selection and on (4) the orientation of its specialised egg parasitoid, Oomyzus galerucivorus. In the field, egg clutch occurrence was positively related to the presence and quantity of two major host plants, Achillea millefolium (yarrow) and Centaurea jacea, and to the number of herbaceous plant species. In two-choice bioassays, female beetles oviposited more frequently on sites surrounded by an odour blend from a diverse plant species composition (including yarrow) than on sites with a pure grass odour blend. In the presence of yarrow odour and an odour blend from a diverse plant mixture (including yarrow) no difference in the oviposition response was recorded. Experienced parasitoid females were attracted to yarrow odours, but showed no response when yarrow odours were offered simultaneously with odours of a non-host plant. In conclusion, it could be shown in laboratory bioassays that the parasitoid responds only to pure host plant odours but not to complex odour blends. In contrast, the herbivore prefers to oviposit within diverse vegetation in the field and in the laboratory. However, the laboratory results also point to a priority of host plant availability over the selection of a potential ‘infochemical shelter’ for oviposition due to high plant diversity.     

d-Pinitol as a key oviposition stimulant for sulfur butterfly, Colias erate: chemical basis for female acceptance of host- and non-host plants

The sulfur butterfly, Colias erate, utilizes various legumes as host plants. We examined the chemical constituents of its primary host plant, Trifolium repens (white clover), to identify phytochemicals inducing oviposition by C. erate females. Since one of the four aqueous subfractions prepared from a methanolic extract of the plant has previously been shown to be the most responsible for the oviposition-stimulatory activity exerted by the plant, chemical analyses were conducted of the fraction concerned. Activity-directed fractionation of the subfraction by ion-exchange chromatography revealed that the key substance(s) resided in the neutral fraction. Preparative TLC of the neutral fraction and subsequent spectral analyses identified d-(+)-pinitol, glycerin, methyl β-d-glucoside, and myo-inositol as characteristic components together with ubiquitous sugars (e.g., sucrose and glucose). Of these, only pinitol singly evoked significant oviposition responses at concentrations over 0.05%. In dual-choice bioassays, however, females laid significantly more eggs on pinitol solutions admixed with glycerin or methyl β-d-glucoside than on pinitol alone. Two cyanoglucosides, linamarin, and lotaustralin, occurring in the other aqueous subfractions, also synergistically increased the oviposition response in combination with pinitol. The results clearly indicated that pinitol is a crucial oviposition stimulant involved in host recognition, while glycerin, methyl β-d-glucoside, linamarin, and lotaustralin function as synergists. We further examined the oviposition responses of C. erate females to aqueous fractions, along with their chemical compositions, that had been prepared from five other host plants and a non-host plant, Aristolochia debilis (Aristolochiaceae), on which oviposition occasionally took place in an outdoor cage during the experiments. The plant species accepted by ovipositing females were all found to contain pinitol in amounts enough to induce egg laying by the butterfly, thus leading to the conclusion that pinitol serves as the essential mediator in recognizing and accepting potential host plants.     

Diet-induced chemical phytomimesis by twig-like caterpillars of Biston robustum Butler (Lepidoptera: Geometridae)

Summary. Polyphagous caterpillars of the giant geometer Biston robustum resemble the twigs of their respective food sources in color and shape. Common predatory ants, including Lasius and Formica, were often observed to freely prowl directly on caterpillars bodies, even after antennal contact. This suggests that the cuticular chemicals of the caterpillars resemble those of the twigs of the foodplants, so we analyzed both by GC and GC-MS. The chemical compositions differed among caterpillars fed on a cherry, Prunus yedoensis, a chinquapin Castanopsis cuspidata, and a camellia Camellia japonica. The cuticular chemicals of the caterpillars resembled those of their corresponding food sources. When the caterpillar diets were switched from the cherry to camellia or chinquapin at the 4^th instars, the caterpillars cuticular chemicals changed after molting to resemble those of their respective foods. Caterpillars also changed their cuticular chemicals when they perched on cherry twigs and fed on camellia or chinquapin leaves, but not when they perched on camellia or chinquapin twigs and fed on cherry leaves. The chemical similarities between the caterpillars and the twigs were due to the digestion of host leaves, which indicates that this is a diet-induced adaptation.     

