The fruit industry's big problem


Fruit flies are a major threat to fruit production because infested fruit cannot be sold and production costs increase due to costly management techniques, resulting in increased fruit prices. Countries that do not have fruit flies are also less likely to import fruit from countries with fruit flies for fear of importing these insects along with the fruit. Preventing fruit from being infested so that it can be exported remains an important challenge to fruit farmers.

South Africa is home to a number of species of fruit fly, three of which - the Mediterranean fruit fly (med-fly); the marula fruit fly; and the Natal fruit fly - are of economic significance owing to their ability to disrupt fruit production and cause export restrictions. It is estimated that crop losses and pest control costs resulting from fruit flies amount to more than R20 million per year in the Western Cape alone.


Dr Chris Weldon, of the Department of Zoology and Entomology at the University of Pretoria, is researching the prevalence of fruit flies and how certain species are able to tolerate certain weather conditions better than others, particularly hot, dry temperatures resulting from climate change. His study looks at how med-flies specifically have adapted, by doing a comparative study of the three indigenous South African flies. As a result of the fruit trade, the med-fly has the widest distribution of any fruit fly in the world and has successfully established themselves in various climates.

Fruit flies lay their eggs in specific types of fruit. The commercially grown fruits that are most affected by these flies include citrus and deciduous fruit. The med-fly has a much wider host range than the other two South African fruit flies, which has contributed to its vast distribution range.


Med-flies are proving to be desiccation tolerant, meaning that they are able to endure extremely dry weather conditions. It seems that as long as there is some source of water, the med-fly can survive. Dr Weldon's research found an interesting reason for the med-fly's ability to tolerate dry conditions: It is able to break down its stored body fat and metabolise it, thus releasing water. To date, he has not been able to find this phenomenon in the other two species. He hopes to extend this research to look at the pathways by which insects lose water and how South African fruit flies differ in this regard.

Dr Weldon notes that although South Africa's current control strategies are working well, in view of the insects' remarkable ability to adapt to changes in the environment, it is important to constantly improve on control systems.

Published by Srinivasu Nadupalli

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