Bactrocera environmental niche modelling

Fruit flies are major economic pests through the world, causing huge economic losses to production of a wide range of commercial fruits. Some of the most notorious invasive species are found in the family Tephritidae, many of which cause widespread damage through puncturing fruit during egg laying and then larvae subsequently developing within the fruit. Climatic suitability is a major driver of invasion success and helps to determine ecological overlap between similarly related species. As many of the tephritids are highly invasive, we need tools to understand the role that climate plays in their pest status and determining spread.

The recent spread of Bactrocera invadens is of concern to many different fruit industries and requires that we understand the potential distribution of this species. There are also questions surrounding the taxonomy of this species, and it is likely that it is in fact Bactrocera dorsalis from Asia even though it has been described separately.

There is good distribution information available for both of these species, which allows for correlation with broad climatic variables to understand limits to distributions. This has lead to modelling attempts for both of these species. However, in both cases they were considered separate species and in doing so it is likely that the full extent of the potential geographic distribution has been underestimated.

It was thus important to examine the species both separately and as one, together with new distribution information describing the recent range expansion of B. invadens in southern Africa. We combined distribution modelling techniques with quantitative niche metrics and environmental overlap analyses to examine ecological similarities between these two fruit flies.

Both B. invadens and B. dorsalis are highly overlapping in environmental space and are largely able to predict the range of the other (although B. dorsalis has much better ability in projecting to the geographic range of B. invadens). We also found that B. dorsalis was better able to predict the incursion in South Africa and this is likely to reflect an ongoing range expansion of B. invadens. That is, B. invadens is still filling its potential geographic range in South Africa.

These results support the growing body of evidence that they are in fact the same species, and requires that further studies are now undertaken to translate the invasion potential generated from this study into proper risk assessments for South Africa so that targeted management strategies may be implemented.