From model to mimic: Age-dependent unpalatability in monarch butterflies

Monarch butterflies (Danaus plexippus) are unpalatable to various vertebrate predators because their larvae sequester bitter and emetic cardiac glycosides (CGs) from milkweed plants (Asclepias spp.). Here we show that the concentration of the defensive CGs decrease as individual butterflies age, regardless of the CGs' initial amounts or specific chemical structures. Consequently, individual monarch butterflies can change from being unpalatable models to palatable mimics during their lifetime. Since monarchs breed continuously over the spring and summer in North America, freshly emerged adult butterflies may serve as noxious models for older individuals which become automimics as they age.     

Lucibufagins,IV. New defensive steroids and a pterin from the firefly,Photinus pyralis (coleoptera: Lampyridae)

Summary Two new defensive steroids (lucibufagins6 and7) and a fluorescent pterin (8) have been isolated and characterized from the fireflyPhotinus pyralis.Acknowledgment. We are grateful to the Fonds National Suisse de la Recherche Scientifique (bourse de relève to M.G.). Partial support of this work by the NIH (grants No. AI 12020 and AI 02908), the NSF (grant No. PCM-77-25807), and the American Heart Association is acknowledged with pleasure. Paper No. 66 of the series Defense Mechanism of Arthropods.     

Sexual dimorphism in the defensive secretion of a carabid beetle

Summary The defensive secretions of male and femaleOodes americanus display striking qualitative differences. Altogether 13 carboxylic acids were identified in the secretions of the two sexes. Methacrylic, crotonic, and tiglic acids are produced exclusively by the female; the male lacks these unsaturated components, but produces their saturated analogs. 2-Methylbutyric acid is a major component produced by both sexes. Shared components also include hexanoic, (E)-2-hexenoic, benzoic, and (E)-2-octenoic acid, of which the latter two had not previously been reported from carabid beetles.Paper no. 98 in the series Defense Mechanisms of Arthropods; no. 97 is by Smedley et al., J. Lepid. Soc., in press.     

Antimicrobial activity in the skin of the channel catfish Ictalurus punctatus: characterization of broad-spectrum histone-like antimicrobial proteins

Three antibacterial proteins were isolated from acid extracts of channel catfish (Ictalurus punctatus) skin by cation exchange chromatography and reverse-phase high-pressure liquid chromatography. The molecular masses of the proteins were 15.5, 15.5 and 30 kD as determined by SDS-polyacrylamide gel electrophoresis. Mass spectrometry, amino acid composition and amino acid sequence data suggest that the most abundant protein is closely related to histone H2B. The H2B-like protein was inhibitory to Aeromonas hydrophila and Saprolegnia spp., which are important bacterial and fungal pathogens of fish. These findings suggest that histones may be important defensive molecules in fish. Received 22 December 1997; received after revision 5 March 1998; accepted 5 March 1998     

Furan fatty acid steryl esters from the marine spongeDictyonella incisa which show inflammatory activity

Summary Three new furan fatty acids, (9Z, 19Z)-3, 6-epoxyhexacosa-3,5,19-tetraenoic acid (1a), (8Z, 11Z, 14Z, 17Z)-3, 6-epoxyeicosa-3,5,8,11,14,17-hexaenoic acid (2a), and (8Z, 11Z, 14Z, 17E)-3, 6-epoxyeicosa-3,5,8,11,14,17-hexaenoic acid (3a), and a new polyunsaturated fatty acid (5Z, 8Z, 11Z, 14Z, 17E)-eicosa-5,8,11,14,17-pentaenoic acid (6a), present in the spongeDictyonella incisa as the respective steryl esters, have been isolated as methyl esters and their structures have been determined by spectral and chemical analysis. The furan fatty acid esters have shown a high inflammatory activity, which suggests their potential role as feeding deterrents.     

Toxic effects of boric acid on the German cockroach

Boric acid is a slow-acting, inorganic insecticide whose mode of action has not been satisfactorily elucidated. Reported here is evidence which shows that ingested boric acid destroys the cellular lining of the foregut of German cockroaches,Blattella germanica (L.). This effect appears to be sufficient to bring about the death of the insects, perhaps ultimately by starvation. This finding is important because resistance to conventional insectivides may re-establish boric acid as a prominent cockroach control chemical.     

