Ecological host-range of Lilioceris cheni (Coleoptera: Chrysomelidae), a biological control agent of Dioscorea bulbifera

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Open-field host-specificity testing assesses the host-range of a biological control agent in a setting that permits the agent to use its full complement of host-seeking behaviors. This form of testing, particularly when it includes a no-choice phase in which the target weed is killed, may provide the most accurate assessment of the ecological host-range of an agent. We conducted a two-phase field host-specificity test with experienced and naïve adults of Lilioceris cheni Gressitt and Kimoto (Coleoptera: Chrysomelidae), a biological control agent of Dioscorea bulbifera L. (Dioscoreales: Dioscoreaceae). We followed field tests with a no-choice laboratory consumption study with the congeneric plant species that received test feeding in the field, and an additional field evaluation of spillover risk. Both experienced and naïve adults strongly preferred D. bulbifera to non-targets in the field. Within 47h post-release, 90% of the released beetles that remained in the plots were found on D. bulbifera. In the laboratory no-choice test, the beetles consumed significantly more D. bulbifera and survived longer on this plant than the non-targets. All naïve beetles in the Dioscorea sansibarensis and Dioscorea villosa treatments and 75% of naïve beetles on Dioscorea floridana died within 7d. Potted plants of the native D. floridana experienced minor test feeding in the spillover experiment when surrounded by large populations of L. cheni in the field. At the end of this experiment, L. cheni eggs and/or larvae were present on 83% of D. bulbifera plants but none of the D. floridana plants. We conclude that L. cheni is host-specific to D. bulbifera and does not pose a spillover risk to the native D. floridana.