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It has been demonstrated that the plants when attacked by herbivorous insects can emit volatile compounds that can attract natural enemies of the insects.  For example, the roots of maize plants when attacked by western corn root-worms (a noxiuos insect pest of corn) can synthesize and emit a volatile compound called (E)-beta-caryophyllene that attracts insect-parasitic nematodes that infect and kill many soil dwelling insect pests (Rasmann et al., 2005; Degenhardt et al., 2009).

Read following scientific papers for more information on insect induced plant volatiles that attract natural enemies of insect pests.

Degenhardt, J., Hiltpold, I., Kollner, T.G., Frey, M., Gierl, A., Gershenzon, J., Hibbard, B.E., Ellersieck, M.R. and Turlings, T.C.J. 2009. Restoring a maize root signal that attracts insect-killing nematodes to control a major pest. Proceedings of the National Academy of Sciences of the United States of America. 106: 13213-13218.

Rasmann, S., Kollner, T.G., Degenhardt, J., Hiltpold, I., Toepfer, S., Kuhlmann, U., Gershenzon, J., Turlings T.C.J. 2005. Recruitment of entomopathogenic nematodes by insect-damaged maize roots. Nature 434: 732–737.

The western corn rootworm (Diabrotica virgifera virgifera) is a very serious pest of corn in the North America and Europe. Larvae of this insect exclusively feed on maize roots, often causing plant lodging whereas adults may reduce yields through silk feeding and interfering maize pollination.  Insect-parasitic Heterorhabditid and Steinernematid nematodes have been applied for the control of D. v. virgifera larvae in the fields.  Heterorhabditis bacteriophora is proved to be as effective as pyrethroid insecticide, tefluthrin in reducing over 65% emergence adults of rootworms.  Application of tefluthrin in combination with Steienernema carpocapsae can result in a synergistic response that can lead to increased mortality of rootworms by 24%.  Also, entomopathogenic nematodes including Steinernema glaseri, Steinernema arenarium, Steinernema abassi and Heterorhabdtis bacteriophora when applied at the rate of 8-16 nematodes per cm² under laboratory condtions caused over 77% larval mortality.

For more information on corn rootworms and entomopathogenic nematode interactions, read following literature

Jackson, J.J. 1995.  Pathogenicity of entomopathogenic nematodes for third instars of the western corn rootworm. J Nematol 27:504.

Jackson, J.J. 1996.  Field performance of entomopathogenic nematodes for suppression of western corn rootworm (Coleoptera: Chrysomelidae). J Econ Entomol 89:366–372.

Jackson, J.J. 1997.  Field efficacy and ecology of three entomopathogenic nematodes with the western corn rootworm. J Nematol 29:586.

Jackson, J.J., Brooks, M.A. 1995.  Parasitism of western corn rootworm larvae and pupae by Steinernema carpocapsae. J Nematol 27:15–20.

Journey, A.M., Ostlie, K.R. 2000.  Biological control of the western corn rootworm (Coleoptera: Chrysomelidae) using the entomopathogenic nematode, Steinernema carpocapsae. Environ Entomol 29:822–831.

Kurtz, B., Toepfer, S., Ehlers, R.U., Kuhlmann, U. 2007.  Establishment and persistence of Heterorhabditis bacteriophora, H. megidis, and Steinernema feltiae for controlling Diabrotica virgifera virgifera larvae in maize. J Appl Entomol 131:420–425.

Pilz, C. 2008.  Biological control of the invasive maize pest Diabrotica virgifera virgifera by the entomopathogenic fungus Metarhizium anisopliae. PhD thesis at the University of Natural Resources and Applied Life Sciences BOKU, Vienna, 155 pp.

Pilz, C., Wegensteiner, R., Keller, S. 2007.  Selection of entomopathogenic fungi for the control of the western corn rootworm Diabrotica virgifera virgifera. J Appl Entomol 131:426–431.

Pilz, C., Keller, S., Kuhlmann, U. and Toepfer, S. 2009. Comparative efficacy assessment of fungi, nematodes and insecticides to control western corn rootworm larvae in maize. Biocontrol 54: 671-684.

Pilz, C., Wegensteiner, R., Keller, S. 2008.  Natural occurrence of insect pathogenic fungi and insect parasitic nematodes in Diabrotica virgifera virgifera populations. BioControl 53:353–359.

Poinar, G.O. Jr., Evans, J.S., Schuster, E. 1983.  Field test of the entomogenous nematode, Neoaplectana carpocapsae, for control of corn rootworm larvae (Diabrotica sp., Coleoptera). Prot Ecol 5:337–342.

Toepfer S, Peters A, Ehlers, R.U., Kuhlmann, U. 2008.  Comparative assessment of the efficacy of entomopathogenic nematode species at reducing western corn rootworm larvae and root damage in maize. J Appl Entomol 132:337–348.

Toepfer, S., Gueldenzoph, C. Ehlers, R.U. and Kuhlmann, U. 2005. Screening of entomopathogenic nematodes for virulence against the invasive western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) in Europe. Bulletin of Entomological Research. 95: 473- 482.