1 Tachigali myrmecophila (Caesalpinaceae) is an Amazonian myrmecophyti
c canopy tree. The saplings are shade-tolerant, surviving in a suppres
sed state for several years in the rainforest understorey, the hollow
leaf rachis and petiole being inhabited by the stinging ant Pseudomyrm
ex concolor (Pseudomyrmecinae). An experiment was designed (a) to eval
uate the role of insect herbivory in the mutualism between T. myrmecop
hila and P. concolor and (b) to test a falsifiable hypothesis proposed
by a current trade-off model of chemical and ant defences which predi
cts that myrmecophytic traits should be limited to plants with leaves
of low longevity. 2 Plants from which the ants were experimentally rem
oved had 4.3 times more herbivorous insects than plants with ants. All
recorded orders of insects were attacked similarly by the ants. Rates
of herbivory were: (a) ten times higher on experimental plants lackin
g ants, (b) about three times higher on immature than mature leaves, (
c) about two and a half times higher in the wet than the dry season. A
fter 18 months, the experimental plants presented an accumulated level
of leaf herbivory which was about twice as high as for the plants wit
h ants. 3 Observations on the phenology of control, experimental, and
naturally unoccupied plants revealed that the leaf longevity of plants
with active ant colonies was unexpectedly high for rainforest (81 mon
ths), and about 1.8 and 2.6 times as high as the experimental (45 mont
hs) and the naturally unoccupied (31 months) plants, respectively. The
high leaf longevity of the myrmecophytic T. myrmecophila does not sup
port the current trade-off model of chemical and ant defences. The rat
e of apical growth was 1.6 times higher for plants with ants than plan
ts from the experimental group. The slow growth rate of T. myrmecophil
a, about 14 cm year(-1), is compatible with the resource availability
hypothesis. 4 Phenological differences between experimental and natura
lly unoccupied plants suggest that descriptive-correlative studies wou
ld not always give a true picture and that the actual paradigm of ant-
plant interactions, derived in part from this approach, should be care
fully revised. 5 The results corroborate the hypothesis that the inter
action between Tachigali myrmecophila and Pseudomyrmex concolor is mut
ualistic, and suggest that attack by phytophagous insects is the prime
factor in the evolution of the myrmecophytism.