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  • 1
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Entomology 47 (2002), S. 361-393 
    ISSN: 0066-4170
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Neonate Lepidoptera are confronted with the daunting task of establishing themselves on a food plant. The factors relevant to this process need to be considered at spatial and temporal scales relevant to the larva and not the investigator. Neonates have to cope with an array of plant surface characters as well as internal characters once the integument is ruptured. These characters, as well as microclimatic conditions, vary within and between plant modules and interact with larval feeding requirements, strongly affecting movement behavior, which may be extensive even for such small organisms. In addition to these factors, there is an array of predators, pathogens, and parasitoids with which first instars must contend. Not surprisingly, mortality in neonates is high but can vary widely. Experimental and manipulative studies, as well as detailed observations of the animal, are vital if the subtle interaction of factors responsible for this high and variable mortality are to be understood. These studies are essential for an understanding of theories linking female oviposition behavior with larval survival, plant defense theory, and population dynamics, as well as modern crop resistance breeding programs.
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  • 2
    ISSN: 1442-9993
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Mortality of first instars is generally very high, but variable, and is caused by many factors, including physical and chemical plant characters, weather and natural enemies. Here, a summary of detailed field-based studies of the early-stage survival of a specialist lepidopteran herbivore is presented. 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, as well as other plant characters, such as leaf hairs, microclimate and concentration of secondary metabolites. Even for a so-called ‘milkweed specialist’, larval performance and survival appears to be related to the concentration of cardenolides produced by the plants (a potential chemical defence against herbivory). This case study of monarchs and milkweeds highlights the need for field-based experiments to assess the effect of plant characters on the usually poor survival of early instar phytophagous insects. Few similar studies concerning the performance and survival of first-instar, eucalypt-specific herbivores have been conducted, but this type of study is considered essential based on the findings obtained using D. plexippus.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Chemoecology 1 (1990), S. 1-2 
    ISSN: 1423-0445
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1423-0445
    Keywords: chemical defence ; comparative sequestration ; feeding guilds ; insect herbivory ; natural enemies ; cardenolides ; Lepidoptera ; Danainae ; Danaus plexippus (L.) ; Homoptera ; Aphidae ; Aphis nerii B. de F. ; Asclepiadaceae ; Asclepias curassavica L
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cardenolide sequestration by a hemimetabolous aphid and a holometabolous butterfly from the neotropical milkweed,Asclepias curassavica L., is compared. The oleander aphid,Aphis nerii B. de F., sequestered a similarly narrow range of cardenolide concentrations to the monarch butterfly,Danaus plexippus (L.), from the wide range of concentrations available in leaves of A.curassavica. However, A.nerii sequestered significantly less cardenolide (269 µg/0.1 g) thanD. plexippus (528 µg/0.1 g). The honeydew excreted by A.nerii was comprised of 46% cardenolide. The complete polarity range of 25 cardenolides detected by thin layer chromatography in A.curassavica was represented in the 17 whole aphid cardenolides and the 20 aphid honeydew cardenolides detected. D.plexippus sequestered a narrower polarity range of 11 cardenolides, having eliminated low polarity cardenolide genins and glycosides. It is suggested that these chemical differences may be related to interactions among the broad feeding tactics of sucking or chewing milkweed leaves, life history constraints of holometabolyversus hemimetaboly, the distribution of milkweed food resources in space and time, and the dynamics of natural enemies.
