Bioecology of the New Invasive Fruit Fly Bactrocera Invadens (Diptera: Tephritidae) in Kenya and its interaction with Indigenous Mango-Infesting Fruit Fly Species

Abstract

Bactrocera invadens Drew, Tsuruta & White (Diptera: Tephritidae), an alien invasive fruit fly species of Asian origin was first detected in Kenya in 2003. This pest has rapidly spread across sub-Saharan Africa and is currently reported from at least 24 countries. Because of its novelty status, there was no information on its biology and ecology that could aid development of management efforts. There was also evidence that B. invadens eo-infested the same fruits with native fruit fly species and it was speculated that this could result in competitive displacement of native fruit flies. This study, therefore, was initiated to establish the bioecology of B. invadens in Kenya and its interaction with indigenous mango-infesting fruit fly species. The first step was to identify the most suitable temperature range for development and survival of immature stages of this pest. Studies were conducted in the laboratory at four constant temperatures of 15, 20, 25, 30 and 35°C. The longest development period occurred at 15°C (75.74 days) and was shortest at 30°C (17.76 days). The optimal temperature for survival was found to be 25°C while 35°C was the most lethal temperature. Countrywide surveys were then initiated to establish the host plants of this pest. The survey revealed that B. invadens infested fourteen plant species particularly Mangifera indica L., Musa sp. AAA and citrus [c. limon (L.) Burm. f., C. sinesis (L.) Osbeck and C. reticulata BIanco.] and the wild plants Sclerocarya birrea (A. Rich) Hochst and Terminalia catappa L. In laboratory host preference studies, M indica and Musa sp. were found to be the most preferred host plants among the nine cultivated plant species tested. The spatial and temporal population dynamics of this pest was also studied and revealed that three fruit fly species infested mango namely B. invadens, Ceratitis capitata (Wiedemann) and Ceratitis cosyra (Walker). The relative abundance index (RAJ) of these pests in infested fruit was in the order B. invadens > C. cosyra > C. capitata which was similar to the indices of adult population obtained by trapping. Percent fruit fly infestation and B. invadens fruit fly density was found to be always higher in mango on the ground than on the trees, demonstrating that mango fruits that fall to the ground serve as a major breeding site and may be a reservoir of non-immigrant B. invadens population in mango orchards in Kenya. The efficacy of the Easy, Multilure and Lynfield traps all baited with Nulure, Torula Yeast, Corn steepwater and a locally produced yeast product for trapping B. invadens was also evaluated. The multilure trap baited with torula yeast or nulure wasthe most attractive trap-bait combination and captured 19.7-30.3 B. invadens/trap/day and 10.54 -22.97 flies/trap/day respectively. In interspecific competition studies, there were significant differences in the larval developmental time, weight of puparia and number of adults that emerged of B. invadens, C. capitata and C. cosyra when the insects were sequentially eo-infested on rearing medium at constant temperatures. When B. invadens was introduced into whole fruit before C. cosyra, the number of emergent adults of the latter was greatly suppressed. Higher number of C. capitata adults was, however, recovered when in cross infestation with B. invadens particularly in the treatments where C. capitata had a two or three days head start. This study demonstrated that the mechanisms contributing to the displacement of C. cosyra by B. invadens may be associated with intricate interactions between resource pre-emption and fluctuations in temperature in mango agroecosystems.