Abstract
Oecophylla ants are appreciated for their control of pests in plantation crops. However, the ants´ nest building may have negative impacts on trees. In this study we tested the effect of ant densities and nest building on the leaf performance of mango trees. Trees were divided into three groups: trees without ants, trees with low and trees with high ant densities. Subsequently, the total number of leaves, the proportion of leaves used for nest construction, and tree growth was compared between these groups. The percentage of leaves used for nests was between 0.42-1.2 % (mean = 0.7%±0.02) and the total number of leaves and tree growth was not significantly different between trees with and without ants. Further, leaf performance was compared between shoots with and without ant nests and between leaves in or outside ant nests. The number of leaves and lost leaves per shoot, leaf size, leaf condition (withered), leaf longevity and hemipteran infection was compared between groups. In the dry season nest-shoots held more leaves than shoots without nests despite nest-shoots showed more lost leaves. Leaves in nests were smaller than other leaves, more likely to wither and more often infested with scales. However, smaller nest-leaf size was probably due to the ants´ preference for young leaves and the higher incidence of withering resulting as leaves in nests cannot fall to the ground. In conclusion, the costs associated to ant nests were low and did not affect the overall number of leaves per tree nor tree growth.
Highlights
Among tropical fruits, mango (Mangifera indica L.) has the highest potential for food security (Vayssières et al, 2008) and incomes (Tinkeu et al, 2010) in West Africa
On the negative side, weaver ants weave leaves together (Crozier et al, 2010) and deposit territorial marking on leaves (Offenberg, 2007) which may reduce the efficiency of photosynthesis on their host plant
The number of leaves and number of nests per tree, the number of leaves used for nest construction, the number of leaves per shoot and leaf areas were transformed with Log10 [x+1] to stabilize the variance and achieve normality of the data before analysis
Summary
Mango (Mangifera indica L.) has the highest potential for food security (Vayssières et al, 2008) and incomes (Tinkeu et al, 2010) in West Africa. In Africa, Oecophylla longinoda Latreille has been detected as an effective plant protector (Way & Khoo, 1992; Dwomoh et al, 2009; Olotu et al, 2013; Anato et al unpublished data) and can increase fruit yields and/or fruit quality compared to conventional synthetic insecticides (Van Mele, 2008; Dwomoh et al, 2009; Anato et al, unpublished data). The relationship, between the ants and their host plants involve negative as well as positive aspects, from a plant point of view. Ants are engaged in mutualistic trophobiotic interactions with plant sap sucking hemipterans and may in this way indirectly damage plants (Buckley, 1987; Van Mele et al, 2007). When ants interlace leaves and turn them out of their original position, they can increase tension on the leaf petiole
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