Pests > Pest Management > Biological control > Fruit flies > Fopius arisanus, introduce or not, Palau

Pests > Pest Management > Biological control > Fruit flies > Fopius arisanus, introduce or not, Palau

Pests Pest Management Biological controlFruit flies Fopius arisanus, introduce or not, Palau

Biological control of fruit flies

March 2000. Sometimes decisions regarding the introduction of biological control organisms are difficult because of their complexity. In 2000, Palau reported the following. In order to assist in attempts to eradicate the Oriental Fruit Fly, Bactrocera dorsalis, it was suggested that the country introduce the fruit fly parasite, Fopius arisanus, from Hawaii. The parasite is not host specific, although its range is limited to several fruit fly species. It was anticipated that the parasite would significantly reduce numbers of B. dorsalis and facilitate the eradication of the pest fruit fly.

This parasite was released in Pohnpei, FSM, several years ago to control the fruit fly B. frauenfeldi, but its impact on the abundance of this pest has not yet been assessed.

However, Palau has recently introduced the phytophagous gall fly, Procecidochares connexa, against Chromolaena odorata, a serious weed in Micronesia, Australia and PNG. The fly has established, but it was yet too early to assess its impact on the weed. As the fly belongs to the Tephritidae and is, therefore, closely related to Bactrocera spp. there is a chance that Fopius arisanus may also attack the biocontrol agent for Chromolaena.

At that time, The University of Hawaii was undertaking research into the non-target effects of exotic parasitoids, which have the potentail to be a serious problem. The research was aimed at assessing the unintended impacts of previously introduced fruit fly parasitoids in Hawaii, looking both at native Hawaiian Tephritidae, as well as at exotic Tephritidae introduced for weed biocontrol. Among other species of interest to the study are gall flies, Procecidochares utilis and P. alani, the congenerics of P. connexa. At the time of the message, the researchers had found no evidence that either of these two species was attacked by Fopius arisanus.

Nevertheless, the University of Hawaii suggested that some host acceptance testing be done within a quarantine facility prior to releasing F. arisanus.

The response from the Northern Territory of Australia, the Australian School of Environmental Studies, Griffith University and CSIRO Entomology, was more forthright in opposing the idea of introducing a biocontrol agent into the eradication program for the following reasons:

1) it would prolong the program while waiting for Fopius arisanus to become abundant;
2) the two programs are opposed to each other, with the eradication program continuously removing the food source of the biocontrol agent – a main factor in preventing establishment;
3) there needs to be a minimum number of flies below which the control agent cannot function effectively.

The conclusion of some was that no parasite will assist in the eradication of B. dorsalis and it would be waste of time and money to import one. B. dorsalis is so virulent that the only method to use is male annihilation plus selective protein bait spraying in breeding hot-spots. The eradication of B. papayae in North Queensland was based on this program and was successful. Other people agreed that release of the parasitoid would not by itself be sufficient to eradicate B. dorsalis, but could lead to significant reduction in fruit fly number, thus facilitating eradication through sterile male annihilation. In this case, the feasibility of introducing F. arisanus prior to eradication attempts will depend largely on the size of the B. dorsalis population.