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Birds as Predators on the Brood of Polybia Wasps (Hymenoptera: Vespidae: Polistinae) in a Costa Rican Deciduous Forest

1976; Wiley; Volume: 8; Issue: 2 Linguagem: Inglês

10.2307/2989631

1744-7429

Donald M. Windsor,

Insect and Pesticide Research

The carton nests of the polistine wasps, Polybia occidentalis and P. barbouri, are frequently destroyed by predators feeding on wasp brood in northwestern Costa Rica. The remains of these nests and the signs left by the predators closely matched those observed after several nests were destroyed by the gray-headed kite, Leptodon cayanensis. The frequency of bird predation appeared lowest during the wet season, increased through the dry season, and reached a peak of 50 percent nest destruction in May 1973. In contrast to observations from wetter tropical habitats, ants appear to be a minor source of nest destruction for highly social wasps in a lowland deciduous forest-savanna habitat. THE NEED FOR DEFENDERS against nest predators and parasites has been cited frequently as one of several possible factors favoring the evolution of social life in the Hymenoptera (Michener 1953, 1964, 1974; Lin and Michener 1972; Wilson 1971). With few exceptions, indices of average female reproductivity have shown an inverse relationship with colony size in both facultatively and obligately colonial Hymenoptera. Presumably, then, the unmeasured value of added females may lie in extending the reproductive life of a nest. While this hypothesis seems extremely reasonable, surprisingly little evidence has accumulated which indicates the frequency of nest destruction by predators. This paper examines the impact of predators through wet and dry seasons on the nest populations of the Neotropical polistine wasps, Polybia occidentalis and P. barbouri. Numerous notes in the ornithological literature document isolated instances of birds preying on the nests of polistine wasps. Summer tanagers (Piranga rubra) have been reported to prey upon the broods of Polistes pallipes, P. canadensis (Rau 1941, Alvarez del Toro 1950), Polybia and Metapolybia (Skutch 1959, 1971). Skutch additionally provided details of the plundering of Synoeca nests by the red-throated caracara (Daptrius americanus), the same bird preying upon the mud nest of Polybia e,maciata, the scarlet-rumped cacique (Cacicus uropygialis) preying on an unidentified carton nest (probably Polybia sp.), and the violaceous trogon (Trogon violaceus) excavating and consuming the brood in the large turbinate nests of the wasp, Epipona guterini. The nests of the latter wasp are probably preyed upon as much for the nesting chamber, which the bird appropriates, as for the brood 1 Current Address: Smithsonian Tropical Research Institute, Box 2072, Balboa, Canal Zone. which it may initially consume. Eugene Morton (pers. comm.) has noted another instance of the scarlet-rumped cacique observed preying on the brood of Polybia emaciatta in Panama. Berto-ni (1911) refers to the white-bellied woodpecker (Leuconerpes candidus) as a principal enemy of fragile nesting Polybia species in Paraguay. Haverschmidt's (1962, 1968) studies of the stomach contents of South American raptors revealed polistine wasps in the diet of the gray-headed kite (Leptodon cayanensis), the plumbeous kite (Icterina plumbea), the shorttailed hawk (Buteo brachyurus), and the redthroated caracara. Brown and Amadon (1968) note that the vespivorous habit of the gray-headed kite is similar to that of the honey buzzard (Pernis apivora) in the Old World; however, the former probably neither digs into subterranean nests for larvae nor feeds extensively on adult wasps as does Pernis. Mammals are potentially an important source of predation on the brood of wasps. Jeanne (1970) has discovered that bats are important predators of polistine wasp brood in Brazil. Oppenheimer (1968) observed that white-faced monkeys (Cebus capucinus) feed on the brood of several Polybia species on Barro Colorado Island (Canal Zone). Spradbery ( 1973) reviewed the many records of avian and mammalian predators of temperate vespine wasps. Ground-nesting Vespinae apparently incur high rates of nest destruction by badgers in some areas of the British Isles, while skunks may be the more important enemies of the Vespinae in North America. There were no convincing signs, such as those described by Jeanne, that any of the polistine nests in this study were preyed upon by mammals. Ants are undoubtedly important enemies of polistine wasps in some areas of the Neotropics. Jeanne (1972) records species of Monomorium, Camponotus, Crematogaster, and an unidentified ponerine as BIOTROPICA 8(2): 111-116 1976 111 This content downloaded from 207.46.13.149 on Thu, 20 Oct 2016 04:19:32 UTC All use subject to http://about.jstor.org/terms brood predators of Mischocyttarus species in Brazil. I have found ant species in these genera plus species of Pheidole and Pseudomyrmex to be fairly frequent nest predators of the open, unenveloped nests of Polistes and Mischocyttarmus in northwestern Costa Rica. These ants, however, were never observed to prey up6n the enveloped nests of highly social wasps such as Polybia in the same habitat. Abandoned nests of Polybia were rapidly colonized by species of Camponotus and Crematogaster. All observations indicated such nests were occupied passively within a day or two following a swarming exodus by the entire colony. Eciton has been reported to prey upon the brood of polistine wasps by many naturalists in the Neotropics including Bates (1864) on the Amazon; Belt (1888) in Nicaragua; Fiebrig (1907) in Paraguay; Wheeler (1925), Schwarz (1931), and Naumann (1970) on Barro Colorado Island; and Vesey-Fitzgerald (1938) on Trinidad. In contrast to the seeming importance of army ants as brood predators of wasps in the wet tropical forests, I failed to record a single instance of army ant predation on wasps in the Costa Rican deciduous forest. Army ants were rarely seen in the study area and only during the wet season. One nest was observed being raided by Eciton in the year prior to the study in the same study area by Stephen Cornelius (pers. comm.). THE STUDY SITE AND OBSERVATIONAL METHODS Seventeen months, June 1972 until October 1973, were spent in the dry forest habitats of Parque Nacional Santa Rosa in northwestern Costa Rica (100 40' N., 850 37' W.), 37 km northwest of the town of Liberia, Guanacaste Province. An irregular area of approximately 10 ha containing grassland savanna, thorn scrub and deciduous forest edge was searched weekly for the nests of polistine wasps. Newly discovered nests were tagged, numbered, and revisited at intervals usually of less than two weeks. Only the two more abundant, highly social, cartonbuilding wasps, Polybia occidentalis and P. barbouri, are treated in this paper. At least six other highly social species were found in the study area (Brachygastra mellifica, B. smithii, Synoeca surinamensis, Parachartergu^s fraternus, Chartergus sp. and Epiponw guerini); however, their numbers were too few for meaningful analysis. The top-shaped nests of P. occidentalis may envelope from one to twelve cell layers and from 10 to several thousand adult wasps of highly variable disposition. The more cylindrical nests of P. barbouri are often 8-12 cm in diameter and occasionally 112 Windsor 40 cm in depth which is within the same range of dimensions as found in P. occidewtalis. The abundance of P. barbouri nests was usually one-tenth that of P. occidentalis or less. The nest carton of P. barbouri is a lighter cream color and has a smoother exterior than that of P. occidentalis. Both species occasionally add brittle processes (driptips) to the lower edges of their nests. Slightly different habitat preferences seem to exist between the two species. P. barbouri is more common in thick successional vegetation along the edge of forests, while P. occidentalis is more common on open savanna vegetation. Both species display similar preferences for nesting in thorny vegetation, especially Acrocomia vinifeira, Bactris sp., Pisonia macranthocarpa and Acacia farnesiana. From the standpoint of vulnerability to nest predators, both wasp species are almost certainly identical. The sizes of workers and painfulness of stings are approximately the same.