Feasibility of developing classical biological control solutions for the herbaceous weed Allium triquetrum in Australia

Abstract

ABSTRACT Allium triquetrum L. (Amaryllidaceae), a bulbiferous monocot, is native to the Mediterranean. It was introduced to Australia in the early 1900s, where it has subsequently become a significant invader of temperate forests throughout south-eastern Australia. Intensive chemical and mechanical control methods can suppress A. triquetrum infestations at the local scale for short periods of time but remain ineffective at sustainably curtailing its invasion at landscape and regional scales. In this context, we undertook field surveys across the Mediterranean (mainland France, Corsica, Sardinia) to determine the feasibility of developing classical biological control solutions for A. triquetrum in Australia. Despite extensive sampling (i.e. 30 surveys at 18 sites over three growing seasons), very few phytophagous arthropod and fungal pathogen taxa were detected on A. triquetrum. The most common arthropod species were the flies Phytomyza gymnostoma and Delia hirticrura, the weevil Oprohinus consputus and the moth Hysterophora maculosana. All identified arthropod taxa were considered generalists, having been found on other plant species, and some are known pests of cultivated Allium species. Twenty-one different fungal isolates were recovered from A. triquetrum, with most considered as saprophytic, secondary/opportunistic pathogens that probably infected already-damaged A. triquetrum leaves. Only four fungal taxa were found to be primary pathogens of A. triquetrum but have been recorded to infect other plant species. None of these enemy taxa were deemed to be suitable candidate biocontrol agents to help manage A. triquetrum invasion in Australia. Future research directions for improved A. triquetrum management in Australia are discussed in this paper.