Status of introduced parasites of Queensland fruit fly (Strumeta tryoni), 1960–1962

Abstract

The paper describes fruit sampling carried out in eastern Australia during January 1960–March 1962 to assess the status of parasites of the oriental fruit fly (Dacus dorsalis) liberated in Australia during 1956–1959 against the Queensland fruit fly (Strumeta tryoni).

Opius oophilus was the only introduced parasite extant on the mainland in 1962, parasitizing up to 78% of the host fly stages in Averrhoa carambola in north Queensland and 0–35% in other fruit types. O. oophilus was well established in north Queensland at five localities near Cairns and two near Innisfail, and less well established at three localities near the Queensland–New South Wales border. It had died out during 1960 from two localities further south in New South Wales in which it had been well established since late 1958.

O. oophilus was present on Lord Howe Island from October 1959 to March 1961 but died out subsequently. O. longicaudatus was extant in low numbers on the island in 1962.

Under Australian conditions Opius oophilus mated satisfactorily. The parasite was able to utilize as hosts fruit flies of the following species: Strumeta barringtoniae, S. cacuminata, S. humeralis, S. tryoni, and possibly Afrodacus jarvisi and S. kraussi, but preferences could not be measured with available techniques. Although it was reared from a total of 14 types of fruits, O. oophilus displayed marked discrimination between fruits, but the preferences varied with season and locality. The most consistent preference was for Averrhoa carambola in north Queensland. O. oophilus showed no preference for operating in the more highly infested fruits of any of the six fruit types tested.

The maximum dispersal recorded of a population of O. oophilus from a liberation site was 5 miles, 46 months after establishment.

A review of climatic factors indicated that winter temperatures of 60°F or less were unfavourable to the persistence of O. oophilus.

The presence of O. oophilus was not associated with a reduction in the degree of infestation of fruits. It is suggested that this is contributed to in the north, where climatic conditions for the parasites are favourable, ,by the presence of abundant fruits which are infested by Dacinae but not favoured by the parasite.