Abundance of herbivores on six milkweed species in Illinois.By Price, P.W. & M.F. Willson.
Price, P.W. & M.F. Willson. 1979. Abundance of herbivores on six milkweed species in Illinois. American Midland Naturalist 101(1): 76–86.
To aid the understanding of the role of insect herbivores as selective agents in the evolution of their host plants a survey of herbivore abundance and impact was undertaken in central Illinois on the six milkweed species: Asclepias incarnata, A. sullivantii, A. syriaca, A. verticillata, A. amplexicaulis
, and A. tuberosa
. These species occur in this order on a moisture gradient from wet to dry soil conditions. This survey revealed that 12 species occurred at an abundance of at least one individual per 100 host stems in 1 plot-year on one host species: Oncopeltus fasciatus*, Lygaeus kalmii*, Aphis nerii*, Labidomera clivicollis*, Tetraopes tetrophthalmus*, T. femoratus, T. quinquemaculatus, Rhyssomatus lineaticollis*, Danaus plexippus, Cycnia tenera*, Euchaetias egle
and a leafminer. All but L. kalmii
are specific to milkweeds in Illinois. Seven of these species, marked with asterisks, were abundant enough to act as major selective forces on the life history patterns of the milkweed species, populations and clones concerned.