Haemolymph defence of an invasive herbivore: its breadth of effectiveness against predators.
Defensive characteristics of organisms affect the trophic linkages within food webs and influence the ability of invasive species to expand their range. Diabrotica v. virgifera is one such invasive herbivore whose predator community is restricted by a larval haemolymph defence. The effectiveness of this haemolymph defence against a range of predator functional and taxonomic guilds from the recipient biota was evaluated in a series of experiments. Eight predator species (Carabidae, Lycosidae, Formicidae) were fed D. v. virgifera 3rd instars or equivalent-sized maggots in the laboratory, and the mean times spent eating, cleaning their mouthparts, resting and walking following attacks on each prey were compared. Prey species were restrained in five Hungarian maize fields for 1 h periods beginning at 09:00 and 22:00 hours. The proportion of each species attacked and the number and identity of predators consuming each prey item were recorded. All predators spent less time eating D. v. virgifera larvae than maggots in the laboratory, and four of the eight predator species spent more time cleaning their mouthparts. The differential responses in the predator species indicate differences in susceptibility to the D. v. virgifera haemolymph defence. The predator communities (numerically dominated by Tetramorium caespitum) in the field showed clear diel patterns in their foraging behaviour, and D. v. virgifera was consumed by fewer predators than maggots. The defence of D. v. virgifera may partly explain how invasive insects that are exposed to an extensive predator community overcome biotic resistance to the invasion process.