Ecosystems

Not only the vegetation but the community of all the plants, insects, and other animals must be considered together to describe the conditions of a particular habitat. The organisms (biocenoses) located in a particular place (biotope) constitute an ecosystem. Within the ecosystem, each organism has a functional role

(niche). The niches of insects in Latin America have been little studied, other than in agricultural monocultures.

Habitats are recognizable on different levels. The most immediate environment where the determinants of life specifically affect an organism is its microhabitat. Examples are infinite in number; the interior of a decaying log or water-filled cup of a bromeliad are examples. The vertical distribution of different species of mosquitoes (Bates 1944) and butterflies (Papageorgis 1975) in forests is evidence of the effects of subtle environmental determinants. The existence of so many microhabitats partly accounts for the vast diversity of the insects, creatures so adept at calling home the smallest and most demanding of living spaces.

Larger, more inclusive areas containing microhabitats, such as the vegetation zones (e.g., forest canopy) and small physiographic features (caves, lakes), are macro-habitats. Still greater groupings and larger expanses of earth forming grossly recognizable macrohabitats are called life zones or biomes (e.g., tropical forest, deserts). The statuses of Latin American insects in several special habitats are discussed below.

Special Habitats

The great number of natural Neotropical insect macro- and microhabitats makes it impossible to discuss more than a few of the most distinctive, peculiar, and important. They form particular places for insects whose structure and activities may be very different from those of the other insects in the surrounding general environment.

Most insects studied in artificial habitats are injurious species and are discussed in Chapter 3, Practical Entomology. A few investigations have focused on other fau-nal elements of plantations (Young 1986a, 19866), habitations, and like areas under human management.

References

Bates, M. 1944. Observations on the distribution of diurnal mosquitoes in a tropical forest. Ecology 25: 159-170. Papageorgis, C. 1975. Mimicry in Neotropical butterflies. Amer. Sci. 63: 522-532. Young, A. M. 1986a. Notes on the distribution and abundance of Dermaptera and Staphy-linidae (Coleoptera) in some Costa Rican cacao plantations. Entomol. Soc. Wash. Proc. 88: 328-343. Young, A. M. 19866. Notes on the distribution and abundance of ground and arboreal nesting ants (Hymenoptera: Formicidae) in some Costa Rican cacao habitats. Entomol. Soc. Wash. Proc. 88: 550-571.

Forest Canopy Until very recently, the forest canopy has been penetrated by insect researchers only with great difficulty (Hingston 1932). The earliest workers had to be content with fortuitous tree falls even to gain a glimpse of upper-story life. The canopy could be reached by skilled native climbers, but they carried no scientific expertise aloft, and their activities had to be directed ineffectively by their earthbound employers. Other approaches, still remote ones, have been to elevate various kinds of traps to catch some of the fauna or knock it down with quick-acting, biodegradable insecticides (Erwin 1983).

Greater improvement in access came with the construction of arboreal ladders and platforms (Porter and DeFoliart 1981), towers (a famous one on Barro Colorado Island, Panama), or elevated causeways, from which observations and collections could be made. However, these offer very limited mobility and are costly to construct and maintain.

Lately, some practical means have been found not only to move about and obtain specimens from this complex realm but even to carry out extended studies within it (Mitchell 1982). Even scientists themselves are now able to go into the canopy, using mountaineering techniques (Perry 1980,

1984; Perry and Williams 1981). Unfortunately, few entomologists are trained in both the academic and athletic aspects of this demanding, although highly rewarding, approach.

The results of these efforts, although fragmented and imperfect, demonstrate the startling fact that the canopy has an extremely rich insect complement. This stratum of forests is considered to be the "last frontier" in tropical entomology and is attracting study from a number of viewpoints: faunistics, pollination ecology, and even populational biology (see below).

References

Erwin, T. L. 1983. Beetles and other insects of tropical forest canopies at Manaus, Brazil, sampled by insecticidal fogging techniques. In S. L. Sutton, T. C. Whitmore, and A. C. Chadwick, eds., Tropical rain forest: Ecology and management. Blackwell, Oxford. Pp. 59-75.

Hingston, R. W. 1932. A naturalist in the Guiana forest. Longmans Green, New York. Mitchell, A. W. 1982. Reaching the rain forest roof (A handbook on techniques of access and study in the canopy). Leeds Phil. Lit. Soc. Leeds, Eng.

