Genetic diversity and insecticide resistance of fruit flies in selected mango-growing agro-ecological zones of Uganda

Abstract

Fruit flies (Tephritidae) represent a major constraint to mango production and export in Uganda, causing direct fruit damage and leading to frequent export rejections. Accurate species identification is essential for effective pest management, yet studies in Uganda have been limited and primarily relied on morphological methods, which are prone to misidentification. This study employed an integrated approach combining morphological and molecular techniques to assess fruit fly diversity and investigate potential insecticide resistance. Biological surveys were conducted on 20 mango farms across seven districts in Uganda’s two main mango-growing agroecological zones. A total of 256,107 fruit flies were trapped using different lures targeting Bactrocera, Ceratitis, Dacus, Zeugodacus, and other fruit fly species. Morphological identification of the fruit fly species was conducted at Makerere University’s Crop Science Laboratory, followed by PCR confirmation at COVAB’s Research Centre for Tropical Diseases and Vector Control (RTC Lab), and Sanger sequencing at Inqaba Biotec in South Africa. In addition, this study examined the presence of target-site mutations in the ace gene region (214ace), which may confer resistance to organophosphate insecticides, the very widely used class in Uganda. Eleven taxa were identified to the genus level, including Ceratitis, Carpomya, Dacus, Rhagoletis, and Zeugodacus. A total of 21 putative species were documented. Ten were confirmed to species level i.e., Bactrocera dorsalis, Ceratitis capitata, C. cosyra, C. anonae, Dacus punctatifrons, D. bivittatus, D. eclipsis, D. humeralis, D. armatus, and Zeugodacus cucurbitae. Notably, D. eclipsis, D. humeralis, and D. armatus were recorded in Uganda for the first time. Bactrocera dorsalis was the most abundant (95.1%) and widely distributed species, followed by D. eclipsis and D. punctatifrons. These findings reveal a high diversity of fruit fly species in Ugandan mango orchards, underscoring the need for continued monitoring and integrated pest management strategies. No missense mutations linked to resistance were detected in the analysed species, suggesting that the observed species diversity and abundance are not related to mutations in this gene region. However, in D. armatus, a substitution was observed at the 148th position of ORF1, with thymine (T) replacing adenine (A), resulting in a TTG codon (leucine) instead of ATG (methionine). This difference may reflect species-specific genetic variation compared to other Dacus and Zeugodacus species. Absence of mutations linked to resistance means that farmers can continue using organophosphates in an integrated pest management system.