Assessing the fundamental host-range of Leptinotarsa texana Schaeffer as an essential precursor to biological control risk analysis

Abstract The leaf beetle Leptinotarsa texana Schaeffer (Coleoptera: Chrysomelidae) was introduced to South Africa from the USA to control silverleaf nightshade Solanum elaeagnifolium Cav. (Solanales: Solanaceae). Subsequent post-release studies in South Africa found the beetle to be an effective, host-specific biocontrol agent of S. elaeagnifolium. Leptinotarsa texana has potential for biological control of S. elaeagnifolium in other countries where the weed adversely impacts agricultural production, including Australia. However, L. texana can only be introduced to Australia if risk analysis demonstrates that the agent poses a negligible or very low risk to the environment and economy. We initiated an assessment of the agent’s possible impact in Australia by prioritising non-target species, and conducting quarantine laboratory experiments on 49 Australian native species and economically important plant species and cultivars. We observed feeding damage greater than 50% leaf area removed on plants of 12 Australian Solanum spp. and two crop species (potato Solanum tuberosum L. and eggplant Solanum melongena L.). Leptinotarsa texana successfully developed from first instar larva to adult on 15 Australian Solanum spp. and two crop species (a single eggplant cultivar and four potato cultivars). When given a choice of S. elaeagnifolium and 10 Australian Solanum spp. in a large cage experiment, L. texana oviposited on S. elaeagnifolium and three of the non-target Australian Solanum spp. We consider possible reasons why potato was not found to be within the beetle’s fundamental host-range in previous host-specificity experiments, and argue there are important differences between potato cultivars that have implications for future host-specificity testing. We outline priorities for further risk analysis, and criteria for assessing the feasibility of these approaches in different contexts.