The family of tephritid fruit flies is very large and contains about 5000 described species. Many species are of major economic importance in agriculture. Some have negative effects, some positive. Various species cause extensive damage to fruit and other plant crops. The genus Bactrocera is globally known for its destructive impact on agriculture. The high morphological similarity between many tephritid species makes identification notoriously difficult and species boundaries are hotly debated.
About 350 species are considered economically important and most of them belong to five genera: Anastrepha, Bactrocera, Ceratitis, Dacus, and Rhagoletis.
China is a globally significant importer of fresh produce; hence, fruit flies are of particular concern. The very large trade of fresh commodities into China, the country’s range of climatic conditions which make it suitable for most exotic fruit fly species, and the economic and social importance of its domestic fresh-commodity production, means that exotic pest fruit flies pose a continual and high profile threat to the country. Intercept information from Chinese ports in the last ten years show that fruit flies have been intercepted from baggage and cargo on a staggering 19000 occasions, with each interception consisting of one or more individuals.
Due to the increasing number and diversity of intercepted fruit flies, a high-throughput method combined with high accuracy, high speed, and low cost has become a necessity not only for China, but all major trading countries. A group of Chinese researchers developed a promising approach to this challenge. They designed species-specific qPCR primer and probe combinations for 27 economically important tephritidae species of the six genera mentioned above. The probes were designed using some 1000 DNA barcodes of fruit fly species available on BOLD. Each primer pair was tested through qPCR. In a follow-up step the colleagues developed a standardized reaction system for detecting all target species based on a microfluidic dynamic array, and also applied the method to identify unknown immature samples from port interceptions and field monitoring.
They were quite successful and were able to properly detect all 27 species in a rather short time (7.5h), using only 0.2μl of reaction system in each reaction chamber. All intercepted specimens were correctly identified which they confirmed by rearing and morphological identification of adults.
Microfluidic dynamic arrays have been used in a number of novel applications, such as medical diagnosis, gene expression, genotyping, and GMO analysis but it has not been applied for species detection in plant quarantine and invasion biology, where it offers great potential for high-throughput and species diversity screening. Available chips can perform as many as 9000 reactions in a single run which makes high-throughput screening a realistic prospect.