Cantharidin production in a blister beetle

Cantharidin, a potent defensive chemical, is present in all ten life stages of the blister beetleEpicauta funebris. The first five larval stages accumulate cantharidin as they feed and grow in size. When disturbed, they exude cantharidin in a milky oral fluid, not in hemolymph which adult beetles reflexively discharge from leg joints. Two subsequent larval stages and the pupa do not feed, grow, regurgitate, or change in their defensive reserves (110 g cantharidin/insect, regardless of sex). Adult beetles kept in isolation for 60–90 d exhibit a pronounced sexual dimorphism in cantharidin production: the male biosynthesizes about 17 mg of the toxin, representing 10% of his live weight, whereas the female actually loses most of her defensive reserves. But in the wild a female beetle repeatedly acquires cantharidin as copulatory gifts from her mates.This study was supported by Grant DK 31186 and by the University of Missouri Institutional Biomedical Research Support Grant RR07053, both from the National Institutes of Health.     

Identification and seasonal quantification of defensive secretion components ofOreina gloriosa (Coleoptera: Chrysomelidae)

Tyrosine betaine, four new cardenolides (4, 5, 6, and7) and three known cardenolides (2, 3, and8) were isolated from the defensive secretion, of the leaf beetleOreina gloriosa and their chemical structure determined. 16 secretion components of individual beetles were quantified. Secretion composition of field-collected beetles was affected by season, sex and body weight.     

Synthesis and metabolism of vertebrate-type steroids by tissues of insects: A critical evaluation

Summary This review covers the synthesis and the metabolism of vertebrate-type steroids (progesterone, testosterone, estradiol, corticosteroids) by insect tissues and discusses the significance of the reactions for insect physiology. Biosynthesis of vertebrate-type steroids from cholesterol hitherto has been demonstrated in only two insect species, i.e. the water beetleAcilius sulcatus (Coleoptera) and the tobacco hornwormManduca sexta (Lepidoptera). InAcilius, steroid synthesis is associated with exosecretion (chemical defense). Nothing, however, is known about a physiological role of the C₂₁ steroid conjugate present in ovaries and eggs ofManduca. No synthesis of vertebrate-type steroids was observed in any other insect investigated to date. Most metabolic conversions of steroids by insects concerned oxidoreduction of oxygen groups (hydroxysteroid dehydrogenase activity) and (polar and apolar) conjugate formation. All important enzymatic steps involved in synthesis and catabolism, as known from studies with tissues of vertebrates, were not, or hardly observed. The conclusion is drawn that typical vertebrate-type (C₂₁, C₁₉ and C₁₈) steroids probably do not act as physiologically active substances in insects.     

1,1-Dimethyl-5,6-dihydroxyindolinium chloride from a deep water marine sponge,Dercitus sp.

Summary 1,1-Dimethyl-5,6-dihydroxyindolinium chloride (1a)was identified from a deep water sample of the marine sponge,Dercitus sp., and its structure was elucidated by spectral methods.Acknowledgments. This is Harbor Branch Oceanographic Institution, Inc., SeaPharm Project Contribution No. 612. We thank Drs K. Rinehart, Jr, S. Pomponi and E. Armstrong for sponge collection.     

Molecular characterization and expression of the antimicrobial peptide defensin from the housefly (Musca domestica)

A 430-bp cDNA encoding the insect antimicrobial peptide defensin was cloned from the housefly, and designated Musca domestica defensin (Mdde). The open reading frame of the cDNA encoded a 92-amino acid peptide with an N-terminal signal sequence followed by a propeptide that is processed by cleavage to a 40-amino acid mature peptide. Northern analysis and in situ hybridization identified the corresponding mRNA in the fat body of bacterially challenged houseflies and in the epidermis of the body wall of naive and challenged houseflies. The Gram-negative bacterium (Escherichia coli) is a strong inducer of the gene. By RT-PCR, Mdde mRNA was also detected in naive and challenged insects. These findings suggest that the defensin gene is constitutively expressed in the epidermis of the housefly body wall. The predicted mature form of Mdde was expressed as a recombinant peptide in E. coli and Pichia pastoris. The recombinant Mdde expressed in Pichia was active against Gram-positive and some Gram-negative bacteria. Received 20 June 2006; received after revision 3 October 2006; accepted 30 October 2006     

Defensive secretions of Nematinae larvae (Symphyta - Tenthredinidae)

Summary The composition of the defensive secretion of larvae of 8 Nematinae species is reported. 7 derivatives have been identified: benzaldehyde, (E)-2-hexenol, (E)-2-hexenal, (E)-4-oxo-2-hexenal, geranial, neral andcis, trans-dolichodial.Maître de recherches du Fonds National de la Recherche Scientifique.We gratefully acknowledge the Fonds National de la Recherche Scientifique for financial support. We express our sincere thanks to Professor B. Zwanenburg and Dr J. M. J. Verlaak for helpful suggestions.     

