Species-specific Leaf Volatile Compounds of Obligate <Emphasis Type="Italic">Macaranga</Emphasis> Myrmecophytes and Host-specific Aggressiveness of Symbiotic <Emphasis Type="Italic">Crematogaster</Emphasis> Ants

Macaranga myrmecophytes harbor species-specific Crematogaster ants that defend host trees from herbivores. We examined ant aggressive behaviors when artificially damaged leaf pieces from another tree were offered to four sympatric species of obligate Macaranga myrmecophytes. The ants showed aggressive behavior in response to leaf pieces regardless of the leaf species; however, aggressiveness was higher when conspecific leaf pieces were offered than when nonhost species were offered. Thus, ants can recognize leaf damage and distinguish among damaged leaf species. Chemical analyses of volatile compounds emitted from damaged leaves that may induce ant defense showed that the composition of the minor compounds differed among the four Macaranga species, although there were many compounds in common.     

The Role of Extrafloral Nectar Amino Acids for the Preferences of Facultative and Obligate Ant Mutualists

Plants in some 300 genera produce extrafloral nectar (EFN) to attract ants as a means of indirect defence. Among Mesoamerican Acacia species, obligate myrmecophytes produce EFN constitutively to nourish symbiotic ant mutualists, while non-myrmecophytes induce EFN secretion in response to herbivore damage to attract non-symbiotic ants. Since symbiotic Acacia ants entirely depend on the host-derived food rewards while non-symbiotic ants need to be attracted to EFN, this system allows comparative analyses of the function of EFN components in ant nutrition and attraction. We investigated sugar and amino acid (AA) composition in EFN of two myrmecophytes (Acacia cornigera and Acacia hindsii) and two related non-myrmecophyte species (Acacia farnesiana and Prosopis juliflora). AA composition allowed a grouping of myrmecophytes vs. non-myrmecophytes. Behavioural assays with obligate Acacia inhabitants (Pseudomyrmex ferrugineus) and non-symbiotic ants showed that AA composition affected ant preferences at high but not at low AA/sugar ratios. Most interestingly, behavioural responses differed between the two types of ants tested: Symbiotic ants showed a clear preference for higher AA concentrations and preferred nectar mimics with those four AAs that most significantly characterised the specific nectar of their Acacia host plant. In contrast, non-symbiotic ants distinguished among nectars containing different sugars and between solutions with and without AAs but neither among nectars with different AA/sugar ratios nor among mimics containing different numbers of AAs. Our results confirm that both AAs and sugars contribute to the taste and attractiveness of nectars and demonstrate that the responses of ants to specific nectar components depend on their life style. AAs are a chemical EFN component that likely can shape the structure of ant–plant mutualisms.     

Similarity of Cuticular Lipids Between a Caterpillar and Its Host Plant: A Way to Make Prey Undetectable for Predatory Ants?

Ithomiine butterflies (Nymphalidae) have long-lived, aposematic, chemically protected adults. However, little is known about the defense mechanisms in larvae and other juvenile stages. We showed that larvae Mechanitis polymnia are defended from ants by a chemical similarity between their cuticular lipids and those of the host plant, Solanum tabacifolium (Solanaceae). This is a novel defense mechanism in phytophagous insects. A field survey during one season showed that larval survivorship was up to 80%, which is high when compared with other juvenile stages. In a laboratory bioassay, live larvae on their host plant were not attacked by the predatory ant Camponotus crassus (Formicidae). Two experiments showed that the similarity between the cuticular lipids of M. polymnia and S. tabacifolium protected the larvae from C. crassus: (a) when the caterpillar was switched from a host plant to a non-host plant, the predation rate increased, and (b) when a palatable larva (Spodoptera frugiperda, Noctuidae) was coated with the cuticular lipids of M. polymnia and placed on S. tabacifolium leaves, it no longer experienced a high predation rate. This defensive mechanism can be defined as chemical camouflage, and may have a double adaptive advantage, namely, protection against predation and a reduction in the cost of sequestering toxic compounds from the host plant.     