Perry, D. R. 1980. 1 probe the jungle's last frontier. Int. Wildlife 10: 5-11. Perry, D. R. 1984. The canopy of the tropical rain forest. Sci. Amer. 251: 138-147. Perry, D. R., and J. Williams. 1981. The tropical rain forest canopy: A method providing total access. Biotropica 13: 283-285. Porter, C. H„ and G. R. DeFoliart. 1981. The man-biting activity of phlebotomine sand flies (Diptera: Psychodidae) in a tropical wet forest environment in Colombia. Arq. Zool. Sao Paulo 30: 81-158.

Amazon Inundation Forests

Vast expanses bordering the Amazon and its major tributaries are annually flooded to a depth of several meters for periods of five to six months or more. These forests (called igapo locally) harbor an insect fauna especially adapted to the stresses of alternately rising and receding waters.

The terrestrial species that live in these forests are numerous and very diverse. They have evolved strategies to compensate for the periodic loss of their terrestrial habitat by exercising mobility to escape into the canopy or to other dry areas or acquiring survival adaptations for coping with inundation (Adis 1977, Adis et al. 1988). Spiders and many flightless species of ground beetles, for examples, are known to ascend into the upper forest level (Erwin and Adis 1982) during flood periods. Members of the cockroach genus Epilampra, however, have acquired the capacity to swim and have the hindmost spiracles situated on short stalks to aid breathing while they are in the water. Only minor elements of the ground fauna are present here (e.g., pseudoscorpions; Adis and Mahnert 1985, Adis et al. 1988), there being no persistent ground litter or stable soil.

In response to the drying phase, aquatic insect inhabitants of these areas return to the main channels from which the floodwa-ters arose. Some may become trapped in small, dammed depressions, but normally they either take to the air and fly to water or burrow into the mud where they may remain inactive for the duration of the dry season.

References

Adis, J. 1977. Programa mínimo para analises de ecosistemas: Artrópodos terrestres em florestas inundáveis da Amazonia central. Acta Amazónica 7: 223-229. Adis, J., and V. Mahnert. 1985. On the natural history and ecology of Pseudoscorpions (Arachnida) from an Amazonian blackwater inundation forest. Amazoniana 9: 297-314. Adis, J., V. Mahnert, J. W. de Moráis, and J. M. Gomes. 1988. Adaptation of an Amazonian pseudoscorpion (Arachnida) from dryland forests to inundation forests. Ecology 69:287-291. Erwin, T. L., and J. Adis. Í982. Amazonian inundation forests: Their role as short-term refuges and generators of species richness and taxon pulses. In G. T. Prance, ed., Biological diversification in the tropics. Columbia Univ. Press, New York. Pp. 358-371.

Soil and Ground Litter

The soil and its overlying layer of organic litter constitute the habitat of a great many small to very small arthropods (Kuhnelt 1961). Dominant among these are ants, springtails, spiders, psocids, thrips, cryptostigmatic mites, and micro-beetles (Penny et al. 1978), but larger insects are sometimes also found here (Young 1983). It is incredible that such arthropods may comprise almost 50 percent of the total soil and litter biota in the central Amazon forest, ants and termites alone forming about 60 percent of this (Fittkau and Klinge 1973). Most occupy the upper 5 to 8 centimeters of the soil.

The composition of this fauna and its ecology have been the subject of many studies in the Neotropics, especially in forests (e.g., Williams 1941, Deboutteville and Rapoport 1962-1968, Lieberman and Dock 1982) where moisture seems to be the major factor determining the seasonal distribution of species and population fluctuations. Augmentations in diversity and abundance generally follow increases in water content (Levings and Windsor 1984), usually from rainfall during the wet season in all life zones (Dantas and Schubart 1980, Lieberman and Dock 1982, Willis 1976). Strickland (1945) concluded that the general environment of an area is more important than the soil type in determining the sizes of ground and litter populations. That a variety of conditions would be determinants was confirmed by studies of forest litter arthropods in southeastern Peru (Pearson and Derr 1986).