Leaf surface compound fromBrassica oleracea (Cruciferae) induces oviposition byPieris brassicae (Lepidoptera: Pieridae)

Summary Chemicals present on the surface of cabbage (Brassica oleracea L.) leaves were extracted by dipping these leaves for 3 s in dichloromethane followed by a 3 s dip in methanol. When offered in dual choice bioassays using green paper cards as a substrate, the methanol extract stimulated oviposition activity byPieris brassicae L. (Lepidoptera: Pieridae) females. The oviposition stimulant was isolated using medium pressure liquid chromatography, reversed-phase HPLC, ion-pair HPLC and ion exchange chromatography. Using¹H-NMR spectroscopy, the stimulant could be identified as glucobrassicin (3-indolyl-methyl-glucosinolate). When pure glucobrassicin was offered at a dose identical to that in the crude methanol extract, butterflies did not discriminate between these two substrates in a dual choice test. It is argued that a high sensitivity for indole glucosinolates as host recognition factors may confer an adaptive value for these specialist crucifer feeders. The nutritional significance of their precursor tryptophan and the non-volatile nature of the aglycones formed upon enzymic hydrolysis in damaged tissues are proposed as properties of indole glucosinolates that contribute to this possible adaptive advantage.     

Plant volatiles affect oviposition by codling moths

Summary. Oviposition in wild codling moth females, collected as overwintering larvae from apple, pear and walnut, was stimulated by volatiles from fruit-bearing green branches of these respective hostplants. Analysis of headspace collections showed that eight compounds present in apple, pear and walnut elicited a reliable antennal response in codling moth females: (E)--ocimene, 4,8-dimethyl-1,(E)3,7-nonatriene, (Z)3-hexenyl acetate, nonanal, -caryophyllene, germacrene D, (E,E)--farnesene, and methyl salicylate. Any one of these compounds is found in many other non-host plants, and host recognition in codling moth is thus likely encoded by a blend of volatiles. A large variation in the blend proportion of these compounds released from apple, pear and walnut suggests a considerable plasticity in the female response to host plant odours. Wild females, collected as overwintering larvae in the field, laid significantly fewer eggs in the absence of host plant volatiles. The offspring of these females, however, reared on a semi-artificial diet in the laboratory, laid as many eggs with or without plant volatile stimulus. Tests with individual females showed that this rapid change in oviposition behaviour may be explained by selection for females which oviposit in the absence of odour stimuli, rather than by preimaginal conditioning of insects when rearing them on semi-artificial diet. Oviposition bioassays using laboratory-reared females are therefore not suitable to identify the volatile compounds which stimulate egglaying in wild females.     

Oviposition site guarding by male walnut flies and its possible consequences for mating success

Field studies showed that male Rhagoletis juglandis and R. boycei flies guard egg-laying punctures (and the eggs within) on host walnut (Juglans major) fruit and defend those sites from conspecific and heterospecific males. In field experiments with artificially punctured fruit,as well as field observations on unmanipulated fruit, males were consistently more likely to be sighted and stayed longer on damaged fruit than on undamaged fruit. On artificially punctured fruit, they consistently spent more time in the vicinity of a puncture than expected by chance alone. Males together on damaged fruit were more likely to engage in contests over those fruit than males together on undamaged fruit. Copulations were consistently more frequent for either species on damaged than undamaged fruit, both in observations of unmanipulated fruit and in artificial puncture experiments. Analyses which controlled for the longer male residence time on damaged fruit suggested strongly that copulations were consistently achieved at higher per capita rates on damaged than on undamaged fruit, indicating that puncture-guarding functions to increase access to females. An exception to the pattern in male mating success was noted at a site where both species used host fruit on the same trees. In this case, R. juglandis males were only slightly more common on punctured fruit than on control fruit and male success in copulation did not differ significantly between the two types of fruit. This anomalous result was apparently due to an almost absolute advantage enjoyed by R. boycei males in on-fruit contests with R. juglandis males. A likely basis for improvements in mating success associated with puncture guarding was a propensity for females to deposit eggs into existing punctures. Both in observations of unmanipulated fruit and in artificial puncture experiments, females consistently attempted oviposition more often in damaged than undamaged fruit. In artificial puncture experiments, both species at both sites deposited most clutches in damaged fruit. Mating generally took place as females initiated oviposition. The possible functions of puncture use by females as well as alternative functions of puncture guarding by males are discussed.     

(<Emphasis Type="Italic">Z</Emphasis>)-9-Pentacosene − contact sex pheromone of the locust borer, <Emphasis Type="Italic">Megacyllene robiniae</Emphasis>

