Butterfly milkweed

Some insects can protect themselves against the toxins present in their food plants by storing them. One example is the monarch butterfly, the caterpillars of which store potentially toxic cardiac glycosides obtained from a food plant, the milkweed (see Harborne 1993). Subsequently, the stored glycosides have a deterrent effect upon blue jays that feed upon them. 

The HPLC analysis of milkweed, the food-plant source for Monarch butterflies, demonstrates that it contains a complex mixture of carotenoids including lutein, several other xanthophylls, xanthophyll epoxides, and (3-carotene, Figure 25.3b. There is a component in the leaf extract that is observed to elute near 8min, which has a typical carotenoid spectrum but is not identical to that of the lutein metabolite observed at near the same retention time in the extracts from larval tissue. 

Mebsa D., Reussa E., and Schneider M. (2005). Studies on the cardenolide sequestration in African milkweed butterflies (Danaidae). Toxicon 45 581-584. 

Ackery, P. R. Vane-Wright, R. I. (1984) Milkweed Butterflies Their Cladistics and Biology (Cornell Univ. Press, Ithaca, NY). 

The relationship between milkweeds and the monarch butterfly demonstrates a synergistic relationship between a plant and an insect (Harborne, 1993). The larvae of the monarch butterfly feed on milkweeds and accumulate cardenolides. Birds feeding on the caterpillars, pupae, or adults, will vomit and subsequently become averted and thus avoid the monarch butterflies. Interestingly, other butterflies, such as viceroy, which do not feed on milkweed, have evolved with nearly identical color pattern (mimicry), so birds avoid these nontoxic insects as well. 

Glycoside diversification also has occurred in the coevolution of monarch butterflies and milkweeds (7). It may be desirable to relate the toxicity of cardenolides to the hydrolytic capabilities of susceptible and nonsusceptible insects. Cardenolides from Rsclepias species can be hydrolyzed by 3-glucosidases present in the plant (6), yet specialized Danans species are able to sequester these compounds, a process wh ich requires control of hydrolysis. 

Cardenolldes appear to be metabolized by a variety of species, possibly as a mechanism for converting these steroids into compounds that can be efficiently sequestered. The milkweed bug, Oncopeltus fasclatus, metabolizes (hydroxylates ) the nonpolar cardenollde dlgltoxln to more polar compounds that are subsequently sequestered In the dorsolateral space fluid (17. 18). Larvae of another cardenolide-adapted Insect, the monarch butterfly, Danaus plexlppus. also convert these steroids Into compounds that are readily sequestered. For example, uscharldln, which contains a carbonyl group at C-3 ( ) of the... 

Certain reductases are important in the detoxification of allelochemicals. For example, the milkweed cardinolide is metabolized by aldehyde reductase to calactin or calotropin (an enantiomer) in the monarch butterfly (Danacus plexippus) (Marty and Krieger, 1984). 

Marty, M.A. and Krieger, R.I., Metabolism of uscharidin, a milkweed cardenolide, by tissue homogenates of monarch butterfly larvae, Danaus plexippus L. /. Chem. Ecol., 10,945,1984. 

Some milkweeds have very attractive flowers and 5 may be grown as ornamentals. The orange-colored flowers of the butterfly-weed (A. tuber os a) are a beautiful aspect of the taller-grass prairies of North America, and this species is sometimes grown in gardens. 

Ecological concerns are real as we do not know what may occur with the widespread propagation of transgenic plants. There were initial fears that Bt corn was toxic not only to the European corn borer but also to the monarch butterfly larvae that may eat milkweed leaves laced with Bt corn pollen. However, EPA studies dismissed this threat. It is possible that other insects, not intended as targets of bioengineered proteins, may also be affected. It is absolutely essential that these ecological issues be addressed. However, these are not food safety issues. The same concerns occur with the widespread use of organic pesticides relative to runoff and water pollution. Both must be addressed on their own merits. 

