TheIndonesian potential Journal of artificial of Agriculture nesting sites 3(1), ... 2010: 45-50 45 THE POTENTIAL OF ARTIFICIAL NESTING SITES FOR INCREASING THE POPULATION DENSITY OF THE BLACK CACAO ANTS Meldy L.A. Hosanga), Christian H. Schulzeb), Teja Tscharntkec), and Damayanti Buchorid) a)Indonesian Coconut and Other Palmae Research Institute, Jalan Bethesda II, Mapanget PO Box 1004, Manado 95001, North Sulawesi, Phone: (0431) 812430, 851430, Facs.: (0431) 812017, Email: [email protected] b)Department of Animal Ecology I, University of Bayreuth, D-95440 Bayreuth, Germany c)Agroecology, University of Göttingen, Waldweg 26, 37073 Göttingen, Germany d)Department of Plant Pests and Diseases, Faculty of Agriculture, Bogor Agricultural University, Kampus IPB Darmaga, Bogor 16680, West Java, Indonesia ABSTRACT In Indonesia, biological control of the mirid bug by introducing the black cacao ants was first documented in The black cacao ant (Dolichoderus thoracicus Smith) the early 1900s. There were large signboards on the main (Hymenoptera: Formicidae) is one of the predators commonly roads of the Siloewok Sawangan estate (Central Java), at found in cacao plantations and known to be an effective biological the time it was the largest cacao estate in Java, saying control agent of cacao pests. One of the limiting factors for the population density of the ants in cacao plantations may be the without black ants no cacao (Giesberger 1983). This availability of adequate nesting sites. The purposes of this study emphasizes the importance of ants in controlling cacao were to evaluate which artificial nesting sites are most successful in pests, but this practice was discontinued as pesticides attracting black cacao ants and in which nesting sites of D. became widely available (Perfecto and Castineiras 1998). thoracicus colonies reach the largest size. The study was conducted More studies on D. thoracicus were conducted in Malaysia in two cacao plantations in the vicinity of the Makmur village in the 1980s. Studies by Khoo and Chung (1989) and Way located at the eastern margin of the Lore Lindu National Park, Palolo valley, Central Sulawesi. At each cacao plantation, 20 trees and Khoo (1989) showed that the black cacao ants could colonized by black cacao ants were selected. In every chosen tree, protect cacao pods against Helopeltis sp. Furthermore, all five nest types were placed for two weeks. D. thoracicus See and Khoo (1996) reported that an increasing significantly preferred artificial nesting sites constructed of bundles abundance of the black cacao ants was associated with a of dry coconut leaflets. Other artificial nests (bundles of dry banana significant reduction of the percentage of unextractable and cacao leaves, hollow bamboo filled with dry leaves, and plastic bags filled with dry cacao leaves) did contain colonies with less pods (all beans stuck to each other and to the husk). They adult ants, larvae, and pupae. also found that the percentage of pods infested by C. cramerella was generally below 50% in plots with a high [Keywords: Dolichoderus thoracicus, Theobroma cacao nesting, ant abundance of D. thoracicus and mostly exceeded the biological control] 50% level in plots where these ants were scarce. While in many plantations the black cacao ant is extremely rare; in some plantations it does not occur at all. INTRODUCTION To study if nesting site was an important limiting factor for Biological control by using natural enemies such as parasitoids, predators, and insect pathogens has gained more interest in the last ten years. The use of ants for controlling insect pests was first reported from China (Flint and van den Bosch 1981; Hölldobler and Wilson 1990). The black cacao ant (Dolichoderus thoracicus Smith) (Figure 1) is one of the well-known predators that has a high potential to act as biological control agent against cacao pests. The ant is capable of decreasing pod damage caused by mirid bugs of the genus Helopeltis sp. and the cacao pod borer (Conopomorpha cramerella Snellen) (Giesberger 1983; Khoo and Chung 1989; Way and Khoo 1989; Khoo and Ho 1992; See and Khoo 1996; Khoo 2001) Figure 1. Black cacao ant (Dolichoderus thoracicus) attending and also can protect cacao trees against folivorous insects white meally bugs (Cataenococcus hispidus Marrison) (Hosang 2004). on the surface of a cacao pod. 46 Meldy L.A. Hosang et al. the abundance of D. thoracicus, five different kinds of bundle of dry coconut leaflets; (2) Ban = bundle of dry artificial nesting sites were placed in two cacao plantations. banana leaves; (3) Cac = bundle of dry cacao leaves; (4) In particular, the purposes of this study were to evaluate Bam = bamboo (length: 25 cm, diameter: 10 cm) filled with which artificial nesting