Abstract
The Carambola fruit fly, Bactrocera carambolae, is an invasive pest in Southeast Asia. It has been introduced into areas in South America such as Suriname and Brazil. Bactrocera carambolae belongs to the Bactrocera dorsalis species complex, and seems to be separated from Bactrocera dorsalis based on morphological and multilocus phylogenetic studies. Even though the Carambola fruit fly is an important quarantine species and has an impact on international trade, knowledge of the molecular ecology of Bactrocera carambolae, concerning species status and pest management aspects, is lacking. Seven populations sampled from the known geographical areas of Bactrocera carambolae including Southeast Asia (i.e., Indonesia, Malaysia, Thailand) and South America (i.e., Suriname), were genotyped using eight microsatellite DNA markers. Genetic variation, genetic structure, and genetic network among populations illustrated that the Suriname samples were genetically differentiated from Southeast Asian populations. The genetic network revealed that samples from West Sumatra (Pekanbaru, PK) and Java (Jakarta, JK) were presumably the source populations of Bactrocera carambolae in Suriname, which was congruent with human migration records between the two continents. Additionally, three populations of Bactrocera dorsalis were included to better understand the species boundary. The genetic structure between the two species was significantly separated and approximately 11% of total individuals were detected as admixed (0.100 ≤ Q ≤ 0.900). The genetic network showed connections between Bactrocera carambolae and Bactrocera dorsalis groups throughout Depok (DP), JK, and Nakhon Sri Thammarat (NT) populations. These data supported the hypothesis that the reproductive isolation between the two species may be leaky. Although the morphology and monophyly of nuclear and mitochondrial DNA sequences in previous studies showed discrete entities, the hypothesis of semipermeable boundaries may not be rejected. Alleles at microsatellite loci could be introgressed rather than other nuclear and mitochondrial DNA. Bactrocera carambolae may be an incipient rather than a distinct species of Bactrocera dorsalis. Regarding the pest management aspect, the genetic sexing Salaya5 strain (SY5) was included for comparison with wild populations. The SY5 strain was genetically assigned to the Bactrocera carambolae cluster. Likewise, the genetic network showed that the strain shared greatest genetic similarity to JK, suggesting that SY5 did not divert away from its original genetic makeup. Under laboratory conditions, at least 12 generations apart, selection did not strongly affect genetic compatibility between the strain and wild populations. This knowledge further confirms the potential utilization of the Salaya5 strain in regional programs of area-wide integrated pest management using SIT.
Highlights
Bactrocera carambolae Drew & Hancock, the Carambola fruit fly, is a key insect pest belonging to the B. dorsalis species complex (Diptera, Tephritidae)
The values of genetic variation of three B. dorsalis populations, two unidentified populations, and the Salaya5 colony (SY5) strain were in the same range as B. carambolae
We found that the SY5 strain had genetic variation, population structure, and genetic similarity comparable to B. carambolae, rather than B. dorsalis, in Southeast Asia
Summary
Bactrocera carambolae Drew & Hancock, the Carambola fruit fly, is a key insect pest belonging to the B. dorsalis species complex (Diptera, Tephritidae). Bactrocera carambolae was reported in other areas of South America: in 1986 in French Guyana (approximately 200 km from Paramaribo); in 1993 in Orealla, Guyana, at the border of Suriname (approximately 220 km from Paramaribo); and in 1996 in the Brazilian city of Oiapoque at the border with French Guyana (about 500 km from Paramaribo) (Malavasi et al 2000, 2013). Bactrocera carambolae is regarded to be a polyphagous pest It has a broad host range, including wild and cultivated fruits such as star fruit, mango, guava, and grapefruit (van Sauers-Mullers and Vokaty 1996, EPPO 2014). Host plants for the fly were occasionally observed to be different between native and introduced areas as reported by van Sauers-Muller (2005).
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