Antimutagenic unusual amino acids from plants

Summary Five unusual amino acids were identified as antimutagens against spontaneous mutation ofSalmonella typhimurium TA100: L-azetidine-2-carboxylic acid (1) from Liliaceae plants, -(methylenecyclopropyl)glycine (2) fromLitchi chinensis seeds, and 2-amino-4-methylhex-5-ynoic acid (3), hypoglycin A (4), and (2S, 4R)-2-amino-4-hydroxyhept-6-ynoic acid (5) fromEuphoria longana seeds. The absolute stereochemistry of5 was determined by its chiral synthesis from L-allylglycine, proving that5 is the C-4 epimer of the amino acid previously isolated from dried longan seeds.This work was partly supported by a Grant-in-Aid form the Ministry of Education, Science, and Culture, Japan, No. 57740283 (to HK).     

Identification of mucondialdehyde as a novel stress metabolite

In a survey of antifungal stress compounds induced by cupric chloride we found that leaves ofChenopodium album exuded a highly fungitoxic metabolite mucondialdehyde (trans-2,trans-4-hexadienedial), which was associated with 13-oxo-9,11-tridecadienoic acids (cis-9,trans-11 andtrans-9,trans-11 isomers) presumably resulting from -scission of 13-hydroperoxy-octadecadi(tri)enoic acid. The biogenesis and role as a general defensive agent in plants are briefly discussed.     

Endocrine-dependent expression of circadian clock genes in insects

Current models state that insect peripheral oscillators are directly responsive to light, while mammalian peripheral clock genes are coordinated by a master clock in the brain via intermediate factors, possibly hormonal. We show that the expression levels of two circadian clock genes, period (per) and Par Domain Protein 1 (Pdp1) in the peripheral tissue of an insect model species, the linden bug Pyrrhocoris apterus, are inversely affected by contrasting photoperiods. The effect of photoperiod on per and Pdp1 mRNA levels was found to be mediated by the corpus allatum, an endocrine gland producing juvenile hormone. Our results provide the first experimental evidence for the effect of an endocrine gland on circadian clock gene expression in insects. Received 31 October 2007; received after revision 7 January 2008; accepted 9 January 2008 D. Dolezel, L. Zdechovanova: These authors contributed equally to this work.     

Gustatory sensitivity of an anuran to cantharidin

Summary Glossopharyngeal nerve stimulation of the bullfrog,Rana catesbiana revealed responsiveness to low levels of cantharidin (1.3×10^–6M), providing a first demonstration of neural gustatory sensitivity of an animal to this defensive chemical from blister beetles, (Meloidae).Acknowledgments. Study supported in part by grant AI 02908 from NIH.     

A simple method for in vivo testing of glandular enzymatic activity on potential precursors of larval defensive compounds inPhratora species (Coleoptera: Chrysomelinae)

The presence of glandular -glucosidase and oxidase-specific activities, and the possible role of phenolglucosides and related compounds as precursors for larval defensive compounds, were directly demonstrated by introducing salicin, saligenin and helicin into the defensive glands ofPhratora species.Ph. tibialis andPh. laticollis that normally secrete endogenously-produced iridoid monoterpenes and do not use phenolglucosides from their food sources as precursors, were able to produce salicyladehyde from helicin when the latter was introduced into the defensive glands.     

Defensive substances of opilionids

Summary The defensive secretions of 4 species of opilionids were analyzed.Leiobunum ventricosum andHadrobunus maculosus produce 4-methylheptan-3-one, whileL. calcar produces E-4,6-dimethyl-6-octen-3-one.L. longipes produces E-4,6-dimethyl-6-nonen-3-one, a new natural product.Paper No. 51 of the seriesDefensive Mechanisms of Arthropods.Acknowledgments. Partial support by the National Institutes of Health (Grant Nos. AI-12020 and AI-02908 and Fellowship No. 1-F32-CA05139 to T.H.J.) and the National Science Foundation (Grant No. BMS 75-15084) is gratefully acknowledged. We thank Dr.W. A. Shear for identifying the opilionids.     

Enzymatic processing of pheromones and pheromone analogs

Summary Pheromone perception requires rapid enzymatic degradation of the active chemical signal in the sensory hairs. Three insects are used to illustrate chemical approaches to studying the degradation of pheromones by antennal enzymes. First, hydrolysis of acetate and haloacetate esters is examined in the diamondback moth,Plutella xylostella. Second, aldehyde oxidation and the selective inhibition of the oxidase and dehydrogenase activities are described for the tobacco budworm moth,Heliothis virescens. Finally, a stereochemical analysis of the epoxide-hydrase catalyzed addition of a water molecule to the oxirane ring of disparlure is described for the gypsy moth,Lymantria dispar.