Even if the main target of a toxin is an insect which causes considerable damage to the crop, very often other insects can feed on the plant. If they are sensitive to the expressed toxin, they will also be affected which, of course, is advantageous in terms of crop protection. However, some insects could be affected in a nonintended way. An example of this is the monarch butterfly Danaus plexippus), a mythic butterfly of North America. Losey et al. [88] observed a higher mortality rate in butterfly larvae fed milkweed coated with 5t-maize pollen as compared to larvae fed leaves coated with nontransformed maize pollen or with leaves free of pollen. However, it is important to note that this study was performed under artificial laboratory conditions which do not reflect most of the characteristics of the monarch way of life [89]. In a very recent report, the EPA (September 22, 2000), on the basis of further trials, concluded that monarch butterflies were at very little risk from Bt com products, contrary to widely published reports. EPA further found that In fact, some authors are predicting that the widespread cultivation of Bt crops may have huge benefits for monarch butterfly survival. ... 

Some animals, as well, use toxins to defend themselves. Some poisonous toads and frogs can synthesize toxins. Others acquire their chemical defenses from plants they eat. The Monarch butterfly is probably the best example of this. The larvae eat milkweed leaves and the toxins are retained in their bodies. The toxins are still there after metamorphosis from larva to butterfly. Birds that eat Monarch butterflies regurgitate their prey and quickly learn to avoid others of the same species. 

Extraction and Fatty Acid Analysis. Milkweed seeds (As-clepias sp.) were obtained from Butterfly Encounters (Mor-aga, CA). For fatty acid analysis, seeds were ground and extracted by supercritical CO2 extraction as described (8). Identification and quantification of extracted oils was also carried out by gas chromatography/mass spectrometry analysis as described (8). 

Schulz, S., Boppr6, M., and Vane-Wright, R. L, 1993, Specific mixtures of secretions from male scent organs of African milkweed butterflies (Danainae), PAi/. Tram. R. Soc. fond. B 342 161-181. 

A small family of tropical or subtropical butterflies with only a few members like the milkweed or monarch species. Their wingspan extends to 7-10 cm, and their annual mass migration is spectacular the North American Monarch butterflies (Danaus plexippus) fly in autumn from southern Canada as far south as Mexico and Florida. 

Milkweed cardenolides and their comparative processing by monarch butterflies, pp. 93-167. In J. W. Wallace and R. L. Mansell (eds.). Biochemical Interactions Between Plants and Insects, Rec. Adv. Phytochem. Plenum Press, NY. 

The North African aposematic grasshopper, Poekilocerus bufonius, like the monarch butterfly, also feeds on milkweeds and accumulates the cardenolides. Unlike the monarch, the grasshopper ejects the cardenolide materials as a noxious foam from specially located poison glands (Seiber et al., 1984). 

Malcolm, S. B., B. J. Cockrell, and L. P. Brower, Cardenolide fingerprint of monarch butterflies reared on common milkweed, Asclepias syriaca L., J. Chem. Ecol., 15, 819-853 (1989). 

Martin, R, A. and S. P. Lynch, Cardenolide content and thin-layer chromatography profiles of monarch butterflies, Danaus plexippus L., and their larval host-plant milkweed, Asclepias asperula subsp. capricornu (Woods.) Woods., in North Central Texas, J. Chem. Ecol., 14, 295-318 (1988). 

Roeske, C.N., J.N. Seiber, L.P. Brower, and C.M. Mofhtt Milkweed Cardeno-lides and their Comparative Processing by Monarch Butterflies. (Danaus plexippus L.). In J.W. Wallace and R.L. Mansell eds., Biochemical Interactions Between Plants and Insects, p. 93-167. New York Plenum Press 1976. 

Brower, L.P., J.N. Seiber, C.J. Nelson, S.P. Lynch, and N.N. Holland Plant Determined Variation in the Cardenolide Content, Thin-Layer Chromatography Profiles and Emetic Potency of Monarch Butterflies, Danaus plexippus L. Reared on Milkweed Plants in California. 2. Asclepias speciosa. J. Chem. Ecol. 10, 601-639 (1984). 

Profiles and Emetic Potency of Monarch Butterflies Danaus plexippus Reared on the Milkweed Asclepias eriocarpa in California. J. Chem. Ecol. 8, 579-633 (1982). 

When hungry or gravid insects move within centimeters of potential host plants and encounter their volatiles, displacement is often delimited by olfactory responses. Monarch butterfly larvae (Danausplexippus) not able to contact host and non-host foliage but moving on a screen immediately over the plants, turn and double back more frequently to milkweed foliage than to nonhost foliage (Dethier, 1937). In similar tests (de Wilde, 1958), Colorado potato... 

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