Tanzania Journal of Agricultural Sciences 2015, Vol. 14(2) : 101-105
The objective of this was to evaluate the effect of African weaver ant (Oecophylla longinoda) on
fruit fly disease-inflicted postharvest losses of oranges in small-scale farming in Coast region,
Tanzania. The treatments consisted of weaver ant population estimated based on the number of
nests (0, 2, 5 and 8) of weaver ants per tree and each was replicated three times. Orange fruits were
randomly picked from farmers’ orchards at color breaker stage and were immediately transported
and placed on benches in a postharvest laboratory at Sokoine University of Agriculture with
average temperature of 19 and 28 °C during the night and day, respectively. Data were subjected
to analysis of variance using GenStat Statistical Programme 12th Edition and treatment means
separation was conducted based on LSD test at P ≤ 5 %. Results indicated that the incidence of
fruit fly infection in orange fruits significantly (P < 0.05) decreased from 0.8 to 0.4 % as weaver
ant population increased from 0 to at 2 nests per tree and the average number of pupae per fruit
decreased from 0.58 to 0.04, respectively. Similarly, orange fruit decays significantly (P < 0.05)
decreased from 20.4 to 10.2 % as weaver ant population increased from 0 to 2 nests per tree.
Specifically, the incidence of decays due to anthracnose (Colletotrichium gloeosporioides Sacc.)
decreased from 11.1 to 7.8 % and that caused by green moulds (Penicillium italicum Wehmer)
decreased from 9.3 to 2.4 % as weaver ant population increased from 0 to 2 nests per tree. It is
concluded that two nests of weaver ants per tree is an optimal population for substantial reduction
of orange postharvest losses caused by fruit fly and fungal infections. The use of weaver ants
can find wide applications in organic farming and small-scale orange farming where pesticide
application is unaffordable. As the number of weaver ants per nest may differ, further studies are
recommended to determine the actual number of weaver ants that can effectively reduce fruit fly
and disease-inflicted decays, particularly in small-scale mixed cropping systems.