This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Queensland is a major producer of strawberries in Australia, mainly providing a winter product for domestic markets, though the production season usually starts in May and finishes in October. Queensland fruit fly (Bactrocera tryoni) is a market access impediment for Queensland strawberries because this endemic quarantine pest can use strawberries as a host. The Market Access Team of Agri-science Queensland has recently completed a research project (BS06002) to assess the risk of fruit fly infestation in strawberries from south east Queensland and to test the efficacy of bait treatments with Naturalure® (Dow AgroSciences) as an alternative to dimethoate sprays for the preharvest control of fruit flies in strawberries. Field trials were conducted on multiple commercial farms in the production season of 2008 and 2009 respectively.

Cue-lure traps were used to monitor the activity of male fruit flies over the production season of 2008 and 2009. Trap catches of male fruit flies were very low between May and mid-September in 2008, though in 2009 significant increases occurred since mid-August. During the 2009 season, McPhail traps were also set up in the field to monitor female fruit fly activity. No female flies were trapped until mid-August and the majority of these early trapped female flies were reproductively immature. The seasonal pattern of activity and reproductive maturation in Queensland fruit fly was related with seasonal changes in environmental temperature. Likewise, assessments of strawberry samples have shown that the risk of fruit fly infestation in strawberries was very low in May, June, July and early August, probably due to low temperatures at this time of year being unfavourable for fruit fly activity and maturation. However, the reproductive maturation of female fruit flies as enhanced by warm temperatures in spring could increase the risk of infestation in strawberries, especially when the pest activity/abundance was high under favourable conditions.

The efficacy of current bait treatments to control fruit flies in strawberries was not adequate, probably due to low attraction of baits applied on plastic mulch. Queensland fruit fly originally inhabited rainforest, and the female flies prefer to shelter and forage food in trees and shrubs. Considering the biology and foraging behaviour of Queensland fruit fly, the method of bait application needs to be modified by applying bait to fruiting trees and other windbreak plants on a farm wide scale, as well as border trap crops wherever practically feasible. Furthermore, our experience with previous field trials suggests that hygiene practices such as removing abandoned fruiting blocks and residual host fruit on strawberry farms will benefit to bait treatment by reducing fruit fly pressure. Therefore, it is recommended that further trials be carried out to optimise the baiting system as a pre-harvest control measure against fruit flies in strawberries.