Fungal Infection Reduces Herbivore-Induced Plant Volatiles of Maize but does not Affect Naïve Parasitoids

Plants attacked by insects release volatile compounds that attract the herbivores' natural enemies. This so-called indirect defense is plastic and may be affected by an array of biotic and abiotic factors. We investigated the effect of fungal infection as a biotic stress agent on the emission of herbivore-induced volatiles and the possible consequences for the attraction of two parasitoid species. Maize seedlings that were simultaneously attacked by the fungus Setosphaeria turcica and larvae of Spodoptera littoralis emitted a blend of volatiles that was qualitatively similar to the blend emitted by maize that was damaged by only the herbivore, but there was a clear quantitative difference. When simultaneously challenged by fungus and herbivore, the maize plants emitted in total 47% less of the volatiles. Emissions of green leaf volatiles were unaffected. In a six-arm olfactometer, the parasitoids Cotesia marginiventris and Microplitis rufiventris responded equally well to odors of herbivore-damaged and fungus- and herbivore-damaged maize plants. Healthy and fungus-infected plants were not attractive. An additional experiment showed that the performance of S. littoralis caterpillars was not affected by the presence of the pathogen, nor was there an effect on larvae of M. rufiventris developing inside the caterpillars. Our results confirm previous indications that naïve wasps may respond primarily to the green leaf volatiles.     

Systemic induction of feeding deterrents in cotton plants by feeding ofSpodoptera SPP. Larvae

Cotton,Gossypium hirsutum L., has been shown to exhibit systemic induced resistance to arthropods under certain conditions. We conducted experiments to determine the effects of previous feeding ofSpodoptera exigua Hübner andSpodoptera littoralis (Boisd.) larvae on feeding behavior, growth, and survival of larvae subsequently feeding on cotton. In one feeding choice test,S. exigua larvae preferred young leaves from undamaged control plants to undamaged young leaves from a previously damaged plant. Feeding deterrence was noticeable after only 6 hr of initial feeding damage by larvae, and there was almost complete deterrence after 30 and 54 hr of continuous feeding. In a second feeding choice test,S. littoralis larvae fed more on mature leaves from undamaged control plants than on undamaged mature leaves from previously damaged plants. In no-choice tests, third instars ofS. littoralis fed undamaged young leaves from damaged plants did not gain weight and died by the seventh day, whereas larvae fed young leaves from undamaged control plants gained weight and pupated within 11 days. Sixth instars ofS. littoralis fed either old damaged leaves, old undamaged leaves, or young undamaged leaves all from previously damaged plants gained weight slowly and took more than 12 days to pupate, whereas larvae fed young leaves from undamaged plants gained weight rapidly and pupated within five days of the beginning of the experiment.     

Economics of chemical defense in chrysomelinae

Chemical defense in chrysomelid larvae (subtribe Chrysomelina and Phyllodectina) is reviewed. Most species secrete autogenous monoterpenes. The diversity of their secretion is interpreted as a mechanism to reduce adaptation by predacious arthropods. The consequences of a host plant shift to the Salicacae are explored. Salicin from these host plants is used as a precursor for the salicylaldehyde secreted by the larvae of many species. This offers several advantages. It provides the larvae with an inexpensive and efficient defense. The recovery of the glucose moiety of the salicin contributes significantly to the larval energy budget. Adults sequester salicin in the eggs at concentrations which are toxic to ants. Owing to this maternal provisioning, neonate larvae produce salicylaldehyde from hatching onwards, whereas other species secreting monoterpenes are not protected at hatching. The secretion of salicylaldehyde by different species is considered to be chemical mimicry reinforcing visual aposematic signals.     

Behavioral and growth responses of specialist herbivore,Homoeosoma electellum,to major terpenoid of its host,Helianthus SPP

The responses of a sunflower specialist,Homoeosoma electellum, the sunflower moth, to the terpenoids produced by its host plant,Helianthus, were measured. Larvae were reared on synthetic diet containing one of three concentrations of the dominant sesquiterpene lactone found in glandular trichomes ofH. maximilliani. Treatments were initiated at each of three larval ages. Pupal weight was significantly reduced, but the effect diminished as the larvae aged. Survival and development time were unaffected by various treatments. In behavioral tests, larvae showed no preference for untreated synthetic diet compared to diet containing the secondary compound at a concentration of 1% by dry weight. When the concentration was raised to 5%, all but last-instar larvae showed a significant preference for the untreated diet. A second behavioral test measured the damage done to whole florets and an array of floral parts offered to larvae of different ages. The damage pattern of floral tissues changed as the larvae grew older, demonstrating that the willingness of larvae to eat tissues contaminated with trichome contents increased with age. The value of the glandular trichome contents as a defense againstH. electellum is discussed.     

