Observations on the Ecology of Weaver Ants (Oecophylla smaragdina Fabricius) in a Thai Mangrove Ecosystem and Their Effect on Herbivory of Rhizophora mucronata Lam.

Abstract

Ants of the genus Oecophylkz are predators of other insects and are able to protect a variety of terrestrial plants against pest insects; however, observations on the ecology of these ants in mangrove forests are lacking. General observations on the ecology of Oecophylkz smaragdina were carried out in a Thai mangrove forest to determine if these ants can protect their host plants in less favorable mangrove habitats. Leaf herbivory and the density of 0. smaragdina ants were measured on Rhizophora mucronata trees at two sites. The results showed a negative correlation between ant density and herbivory. At both sites, the mean percent damaged leaf area was more than four times higher on trees without ants compared to "ant-trees." A significant negative correlation was found between tree mean percent leaf damage and the density of ants on the tree. Furthermore, on trees with ants, there was less herbivory on leaves close to ant nests compared to other leaves on the tree. Most damage was caused by chrysomelid beetles (62%) and sesarmid crabs (25%) and both types of herbivory were significantly reduced on ant-trees.

Leaf damage in a mangrove swamp at Sepetiba Bay, Rio de Janeiro, Brazil

“…The activities of leaf-consumer organisms have been examined in only a few localities in the world, and generally only moderate damage has been reported (not exceeding 50% of the leaf area) (Erickson et al 2004, Offenberg et al 2004. Leaves of mangrove swamp plants are, in fact, considered to show relatively little damage because they are heavily protected by tannin compounds and other effi cient inhibitors of insect herbivores (Huffaker et al 1984, Hernes et al 2001, Skov & Hartnoll 2002.…”

Host plants and associated trophobionts of the weaver ants Oecophylla spp. (Hymenoptera: Formicidae).

“…O. smaragdina has been used by Chinese farmers to protect citrus crops since 304 A.D. [3]. Many studies on the bionomics of this ant genus [4][5][6][7][8][9] are from its application in the field. Farmer-friendly guides on applying O. smaragdina to fruit trees [10] and cashew [11] also exist that synthesize knowledge available on the ant in those habitats.…”

Evidence that insect herbivores are deterred by ant pheromones

“…The weaver ant Oecophylla smaragdina preys on the chrysomelid beetle Rhyparida wallacei and protects the mangrove tree Rhizophora mucronata against these beetles (Offenberg et al 2004). To test the pheromone avoidance hypothesis, we observed whether O. smaragdina marked R. mucronata host trees with pheromones in the field, and whether R. wallacei showed a feeding preference between leaves sampled inside versus outside ant territories.…”