References

Dantas, M., and H. O. R. Schubart. 1980. Correlaçâo dos indices de agregaçâo de Acari e Collembola com 4 fatores ambientais numa pastagem de terra firme da Amazonia. Acta Amazonica iO: 77Î-774. Deboutteville, C. D., and E. Rapoport, eds. f 962-1968. Biologie de l'Amérique Australe. Etudes sur la faune de sol; 2: Etudes sur la faune du sol; 3: Etudes sur la faune du sol +

Documents biogéographiques; 4, Documents biog. el ecologiques. Ed. Cen. Nat. Rech. Sci., Paris.

Fittkau, E. J., and H. Klince. 1973. On biomass and trophic structure of the central Amazonian rain forest ecosystem. Biotropica 5: 2-14.

Kühnelt, W. 1961. Soil biology with special reference to the animal kingdom. Faber & Faber, London. Levings, S. C., and D. M. Windsor 1984. Litter moisture content as a determinant of litter arthropod distribution and abundance during the dry season on Barro Colorado Island, Panama. Biotropica 16: 125-131. Lieberman, S., and C. F. Dock. 1982. Analysis of the leaf litter arthropod fauna of a lowland tropical evergreen forest site (La Selva, Costa Rica). Rev. Biol. Trop. 30: 27-34. Pearson, D. L., and J. A. Derr 1986. Seasonal patterns of lowland forest floor arthropod abundance in southeastern Perú. Biotropica 18: 244-256. Penny, N. D., J. R. Arias, and H. O. R. Schubart. 1978. Tendencias populacionais de fauna de Coleópteros do solo sob floresta de terra firme na Amazonia. Acta Amazónica 8: 259-265.

Strickland, A. H. 1945. A survey of the arthropod soil and litter fauna of some forest reserves and cacao estates in Trinidad, British West Indies. J. Anim. Ecol. 14: 1-11. Williams, E. C. 1941. An ecological study of the floor fauna of the Panamanian rain forest. Chicago Acad. Sci. Bull. 6: 63-124. Willis, E. D. 1976. Seasonal changes in the invertebrate litter fauna on Barro Colorado Island, Panamá. Rev. Brasil. Biol. 36: 643-657.

Young, A. M. 1983. Patterns of distribution and abundance in small samples of litter-inhabiting Orthoptera in some Costa Rican cacao plantations. New York Entomol. Soc. J. 91: 312-327.

Black Water Lakes and Rivers Some lowland tropical river basins contain tributaries and landlocked basins (oxbow lakes, cochas) with tea-colored water that in the depths appears black. These are distinguished from so-called white waters not only by their color but by physical and chemical properties. White waters (actually a milky chocolate color) are nutrient rich, neutral to slightly alkaline, and turbid.

Black waters usually flow from nutrient-poor, sandy soils and thus are low in minerals but are acidic and may contain high concentrations of organic compounds (tannic acids, phenolics) leached from vegetation and toxic to insects. The water and surrounding land thus afford unfavorable conditions for insects, and such black water basins generally have depauperate entomo-faunas (Janzen 1974). Some specially adapted aquatic types, however, such as certain chironomid midges (Fittkau 1971) and water mites (Tundisi et al. 1979), can be very numerous, even in the most heavily charged water.

The Guiana Shield of northern South America is a large black water area and is notorious for the poorness of its productivity. Other similar such regions are found in the Brazilian Highlands and on the Yucatán Peninsula.

Clear waters (greenish to clear) are also recognized but are biologically similar to black water.

References

Fittkau, E.J. 1971. Distribution and ecology of Amazonian chironomids (Diptera). Can. Entomol. 103: 407-413. Janzen, D. H. 1974. Tropical blackwater rivers, animals and mast fruiting by the Diptero-carpaceae. Biotropica 6: 69—103. Tundisi, J. G., A. M. P. Martins, and T. Matsu-mura. 1979. Estudos ecológicos preliminares em sistemas aquáticos em Aripuaná. Acta Amazónica 9: 311-315.

Caves

Insects and many related terrestrial arthropods of diverse groups are true troglobites (obligate cavernicoles, i.e., animals narrowly and specifically adapted for life deep in caves; Culver 1982, Hoffmann et al. 1986). However, tropical caves are usually dominated by species classed as troglo-philes, which also live in noncave habitats. Some are omnivores, but they are more normally specialized for particular foods and are of two basic types: scavengers and predators. The former feed on the droppings of bats (Gnaspini 1989), oil birds, and other higher fauna (guanophages) or take nourishment from organic debris such as insect and vertebrate carrion and plant matter that washes or falls into the caves or is brought in and dropped by other animals (detritivores). Those among the predators survive by catching and consuming other live cave dwellers. A widespread example are the long-legged cave crickets of the genus Amphiacusta.

