The potential of arid/semiarid land plants a s sources of commercial products is illustrated by the following examples: candelilla (wax); jojoba (oil, protein); Acacia spp. (gum); Astragalus spp. (tragacanth gum); guayule (rubber); rabbitbrush (rubber, chemicals); sunflowers (rubber, chemicals); yucca (soap); and cresote bush (antioxidants, phenolic resins). co-evolutionary selection is a cause...

Sixteen selections of Apocynum cannabinum (Indian Hemp) and nine of Asclepias syriaca (Common Milkweed) from midwestern USA were exposed to 40 or 80 ppb ozone under controlled conditions within greenhouse continuously stirred tank reactor (CSTR) chambers to evaluate their relative ozone sensitivity. The incidence and severity of ozone-induced symptoms on both species were directly related to oz...

Long-standing theory has predicted that plant defensive and nutritional traits contribute to the population dynamics of insect herbivores. To examine the role of plant variation in density dependence, I took a comparative approach by conducting density manipulation experiments with the specialist aphid, Aphis nerii, on 18 species of milkweed (Asclepias spp.). The strength of density dependence ...

Predators determine herbivore and plant biomass via so-called trophic cascades, and the strength of such effects is influenced by ecosystem productivity. To determine whether evolutionary trade-offs among plant traits influence patterns of trophic control, we manipulated predators and soil fertility and measured impacts of a major herbivore (the aphid Aphis nerii) on 16 milkweed species (Asclep...

1 We studied the genetic and environmental determinants of attack by the specialist stem-attacking weevil, Rhyssomatus lineaticollis on Asclepias syriaca . 2 In natural populations, the extent of stem damage and oviposition were positively correlated with stem width, but not stem height. We hypothesized that both genotypic and environmental factors influencing stem morphology would affect attac...

Anthropogenic nitrogen deposition has shifted many ecosystems from nitrogen (N) limitation to phosphorus (P) limitation. Although well documented in plants, no study to date has explored whether N deposition exacerbates P limitation at higher trophic levels, or focused on the effects of induced plant P limitation on trophic interactions. Insect herbivores exhibit strict N : P homeostasis, and s...

defence of common milkweed Asclepias syriaca to two lepidopteran herbivores Robin A. Bingham* and Anurag A. Agrawal Department of Natural and Environmental Sciences, Western State College of Colorado, Gunnison, CO 81231, USA; Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA; and Department of Entomology, and Center for a Sustainable Future, Cornell Unive...

Two cercosporoid species are respectively described from Mexican whorled milkweed (Asclepias fascicularis), and spineless safflower (Carthamus tinctorius) from California. Passalora californica represents a new pathogen on Asclepias fascicularis, while Ramularia cynarae is confirmed on Carthamus tinctorius and Cynara cardunculus (Asteraceae), and an epitype designated. Pathogenicity is also est...

Below-ground (BG) symbionts of plants can have substantial influence on plant growth and nutrition. Recent work demonstrates that mycorrhizal fungi can affect plant resistance to herbivory and the performance of above- (AG) and BG herbivores. Although these examples emerge from diverse systems, it is unclear if plant species that express similar defensive traits respond similarly to fungal colo...

1. Trade-offs in an herbivore’s ability to feed, avoid predation and succeed on alternative hosts are thought to be major driving factors in host specialization. In this study, we compared how two closely related milkweed beetles (Tetraopes spp.) that have specialized on separate Asclepias species respond to host switching to alternative milkweed plants. By additionally examining effects on the...