Stephen Malcolm

Monarch butterflies (Danaus plexippus) are familiar herbivores of milkweeds of the genus Asclepias, and most monarchs migrate each year to locate these host plants across North American ecosystems now dominated by agriculture. Eastern migrants overwinter in high-elevation forests in Mexico, and western monarchs overwinter in trees on the coast of California. Both populations face three primary threats to their viability: (a) loss of milkweed resources for larvae due to genetically modified crops, pesticides, and fertilizers; (b) loss of nectar resources from flowering plants; and (c) degraded overwintering forest habitats due to commercially motivated deforestation and other economic activities. Secondary threats to population viability include (d) climate change effects on milkweed host plants and the dynamics of breeding, overwintering, and migration; (e) the influence of invasive plants and natural enemies; (f) habitat fragmentation and coalescence that promote homogeneous, speci...

Running title: Monarch alternative migration: We collected 434 adult monarchs and surveyed milkweeds for immature monarchs in southwest Michigan, USA in order to test the hypothesis that monarchs are temporally variable, sequential partial migrants rather than partial migrants that may be spatially separated. Adult size, wing wear, female egg counts, fat content and sequestered chemical defenses were measured in monarchs across an entire season from spring migrant arrival, through breeding, until autumn migrant departure. We predicted that a population characterized by starting from all migrants and no residents, through breeding residents, to all migrants and no residents should show life history measures consistent with changes in these proportions. Results show that female monarch spring migrants arrive with chorionated eggs and high wing loads in both intact and fat-extracted adults. Wing loads of both males and females decrease during the summer and increase again immediately b...

Distributions of the host plants of mobile herbivorous insects form complex mosaics in space and time. Thus it is difficult to track large scale patterns of herbivorous insect movement without time-and labour-intensive trapping, tracking, and marking techniques that are subject to misinterpretation. Here we summarize the use of a chemical fingerprinting technique to describe the continental scale pattern of migration by the monarch butterfly (Danaus plexippus (L.)) in relation to the spatial and temporal distributions of its milkweed larval host plants (Asclepias spp.) in North America.

A common-sense evolutionary scenario predicts that well-defended plants should have a moderate diversity of secondary compounds with high biological activity. We contend that plants actually contain a very high diversity of mostly inactive secondary compounds. These patterns result because compounds arising via mutation have an inherently low probability of possessing any biological activity. Only those plants that make a lot of compounds will be well defended because only high diversity confers a reasonable probability of producing active compounds. Inactive compounds are retained, not eliminated, because they increase the probability of producing new active compounds. Plants should therefore have predictable metabolic traits maximizing secondary chemical diversity while minimizing cost. Our hypothesis has important implications to the study of the evolution of plant defence.

Migration is a common life‐history strategy that includes traits such as directed flight, increased wing size, seasonal lipid deposition and reproductive arrest. The degree of investment in these traits ultimately determines the life‐history strategy of individuals. Partial migration is a common mixed life‐history strategy where species or populations consist of both migrant and resident individuals. While this phenomenon is widespread across taxa, the ecological factors that select for and maintain partial migration are poorly understood, especially among insects. Here, we investigate regional life‐history traits associated with migration in the southern monarch, Danaus erippus, and describe a mixed life‐history strategy in this butterfly. Individuals from the Bolivian lowlands were observed throughout the year exhibiting mate‐ and milkweed‐directed behaviors. These butterflies had smaller wings, lower wing loads and maintained constant lipid and egg loads across summer and autumn ...

Plant chemical defenses that are sequestered by aposematic insect herbivores present a problem for plants that may be resolved at the third trophic level by natural enemies. It has been shown that a neotropical milkweed reduced source cardenolide expression when the density of an aposematic aphid was low and then induced cardenolide expression as the density increased. We tested the hypothesis that such U-shaped cardenolide expression in response to changing herbivore density should impact both aphid defense and the functional response of an aphidophagous predator. We manipulated the density of the aposematic oleander aphid, Aphis nerii on the neotropical milkweed, Asclepias curassavica, to determine whether plant cardenolides change in response to phloem-feeding aphids as well as sequestration of these steroidal defenses by the aphids at different densities. Aphids from varying density plants were fed to newly emerged, 4th instar larvae of Coccinella sepempunctata to measure their ...

... It specifically contradicts sugges-tions of three or four (Urquhart 1960) or even five (Eanes and Koehn 1978, Eanes 1979) generations in the south, compared with only one or two generations in the north (Urquhart 1960, Eanes and Koehn 1978, Eanes 1979 ... Press, Raleigh, pp. ...

... He and He et al., 1999) have integrated AGNPS with GRASS and ArcView GIS ... and the work on biological processes and indicators of ecosystems for integrating these indicators ... of watershed conditions for watershed planning and management requires the integration of natural ...

