Submitted to: Journal of Applied Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/28/2009
Publication Date: 5/2/2010
Citation: Lundgren, J.G., Toepfer, S., Haye, T., Kuhlmann, U. 2010. Hemolymph Defense against an Invasive Herbivore: Its Breadth of Effectiveness Against Predators. Journal of Applied Entomology. 134:439-448. Interpretive Summary: Western corn rootworms are one of the worst pests of maize production in North America, and have recently invaded Europe. Although many predators have been documented to feed on this insect under field conditions, there are clear differences in how much different predator species rely on this pest. We recently discovered that rootworm larvae have sticky, repellent blood that repels predators in the laboratory. Here, we describe how 8 different predator species react to the pest larvae in the laboratory, and document whether rootworms are more or less consumed than a palatable surrogate prey item (maggots) under field conditions in Hungary. All predators were repelled by the rootworm larvae in the lab, but they responded to different degrees and with different reactions. Ants were particularly repelled by the rootworm blood in the laboratory. Under field conditions, rootworm larvae were less attacked than maggots, suggesting that this defense operates under natural conditions. The diverse predator community in Hungarian corn fields was primarily composed of ants (especially during the day), and very different predators were found consuming prey during the day and at night. In sum, the rootworm defenses do not preclude predation, but certainly influence which predators will be most useful as biological control agents of this important international pest.
Technical Abstract: Defensive characteristics of organisms shape the trophic linkages within food webs and influence the ability of invasive organisms to expand their range. Diabrotica virgifera virgifera is an invasive herbivore in European maize, and its subterranean larval feeding affects the entire maize ecosystem. Diabrotica v. virgifera larvae are eaten to varying degrees by a diverse predator community, and this research was designed to 1) investigate whether predator species are differentially affected by the hemolymph defense of D. v. virgifera in the laboratory, and 2) substantiate that D. v. virgifera are attacked less intensively than palatable prey species, e.g. fly maggots of equal size in Central European maize fields. 1) Predator species (6 carabids, a wolf spider, and the ant Tetramorium caespitum) were independently fed D. v. virgifera 3rd instars or equivalent-sized maggots of C. vicina (or Sarcophaga bullata for one predator), and the mean time spent eating, cleaning their mouthparts, resting, and walking during the first 2 min following attack was compared between predators fed the two prey items. All predators spent less time eating D. v. virgifera larvae than maggots, and four of the eight predator species spent more time cleaning their mouthparts. The differential responses in the predator species suggest differences in susceptibility to the D. v. virgifera hemolymph defense. 2) D. v. virgifera larvae and C. vicina maggots were restrained in five Hungarian maize fields over two years for 1 hr observation periods beginning at 09:00 and 22:00. The proportion of each species attacked and the number and identity of predators consuming each prey item were recorded. The predator communities (numerically dominated by T. caespitum) showed clear diel patterns in their foraging behaviour on the prey species. Diabrotica v. virgifera was consumed by fewer predators than C. vicina maggots. The defence of D. v. virgifera may partly explain the success of this species as an invasive pest.