The scavengers are more numerous than predators in kinds and numbers of individuals. Among these are the terrestrial isopods (Trichorhina), millipedes (Eurhino-cricus), cockroaches (Periplaneta, Blaberus), tineid moths, dung beetles (Ataenius), and many others. They are often extremely numerous; darkling beetles (Tenebrionidae) or mites (Acari) may carpet portions of the floor of caves to a depth of a centimeter or more.

Predators are conspicuous for their large size and aggressiveness. Spectacular in these respects are the giant tailless whip scorpions (Amblypygi, Phrynus) that prey on crickets and cockroaches. Others in the category are centipedes, many spiders, ants, and various beetles, principally rove beetles (Staphylinidae) and ground beetles (Carabidae). Many soil mites may occupy these niches as well.

Cave insects often exhibit morphological adaptations to life in the dark (Dessen et al. 1980), including eyes reduced or absent, lack of integumentary pigmentation, reduction and loss of wings, and greatly elongated, highly sensitive appendages (especially the antennae).

The entomology of Neotropical caves has been the subject of much study (Peck 1977, Strinati 1971), but more remains to be done. Best known are the cave faunas of Mexico (Reddell 1971), Cuba (Orghidan et al. 1973-1983), Jamaica (Peck 1975), Puerto Rico (Peck 1974, 1981a), Barbados (Peck 19816), and Venezuela (Chapman

1980). Recent work, yet unpublished, has found over thirty species of eyeless cave and soil arthropods in volcanic caves in the

Galápagos Islands (Peck pers. comm.).

References

Chapman, P. 1980. The invertebrate fauna of caves of the Serranía de San Luis, Edo. Falcon, Venezuela. Brit. Cave Res. Assoc. Trans. 7: 179-199.

Culver, D. C. 1982. Cave life, evolution and ecology. Harvard Univ. Press, Cambridge.

Dessen, E. M. B., V. R. Eston, M. S. Silva, M. T. Temperini-Beck, and E. Trajano. 1980. Levantamento preliminar de fauna de cavernas de algumas regiöes do Brasil. Cien. Cult. 32: 414-725.

Gnaspini, N. P. 1989. Análise comparativa da fauna associada a depósitos de guano de morcegos cavernícolas no Brasil: Primeira Approximafäo. Rev. Brasil. Entomol. 32: 183-192.

Hoffmann, A., J. G. Palacios-Vargas, and J. B. Morales-Malacara. 1986. Manual de biospeleología. Univ. Nac. Aut. México, México.

Orghidan, T., A. Núñez Jiménez, V. Decon, S. Negrea, and N. V. Bayes. 1973-1983. Résultats des expéditions biospéleologique cubano-Roumaines ä Cuba. Vols. 1-4. Ed. Academiei, Bucharest, Republicii Socialiste Románia.

Peck, S. B. 1974. The invertebrate fauna of tropical American caves. Pt. II: Puerto Rico, an ecological and Zoogeographie approach. Biotropica 6: 14—31.

Peck, S. B. 1975. The invertebrate fauna of tropical American caves. Pt. Ill: Jamaica, an introduction. Int. J. Speleol. 7: 303-326.

Peck, S. B. 1977. Recent studies on the invertebrate fauna and ecology of sub-tropical and tropical American caves. 6th Intl. Cong. Speleol. Proc. 5: 185-193.

Peck, S. B. 1981a. Zoogeography of invertebrate cave faunas in southwestern Puerto Rico. Natl. Speleol. Soc. Bull. 43: 70-79.

Peck, S. B. 19816. Community composition and zoogeography of the invertebrate cave fauna of Barbados. Fla. Entomol. 64: 519-527.

Reddell, J. R. 1971. A review of the cavernicole fauna of Mexico, Guatemala, and Belize. Texas Mem. Mus. Austin Bull. 27: 1-327.

Strinati, P. 1971. Recherches biospéleo-logiques en Amerique du Sud. Ann. Spéleol. 26: 439-450.