sites were most successful in dry cacao leaves; and (5) Bag = transparent plastic bag attracting black cacao ants and in which nesting sites D. filled with dry cacao leaves thoracicus colonies reach the largest size. At both cacao plantations, 20 trees colonized by black cacao ants were selected (2 x 20 trees = 40 trees). In every tree all five nest types were placed to black cacao ants by MATERIALS AND METHODS tying the artificial nests on the trunk or main branch of tree (2 x 20 nests per nest type = 40 nests per nest type; 40 The study was conducted at the eastern margin of the nests x 5 nest types = total of 200 nests). Due to this Lore Lindu National Park in Palolo valley, Central Sulawesi. experimental design, the ants had the possibility to choose The two selected cacao plantations, Makmur 1 (S 01°08.29' between the different nest types in every tree (Figure 2). E 120°03.22') and Makmur 2 (S 01°08.28' E 120°03.34'), were After exposing all nests for 2 weeks, they were located in the vicinity of the Makmur Village (Palolo Sub- recollected from the trees and the size of the established district, Donggala District) at an altitude of 620 and 610 m colonies was quantified for all nests by counting the asl, respectively. number of adult ants, larvae, and pupae. Additionally, D. The study was conducted in October 2002 thoracicus ants active at the tree trunks of 1.0-1.5 m above synchronously at both selected study sites, Makmur 1 ground and on the leaves and branches of the lower canopy and Makmur 2. In both cacao plantations, five different were counted or estimated for all treated trees and trees kinds of artificial nesting sites were placed, i.e. (1) Coc = nearby which were not equipped with artificial ant nesting Figure 2. Artificial nesting sites placed to black cacao ants: bundle of dry coconut leaflets (top left), bundle of dry banana leaves (top center), bundle of dry cacao leaves (top right), plastic bag filled with dry cacao leaves (bottom left), and bamboo filled with dry cacao leaves (bottom right). The potential of artificial nesting sites ... 47 123 sites but colonized naturally by black cacao ants. Therefore, 100 Makmur 1 123 Makmur 2 123 123 123 for each studied plantation, 20 pairs of trees colonized 123 123 80 123 123 with black cacao ants but with and without artificial ant 123 123 123 123 123 123 123 nests are available for comparison. 60 123 123 123 123 123 123 123 123 One-way analysis of variance (ANOVA) was used to 123 123 123 123 123 123 123 123 123 123 40 123 123 123 123 123 analyse effects of artificial nest types on colonization 123 123 123 123 123 123 123 123 123 123 success and colony size of the black cacao ants. Scheffé 123 123 123 123 123 20 123 123 123 123 123 test was applied to compare the population of black cacao 123 123 123 123 123 123 123 123 123 123 123 123 123 123 123 123 123 123 123 123 ants on trees with and without artificial nests. The program Colorization rate (%) 0 Statistica 5.5 (StatSoft 1999) was used to perform all Coc Ban Cac Bam Bag statistical analyses. Means were given ± standard devia- Artificial ant nest tion. Figure 3. Colonization rates of Dolichoderus thoracicus on different types of artificial nesting sites placed in RESULTS AND DISCUSSION two cacao plantations (Makmur 1 and Makmur 2) in cacao trees already occupied by D. thoracicus; Coc = bundle of dry coconut leaflets, Ban = bundle of dry Effect of Type of Nesting Sites on Colonization banana leaves, Cac = bundle of dry cacao leaves, Success Bam = bamboo filled with dry cacao leaves, and Bag = transparent plastic bag filled with dry cacao leaves. Black cacao ants colonized all types of artificial nesting sites placed in cacao trees, but the five types of nests differed in respect to their colonization rate. In Makmur 1, D. thoracicus colonized all (100%) Coc nesting sites. In p < 0.0001; Makmur 2: F4,15 = 9.10, p < 0.0001). In Makmur 1, respect to their colonization rate, the remaining four types significantly more queens were counted in Coc and Ban of nesting sites were ranked in the following sequence: nests compared to Bam and Bag nests. Cac nests did not Ban (83.75% of placed nesting sites colonized), Cac differ from other artificial nesting sites. In Makmur 2, (78.75%), Bam (60.00%), and Bag (36.25%). A similar significantly more queens were recorded in Coc nests than ranking of nesting sites was found at Makmur 2, although that in all other types of artificial nesting sites (Figure 5). lower colonization rates were found on Coc (88.5%), Ban The number of ant larvae at both study sites differed (63.75%) and Cac (58.75%), and a higher percentage of significantly between the placed artificial nesting sites Bam (83.75) and Bag nesting sites (46.25%) were colonized colonized by D.