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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGY AND MANAGEMENT OF INVASIVE WEEDS IN THE WESTERN UNITED STATES Title: Field testing Diorhabda elongata (Coleoptera:Chrysomelidae) from Crete, Greece to assess potential impact to non-target native California plants in the genus Frankenia

Authors
item Herr, John
item Reddy, Angelica
item Carruthers, Raymond

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 28, 2014
Publication Date: June 1, 2014
Citation: Herr, J.C., Reddy, A.M., Carruthers, R.I. 2014. Field testing Diorhabda elongata (Coleoptera:Chrysomelidae) from Crete, Greece to assess potential impact to non-target native California plants in the genus Frankenia. Environmental Entomology. 43:642-653.

Interpretive Summary: Before new weed biocontrol agents can be released, they are thoroughly tested in the laboratory to make sure that they will not cause damage to non-target plants, such as crops, ornamentals or natives. Occasionally, laboratory tests produce conflicting results, so field tests (in large cages or in the open, with no cages) can be used to more accurately predict how safe new biocontrol agents will be. The beetle Diorhabda elongata from Crete, imported to the US for the control of saltcedar (Tamarix), showed a variable egg-laying response to the non-target Frankenia salina in previous laboratory tests, where up to 11.4 percent of eggs were laid on this native plant. Results from field tests presented in this paper show that significantly more eggs were always laid on saltcedar than F. salina, and that the egg-laying response to the non-target was much lower than that recorded in lab tests. The percent of eggs laid on F. salina in field tests was 3.7 in the paired choice cage test, 4.3 in the multiple choice cage test, and 1.2 in the multiple choice open field test. Substantial damage was caused to F. salina plants by larval and adult feeding, but this occurred only at the end of the open field test, when beetle densities were extremely high, and surrounding saltcedar had been defoliated. Representatives from concerned stakeholder organizations (state, county, university, and environmental) who were invited to view the open field test when in progress, and review the final results concluded that redistribution of D. elongata in California was warranted due to its significant ability to defoliate saltcedar, and its moderate, possibly transitory, feeding on non-target Frankenia. The introduction of D. elongata provides an interesting case study for risk assessment of a potentially useful weed biocontrol agent that is also capable of feeding on a non-target native plant.

Technical Abstract: When laboratory host specificity tests on weed biological control agents produce ambiguous results or are suspected of producing false positives, field cage or open field tests can be utilized in an attempt to determine the true ecological host range of the agent. The leaf beetle Diorhabda elongata (Brullé) from Crete, imported to the US for the control of saltcedar (Tamarix spp., Tamaricaceae), showed a variable ovipositional response to non-target Frankenia spp. (Frankeniaceae) in previous laboratory tests, where up to 11.4 percent of eggs were laid on the native plants. Results from field tests presented in this paper show that significantly more eggs were always laid on Tamarix ramosissima Ledebour than Frankenia salina (Molina) I. M. Johnston, and that the ovipositional response to the non-target was substantially lower than that recorded in lab tests. The percent of eggs laid on F. salina in field tests was 3.7 in the paired choice cage test, 4.3 in the multiple choice cage test, and 1.2 in the multiple choice open field test. Substantial damage was caused to F. salina plants by larval and adult feeding, but this occurred only at the end of the open field test, when D. elongata densities were extremely high, and surrounding saltcedar had been defoliated. Representatives from concerned stakeholder organizations (state, county, university, and environmental) who were invited to view the open field test when in progress, and review the final results concluded that redistribution of D. elongata in California was warranted due to its significant ability to defoliate saltcedar, and its moderate, possibly transitory, feeding on non-target Frankenia spp. The introduction of D. elongata provides an interesting case study for risk assessment of a potentially efficacious weed biocontrol agent that is also capable of utilizing non-target native plants.

Last Modified: 12/19/2014
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