Plant Latex and First-Instar Monarch Larval Growth and Survival on Three North American Milkweed Species

First-instar larvae of the monarch butterfly, Danaus plexippus, a milkweed specialist, generally grew faster and survived better on leaves when latex flow was reduced by partial severance of the leaf petiole. The outcome depended on milkweed species and was related to the amount of latex produced. The outcome also may be related to the amount of cardenolide produced by the plants as a potential chemical defense against herbivory. Growth was more rapid, but survival was similar on partially severed compared with intact leaves of the high-latex/low-cardenolide milkweed, Asclepias syriaca, whereas both growth and survival were unaffected on the low-latex/low-cardenolide milkweed A. incarnata. On the low-latex/low-cardenolide milkweed A. tuberosa, both growth and survival of larvae were only marginally affected. These results contrast sharply to previous results with the milkweed, A. humistrata, in Florida, which has both high latex and high cardenolide. Larval growth and survival on A. humistrata were both increased by partially severing leaf petioles. Larval growth rates among all four milkweed species on leaves with partially severed petioles were identical, suggesting that latex and possibly the included cardenolides are important in first-instar monarch larval growth, development, and survivorship.     

Hostplant Suitability and Defensive Chemistry of the Catalpa Sphinx, Ceratomia catalpae

The growth and survival of the Catalpa sphinx, Ceratomia catalpae (Sphingidae), were measured on five different species of Catalpa: C. bignonioides, C. bungeii, C. fargeseii, C. ovata, and C. speciosa. Larval growth varied significantly among these host plant species; however, survival did not differ. Quantification of the iridoid glycoside content of larvae, pupae, adults, larval frass, and leaves of the larval host plant, C. bignonioides, by gas chromatography showed that leaves contained both catalpol and catalposide; larvae, pupae, and frass contained only catalpol; and the adults contained no detectable iridoid glycosides. Amounts were highest in the larvae and declined in the pupal stage. Very small amounts of catalpol were detected in adults of the parasitoid, Cotesia congregata, and in the silken cocoons. The hemolymph in which the parasitoid larvae grew contained over 50% dry weight catalpol. Larvae of C. catalpae often regurgitate when disturbed. This may serve as a defense against predators. A comparison of the growth of larvae pinched with forceps to induce regurgitation with those that were not so treated showed that larvae that were pinched, and usually regurgitated, grew significantly more slowly than those that were not.     

Protected by Fumigants: Beetle Perfumes in Antimicrobial Defense

Beetles share with other eukaryotes an innate immune system that mediates endogenous defense against pathogens. In addition, larvae of some taxa produce fluid exocrine secretions that contain antimicrobial compounds. In this paper, we provide evidence that larvae of the brassy willow leaf beetle Phratora vitellinae constitutively release volatile glandular secretions that combat pathogens in their microenvironment. We identified salicylaldehyde as the major component of their enveloping perfume cloud, which is emitted by furrow-shaped openings of larval glandular reservoirs and which inhibits in vitro the growth of the bacterial entomopathogen Bacillus thuringiensis. The suggested role of salicylaldehyde as a fumigant in exogenous antimicrobial defense was confirmed in vivo by its removal from glandular reservoirs. This resulted in an enhanced susceptibility of the larvae to infection with the fungal entomopathogens Beauveria bassiana and Metarhizium anisopliae. Consequently, we established the hypothesis that antimicrobial defense in beetles can be expanded beyond innate immunity to include external disinfection of their microenvironment, and we report for the first time the contribution of fumigants to antimicrobial defense in animals.     

Influence of cnicin,a sesquiterpene lactone ofCentaurea maculosa (Asteraceae), on specialist and generalist insect herbivores