Monarch butterfly,Danaus plexippus (L.), larvae were collected during August 1983 from the common milkweed,Asclepias syriaca L., across its extensive North American range from North Dakota, east to Vermont, and south to Virginia. This confirms that the late summer distribution of breeding monarchs in eastern North America coincides with the range of this extremely abundant milkweed resource. Plant cardenolide concentrations, assayed by spectrophotometry in 158 samples from 27 collection sites, were biased towards plants with low cardenolide, and ranged from 4 to 229 μg/ 0.1 g dry weight, with a mean of 50 μg/0.1 g. Monarch larvae reared on these plants stored cardenolides logarithmically, and produced 158 adults with a normally distributed concentration range from 0 to 792 μg/0. l g dry butterfly, with a mean of 234 μg/0.1 g. Thus butterflies increased the mean plant cardenolide concentration by 4.7. The eastern plants and their resultant butterflies had higher cardenolide concentrations than those from the west, and in some areas monarchs sequestered more cardenolide from equivalent plants. Plants growing in small patches had higher cardenolide concentrations than those in larger patches, but this did not influence butterfly concentration. However, younger plants and those at habitat edges had higher cardenolide concentrations than either older, shaded, or open habitat plants, and this did influence butterfly storage. There were no apparent topographical differences reflected in the cardenolides of plants and butterflies. Twenty-eight cardenolides were recognized by thin-layer chromatography, with 27 in plants and 21 in butterflies. Butterflies stored cardenolides within the more polar 46% of the plantR d range, these being sequestered in higher relative concentrations than they occurred in the plants. By comparison with published TLC cardenolide mobilities, spots 3, 4, 9, 16, 24 or 25, 26, and 27, may be the cardenolides syrioside, uzarin, syriobioside, syriogenin, uzarigenin, labriformidin, and labriformin, respectively. Cochromatography with cardenolide standards indicated that desglucosyrioside did not occur in the plants but did occur in 70% of the butterflies, and aspecioside was in 99% of the plants and 100% of the butterflies. The polar aspecioside was the single most concentrated and diagnostic cardenolide in both plants and butterflies. ButterflyR d values were dependent on those of the plant, and both showed remarkable uniformity over the range of areas sampled. Thus contrary to previous reports,A. syriaca has a biogeographically consistent cardenolide fingerprint pattern. The ecological implications of this for understanding the monarch's annual migration cycle are significant.

... in space and time with a total of 4 to 5 broods occurring over the entire sea-son (Malcolm et al., 1987; Cockrell et al ... wood collection, charcoal preparation, and spring fires lit to clear land are causing major disruption of the overwintering butterfly colonies (see also Marcus, 1988 ...

ABSTRACT 1. Female monarchs were observed in the field ovipositing on a native North American milkweek host, Asclepias humistrata L. As in a comparable Australian study on an introduced novel host (Asclepias fruticosa L.) we found post-alighting rejection of plants with low and high cardiac glycoside concentration (CG). 2. Most oviposition took place on plants with CG in the range 200–500 μg/0.1 g dry weight. Thin-layer chromatography showed no obvious qualitative difference in cardenolide types between accepted and rejected plants, excepting an indication that rejected plants may have a higher level of more polar cardenolides. 3. In a controlled laboratory experiment comparing oviposition on a low (A.incarnata L.) vs high (A.curassavica L.) CG host plant species we found no relationship between CG and oviposition on the low CG species, but a negative relationship in the high CG species. This corroborates our findings on oviposition on single host species in the field. 4. We also record the first indication of a physiological cost of monarch larvae feeding on plants high in CG. There was a significant negative relationship between survival of first instar larvae and CG levels in plants. This study opens the way for further work on the association of monarch butterflies and their toxic milkweed hosts.

ABSTRACT Monarch butterflies sequester cardenolides from their larval host plants in the milkweed genusAsclepias for use in defense against predation. Of 108Asclepias species in North America, monarchs are known to feed as larvae on 27. Research on 11 of these has shown that monarchs sequester cardenolides most effectively, to an asymptote of approximately 350 g/0.1 g dry butterfly, from plants with intermediate cardenolide contents rather than from those with very high or very low cardenolide contents. SinceAsclepias host plant species are distributed widely in space and time across the continent, monarchs exploit them by migration between breeding and overwintering areas. After overwintering in central Mexico, spring migrants east of the Rocky Mountains exploit three predominantAsclepias species in the southern USA that have moderately high cardenolide contents. Monarchs sequester cardenolides very effectively from these species. First generation butterflies are thus well protected against predators and continue the migration north. Across the northern USA and southern Canada most summer breeding occurs on a fourthAsclepias species and in autumn most of these monarchs migrate back to Mexican overwintering sites. The ecological implications of this cycle of cardenolide sequestration for the evolution of monarch migration are discussed.

ABSTRACT Euploea core amymone, a Mullerian Mimic, when reared on Serium oleander and Asclepias curassavica, stores emetic cardiac glycosides only in the larval stages, and not as pupa and adult. Danaus plexippus erippus. which exhibits less cardioactivity if tested on the isolated rat heart than E. c. amymone, nevertheless stores them at all three stages of development; polar cardenolides not present in its food plant A. curassavica, were found in the pupa and imago.