Abstract
Managed populations of weaver ants in mango trees have been used successfully in Australia, SE Asia and parts of Western Africa to deter fruit flies from ovipositing in ripening fruits. The presence of indigenous weaver ants in mango trees of smallholder growers in Tanzania offers the possibility of exploiting them as an affordable, environmentally -friendly method to improve marketable fruit yield and quality. In a preliminary interview study in a mango-growing region of rural Tanzania, the farmers were not convinced of any beneficial, deterrent effect attributable to the indigenous weaver ants in their trees and were sceptical of any likely value as a biological control technique. Additionally, fruit fly infestation was not seen as a priority problem and subsequent enquiry and investigation showed that, fortuitously, traditional, local practices for storage and enhancing ripening prevented the development of a significant proportion of any deposited eggs. Subsequent field studies supported the grower perceptions as they recorded only an erratic and limited deterrent effect.
Highlights
Fruit flies are responsible for the economic loss of a significant proportion of the commercial and livelihood mango crop in Africa with fruit infestation ranging from 5% to 100% depending on climate, locality, mango variety and season (Lux, Ekesi, Dimbi, Mohamed & Billah, 2003; Niyibigira, Lada & Abdullah, 2003; Vayssiéres, Goergen, Lokossouy, Dossa & Akponon, 2009; Vayssières, Korie & Ayegnon, 2009; Vayssières et al 2009)
The widespread scepticism in Kiroka concerning any positive impact of weaver ants on fruit fly activity, together with the view that any commercial impact of fruit flies was limited, would seem to make this aspect of biological control a poor candidate for adoption in the region
Eleven of the 13 mango growers with ant-colonised trees and 3 of the 4 mango pickers interviewed did not believe that weaver ants had any effect on the fruit fly infestation level, which is comparable to a study in Guinea where none of 88 growers mentioned weaver ants as beneficial with respect to fruit flies (Van Mele, Camara & Vayssieres, 2009), and in Vietnam where only 2 of 93 growers mentioned the ants as beneficial (Van Mele, Cuc & Van Huis, 2001)
Summary
Fruit flies are responsible for the economic loss of a significant proportion of the commercial and livelihood mango crop in Africa with fruit infestation ranging from 5% to 100% depending on climate, locality, mango variety and season (Lux, Ekesi, Dimbi, Mohamed & Billah, 2003; Niyibigira, Lada & Abdullah, 2003; Vayssiéres, Goergen, Lokossouy, Dossa & Akponon, 2009; Vayssières, Korie & Ayegnon, 2009; Vayssières et al 2009). Local markets may tolerate a very limited number of hatched larvae in some fruits that can be used, in part, for juice production but, generally, infestation makes fruit unsaleable. In Eastern Africa some 80% of the mango production is by small-scale growers and is predominantly destined for local markets, and the generated income is important for the livelihood strategy of these growers (Association of Mango Growers (AMAGRO), 2011; Ekesi & Mohamed, 2011). Any control method that limits fruit fly infestation, even though it may not eradicate it, may offer a valuable, economic advantage to these smallholder growers, if the resource costs are compatible with their rural supply chain
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