Conservation biological control of the fruit fly parasitoid Fopiusa arisanus (Hymenoptera: Braconidae)

Abstract

Fopius arisanus is a parasitoid of Bactrocera fruit flies. In sub-tropical Australia, it can cause >30% parasitism of Queensland fruit fly, Bactrocera tryoni. There has been minimal research effort globally, and none in Australia, to determine how the abundance of this species can be maintained and increased through conservation biological control. We carried out three research activities aimed at conserving this species in a landscape: (i) testing mesh sizes for augmentoria, devices into which fallen fruit can be placed that capture emergent flies while allowing parasitoid release; (ii) investigation of the suitability of wild tobacco, Solanum mauritianum, and wild tobacco fly, Bactrocera cacuminata, as a non-crop refuge for the parasitoid; and (iii) the value of floral resources for companion planting to increase carbohydrate sources. We determined that a mesh size of approximately 2 mm² retained near 100% of fruit flies while releasing ~90% of parasitoids. A readily obtainable 50% shade cloth maintained a mesh pore of this size and was confirmed as suitable for making augmentoria. In South East Queensland, the wild tobacco/wild tobacco fly system was demonstrated to host F. arisanus continuously through the year, with an annual parasitism rate of 31%, peaking in the spring at 60%. A second fruit fly parasitoid, Diachasmimorpha kraussii, was also collected from this system, but at lower levels. Fopius arisanus were able to move >120 m from a wild tobacco patch to parasitise fruit fly-infested fruit. None of five floral resources trialled increased wasp longevity beyond the mean of 5.3 days achieved by a water-only control. When five additional fruit juice/fruit pulp resources were tested, only one increased wasp longevity, by 1.3 days, over the water-only control. In contrast, wasps fed on honey and water survived for a mean of nearly 40 days. We thus concluded that in the field F. arisanus does not gain its nutritional needs from either flowers or fruit. Augmentoria offer an easily scalable tool, suitable for backyard growers through to commercial producers, which provides the control benefits of crop hygiene while not disrupting the parasitoid cycle. Where wild tobacco can be maintained without impacting the quality of farm habitat, it has great potential as a year-round reservoir of the wasp. Companion planting to increase nectar resources is not recommended for F. arisanus conservation biological control.