Abstract
Avocado (Persea americana) fruits are an important source of income and a nutritious food for small-scale growers and other stakeholders involved in farming along the Afrotropical highlands of Taita Hills and Mount Kilimanjaro in Kenya and Tanzania, respectively. Avocado fruits are infested by several insect pests, namely the Asian invasive fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), and the false codling moth, Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae). However, there is inadequate information on the distribution patterns of these pests in small-scale avocado cropping systems in the East African highlands. This study was initiated to generate a spatial distribution map of B. dorsalis and T. leucotreta in avocado orchards at Taita Hills and Mount Kilimanjaro in Kenya and Tanzania, respectively. The two pests were monitored by using their respective parapheromone lures for two years between August 2012 and July 2014. Fruit damage was assessed by computing the proportion of infested fruits for B. dorsalis, whereas the damage score was used for T. leucotreta. Our results indicated that the mean number of B. dorsalis per trap per day differed significantly across elevation, being highest in lowland zone for both Taita Hills (15.90) and Mount Kilimanjaro (24.45). Similarly, the percentage infestation of ground collected fruits by B. dorsalis varied with altitude, being lowest at highlands above 1500 m.a.s.l. (0.66% and 0.83% for Taita Hills and Mount Kilimanjaro, respectively). Conversely, the mean number of T. leucotreta did not vary with altitude in either study area. However, the damage score for T. leucotreta infestation was significantly lower in the highlands of both transects (7.0% and11.1% for Taita Hills and Mount Kilimanjaro, respectively). These findings describe spatial trends that are important in formulating strategies aimed at suppressing the populations of B. dorsalis and T. leucotreta in East African avocado cropping systems.
Highlights
Kenya is one of the major avocado-growing countries in Africa, with an annual production of 186,292 metric tonnes, while Tanzania witnessed a 20% growth in avocado production between2005 and 2012 [1,2,3,4,5,6]
The mean number of B. dorsalis per trap per day was different across elevation for both transects, Taita Hills (χ2 = 137.03, df = 2, p < 0.0001) and Mount Kilimanjaro (χ2 = 7.12, df = 2, p = 0.03), being highest at the lowland zone (15.90 ± 1.5 and 24.45 ± 2.9 B. dorsalis/trap/day for Taita Hills and Mount Kilimanjaro, respectively) (Figure 2)
Comparing fruits damaged by B. dorsalis in the same altitudinal zone of the two transects, the percent infestation was comparable for all agro-ecological zones for both fruits picked from the tree (V = 1069.5, n = 60, p = 0.2537; V = 357, n = 60, p = 0.1581 and V = 353, n = 60, p = 0.1469 for low, medium, and high elevations, respectively; Figure 3a) and ground collected (V = 1098, n = 60, p = 0.1771 and V = 294, n = 60, p = 0.8056 for low and high elevations, respectively; Figure 3b), except for the fruits collected
Summary
Kenya is one of the major avocado-growing countries in Africa, with an annual production of 186,292 metric tonnes, while Tanzania witnessed a 20% growth in avocado production between2005 and 2012 [1,2,3,4,5,6]. Bactrocera dorsalis and Thaumatotibia leucotreta cause tremendous yield losses of various fruit crops including avocadoes [10,11,12,16,17,18,19]. Both B. dorsalis and T. leucotreta are considered A1 quarantine pests because of the enormous losses they inflict due to direct infestation of fruits and quarantine restrictions imposed by importing countries [19,20,21]. The invasion of B. dorsalis in Kenya and Tanzania led to a loss of the avocado export market to South Africa in 2007, causing revenue losses of US$1.9 million [20] with cumulative losses amounting to $15.2 million by the end of 2014 [12]
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