A world-wide program for the continuous monitoring of solar UV radiation using poly(phenylene oxide) film,and a consideration of results

The use of poly(phenylene oxide) film to monitor UV radiation is demonstrated, and the results from the continuous monitoring of solar UV radiation at 24 sites throughout the world are presented. The global and diffuse measurements from a temperate and from a tropical site are analyzed in detail, and the effects of season and weather conditions on the UV contribution to solar radiation and the relative importance of the diffuse and direct components of solar UV are discussed.     

Fate of iridoid glycosides in different life stages of the Buckeye,Junonia coenia (Lepidoptera: Nymphalidae)

The buckeye butterfly,Junonia coenia (Lepidoptera: Nymphalidae), specializes on plants that contain iridoid glycosides. To determine the fate of these compounds in larvae, pupae, and adults of this species, we reared larvae on artificial diets with and without iridoid glycosides, and on leaves of a host plant,Plantago lanceolata (Plantaginaceae). Quantification by gas chromatography showed that newly molted third-, fourth-, and fifth-instar larvae reared on leaves ofP. lanceolata contained means of 5.13, 2.88, and 6.83% dry weight iridoid glycoside. In contrast, the mean iridoid glycoside concentration of actively feeding fifth-instar larvae was 0.28% dry weight, that of pupae was 0.19% dry weight iridoids, and adults contained no detectable iridoids. Feeding experiments suggested that this reduction in actively feeding larvae was due to the metabolism of iridoid glycosides.P. lanceolata leaves in these experiments contained a mean of 1.00% dry weight iridoid glycoside, with a 2:1 ratio of aucubin to catalpol. Calculation of iridoid consumption and utilization indices showed that larvae fed artificial diets consumed, digested, and sequestered aucubin and catalpol in similar ways. When these indices were calculated for larvae fed leaves ofP. lanceolata, catalpol was sequestered twice as efficiently as aucubin.     

Plant Induced Defenses Depend More on Plant Age than Previous History of Damage: Implications for Plant-Herbivore Interactions

Herbivore-induced plant responses can significantly change as a function of plant developmental stage and previous history of damage. Yet, empirical tests that assess the combined role of multiple damage events and age-dependent constraints on the ability of plants to induce defenses within and among tissues are scarce. This question is of particular interest for annual and/or short-lived perennial plant species, whose responses to single or multiple damage events over a growing season are likely to interact with ontogenetic constraints in affecting a plant’s ability to respond to herbivory. Using Plantago lanceolata and one of its specialist herbivores, Junonia coenia, we examined the effect of plant ontogeny (juvenile vs. mature developmental stages) and history of damage (single and multiple damage events early and/or late in the season) on plant responses to leaf damage. Plant responses to herbivory were assessed as induced chemical defenses (iridoid glycosides) and compensatory regrowth, in both above- and below-ground tissues. We found that constitutive concentration of iridoid glycosides markedly increased as plants matured, but plant ability to induce chemical defenses was limited to juvenile, but not mature, plant stages. In addition, induced defenses observed 7 d following herbivory in juvenile plants disappeared 5 wk after the first herbivory event, and mature plants that varied considerably in the frequency and intensity of damage received over 5 wk, did not differ significantly in their levels of chemical defenses. Also, only small changes in compensatory regrowth were detected. Finally, we did not observe changes in below-ground tissues’ defenses or biomass a week following 50% removal of leaf tissues at either age class or history of damage. Together, these results suggest that in P. lanceolata and perhaps other systems, ontogenetic trajectories in plant growth and defenses leading to strong age-dependent induced responses may prevail over herbivore-induced indirect interactions.     

The Perennial <Emphasis Type="Italic">Penstemon</Emphasis>: Variation in Defensive Chemistry Across Years,Populations, and Tissues

Plants produce a variety of secondary metabolites that function as a defense against their natural enemies. Production of these secondary metabolites is genetically controlled, but is also phenotypically plastic and varies in response to both biotic and abiotic factors. Therefore, plant species may vary widely in their chemical defenses and such variation can be evident at temporal, spatial and tissue levels. Focusing on the chemical defenses of a native Colorado wildflower, Penstemon virgatus, we assessed the variation in iridoid glycoside (IG) content across two non-consecutive growing seasons, six natural populations and three tissue types: leaves, stems and flowers. Our results indicate that P. virgatus plants contain high concentrations of IGs (mean = 23.36% dry weight of leaves) and that IGs were differentially allocated among tissue types. Leaves contained the highest concentration of IGs, which varied quantitatively between sampling years, among plant populations, and plant parts. We also quantified leaf herbivore damage at all six populations but we found very little herbivore damage. Our study indicates that the IG concentrations of P. virgatus plants are both spatially and temporally variable. Furthermore, the high concentrations of secondary metabolites combined with the low levels of damage suggest that these plants are well defended against generalist herbivores.     

