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breeding stocks that may be used to correct line deficiencies.

REFERENCES BERRY, R. J. (1972): Conservation and the genetical constitution of populations. In ScientiJic management of plant and animal communities for conservation: 117-206. Duffey, E. & Watt, A. S. (Eds). Oxford: Blackwell Scientific Publications. DUFFEY, E. (1977): The re-establishment of the large copper butterfly Lycaena dispar batava Obth. on Woodwalton Fen National Nature Reserve, Cambridgeshire, England 1969-73. Biol. Conserv.

EHRLICH, P. R. (1984): The structure and dynamics of butterfly populations. In The biology of butterflies: 2540. Vane-Wright, R. I. & Ackery, P. R. (Eds). London: Academic Press. GILBERT, L. E. & SINGER, M. C. (1975): Butterfly ecology. A. Rev. Ecol. Syst. 6 365-397. MAYR, E. (1971): Populations, species and evolution. Cambridge, MA: Harvard University Press.

12 143-158.

MORTON, A. C. (1985): The population biology of an insect with a restricted distribution: Cupid0 minims Fuessly (Lepidoptera; Lycaenidae) . PhD thesis, University of Southampton. SHAPIRO, A. M. (1979): The phenology of Pieris napi microstriata (Lepidoptera: Pieridae) during and after the 1975-77 California drought, and its evolutionary significance. Psyche, Camb. 86: 1-10, SPURWAY, H. (1955): The causes of domestication: an attempt to integrate some ideas of Konrad Lorenz with evolutionary theory. J. Genetics 53:

THOMAS, J. A. (1984): The conservation of buttedies in temperate countries: past efforts and lessons for the future. In The biology of butterflies: 333-353. Vane-Wright, R. I. & Ackery, P. R. (Eds). London: Academic Press. THOMAS, J. A. (1987): The return of the large blue. News, Br. Butterfly Conserv. Soc. 38: 22-26.

325-362.

Manuscript submitted 15 January 1991

Int. Zoo Yb. (1991) 30: 97-107 0 The Zoological Society of London

The educational value of leaf-cutting ant colonies and their maintenance in captivity ROY POWELL Paignton Zoological and Botanical Gardens, Totnes Road, Paignton, Devon TQ4 7EU and The University of Exeter, Department of Biological Sciences, Prince of Wales Road, Exeter, Devon EX4 4PS, Great Britain

There is no doubt that today the general public is more aware of the diversity of plant and animal life than ever before. While television wildlife documentaries and the public awareness campaigns of wildlife conservation bodies have played a large part in attracting this attention, the efforts of good zoos, aquaria and bota- nical gardens have not been insignificant. Although even now it is usually the more conspicuous vertebrates that attract the most attention, the importance of inverte- brates is beginning to be recognized. In Britain advances in macrophotography achieved by such pioneering companies as

Oxford Scientific Films (Thompson et al., 1981) and more recently the BBC Natural History Unit have brought about the inclusion of invertebrates in wildlife filming. Photographers such as Stephen Dalton have helped to bring insects into popular publications with startling close- up shots. Through the media and with the recent upsurgence of butterfly and insect houses, the public’s attention is being drawn towards invertebrates in a way hitherto unimagined.

Invertebrates are not only becoming more prominent in the public eye but also in the view of professional bodies which

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are taking invertebrate conservation more seriously than ever before. A significant recent development is that the Captive Breeding Specialist Group now has an invertebrate working party concerned with the conservation of insects and other invertebrate fauna (see Hughes & Bennett, this volume). The Royal Ento- mological Society of London held its 15th symposium in 1989 on the conservation of insects and their habitats (Collins, in press) and has contributed to the Second World Conservation Strategy presented to the IUCN General Assembly in 1990. The RESL has also recently created a post of Youth Development Officer, initially based at the Exeter University, whose role is to stimulate young people’s interest in entomology and draw their attention to insect ecology and conservation issues (Harrington, 1990).

The potential for captive breeding in making any real impact on insect conser- vation is not great compared with that for vertebrates, simply because of the huge numbers of species involved, the wide range of habitats and complexity of the biological associations in which many insects live. Relevant organizations and groups would probably all agree that their main role is to boost public awareness of the invertebrate fauna and thus increase pressure upon governments to conserve wild habitats, especially the ‘megadiver- sity’ areas of the world in which the majority of insect species live. This would, of course, indirectly benefit other endan- gered flora and fauna living in such regions.

