Abundance of Weaver Ants (Oecophylla smaragdina) in Three Forest Stands
Abstract
Weaver ants, Oecophylla smaragdina (Hymenoptera: Formicidae) are aggressive predators and consume various species of pests of agricultural and forest plants. The ants build nests and live in the trees. This research was done to know the percentage of trees colonized by weaver ants, individual number of weaver ants, and the number of nest of weaver anton teak, eucalypt, and acacia stands and also the occurrence of trophobionts on these trees. The research was done in May, July and September 2015. The abundance of weaver ants was determined by counting the number of nests ~~and the individual number of weaver ants on the trees~~ as the primary measure of colony presence. Foraging activity near the ground was also estimated by counting ants on tree trunks up to 1 meter in height. Trophobionts which were living on the trees were also observed. The results showed that the percentage of trees colonized by weaver ants was the highest in eucalypt stand (7.0-8.6 %) followed by teak stand (1.1-4.2%) and no weaver ant nest found in acacia stand. The highest individual numbers of ant activity on trunks was found in teak stand (2-38 individuals) followed by eucalypt stand ( 8-20 individuals) and no weaver ant found in acacia stand. The number of nest was 1.0-5.4 nests/ tree on teak stand, 1.8-4.2 nests/tree on eucalypt stand and 0 on acacia stand. On teak stands, a decline of weaver ants nest population occurred in September (dry season), whereas on acacia stands, there were no nests found in any season. Weaver ants symbiotically coexisted with trophobionts of Coccidae and Pseudococcidae on teak stand. Meanwhile, trophobiont was not found on eucalypt stands. Weaver ants probably obtain sugar from extraforal nectar on young leaf of eucalypt.
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Introduction
Weaver ants O.smaragdina, (Hymenoptera: Formicidae) build nests in the trees. These insects live in tropical areas in Asia and Africa, and the ants are not found in subtropical areas. Weaver ants are social insects that live in colonies which consist of queen, male and worker ants (Hodleber, 1983).The queen lays eggs and it usually has a bigger body size (15-16 mm), and her body is brownish green. The queen ant stays in the nest, which is hidden and located at the higher part of a tree. During rainy seasons, it is common for a colony to have several queens, because during the rainy season there is plenty of food available for the ants. Male ants mate with the queen ant and they only live for one week, and they die after one week. Worker ants are infertile females and these ants are responsible for caring for the young, the pupae and the queen. These worker ants are also responsible for collecting food, defending the nest, and transferring larvae and pupae (Kaleka and Haryadi, 2012). Weaver ants go through a complete metamorphosis process. The life cycle of an ant colony begins when a mated queen finds a favorable location for its first nest among the leaves of a tree or a shrub; she lays around 35 eggs within 5-10 days after it breaks off its wings (Lokker, 1990).
The larvae undergo several skin changes before they develop into pupae (Kaleka and Haryadi, 2012). The final instar of larvae (15 days old) can produce silk which is used to cover the cavities in the nest (Lokker, 1990). By the age of 17 days, the larvae develop into pupae, and the first worker ants appear after 28 days (Lokker, 1990; Putranto, 2012).
There are two types of food consumed by weaver ants, honey that comes from Homoptera other insects. The honey is collected from Homoptera members, such as Coccidae, Stictococcidae, Pseudococcidae, Coccidadae, Aphididae, Margarodidae, and Ciicadellidae. The relations between Homoptera and the ants are mutualistic, in which the ants receive food that is rich in sugar and amino acids; and the bugs receive protection from predators and parasites. Weaver ants are generalist predators; they feed on almost all species of arthropods that they find. The common taxa of insects consumed by weaver ants are Heteroptera, Coleoptera, Orthoptera, Blattodea, mantid, Diptera and Arachnida (Locker, 1990).
Weaver ants need food that contains protein, fat and carbohydrate or sugar. Protein is obtained from insects eaten by the ants, every time the ants find food, they will bring it into the nest (Kaleka and Haryadi, 2012). Weaver ants obtain sugar which comes from exudates secreted by insects and from flower nectars. The sugar liquid is used as energy source to build a new nest. Flower nectars are taken from plants such as Hibiscus tiliceaus, Entada phaseoloides, Caesalpinia traceyi, Flagellaria indica dan Smilaxaustralis (Bluthgen and Konrad, 2004). A research by Kartikasari (2013) shows that weaver ants prefer eucalypt trees as their hosts.
O. smaragdina has been used for biological pest control in orange plantations in the year 340 before Christ. On cacao plants, weaver ants can reduce the damage from capsid pest. Weaver ants are also effective in controlling Pseudococcidae pest. In Australia weaver ants are used to control pests that infest mango plants. In Asia, the use of ants as pest predators has been practiced for along time and has been tested scientifically (Way & Kho; 1992). Weaver ants (Oecophylla smaragdina) are members of the ant family that prove to be the most effective predators in tropical area. Weaver ants can be the predators for more than 50 species of pests from 12 species of different plants (Way & Khoo, 1992). Weaver ants have been used for more than 1600 years in Vietnam and China to control pests on orange plants. Weaver ants are also effective to control pests that harm cashew plants in Papua New Guinea. These predators are also useful to control bagworm pest that attacks oil palm plantations.
In Indonesia weaver ants are not yet commonly used for pest control. Forest stands are often troubled by pests such as Hyblaea puera caterpillars on teak plants and Hypsipilla sp. shoot borer on mahogany plants. Information about the role of weaver ants as predators in the forest hasn’tbeen available. In Wanagama Forest Gunung Kidul, Yogyakarta there are some forest stands such as teak stand, eucalypt stand and acacia stand. Weaver antis potential predators of pest attacking these stands. Therefore it is necessary to evaluate the abundance of weaver ants in these stands. This research is expected to open the path towards using weaver ants for pest control on forest plants.
The objective of the research is to determine 1) The percentage of trees colonized by weaver ant and the abundance of weaver ants (individual numbers of weaver ants and the number of weaver ant nest on teak, eucalypt and acacia stands). 2) Trophobionts that are involved in symbiosis with weaver ants.
Conclusion
Weaver ant (Oecophylla smaragdina) colony occurrence, as measured by nest presence, varied significantly among teak, eucalypt, and acacia plantation stands. Eucalypt supported the most consistent colonization, likely due to its evergreen foliage and extrafloral nectar sources. Colonies indeciduous teak declined during the dry season leaf-shedding period. No colonies were found in acacia, suggesting it is not a functional host in this system, possibly due to anthropogenic pressure or biotic competition. The ants exhibited a flexible trophic strategy, engaging in mutualism with trophobionts on teak while potentially exploiting direct plant resources on eucalypt. These findings underscore that host tree species identity and phenology are key determinants of weaver ant distribution in managed forests, with important implications for their potential role in conservation biological control.
CONFLICT OF INTEREST The authors declare no conflict of interest.