Incorporation of an Introduced Weed into the Diet of a Native Butterfly: Consequences for Preference, Performance and Chemical Defense

The introduction of exotic plants, animals, and pathogens into non-native ecosystems can have profound effects on native organisms. Plantago lanceolata, narrow-leaf or ribwort plantain (Plantaginaceae), is a weed that was introduced to North America from Eurasia approximately 200 years ago and that has been incorporated into the diet of a variety of native North American herbivores. Plantain contains two iridoid glycosides, aucubin and catalpol, that can be toxic or deterrent to non-specialized herbivores or herbivores that have recently incorporated this species into their diet. Anartia jatrophae (Nymphalidae), the white peacock, feeds on plants in five families including the Plantaginaceae, and was recently observed feeding on plantain; however, the effects of feeding on this novel host plant are unknown. In this study, we performed a series of experiments to assess larval preference and performance on the introduced P. lanceolata and on a native host plant that does not contain iridoid glycosides, water hyssop, Bacopa monnieri (Plantaginaceae). We also tested whether or not white peacocks were able to sequester iridoid glycosides and compared this ability with an iridoid specialist, the buckeye, Junonia coenia (Nymphalidae). White peacocks successfully developed to the adult stage on plantain; larvae grew more slowly but pupae were heavier when compared with larvae and pupae reared on the native host plant. Larvae showed induced feeding preferences for the host plant on which they were reared. Furthermore, larvae sequestered small amounts of iridoids that were also retained in pupae and adults. These results suggest that incorporation of the introduced weed, plantain, into the diet of the white peacock may have important consequences for larval performance and preference, as well as for interactions with natural enemies.     

Acquired chemical defense in the lycaenid butterfly,Eumaeus atala

The lycaenid butterfly,Eumaeus atala, was found to contain cycasin, an azoxyglycoside, by thin-layer chromatography (TLC). Quantification of cycasin content in 10 individual freshly killed and frozen males and females, using capillary gas chromatography (GC), showed that cycasin contents of individual butterflies ranged from 0.21 to 0.51 mg (1.24–2.75% dry weight). A museum specimen ofE. atala of unknown age had undetectable amounts of cycasin by GC. GC showed that larval frass contained about 0.10% cycasin, which was not detectable by TLC. Cycasin in the host plant was not detectable by TLC but was detected by GC and found to be 0.02% dry weight. There was no macrozamin, another azoxyglycoside characteristic of many cycads, in the butterfly or plant. Feeding trials with a colony of the ant,Camponotus abdominalis floridanus, showed that both cycasin and the adult ofE. atala were deterrent to the ants.     

Host Plant Influences on Iridoid Glycoside Sequestration of Generalist and Specialist Caterpillars

The effect of diet on sequestration of iridoid glycosides was examined in larvae of three lepidopteran species. Larvae were reared upon Plantago major, or P. lanceolata, or switched from one to the other in the penultimate instar. Junonia coenia is a specialist on iridoid glycoside-producing plants, whereas the arctiids, Spilosoma congrua and Estigmene acrea, are both polyphagous and eat iridoid-producing plants. All species sequestered iridoids. The specialist J. coenia sequestered from three to seven times the amounts sequestered by the two generalist species. Junonia coenia iridoid glycoside content depended on diet, and they sequestered from 5 to 15% dry weight iridoid glycosides. Estigmene acrea iridoid glycoside sequestration was relatively low, around 2% dry weight and did not vary with diet. Spilosoma congrua sequestration varied with diet and ranged from approximately 3 to 6% dry weight.     

The importance of sequestered iridoid glycosides as a defense against an ant predator

We reared larvae ofJunonia coenia Hubner (Nymphalidae) on artificial diets with trace concentrations of iridoid glycosides and on leaf diets with higher concentrations of iridoid glycosides. We offered these caterpillars to predacious ants and observed the effects of the following on predation: diet (artificial vs. leaf), site (ant colonies in dry vs. wet areas), instar (early vs. late), and time (changes in predation over five days). Diet and site were consistently significant predictors of the ants' propensities to reject prey and the caterpillars' abilities to escape predation. Leaf-diet caterpillars escaped more frequently than artificial-diet caterpillars, and ants from dry sites were more likely to reject prey than ants from wet sites. The percentage of iridoid glycosides found in individual caterpillars was also a good predictor of the probability of rejection by predators and prey escape. Caterpillars with higher levels of iridoids were more likely to be rejected and to escape, suggesting that sequestered iridoid glycosides are a defense against predaceous ants.     

Efficient heuristics for wireless network tower placement

Over the last decade, telecommunications companies have invested nearly 100 billion dollars in the development of an impressive fiber optic backbone which is capable of transmitting data at incredible speeds. However, much of this backbone remains unused because of the data capacity bottleneck which exists at the user level. While various technologies have emerged to provide greater end-point capacity, many of these are of limited availability due to cost or technical considerations. One promising technology has been high-speed wireless service. Wireless service has the potential to provide widespread coverage, but the cost of developing the infrastructure such as antenna towers can be formidable. While models have been developed to assist in the planning for minimum cost tower placement, these models can be quite large and complex to solve. This paper explores alternate solution methods based on heuristic approaches which may allow for the solution of much larger tower placement problems.