The sesquiterpene lactone cnicin was extracted fromCentaurea maculosa andCentaurea vallesiaca. We examined its effects on the ovipositional response and larval development of generalist and specialist insect herbivores associated withC. maculosa. For the oviposition trials, three plant species (C. maculosa, Achillea millefolium, andCichorium intybus), half of which were sprayed with 3% of cnicin, were exposed to the specialist mothsStenodes straminea, Agapeta zoegana, andPterolonche inspersa in field cages. All three species significantly preferredC. maculosa to other plants andP. inspersa significantly preferred cnicin-sprayed plants to untreated plants for oviposition. Tested over all species, cnicin significantly increased the number of eggs laid on a given plant. A larval diet test examined the toxicity of cnicin for larvae of the generalist noctuid mothSpodoptera littoralis. Cnicin concentrations of 3% and 6% were lethal and 1% and 0.5% seriously inhibited growth and development. The larvae of theC. maculosa specialistStenodes straminea survived at 6% cnicin, but none of the pupae hatched.Agapeta zoegana was able to survive at 1% and 3% cnicin. Both specialists had difficulties with the artificial diet, but weight increase and survival was not further reduced when cnicin was present compared with on the control diet. In conclusion, cnicin influenced host recognition by the specialist species, and larvae of the generalist did not survive on natural levels of cnicin. Growth and survival of the specialist were not influenced by cnicin but were considerably hampered on artificial diet.     

Antipredator Defense of Biological Control Agent Oxyops vitiosa Is Mediated by Plant Volatiles Sequestered from the Host Plant Melaleuca quinquenervia

The weevil Oxyops vitiosa is an Australian species imported to Florida, USA, for the biological control of the invasive weed species Melaleuca quinquenervia. Larvae of this species feed on leaves of their host and produce a shiny orange secretion that covers the integument. When this secretion is applied at physiological concentrations to dog food bait, fire ant consumption and visitation are significantly reduced. Gas chromatographic analysis indicates that the larval secretion qualitatively and quantitatively resembles the terpenoid composition of the host foliage. When the combination of 10 major terpenoids from the O. vitiosa secretion was applied to dog food bait, fire ant consumption and visitation were reduced. When these 10 terpenoids were tested individually, the sesquiterpene viridiflorol was the most active component in decreasing fire ant consumption. Fire ant visitation was initially (15 min after initiation of the study) decreased for dog food bait treated with viridiflorol and the monoterpenes 1,8-cineole and -terpineol. Fire ants continued to avoid the bait treated with viridiflorol at 18 g/mg dog food for up to 6 hr after the initiation of the experiment. Moreover, ants avoided bait treated with 1.8 g/mg for up to 3 hr. The concentrations of viridiflorol, 1,8-cineole, and -terpineol in larval washes were about twice that of the host foliage, suggesting that the larvae sequester these plant-derived compounds for defense against generalist predators.     

Chemical Analysis of Squirt-gun Defense in Bursera and Counterdefense by Chrysomelid Beetles

The genus Bursera produces resin stored in canals in the leaf. When leaves are damaged, some, but not all, species release abundant resin. Species of Blepharida are specialized herbivores of Bursera, and they exhibit variation in their counterdefensive behavior. Species feeding on resin-releasing plants cut the leaf veins before feeding, which often makes them more prone to predation. They also adorn their backs with their feces and may regurgitate and release an anal secretion when attacked or disturbed by predators. Species that feed on Bursera species that release no fluids do not sever the leaf veins prior to feeding, and they do not carry their feces on their backs. Instead, they face their predators, raise their heads in a "boxing-like" display, and rapidly swing their abdomens from side to side. We performed a comparative chemical analysis of the compounds found in Bursera schlechtendalii, a species that releases abundant resins, and B. biflora, a species that does not. We also analyzed the frass, enteric discharges, and larvae of the two species of Blepharida that feed on each of these plants. The compounds found in the body, feces, and discharges of the Blepharida species that adorns itself with feces match the chemical mixture of its host plant, suggesting that this beetle species can compensate its higher risk of predation by using the compounds present in the plant for defense. The chemical mixture of B. biflora is more complex and does not match the compounds found in the body or frass of its beetle herbivore, suggesting that the defensive strategy of this insect is behavioral and does not rely on its host's constituents.     

Fate of the chromene encecalin in the interaction ofEncelia farinosa and its specialized herbivoreTrirhabda geminata

Leaf beetles of the speciesTrirhabda geminata are specialized herbivores that are able to feed on the chemically well-protected foliage of the desert sunflowerEncelia farinosa, which contains the insecticidal chromene derivative encecalin. Chemical analysis of the beetles and their fecal excretions indicated that encecalin is present only in the alimentary canal and is not absorbed across the gut membrane, as previously shown for other herbivorous insects (e.g., the Egyptian armyworm,Spodoptera littoralis) that are susceptible to this chromene derivative. Further differences betweenT. geminata and nonadapted insects were observed with regard to the metabolism of encecalin. Whereas the encecalin-resistent leaf beetles metabolize encecalin mainly to encecalol by reduction of the acetyl group, susceptible insects, such as larvae ofS. littoralis, metabolize encecalin mainly by exoxidation of the 3,4 double bond, which creates a powerful alkylating agent and is responsible for the toxicity of encecalin. Reductive rather than oxidative metabolism of encecalin therefore seems important for the resistance ofT. geminata against the chemical defense of their host plantE. farinosa.     

