A phytosanitary breakthrough that eliminates fruit flies can give South African blueberry producers access to markets in the East. This development will sustain the local industry’s growth and boost rural economies and employment.
The world is going mad over blueberries. According to Berries ZA, SA exported 15 800 tonnes of blueberries in the 2020/21 season (up 30% from the previous season’s 12 282 tonnes). This set a new industry record.
Global demand for blueberries, fuelled by the fruit’s well-marketed health properties, has grown by 12% annually since 2013, according to the International Trade Centre. Packed with antioxidants purported to help prevent cancer, diabetes, heart disease and other ailments, blueberries’ popularity is expected to continue.
Almost 70% of SA’s blueberries are destined for export markets. The UK imported about 46% of our local production last year, with the rest of Europe accounting for another 46%.
The popularity of locally grown blueberries is due to great varieties and high quality fruit, and the fact that SA is closer to Europe and the UK than our main competitors, namely, Peru and Chile. In addition, SA’s blueberry production coincides with the off-season in the export market (which guarantees demand).
Less than 5% of South African blueberries currently goes to markets in the Far East, and producers do not yet have access to the Chinese market. A recently completed study into cold treatment against fruit flies will hopefully change this.Read More
With each hectare resulting in direct employment of 2.64 fulltime equivalent workers, blueberries are the most labour intensive crop of all the major fruits grown in SA.
Fruit flies are considered a phytosanitary threat to countries where they do not occur naturally. Although blueberries are not a natural fruit fly host, they can support populations of the pest. It is therefore necessary to find a mitigating treatment that gives import markets peace of mind.
Cold sterilisation is commonly used to eliminate insect pests on fruit without causing damage to the produce. The challenge was to determine the efficacy of cold treatment to rid blueberries of possible fruit fly infestations.
Dr AB Ware, director at Agri-Biotech Research Consultancies, registered a project to undertake the necessary research with funding support from the Post-Harvest Innovation (PHI) Programme and the South African Blue Berry Producers’ Association. The entities each contributed R689 250 towards the project.
Between October 2019 and November 2020, Dr Ware conducted a four-phase research study.
In the first phase, he inoculated five different blueberry species, Mediterranean (Ceratitis capitata) and Oriental (Bactrocera dorsalis) fruit fly. The fruit had been kept under cold storage conditions but, once inoculated with fruit fly eggs, were stored at an ambient temperature of 26 °C.
Following inoculation, a subsample of fruit was dissected daily to determine the number of immature life stages (eggs and three larval life stages) present in the berries. The experiment was repeated three times for each of the two fruit fly species.
Phase two of the study determined the life stage during which a fruit fly can best tolerate cold. This was done by subjecting eggs, young larvae and mature larvae of both fruit fly species to various periods of cold.
In phase three, the cold treatment period that would achieve a 99,9% mortality rate was determined. Using the results of phase two, the larvae in the fruit were allowed to develop at 26°C to the most cold-tolerant life stage. A control sample was kept at 26°C, while the rest of the fruit was transferred into the cold chamber. The control fruit was dissected within 24 hours. Every three days, a sample of the chilled fruit was removed and placed at 26°C for 24 hours before being dissected. By counting the number of live and dead larvae, the 99,9% mortality treatment was determined mathematically.
The final phase involved validation to a Probit-9 level of disinfestation. Three replicates of approximately 10 000 individuals each at a very low temperature were done. After a set period of disinfestation at this temperature, the fruit was removed and placed at 26°C for 24 hours before dissection to determine the number of living larvae. The experiment was controlled using insect-containing fruit that had not been chilled.
“In the study, sterilisation at a low temperature for a set number of days killed all 49 488 third-instar larvae in the blueberries that were subjected to the treatment,” says Dr Ware. In both fruit fly species tested in the study, mature C. capitata larvae proved to be the most cold-tolerant. Hence, it can be safely deduced that cold sterilisation will be as effective against Bactrocera dorsalis fruit flies.
“This degree of efficacy, combined with the fact that blueberries are not a natural fruit fly host, should satisfy the concerns of most importing authorities,” concludes Dr Ware.
Photography by PETER STEPHEN | RESEARCH INTERNATIONAL (1,2) and DR A. B. WARE (3)