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  • 5
    ISSN: 1423-0445
    Keywords: aposematism ; cardenolide fingerprint ; chemical defense ; emesis ; plant-insect interaction ; migration ; Asclepiadaceae ; Apocynales ; Asclepias humistrata ; milkweed ; Lepidoptera ; Danainae ; Danaus plexippus ; monarch butterfly
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This paper is the fourth in a series on cardenolide fingerprints of monarch butterflies (Danaus plexippus, Danainae) and their host-plant milkweeds (Asclepiadaceae) in the eastern United States. Cardenolide concentrations ofAsclepias humistrata plants from north central Florida ranged from 71 to 710 µg/0.1 g dry weight, with a mean of 417 µg/0.1 g. Monarchs reared individually on these plants contained cardenolide concentrations ranging from 243 to 575 µg/0.1 g dry weight, with a mean of 385 µg/0.1 g. Cardenolide uptake by butterflies was independent of plant concentration, suggesting that sequestration saturation occurs in monarchs fed cardenolide-rich host plants. Thinlayer chromatography resolved 19 cardenolides in the plants and 15 in the butterflies. In addition to humistratin,A. humistrata plants contained several relatively non-polar cardenolides of the calotropagenin series which are metabolized to more polar derivatives in the butterflies. These produced a butterfly cardenolide fingerprint clearly distinct from those previously established for monarchs reared on otherAsclepias species. In emetic assays with the blue jay,Cyanocitta cristata, the 50% emetic dose (ED50) per jay was 57.1 µg, and the average number of ED50 units per butterfly was 13.8, establishing that this important south eastern milkweed produces highly emetic, chemically defended monarchs. Our data provide further support for the use of cardenolide fingerprints of wild-caught monarchs to make ecological predictions concerning defence against natural enemies, seasonal movement and larval host-plant utilization by monarch butterflies during their annual cycle of migration, breeding and overwintering.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Chemoecology 4 (1993), S. 1-2 
    ISSN: 1423-0445
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Chemoecology 5-6 (1994), S. 101-117 
    ISSN: 1423-0445
    Keywords: cardenolides ; cardiac glycosides ; chemical defence induction ; latex ; parasitism ; predation ; sequestration ; Insecta ; Diptera ; Tachinidae ; Lepidoptera ; Nymphalidae ; Danainae ; Danaus plexippus ; Asclepiadaceae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The contribution of Miriam Rothschild to the “monarch cardenolide story” is reviewed in the light of the 1914 challenge by the evolutionary biologist, E.B. Poulton for North American chemists to explain the chemical basis of unpalatability in monarch butterflies and their milkweed host plants. This challenge had lain unaccepted for nearly 50 years until Miriam Rothschild took up the gauntlet and showed with the help of many able colleagues that monarchs are aposematically coloured because they sequester toxic cardenolides from milkweed host plants for use as a defence against predators. By virtue of Dr Rothschild's inspiration and industry, and subsequently that of Lincoln Brower and his colleagues, this tritrophic interaction has become a familiar paradigm for the evolution of chemical defences and warning colouration. We now know that the cardenolide contents of different milkweeds vary quantitatively, qualitatively and spatially, both within and among species and we are starting to appreciate the implications of such variation. However, as Dr Rothschild has pointed out in her publications, cardenolides have sometimes blinded us to reality and it is curious how little evidence there is for a defensive function to cardenolides in plants — especially against adapted specialists such as the monarch. Thus the review will conclude with a discussion of the significance of temporal variation and induction of cardenolide production in plants, the “lethal plant defence paradox” and an emphasis on the dynamics of the cardenolide-mediated interaction between milkweeds and monarch larvae.
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  • 8
    ISSN: 1423-0445
    Keywords: plant defense ; plant chemistry ; insect herbivore ; metapopulation dynamics ; spatial models ; spatial heterogeneity ; plant-insect interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Modern population ecology is becoming increasingly spatially-explicit. For insect hervibores, spatial variation in plant quality is a critical component of distribution and abundance. We argue that populationlevel measurements of phytochemical variation among individual plants has not kept pace with recent developments in population ecology. With examples from our own work, we demonstrate the importance of spatial variation in plant chemistry for insect herbivores, and suggest that phytochemistry should play a central role in the development of any spatially-based ecological theory.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Entomologia experimentalis et applicata 80 (1996), S. 193-196 
    ISSN: 1570-7458
    Keywords: Danaus plexippus ; Asclepias syriaca ; secondary plant metabolites ; induced plant defence ; cost of defence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical ecology 15 (1989), S. 1699-1716 
    ISSN: 1573-1561
    Keywords: Spider web structure ; Zygiella x-notata ; Araneae ; predator foraging ; aposematic aphid prey ; Aphis nerii ; Homoptera ; Aphididae ; chemical defense ; cardenolides ; Asclepias ; milkweed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Two toxic and bitter-tasting cardenolides (cardiac-active steroids) were sequestered by the brightly colored oleander aphid,Aphis nerii B. de F., from the neotropical milkweed host plantAsclepias curassavica L. After feeding on milkweed-reared aphids, the orb-web spiderZygiella x-notata (Clerck) built severely disrupted webs and attacked fewer nontoxic, control aphids, whereas the webs of spiders fed only nontoxic aphids remained intact. The regularity and size of the prey-trapping area of webs were reduced significantly in proportion to the amount of toxic aphids eaten. The effects of toxic aphids on spider web structure were mimicked by feeding spiders the bitter-tasting cardenolide digitoxin, a cardenolide with similar steroidal structure and pharmacological activity to the two aphid cardenolides. These results show that the well-known effects of psychoactive drugs on spider web structure are more than interesting behavioral assays of drag activity. Similar effects, produced by plant-derived chemicals in the spider's aphid prey, are relevant to the ecology and evolution of interactions between prey defense and predator foraging.
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