Aspects of the biology and morphology of Anisoplaca ptyoptera meyrick (Lepidoptera: Gelechiidae), a potential biological control agent of gorse

Abstract

Anisoplaca ptyoptera Meyrick (Lepidoptera: Gelechiidae) is a stem miner which attacks some members of the tribe Cannichaelieae (Fabaceae). Carmichaelieae and A. ptyoptera are both endemic to New Zealand. Recently it was noticed that the moth also attacks the exotic weed gorse (Ulex europaeus L.) (Butler 1979).

Larval feeding by A. ptyoptera structurally weakens the host and disrupts vascular transport; this causes dieback of branches, reduces flowering and growth and occasionally contributes to plant death. While various factors limit its potential in New Zealand, A. ptyoptera has been identified as a potentially useful insect in biological control programmes against gorse in Hawaii, Oregon and Chile.

A preliminary assessment of the suitability of A. ptyoptera as a biological control agent has been carried out in New Zealand. Aspects of the biology of A. ptyoptera on gorse have been investigated, the destruction of gorse by the moth in parts of Canterbury has been measured, the ease by which it can be artificially reared has been assessed, and techniques suitable for host specificity screening have been developed. Descriptions of A. ptyoptera adult and larva are also given.

The life history strategy of A. ptyoptera appears to be opportunistic univoltinism. The seasonal distribution of life stages is loosely synchronised. The possibility of diapause is discussed, although evidence of this is only slight. Adults emerge from late spring to autumn and larvae develop throughout the year. Thus damage to gorse continues throughout the entire growth and reproductive periods of gorse. Up to 94 percent of the mature plants at a site have been attacked. The loss of as much as 85 percent of foliage can be directly attributed to A. ptyoptera damage.

The mean potential fecundity is 196 eggs per female. The endemic population reaches high levels and is widespread, despite 33-49 percent parasitism of the larvae. Two undescribed species of larval parasitoid have been isolated: an endemic eulophid (Zealachertus sp.) and an ichneumonid (Diadegma sp.), which is probably also endemic. As these parasitoids appear to be restricted to New Zealand, the potential for A. ptyoptera to achieve high population levels outside New Zealand appears favourable.

The oligophagous feeding habits of A. ptyoptera necessitate a cautious approach to assessing its suitability as a biological control agent. Host specificity will be more thoroughly investigated in the 1989-1990 and 1990-1991 seasons. If an acceptable degree of specificity is found, there are excellent prospects for A. ptyoptera to make a significant contribution to biological control of gorse growing outside New Zealand.