Lomas

The low coastal desert hills of central Peru provide one of the most unusual habitats for insects in the Neotropic (Dogger and Risco 1970). It is speculated that, historically, the lomas were part of a larger chaparral biome that once extended along the entire western slopes of the Andes (Péfaur 1978). In this zone of extreme general aridity, wetness in the form of rain comes only at multiyear intervals, decades or more. At these times, explosions of plant life occur on the otherwise parched hills, and they become green islands in the bleak desert. Normally, only the regular annual fogs (garúas, May—October) bring moisture to these slopes to maintain a less plush but more reliable vegetation.

Also adapted to these climatic and vegetative cycles and living on the lomas vegetation is a complex and diverse community of insects and other terrestrial arthropods, some species of which are known from nowhere else (Aguilar 1964). The more important groups are spiders (Aguilar, Pacheco, and Silva 1987), mites, springtails, wax insects, beetles (especially Tienebrionidae), flies, and ants (Aguilar 1981), which are most abundant and numerous in kinds in the damper upper elevations. Some special forms are wingless sticklike forms ("palitos vivientes de Lima"), including two walkingsticks, a jumping stick (Proscopiidae), and assassin bugs (Reduviidae). One walkingstick (Libe-thra minuscula) is omnivorous but dies with the failing plants at the end of the damp season. The other (Bostra scabrinota) feeds on one plant but can change its color to match seasonal changes and is present year-round (Aguilar 1970). An unexpected element is the water measurer (Bacillometra woytkowskii, Hydrometridae), a heteropterous insect normally associated with bodies of fresh water (Aguilar, Oyeyama, and Aguilar 1987). Its presence is associated with the high humidity of the lomas in the winter.

References

Aguilar, P. G. 1964. Especies de artrópodos registrados en las lomas de los alrededores de Lima. Rev. Peruana Entomol. 7: 93-95. Aguilar, P. G. 1970. Los "palitos vivientes de Lima." 1: Phasmatidae de las lomas. Rev. Peruana Entomol. 13: 1—8. Aguilar, P. G. 1981. Fauna desértico-costera Peruana. Vil: Apreciaciones sobre diversidad de invertebrados en la costa central. Rev. Peruana Entomol. 24: 127-132. Aguilar, P. G., F. Oyeyama, and Z. P. Aguilar. 1987. Los "palitos vivientes de Lima." 111: Un Hydrometridae de las lomas costeras. Rev. Peruana Entomol. 28: 89-92. Aguilar, P. G., V. R. Pacheco, and R. Silva. 1987. Fauna desértico-costera peruana. VIII: Arañas de las lomas Zapalla!, Lima (nota preliminar). Rev. Peruana Entomol. 29: 99— 103.

Dogger, J., and S. H. Risco. 1970. La fauna insectil de las lomas de Trujillo, Estudio del cerro "Campana." Bol. Tec. Circ. Entomol. Norte (Lambayeque) 1(2): 1-5. Péfaur, J. E. 1978. Composition and structure of communities in the lomas of southern Peru. Ph.D. diss., Univ. Kansas, Lawrence.

The Ocean

At first thought, it seems incongruous that the insects, so tremendously successful in dominating the land and the inland waters of the world, have failed to conquer the seas. Intolerance of hypersaline water is certainly not to blame, because many aquatic insects live in highly salinated lakes and ponds inland and at the ocean's margin. The reasons apparently lie in the fact that they arrived on the scene long after their other invertebrate predecessors had locked up all the ecological niches. There are a few examples, however, of marine-adapted groups (Cheng 1976).

Insects truly adapted to life far out to sea are the fewest and consist only of the marine water striders or "ocean skaters" (several genera of Gerridae, see water striders, chap. 7). Closer to shore, the number and kinds of marine insects greatly increases. There one finds the marine midges (Chironomidae). These live on rocky shores and have larvae that are completely at home in the salt spray and are even submerged by seawater during high tide. Other intertidal insects and arachnids are found among the springtails and mites (especially Halacaridae).

Several kinds of lice are parasitic on seagoing mammals, seals and sea lions particularly. When the host submerges, they escape osmotic dessication by sea-water and drowning by hiding close to the skin in air pockets under the host's fur.