Defense by Volatiles in Leaf-Mining Insect Larvae

The defense strategy of an insect toward natural enemies can include a trait that appears at first sight to contradict its defensive function. We explored phylogeny, chemistry, and defense efficiency of a peculiar group of hymenopteran sawfly larvae where this contradiction is obvious. Pseudodineurini larvae live in leaf mines that protect them from some enemies. Disturbed larvae also emit a clearly perceptible lemon-like odor produced by ventral glands, although the mine hampers the evaporation of the secretion. The mine could also lead to autointoxication of a larva by its own emitted volatiles. Citral was the major component in all Pseudodineurini species, and it efficiently repels ants. We conclude that full-grown larvae that leave their mine to pupate in the soil benefit from citral by avoiding attacks from ground-dwelling arthropods such as ants. In some species, we also detected biosynthetically related compounds, two 8-oxocitral diastereomers (i.e., (2E,6E)- and (2E,6Z)-2,6-dimethylocta-2,6-dienedial). Synthetic 8-oxocitral proved to be a potent fungicide, but not an ant repellent. The discrete distribution of 8-oxocitral was unrelated to species grouping in the phylogenetic tree. In contrast, we discovered that its presence was associated with species from humid and cold zones but absent in species favoring warm and dry environments. The former should be protected by 8-oxocitral when faced with a fungal infestation while crawling into the soil. Our work shows the importance of integrating knowledge about behavior, morphology, and life history stages for understanding the complex evolution of insects and especially their defense strategies.     

Induction of volatile emissions in maize by different larval instars of Spodoptera littoralis

Maize plants under attack by caterpillars emit a specific blend of volatiles that is highly attractive to parasitic wasps. The release of these signals is induced by elicitors in the caterpillar regurgitant. Studies suggest that plants respond differently to different herbivore species and even to different herbivore stages, thus providing parasitoids and predators with specific signals. We tested if this is the case for different larval instars of the noctuid moth Spodoptera littoralis when they feed on maize plants. Cut maize plants were incubated in diluted regurgitant from second, third, or fifth instar caterpillars. There were no differences in total amount released after these treatments, but there were small differences in the release of the minor compounds phenethyl acetate and -humulene. Regurgitant of all three instars contained the elicitor volicitin. To test the effect of actual feeding by the larvae, potted plants were infested with caterpillars of one of the three instars, and volatiles were collected the following day. The intensity of the emissions was correlated with the number of larvae feeding on a plant, and with the amount of damage inflicted, but was independent of the instar that caused the damage. We also used artificial damage to mimic the manner of feeding of each instar to test the importance of physical aspects of damages for the odor emission. The emission was highly variable, but no differences were found among the different types of damage. In olfactometer tests, Microplitis rufiventris, a parasitoid that can only successfully parasitize second and early third instar S. littoralis, did not differentiate among the odors of maize plants attacked by different instar larvae. The odor analyses as well as the parasitoid's responses indicate that maize odors induced by S. littoralis provide parasitoids with poor information on the larval developmental stage. We discuss the results in the context of variability and lack of specificity in odorous plant signals.     

Inter- and Intraspecific Comparisons of Antiherbivore Defenses in Three Species of Rainforest Understory Shrubs

