Friday, October 31, 2014

...and then there were two

The tephritid fruit fly genus Bactrocera is very large and contains about 500 described species. One of those, the oriental fruit fly, Bactrocera dorsalis, is considered a very destructive pest of fruit in all areas it occurs. It is established in numerous regions in Asia, and is often intercepted in the United States, sometimes reestablishing infestations that were previously eradicated. 

The species belongs to a species complex that contains almost 100 morphologically very similar taxa. Most species in this complex are of no economic concern; however, the oriental fruit fly and four of its closely related species, namely the Asian Papaya fruit fly, Bactrocera papayae , the Philippine fruit fly, Bactrocera philippinensis , the Carambola fruit fly, Bactrocera carambolae, and the Invasive fruit fly, Bactrocera invadens, belong to the world's most important horticultural pests.

The high morphological and even genetic similarity between all these species makes identification notoriously difficult and species boundaries were hotly debated. Reason enough to start a multidisciplinary approach to solidify taxonomic reassignments. Such an integrative taxonomic study has now been published by a large group of researchers. They provide multiple lines of evidence across a range of disciplines (morphology, molecular genetics, cytogenetics, sexual compatibility, chemoecology) undertaken by independent research groups spanning a period of 20 years. Based on their evidence  they actually propose the synonymy of Bactrocera papayaeBactrocera invadens, and Bactrocera philippinensis under the senior name Bactrocera dorsalis. Bactrocera carambolae on the other hand is still considered a valid species.

That leaves us with the question on the actually impact of these results. The authors have a lot to say about that as they think the impact of the name changes are significant:

Currently, the distributions of B. dorsalis complex species dealt with in this paper are almost entirely disjunct, with most countries having only one of the species (Thailand is unique in having three – B. dorsalis, B. papayae and B. carambolae). Under the rules of the International Plant Protection Convention, a country with one of the species but not another has a sovereign right to impose risk reduction treatments on commodity imports from a country with another pest member of the B. dorsalis complex species; this reality severally restricts trade for many nations. Recognition that B. dorsalis, B. invadens, B. papayae and B. philippinensis are one species will ease restrictions to fresh commodity trade between countries where these are native or nonregulated invasive taxa.

A key element of quarantine is risk assessment. As demonstrated by Hill & Terblanche (2014), basic quarantine issues such as enhanced predictive power to determine the likely spread, and ultimate distribution, of invasive members of the B. dorsalis complex are greatly improved by accurately recognizing species boundaries.

Pest management
Many pest management tools will be improved by resolving the species limits, of which application of the SIT [Sterile Insect Technique] is one. The SIT requires mass release of sterilized male flies to mate with, and so make infertile, wild conspecific females. A great body of SIT knowledge exists for B. dorsalis, but much less so for the other members of the complex. The recognition of conspecificity among key pest taxa within the complex will allow B. dorsalis SIT to be applied in new countires and regions.

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