The seashores of the continents and islands of Latin America also support an even more extensive group of marine littoral insects (Evans 1968). Many of these are freshwater groups, including inland hyper-saline lake types, that have shifted to the similar habitats at the sea margins, especially salt marshes and mangroves. A majority prey on invertebrates, feeding on other shore life, such as tiger beetles, rove beetles, pseudoscorpions, spiders, and shore bugs (Saldidae).

Many of these are associated with seaweed and kelp that accumulates on beaches, feeding either directly on this material (kelp fly larvae, Fucellia; see chap. 11; Coelopi-dae, shore flies [Ephydridae]) or catching and devouring the wrack scavengers (spiders, ground beetles, rove beetles). The adults of some, such as salt marsh mosquitoes and tabanids and mudflat-breeding punkies, are feeders on vertebrate blood. Their population explosions can make human life impossible in seaside areas. Several water boatmen species (especially Tricho-corixa reticulata) live in highly saline shore pools (Davis 1966) and have even been collected in plankton tows in the Gulf of California.

References

Holland, Amsterdam. Davis, C. C. 1966. Notes on the ecology and reproduction of Trichocorixa reticulata in a Jamaican salt-water pool. Ecology 47: 850— 852.

Evans, W. G. 1968. Some intertidal insects from western Mexico. Pan-Pacific Entomol. 44: 236-241.

Torrential Waters

Stream waters flowing in the range of 60 to 200 centimeters per second or greater are considered torrential and are common in the upland drainages of mountainous regions. Originating in countless springs and snowfields on the heights of the Cordillera, bounding over boulders and crashing into foam-covered pools, torrential streams descend through gorges and narrow canyons, over hard, rocky beds, before reaching the lower, gentle slopes.

Fast, cold water offers a refugial niche to many insects, comparatively free from vertebrate predation because few such large animals can live in such an inhospitable medium. Exceptions are a few hardy insectivorous types, such as torrent ducks, dippers, and a few fish (introduced trout and possibly some astroblephid catfishes). As a result, some very ancient representatives of several aquatic groups have persisted for geologic ages as torrenticolous (rheophi-lous) relicts. These include entire families, most prominently the net-winged midges (Blephariceridae) and various beetles (Elmi-dae, Dryopidae, Psephenidae). Other similarly adapted taxa are the larval stages of lance-winged moth flies (Maruina, Psy-chodidae) and blackflies (Simuliidae) and many species of Trichoptera (especially in the family Hydrobiosidae), Hemiptera (Cry-phocricos, Naucoridae), Plecoptera (Arau-canioperla, Gripopterygidae), water midges (Chironomidae), and Ephemeroptera (Epe-orus, Heptageniidae).

Extreme structural and physiological adaptations have evolved in these forms in response to the strong selective pressures of fast current and smooth substrates. These include holdfast structures (ventral suckers, claws), streamlining, and plastron respiration. The latter makes use of the function of air films and pockets as "physical gills." A requirement for proper function of this system is cold, clean, oxygen-rich water. The presence of these insects therefore indicates healthy stream conditions.

Food habits for the relatively passive grazers and predators do not require rapid movement. Adult emergence is often "explosive." To avoid drowning, the imago rises to the surface in a bubble and takes wing immediately after contacting the air.

Torrenticolous insects are not well known in Latin America. Some famous early studies were made on Diptera in southeastern Brazil by Fritz Müller (1879, 1895) and Adolfo Lutz (1930). New species are commonly discovered in the habitat, especially in remote mountains.

References

Lutz, A. 1930. Biología das águas torrenciais e encachoeiradas. Soc. Biol. Montevideo, Arch, suppl. 1: 114-120. Müller, F. 1879. A metamorphose de um insecto díptero. Mus. Nac. Rio de Janeiro, Arch. 5/6: 47-85, pis. 4-7. Müller, F. 1895. Contributions towards the history of a new form of larvae of Psychodidae (Diptera) from Brazil. Entomol. Soc. London, Trans. 1895: 479-482, pis. 10-11.

Tank Plants

Some Neotropical plants have parts of their anatomy developed into cup-shaped water-holding structures (phytotelmata) (Frank and Lounibos 1983) and are referred to as reservoir or tank plants. They are of several types. The best known are the bromeliads (Bromeliaceae) (Gómez 1977) whose water accumulations provide a home for small aquatic animals. This microcosm was first studied comprehensively as an ecosystem by Picado (1913), who distinguished between the aquatic milieu ("aquarium") and terrestrial portion ("terrarium").

