Previous herbivore attack of red alder may improve food quality for fall webworm larvae

Abstract

Summary. Three hypotheses of insect-plant interactions were tested by rearing fall webworm larvae in the laboratory on foliage from red alder trees with different histories of western tent caterpillar herbivory. Fall webworm larvae raised on foliage from trees which had been attacked previously for two summers by moderate densities of western tent caterpillars grew faster and attained heavier pupal weights than did those fed foliage from unattacked trees. This contradicts the hypothesis that moderate levels of previous herbivory induces the production of plant defensive chemicals in red alders. Growth of webworms, when fed foliage from unattacked trees adjacent to alders that were attacked by fall webworm larvae, was the same as when fed foliage from trees isolated by distance from attacked trees. This contradicts the hypothesis that attacked trees stimulate the production of defensive chemicals in neighboring trees. Young and mature alder foliage was equally good for fall webworm growth and survival, and foliage from trees heavily attacked by both fall webworm and western tent caterpillars for three years produced slow growth rates and small pupal sizes. This supports the hypothesis that continued heavy insect attack can cause the deterioration of the food quality of attacked trees.

PAIRWISE VERSUS DIFFUSE NATURAL SELECTION AND THE MULTIPLE HERBIVORES OF SCARLET GILIA, IPOMOPSIS AGGREGATA

“…First, herbivores may compete directly on a shared host plant tissue (Lawton and Strong 1981;Lawton and Hassell 1984;Karban 1989;Fritz 1992), and these interactions may reduce or facilitate the impact of each herbivore on plant growth and reproduction (Karban and Strauss 1993;Karban et al 1994). Similarly, early-season herbivores may influence late-season herbivores by altering the phenology, tissue quality, or architecture of the host plant (Schultz and Baldwin 1982;Williams and Myers 1984;Harrison and Karban 1986;Gange and Brown 1989;Karban and Myers 1989;Tisdale and Wagner 1991;Pilson 1992;Brown and Weiss 1995;Inbar et al 1995;Alonso and Herrera 1996) or by altering susceptibility to predators (Faeth 1985;Damman 1987). Finally, because plants commonly respond to multiple stresses (e.g., drought and nutrient stress) in a nonadditive manner (Louda 1986;English-Loeb 1989Mooney et al 1991), plants may respond nonadditively to the damage imposed by multiple herbivore attack.…”

Tree Defenses Against Insects

“…After mammalian browsing, plants may become better for insects (Danell and Huss-Danell, 1985); insect feeding can lead to a similar outcome (Bryant et al, 1991). Since responses to the breaking of apical dominance are of a very general nature, it is not surprising that induced susceptibility has been found in many types of woody plants, including eucalypts (Landsberg, 1990), birch , oak (Hunter and West, 1990), alder (Williams and Myers, 1984), willows (Hjälten and Price, 1996), and pines (Trewhella et al, 1997;Raffa et al, 1998).…”

Variability in grazer-mediated defensive responses of green and red macroalgae on the south coast of South Africa

“…(2) Complex ecological interactions could ultimately increase the fitness of the alga and the grazer, for example by attracting grazers that clean the alga of epiphytes or possible competitors (Stachowicz 2001b). Such interactions have been described for aquatic plants (Underwood et al 1992;Kerffoot et al 1998;Jones et al 1999) and terrestrial plants (Williams and Myers 1984).…”