Summary. Male locust borers, Megacyllene robiniae (Förster), responded to females only after contacting them with their antennae, indicating that mate recognition was mediated by a contact sex pheromone. GC-MS analyses of whole-body extracts of males and females determined that the profiles of compounds in the extracts were qualitatively similar, but differed considerably in the ratios of compounds between sexes. Biological activities of reconstructed blends of the most abundant straight-chain (nC₂₃, nC₂₄, nC₂₅, nC₂₆), methyl-branched (3me-C₂₃, 3me-C₂₅), and unsaturated (Z9:C₂₃, Z9:C₂₅, Z9:C₂₇ compounds in extracts from females were assessed in arena bioassays, assessing four distinct steps in the mating behavior sequence of males (orientation, arrestment, body alignment, mounting and attempting to couple the genitalia). Males were unresponsive to freeze-killed, solventwashed females treated with blends of straight-chain and methyl-branched alkanes, but responded strongly to females treated with the blend of alkenes. Further trials determined that the complete sequence of mating behaviors, up to and including coupling the genitalia, was elicited by Z9:C₂₅ alone. Z9:C₂₅ comprised 16.4 ± 1.3% of the total hydrocarbons in whole-body hexane extracts of females and was co-dominant with two other hydrocarbons that were not active. In contrast, in solid phase microextraction (SPME) wipe samples from several areas of the cuticle, Z9:C₂₅ appeared as the single dominant peak, comprising 34.6 – 37.8% of the sampled hydrocarbons. Our data indicate that Z9:C₂₅ is a contact sex pheromone of M. robiniae, being the most abundant hydrocarbon on the surface of the cuticular wax layer of females where it is readily accessible to the antennae of males.     

The effects of larval experience with a complex plant latex on subsequent feeding and oviposition by the cabbage looper moth: Trichoplusia ni (Lepidoptera: Noctuidae)

Summary. Leaf disc choice and oviposition bioassays were used to examine the effects of larval experience with a Hoodia gordonii latex on subsequent behaviors. The latex deterred feeding and oviposition by “naïve” cabbage looper (Trichoplusia ni, Noctuidae) larvae and moths with no previous exposure to the material. “Experienced” insects, reared on a diet with the H. gordonii latex (1000 ppm), exhibited lesser feeding deterrence relative to naïve insects. Experienced female moths actually preferred to lay eggs on treated rather than control leaves. There was no observed transfer of behavioral preferences from experienced parents to their offspring. Our results suggest that moths may be acquiring oviposition preferences from larval feeding experience as described by Hopkins’ host selection principal (HHSP) or through chemical legacy.     

(Z)-11-Pentacosene is the major sex pheromone component inDrosophila virilis (Diptera)

Summary A crude cuticular extract from 3450 virgin 9–13 day old female fruit flies(Drosophila virilis), was subjected to chromatography accompanied by bioassay for sex pheromone activity. After three chromatographic steps, fractions containing active monoenes and dienes were obtained. Chemical analysis by infrared absorption, gas liquid chromatography and gas chromatography/mass spectrometry of the active fraction indicated that active monoenes were comprised chiefly of (Z)-11-pentacosene (abbreviated (Z)-11-C_25:1), (Z)-13-C_27:1, (Z)-13- and (Z)-14-C_29:1. Synthetic monoenes were made, and only (Z)-11-C_25:1 elicited good courtship behaviour in maleD. virilis. Therefore it was concluded that (Z)-11-C_25:1 was a major sex pheromone. A total of 16.2±1.32 µg of cuticular hydrocarbons was isolated from 10 day old females, including 5.9±0.56 µg of (Z)-11-C_25:1. An additive effect was suggested from the higher observed courtship response when using a mixture of active dienes with the active monoene.     

On the consequences of aggressive male mate-locating behaviour and micro-climate for female host plant use in the butterfly <Emphasis Type="Italic">Lycaena hippothoe</Emphasis>

The distribution of ecological resources and their significance for males and females may vary considerably. Intersexual behavioural interactions may lead, combined with particular resource configurations, to sexual spatial segregation. We investigated this issue relative to host plant use in females of the purple-edged copper butterfly, Lycaena hippothoe. Males exhibited nectar resource-based territoriality, which is an uncommon mate-locating system in butterflies. They perched and patrolled in large territories harassing every passing female. In our study system, the percentage of spatial dimension shared for adult and larval resources was estimated at 50%, and males monopolised 28% of the nectar-rich zones. Under these conditions of harassment, females travelled between nectar-rich zones for feeding and zones with suitable host plants for egg laying, but often without nectar and hence with low male density. This is likely to limit their time budget and, potentially, their realised fecundity as suggested by the low number of eggs found relative to population size. Females were also highly specialised in selecting host plants under particular environmental conditions. Using test choice in experimental cages, we showed that, in the absence of males, only micro-climatic conditions may significantly influencing egg-laying decisions. Moreover, results of egg-rearing experiments under different temperature treatments suggested that eggs were laid in thermally suitable micro-environments. The highly selective egg-laying behaviour can be viewed as a preference-performance choice. Knowledge of individuals' behaviour, including sexual interactions, can be highly significant for our understanding of habitat use, which in turn can be essential for conservation. We discuss this for L. hippothoe, a species of regional conservation concern.     

<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.