The aquarium consists of a spacious central cup and expanded lateral leaf bases that collect rainwater. Large plants may store a liter or more and may have a cup 5 to 10 centimeters, in diameter and equally deep. These reservoirs of water provide habitats suitable for the development of many aquatic insects, including mosquitoes, especially Wyeornyia and other sabethines and Aedes. An abundance of bromeliads in a particular area can foster a substantial mosquito population, a good example being Anopheles darlingi, the main malaria vector in Trinidad in the 1940s (Downs and Pittendrigh 1946). Other representative aquatic inhabitants include water midges (Chironornus), punkies (Bezzia), damselflies (Pseudostigmatidae), beetles (Helodidae), and water mites. The detailed ecology of this fraction has been studied by many entomologists, including Laessle (1961). (See the bibliography of bromeliad and pitcher plant reservoir plant entomology by Fish and Beaver [1978].)

Detritus collects also in the lateral bracts, and a special kind of arboreal soil is created which is like a "terrarium" to another group of insects. Here are found spiders, carabid beetles, ants, isopods, millipedes, mites, springtails, and other terrestrial forms (Murillo et al. 1983). A few insects actually feed on the leaves of bromeliads and form yet another guild in association with these plants (Beutelspacher 1972).

Another category of Neotropical tank plants are the insectivorous "pitcher plants" of the family Sarraceniaceae. In these, deep, urn-shaped leaves have evolved to hold fluids that normally kill and digest hapless insects that fall into them. However, immatures of some insect species, mostly mosquitoes of the tribe Sabethini, are immune to the corrosive action of these chemicals and actually develop normally in this very peculiar aquatic microhabit. In the Neotropics, pitcher plants of only the genus Heliamphora are known, found in the Venezuelan-Guianan region. They are known to be occupied by Wyeornyia mosquitoes of the subgenus Zinzala (Zavortink 1985), but their other occupants are not studied.

Flower bracts, especially those of the genus Heliconia (Musaceae), hold watery fluids, secreted by the plant itself, as well as rainwater and host a specific micro-community of insects similar to that of bromeliads (Seifert 1982). The inflorescences harbor one of two kinds of insect groupings depending on size and shape, amount of water, and age. The first is composed of fly larvae (nonmosquito) and beetles in older, less voluminous bracts with small amounts of water. The most common fly larvae are of pomace flies (Droso-philidae), hover flies (Syrphidae, Cope-slylum), and soldier flies (Stratiomyiidae, Merosargus). The beetles are primarily scavenging water beetles (Hydrophilidae, Gillisius), leaf beetles (Chrysomelidae, His-pinae, Cephaloleia), and rove beetles (Sta-phylinidae, Odontolinus and Quichuana). There are also earwigs (Dermaptera, Car-cinophora) and cockroaches (Blattidae, Litopeltis).

In the second group, mosquito larvae are dominant (Seifert 1980), in younger, larger inflorescences with larger amounts of water. At least five genera are represented: Wyeomyia, Trichoprosopon, Toxorhyn-chites, Culex, and Sabethes.

Various interactions among the insects in these communities have been observed, including predation, commensalism, colonization, and competition, although the last seems to be weak. The clearly defined nature of the communities, the commonness of Heliconia plants, and the ease with which the insects may be manipulated experimentally make them ideal for investigations of species interactions and other ecological phenomena (Seifert 1975, 1981; Seifert and Seifert 1976a, 19766, 1979).

References

Beutelspacher, C. R. 1972. Some observations on the Lepidoptera of bromeliads. J. Lepidop.

Soc. 26: 133-137. Downs, W. G., and C. S. Pittendrigh. 1946.

Bromeliad malaria in Trinidad, British West

Indies. Amer. J. Trop. Med. Hyg. 26: 46-66. Fish, D., and R. A. Beaver 1978. A bibliogra phy of the aquatic fauna inhabiting bromeliads (Bromeliaceae) and pitcher plants (Nepen-thaceae and Sarraceniaceae). Florida Anti-mosq. Assoc., Proc. 49: 11-19.

Frank, J. H., and L. P. Lounibos, eds. 1983. Phytotelmata, terrestrial plants as hosts for aquatic insect communities. Plexus, Medford,

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