Browsing by Author "Isabirye, B.E."

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    Geometric Morphometrics of Geographic and Host-Associated Population Variations of Bactrocera Invadens in Uganda
    (AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA, 2014) Isabirye, B.E.; Masembe, C.; Nankinga, C. K.; Muyinza, H.; Akol, A. M.
    Fruit flies (Diptera: Tephritidae) are among the most economically important pests of edible fruits worldwide. Because of the cryptic nature of most species in Bactrocera complex, it is not clear whether allopatric and host associated speciation has taken course among B. invadens populations in the different zones in Uganda. This would be important in the design of efficient management strategies. The morphological variation of 3 allopatric and host-associated populations of B. invadens was studied using Euclidean distance matrix analysis and variance structure coordinate system geometric morphometrics techniques. Size and shape were analyzed throughout 15 landmarks for 360 specimens after symmetrization process. Host type significantly affected wing size and shape (P = 0.0001), with CVA showing host population discrimination with very high degree of population classification (95.03%) accuracy. Mango wings were significantly smaller than tropical almond, but the former did not significantly differ with guava. Similarly, mean wing size and shape among the three zones differed significantly (P = 0.000). B. invadens from the WMHF had relatively bigger wings, while the NMF recorded the smallest wings. CVA discriminant functions showed a very high degree of zonal population classification (95.48%) accuracy. LVC population wing shape was significantly different from NMF (P = 0.000) and WMHF (P = 0.000), while the latter two were also different (P = 0.000). There were significant differences in allometry and developmental instability fluctuating asymmetry among fruit hosts in the order: mango > guava > almonds. The results have added to the evidence that geographic and host-associated adaptation can produce reproductive isolation and produce ecotypes. The ability of B. invadens to undergo rapid ecological evolutionary radiations might affect the efficiency of common control methods, and our results should help to recast fruit fly management strategies.
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    Modeling the Potential Geographical Distribution and Ecological Niche of Selected Fruit Fly (Diptera: Tephritidae) Species in Uganda
    (Journal of Plant and Pest Science, 2015) Isabirye, B.E.; Masembe, C.; Akol, A.M.; Muyinza, H.; Rwomushana, I.; Nankinga, C.K.
    Despite their overwhelming economic importance, efforts to assess the distribution of fruit flies (Diptera: Tephritidae) in Uganda have been minimal. Consequently, in this study, potential geographical distributions and climatic envelopes of 10 selected fruit fly species were modeled. Two presence-only predictive models namely, Maxent and Bioclim, were run using 19 bioclimatic parameters at a resolution of 30 arc seconds. New detections and existing records of fruit flies were used in the model. The climatic profiles of the selected fruit flies were described and the relative importance of the bioclimatic variables was explored. There was a close agreement between the two models about the distribution and suitability patterns matching the main fruit agro ecological zones. Precipitation (PC-1 = 61.4190%) and temperature (PC-2 = 29.214%) significantly shaped fruit fly niches across the country. Central and mid north zones provided the most suitable niches, while the western, northeastern and areas around Albert Nile were characterized as marginally suitable. The models were mostly robust in performance (AUC: 0.815 – 0.974), with model test performance ranging from random (C. capitata: 0.486) to excellent (C. cosyra: 0.965). Predicted marginal sites, such as higher altitude zones matched negative areas of the models, which reflected higher model prediction abilities. These results provide an initial insight into the bioclimatic tolerance ranges of fruit flies in Uganda and should assist in identification of sites for future sampling efforts and fruit fly management planning.
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    Oviposition Preference and Offspring Performance in Phytophagous Fruit Flies (Diptera: Tephritidae): The African Invader, Bactrocera invadens
    (International Research Journal of Horticulture, 2013) Akol, A. M.; Masembe, C.; Isabirye, B.E.; Kukiriza, C. K.; Rwomushana, I.
    Behavioral choices have been hypothesized to reflect fine-tuned evolutionary adaptation by the preference-performance hypothesis (PPH), which states that female insects will evolve to oviposit on hosts on which their offspring fare best. The extent to which this is true in the African invader, Bactrocera invadens (Diptera: Tephritidae) was assessed in this study. Five host-plant species: Terminalia catappa (Combretaceae), Persea americana (Lauraceae), Psidium guanjava (Myrtaceae), Mangifera indica (Anacardiaceae), and Citrus sinensis (Rutaceae), and 11 mango varieties: Tommy, Zillatte, Keitt, Kent, Kagogwa, Apple, Palvin, Dodo, Kate, Biire and Glen, were tested for their conformity to the PPH. The fruits were incubated, larvae reared, and the adults maintained on an artificial diet in the laboratory. There was significant variability in host species (P = 0.038) and variety (P = 0.015) preference in the orders: T.catappa > P.guanjava > M. indica > C. sinensis > P.americana; while Glen & Biire and Zillate & Tommy were the most and least preferred varieties, respectively. Offspring performance (development rate, survival, weights and sex ratio) differed significantly and followed a very similar trend only that for fruit species P.americana performed better than C. sinensis. The relationship between host preference and the offspring performance measures showed strong support for the PPH with overall coefficient of determination of 75.4% (P = 0.000) and 65% (P = 0.003) for host species and varieties, respectively. This study has generally increased the knowledge on the role of host species and varieties on the biology of the pest and re-affirmed the growing credence that host-specific variation in adult performance has an important role in shaping host preference of phytophagous insects, as proposed by PPH.
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    Species Composition and Community Structure of Fruit Flies (Diptera: Tephritidae) across major Mango-growing Regions in Uganda
    (International Journal of Tropical Insect Science, 2015) Isabirye, B.E.; Akol, A.M.; Mayamba, A.; Nankinga, C.K.; Rwomushana, I.
    The species diversity of tephritid fruit flies in major mango-growing regions in Uganda was monitored over a 2-year period (2010–2012) using fruit bait and lure traps. A total of 368,332 specimens belonging to 10 species in four genera (Bactrocera, Ceratitis, Trirhithrum and Dacus) were collected. Of these, 98.9% belonged to Bactrocera invadens, while the second and third most common species were Dacus bivittatus (0.4%) and Ceratitis anonae (0.3%), respectively. Significant differences in the evenness and diversity of fruit fly species were noted across the regions. Fruit fly community structure was significantly different across the three regions. The Lake Victoria Crescent and Mbale Farmlands harboured significantly more D. ciliatus, T. coffeae, D. bivittatus and B. cucurbitae in contrast to the Northern Moist Farmlands and the Western Medium High Farmlands. Ceratitis rosa contributed the highest difference in regional structure, followed by C. fasciventris and C. cosyra. Rank abundance curves depicted a geometric series distribution of the species composition in the three regions, confirming a scenario of competitive displacement of native fruit fly species by B. invadens. A comprehensive and sustainable response strategy to B. invadens and other fruit flies needs to be urgently devised to protect the horticulture industry in Uganda.