Plants defend themselves against herbivores and pathogens with a suite of morphological, phenological, biochemical, and biotic defenses, each of which is presumably costly. The best studied are allocation costs that involve trade-offs in investment of resources to defense versus other plant functions. Decreases in growth or reproductive effort are the costs most often associated with antiherbivore defenses, but trade-offs among different defenses may also occur within a single plant species. We examined trade-offs among defenses in closely related tropical rain forest shrubs (Piper cenocladum, P. imperiale, and P. melanocladum) that possess different combinations of three types of defense: ant mutualists, secondary compounds, and leaf toughness. We also examined the effectiveness of different defenses and suites of defenses against the most abundant generalist and specialist Piper herbivores. For all species examined, leaf toughness was the most effective defense, with the toughest species, P. melanocladum, receiving the lowest incidence of total herbivory, and the least tough species, P. imperiale, receiving the highest incidence. Although variation in toughness within each species was substantial, there were no intraspecific relationships between toughness and herbivory. In other Piper studies, chemical and biotic defenses had strong intraspecific negative correlations with herbivory. A wide variety of defensive mechanisms was quantified in the three Piper species studied, ranging from low concentrations of chemical defenses in P. imperiale to a complex suite of defenses in P. cenocladum that includes ant mutualists, secondary metabolites, and moderate toughness. Ecological costs were evident for the array of defensive mechanisms within these Piper species, and the differences in defensive strategies among species may represent evolutionary trade-offs between costly defenses.     

Chemical Ecology of the Defense of Two Nymphalid Butterfly Larvae Against Ants

We analyzed the behavioral responses of the ants Camponotus rufipes and Solenopsis geminata towards all instars of Dione junio and Abananote hylonome. We also analyzed ant behavior towards hexane extracts of larvae and extracts of the spines and neck glands of the fifth instars of both species and identified the chemical compounds present. Larvae of both species were repellent to ants from the first instar onward. Later instars survived ant attacks better than earlier instars. The spines and neck glands of the larvae influenced the behavior of C. rufipes. The chemical compounds contained in the hexane extracts of whole first and fifth instars and in the spines and neck glands of fifth instars were principally carboxylic acids and terpenes. Further bioassays confirmed the repellent effect of some of these acids toward ants.     

Foliar Phenolics are Differently Associated with Epirrita autumnata Growth and Immunocompetence

The quality of available food may affect insect herbivores directly (via growth and survivorship) and/or indirectly (by modifying insect vulnerability to parasitoids and pathogens). We examined the relationship between different phenolic compounds, belonging to various phenolic groups, in Betula pubescens spp. czerepanovii (mountain birch) foliage and the larval performance of the geometrid Epirrita autumnata (autumnal moth). Direct effects on insect performance were described by pupal weight, developmental rate, and survivorship; indirect effects were described by the encapsulation rate of an implant inserted into the insect hemocoel, a commonly used way to describe insect immune defense. We found profound differences in the effects of different phenolic categories: several individual hydrolyzable tannins were associated positively with larval performance but negatively with level of immune defense, whereas flavonoid glycosides were inversely related to larval survival but showed no association with the larvae immune defense.     

Sequestration and metabolism of protoxic pyrrolizidine alkaloids by larvae of the leaf beetle Platyphora boucardi and their transfer via pupae into defensive secretions of adults

Several neotropical leaf-beetles of the genus Platyphora ingest and specifically metabolize plant acquired pyrrolizidine alkaloids (PAs) of the lycopsamine type (e.g., rinderine or intermedine) and enrich the processed alkaloids in their exocrine defensive secretions. In contrast to the related palaearctic leaf beetles of the genus Oreina, which absorb and store only the non-toxic alkaloid N-oxides, Platyphora sequesters PAs exclusively as protoxic tertiary amines. In this study, the ability of P. boucardi larvae to accumulate PAs was investigated. Tracer studies with [¹⁴C]rinderine and its N-oxide revealed that P. boucardi larvae, like adult beetles, utilize the two alkaloidal forms with the same efficiency, but accumulate the alkaloid as a tertiary amine exclusively. Ingested rinderine is rapidly epimerized to intermedine, which is localized in the hemolymph and all other tissues; it is also detected on the larval surface. Like adults, larvae are able to synthesize their own alkaloid esters (beetle PAs) from orally administered [¹⁴C]retronecine and endogenous aliphatic 2-hydroxy acids. These retronecine esters show the same tissue distribution as intermedine. A long-term feeding experiment lasting for almost four months revealed that retronecine esters synthesized from [¹⁴C]retronecine in the larvae are transferred from larvae via pupae into the exocrine glands of adult beetles. Pupae contain ca. 45% of the labeled retronecine originally ingested, metabolized, and stored by larvae; ca. 12% of larval radioactivity could be recovered from the defensive secretions of adults sampled successively over two and a half months. Almost all of this radioactivity is found in the insect-made retronecine esters that are highly enriched in the defensive secretions, i.e., more than 200-fold higher concentration compared to pupae.