Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Influence of nectar source plants on the New Guinea sugarcane weevil parasite, Lixophaga sphenophori (Villeneuve).

Abstract

An account is given of further work in 1972-73 on the influence of plants affording a source of nectar on parasitism of Rhabdoscelus obscurus (Boisd.) on sugar-cane in Hawaii of Lixophaga sphenophori (Villen.) [cf. RAE/A 63, 4620]. Two additional plants that occur in and near cane fields in Oahu and are utilised for nectar by the parasite were recorded in 1971. They are referred to as Euphorbia geniculata and E. heterophylla and in a greenhouse experiment they were preferred to the previously known species, E. pilulifera (hirta) and E. glomifera. Evidence was obtained that both sexes of L. sphenophori were significantly more numerous along the margins of the sugar-cane fields than within the fields, that males were significantly more numerous than females along the margins, and that few males occurred within the fields. Adult parasites were found to be virtually absent from the margins of fields that received five applications of herbicides at irregular intervals between March and July; their absence was attributed mainly to migration to other areas, though the herbicides may have caused some direct mortality. In an untreated control field, numbers of L. sphenophori varied from week to week with weather conditions. Where no herbicides were applied, other faster growing weeds often eventually crowded out the desirable species of Euphorbia. E. geniculata and E. heterophylla appeared to be somewhat resistant to herbicides and E. pilulifera quickly re-established itself. In an experiment in which larvae of R. obscurus were exposed along the margins of two fields one of which was treated with herbicides and the other was not, parasitism in the treated field was significantly reduced 35 days after the application. For maximum utilisation of L. sphenophori for biological control, the development of a herbicide programme making use of materials and application intervals that will favour continuous maintenance of stands of nectar-producing species of Euphorbia along the field margins appears necessary.