| dc.description |
Cashew, Anacardium occidentale Linnaeus, is an economically important
cash crop for more than 300,000 rural households in Tanzania. Its production
is, however, severely constrained by infestation by sap-sucking insects such
as Helopeltis anacardii Miller, H. Schoutedeni Reuter and Pseudotheraptus
wayi Brown. The African weaver ant (AWA), Oecophylla longinoda Latreille, is
an effective biocontrol agent of hemipteran pests in coconuts in Tanzania; but
its efficacy for the control of sap-sucking insects, especially Helopeltis spp.
and P. wayi, has not been investigated so far in cashew crops in Tanzania.
Field trials were carried out at the Coast region of Tanzania to evaluate the
effect of seasonality and abundance of AWA on Helopeltis spp. and P. wayi.
Results showed that AWA abundance expressed, as number of leaf nests per
tree, and colonization of trails on main branches varied significantly between
cashew-seasons and off-seasons. There was a negative correlation between
numbers of nests and pest damage. AWA-colonized cashew trees had the
lowest shoot damaged by Helopeltis spp., 4.8 and 7.5% in 2010 and 2011,
respectively, compared to 36 and 30% in 2010 and 2011, respectively, in
uncolonized cashew trees. Similarly, nut damage by P.wayi was lowest in
AWA-colonized trees with 2.4 and 6.2% in 2010 and 2011, respectively, as
compared to 26 and 21% in 2010 and 2011, respectively, in uncolonized
trees. Interaction between AWA and dominant ant species, namely bigheaded
ant (BHA), Pheidole megacephala Fabricius, and common
pugnacious ant (CPA), Anoplolepis custodiens Smith, was examined because
of the implication that the dominant ant species may have on the efficacy of
AWA in its control of sap-sucking pests of cashew. Abundance of AWA was
significantly negatively correlated to BHA (r(39) = -0.30; P < 0.0001) and CPA
(r(39) = -0.18; P = 0.01) at Bagamoyo in 2010. A similar trend was also
observed at Mkuranga. The presence of these ant species may therefore
hinder effectiveness of AWA to control sap-sucking pests in cashew in
Tanzania. Therefore, suppression of these two inimical ant species should be
emphasized for effective control of the sap-sucking pests in cashew fields. It |
|