DEFENSE OF BRACKEN FERN BY ARTHROPODS 
ATTRACTED TO AXILLARY NECTARIES 
By Matthew M. Douglas 
Adjunct Senior Research Scientist 
Snow Entomological Museum 
The University of Kansas* 
Introduction: 
The phenotypically variable bracken fern, Pteridium aquilinum 
(L.) Kuhn, is an economically important plant that establishes dense 
monocultural stands by spore dispersal and by spreading subterra- 
nean rhizomes throughout the world, except for hot and cold desert 
regions (Page, 1976). Bracken produces a number of so-called 
“secondary plant compounds” that have been shown to protect it 
from some nonadapted insects (Cooper-Driver et. al., 1977). These 
compounds include the cyanogenic glucoside, prunasin (Cooper- 
Driver and Swain, 1976; Cooper-Driver et. al., 1977), lignins and 
silica (Lawton, 1976), sesquiterpene pterosins (Jones and Firn, 
1979a), phytoecdysteroids (Jones and Firn, 1978), and the protein 
thiaminase (Evans, 1976). Tannins, flavonoids, and phenolics have 
also been implicated as possible defensive compounds in bracken 
fern (Cooper-Driver et. al., 1977; Jones and Firn, 1979b). 
Despite bracken’s well-developed biochemical arsenal, adapted 
and nonadapted herbivorous insects in experimental plots located in 
Michigan and Massachusetts often destroy up to 30 percent of a 
frond’s biomass after the pinnae are completely expanded. In addi- 
tion to these herbivores, stands of Michigan bracken also support a 
diverse community of ectoparasites, parasitoids, and predators of 
bracken herbivores, including nearly 20 species of ants and spiders 
that form temporary symbiotic relationships with the bracken 
croziers. 
♦Research Address: 1503 Woodland St., Jenison, Michigan, 49428 
Manuscript received by the editor May 2, 1983 
313 
