Submitted to: Biocontrol Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/7/2009
Publication Date: 9/8/2009
Citation: Lundgren, J.G., Haye, T., Toepfer, S., Kuhlmann, U. 2009. A Multifaceted Hemolymph Defense Against Predation in Diabrotica virgifera virgifera Larvae. Biocontrol Science and Technology. 19(8):871-880. Interpretive Summary: The western corn rootworm is a notorious pest of corn, but little is known of how it interacts with natural enemies like predators. We found that larval hemolymph of rootworms coagulates onto the mouthparts of carabid beetle attackers; predators recoil after their attack, vigorously cleaning their mouthparts. The ethanol-soluble fraction of this hemolymph reduces predator feeding. Sticky, chemically repellent properties of rootworm larval hemolymph partially explain its success as an invasive pest.
Technical Abstract: Defensive chemistry mitigates the strength of trophic interactions between an herbivore and its diverse assemblage of predators. Diabrotica virgifera virgifera is a chrysomelid beetle whose subterranean larvae are a notorious pest of maize production, although they succumb a number of generalist predators. Despite the large number of studies on this pest, defense mechanisms of its larvae had never been investigated. The contributions of physical and chemical aspects of D. virgifera hemolymph were quantitatively assessed against two predatory beetle species in the laboratory. Adult Poecilus cupreus and Harpalus pensylvanicus (Coleoptera: Carabidae) were fed pupae, 2nd or 3rd instar D. v. virgifera or a palatable surrogate prey of equivalent size, i.e. Calliphora vicina or Sarcophaga bullata larvae (Diptera: Calliphoridae, Sarcophagidae, respectively) of equivalent size. The ethanol-soluble fraction of 3rd instar D. v. virgifera hemolymph was extracted and suspended in a 0.24 M sucrose solution and offered to H. pensylvanicus (using a sucrose only control for comparison). The mean duration until first consumption was recorded for each predator, as was the amount of time spent eating, cleaning, resting, or walking for 2 min post-attack (or 5 min for the sugar assay). Maggots and D. virgifera larvae and pupae were attacked equally by both predators. But upon attack, Diabrotica virgifera larval hemolymph quickly coagulated onto the mouthparts of the predators, and they immediately backed away from the prey vigorously cleaning their mouthparts. Predators ate the sucrose solution for significantly longer than hemolymph + sucrose solution, indicating the presence of deterrent chemicals in the hemolymph. This research suggests that D. v. virgifera larvae are defended from predation by sticky and repellent hemolymph. This defense is independent of the well documented pharmacophagous relationship that this and closely related Diabroticina species have with cucurbitacins. We hypothesize that this defense partially explains the widespread success of D. v. virgifera as an invasive pest.