Risk posed by the invasive defoliator Uraba lugens to New Zealand native flora

Abstract

The risk posed to New Zealand native flora by the recently-established pest of Australian origin Uraba lugens Walker (Lepidoptera: Nolidae) (gum leaf skeletonizer) was assessed. Weed biological control host range testing methods were applied to identify those New Zealand plant species potentially at risk. Native plants tested were primarily in the Myrtaceae, the family that contains all the Australian hosts of U. lugens. 2 Experimental methods included no-choice larval feeding assays and field cage and laboratory oviposition trials. Difficulty in ascertaining reliable oviposition preference data from cage oviposition trials limited the confidence with which the invader's field host range could be predicted. 3 Field surveys of plants attacked by U. lugens in the infested area supported the initial predictions but only some of the at-risk native Myrtaceae were present in the area. 4 The risk to native New Zealand plants is presented in terms of two mechanisms: development of self-sustaining populations and temporary spill-over of solitary larvae. Development of self-sustaining populations of the pest within native forests is deemed to be highly improbable. 5 Temporary spill-over impacts are most likely in urban areas within mixed species plantings or boundaries between native/exotic forests and coinciding with the mobile larval life stages. Spill-over impacts from U. lugens have only been recorded to date on Metrosideros excelsa.