Host-range testing, introduction, and establishment of Cydia succedana (Lepidoptera: Tortricidae) for biological control of gorse, Ulex europaeus L., in New Zealand

Cydia succedana Denis and Schiffermüller (Lepidoptera: Tortricidae) has been introduced to New Zealand as a biological control agent to attack the seeds of gorse (Ulex europaeus; Fabaceae). Gorse is a major weed in New Zealand and in other temperate parts of the world including Oregon and California (USA), at high elevations in Hawaii (USA), Chile, and Australia. This paper describes the host-range tests conducted to assess the risk that C. succedana posed to nontarget plants, and to gain approval for the introduction of this moth into New Zealand. The release and establishment of C. succedana are recorded. First-instar larvae transferred onto excised pods of 39 leguminous test plants completed development on gorse controls (40.0%), Pisum sativum (7.2 and 8.0%), and the rare native species Clianthus puniceus (10.0%). Larvae also fed on pods of Lens culinaris and Sophora spp. but none completed development. Excised shoots bearing flowers and pods of 33 leguminous plants were exposed to female moths in small cages. No eggs were laid on 17 species. Oviposition on the other 16 plants never exceeded 10% of that on controls. Eggs were laid on C. puniceus and Sophora microphylla, but not on P. sativum or L. culinaris. Tests were conducted in larger cages outdoors using whole plants of 17 leguminous species. Moths were more selective in this arena. No eggs were laid on C. puniceus, but occasional eggs were laid on S. microphylla in both “choice” and “no-choice” tests. Behavioral observations suggested that larvae tend to actively seek out gorse pods in preference to pods of S. microphylla. It was concluded that C. succedana posed no significant threat to Sophora spp., or to any other plants with economic or environmental value in New Zealand. C. succedana was released in 1992, and since then has been distributed at 134 sites in New Zealand. It has established at 78% of the sites that have been adequately assessed. There appears to be no geographic establishment pattern, and this species may establish wherever gorse occurs. The potential effect of C. succedana on the population dynamics of gorse in New Zealand is discussed. Introduction of this species to Hawaii and Australia is being considered.