Issue No. 5, Article 5/April 22, 2005
European Researchers Investigate the Influence of Maize Roots and Subsequent Infection Rates of Western Corn Rootworm Larvae by Nematodes
The use of biological control to limit the severity of corn rootworm injury has proven largely to be a frustrating experience for entomologists in North America. With respect to biological control of the western corn rootworm, U.S. entomologists have focused their efforts on selected species of entomopathogenic nematodes, such as Steinernema carpocapse (Weiser). In many instances, these parasitic nematodes were used experimentally in areas of the Corn Belt in which corn was produced under irrigation. Nematodes are somewhat susceptible to dessication, and moist soils were believed to enhance the potential for them to infect corn rootworm larvae. Thus far, these studies have produced mixed results at best with regard to efficacy of nematodes against western corn rootworm larvae. Consequently, American producers have not adopted this biological control tactic.
In a recent paper in Nature (vol. 434, April 2005), "Recruitment of Entomopathogenic Nematodes by Insect-Damaged Maize Roots," European scientists reported on some very interesting laboratory and field studies that described the release of a sesquiterpene, (E)-β-caryophyllene, from corn roots that had been injured by western corn rootworm larvae. The authors indicated that this compound "strongly attracts" an entomopathogenic nematode, Heterorhabditis megidis. The authors reported that in field studies, western corn rootworm larvae had significantly higher infection rates (5X) of this parasitic nematode in plots where corn plants released this sesquiterpene compared with plots in which a variety of corn did not release this compound.
In their abstract, the authors made the following statement: "Most North American maize lines do not release (E)-β-caryophyllene, whereas European lines and the wild maize ancestor, teosinte, readily do so in response to D.v. virgifera attack." This paper raises some very interesting questions, and this line of research is worthy of further investigation. As the use of soil insecticides escalates in response to the adaptation of the western corn rootworm to crop rotation, we need to continue our search for alternative management tactics for this key insect pest. Although the use of biological control has largely been discounted for western corn rootworms, this paper suggests that perhaps we should reexamine previously held convictions about this approach.--Mike Gray