The roles of plant-trapped carrion and enemy-free space in indirect defense against two herbivores on a sticky plant (Madia elegans)

Common tarweed (Madia elegans) produces glandular trichomes that appears to exclude certain predators (i.e. lacewings and ladybeetles) while increasing the abundances of others (i.e. reduviids). We investigated the effects of these glandular trichomes on direct and indirect defense against two herbivores on common tarweed (M. elegans): a bud-eating caterpillar (Heliothodes diminutiva) and an aphid.  Field experiments in 2011 showed that tarweed (M. elegans) plants bearing higher densities of glandular trichomes accumulate more insect carrion than less glandular plants (P < .001), and that this carrion enhances indirect defense against caterpillars (P = .013) and increases plant lifetime fitness (P = .048) by increasing the densities of caterpillar predators (P < .001) (e.g. reduviids and thomisid and lynx spiders) that also scavenge on insect carrion. Data is also presented from ongoing field and laboratory experiments using glandular and eglandular genotypes of M. elegans to quantify the costs associated with glandular trichomes excluding aphid predators (e.g. lacewing and ladybeetle spp.).