The choice of an educational inverte- brate exhibit has to be made carefully. Visitors are unfavourably impressed by exhibits where specimens cannot be easily seen or are inactive. Butterfly houses are popular because the insects are attractive in appearance, usually active, often carry- ing out their complete life cycle in full view, and are free flying in a naturalistic setting, offering the visitor the oppor- tunity of close encounters.

It is rare in zoo animal exhibits for

some activity to be taking place all the time. However, with careful planning this can be achieved with colonies of leaf- cutting ants of the genera Atta and Acro- myrmex (Hymenoptera, Formicidae). These ants offer a fascinating spectacle; apparently tireless they can be seen cutting fragments from fresh plant leaves and flowers and transporting them head high like miniature parasols back to the nest. A colony of these ants can be used to tell many stories and has tremendous educational potential. Through the medium of appropriate interpretation signs, or worksheets for schoolchildren, visitors can discover a great deal even in a short time by observing a colony of attines. It provides information on ants as examples of insects, ant societies in general and leaf-cutting ants in particular and the concepts of symbiosis, basic mycology and the evolving plant/herbi- vore ‘arms race’.

Zoo displays of leaf-cutting ants began to appear in the United States, Europe and Great Britain in the mid-1970s. As the ants are considered agricultural pests in Central and South America, a number of universities in the United States and at least four British university biology departments have held colonies for research.

ANTS AS INSECTS In order to study insect morphology, it is just as easy for a schoolchild to observe and examine snts as to look at the more traditional demonstration species, such as cockroaches or locusts. They will not fly away and, although they are fast movers, they can easily be confined in a small container for detailed examination with a hand lens or a binocular microscope. Ants exhibit the classical insect body plan having a chitinous exoskeleton, jointed appendages, three distinct body regions, three pairs of walking legs and com- pound eyes. While ant workers lack the two pairs of wings found in the majority of insects, even these are present on $6 and reproductive QQ.

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An ant’s life cycle involves complete metamorphosis; their tiny eggs, less than 1 mm in length hatch into maggot-like larvae, which in most species are immo- bile and which will grow and moult several times before pupating and meta- morphosing into the familiar ant shape. Eggs, larvae and pupae of leaf-cutters are kept in cavities in the fungus garden.

ANT SOCIETIES A colony of leaf-cutters will exhibit a great many typical ant features. Common to virtually all ant species is their sociality. Most species have a society consisting of one or more queens attended by many Q workers with unmated queens and 88 found in the colony at times. There are always workers visible outside but the queen and JJ are usually difficult to see, being hidden inside the nest along with the young stages. In an exhibit of leaf- cutting ants it is possible to offer the visitor a view inside the nest to show the queen and the brood being attended by workers.

Where the internal workings of the nest are displayed, it is easy to demonstrate the division of labour that exists between the various members of the society. Both inside and outside the nest the visitor may observe interactions between individual ants, such as antennation, that is the use of the antennae gently to touch another individual, or trophyllaxis, the exchange of droplets of liquid food from the mouth of one ant to another.

The majority of ant communications are camed out by means of pheromones (see Brian, 1983; Holldobler & Wilson, 1991). The queen exerts her influence on the rest of the colony and the workers communicate by means of these chemical substances. Alarm pheromones released from a distressed ant will cause all the workers in the vicinity to become alert and aggressive; when the source indivi- dual is removed from the scene the commotion subsides. Other pheromones are used to produce foraging trails to and

from a source of food. In leaf-cutting ants the trails are distinct with ants moving in long lines on invisible paths. Workers returning from a successful foraging expe- dition produce a pheromone from the tip of the abdomen which is touched on the ground at intervals leaving a trail which subsequent foragers follow and, in their turn, reinforce as they return with food. When the interest in the food ceases the pheromone will eventually vaporize.

Most ants are able to defend themselves and assist in defending the colony. They may also need weapons with which to attack prey. A popular myth is that all ants produce formic acid but it is not true of the majority of ant species. Some species exude other noxious chemicals while many possess a sting to paralyse insect prey. Whatever method has been adopted most ants use it in combination with their jaws in battle. Although the herbivorous leaf-cutting ants have no need of sting or formic acid for offence, they are quite able to defend themselves and the colony with their sharp jaws. In the genus A m a caste of soldier ants, with disproportionately large heads and strong muscles, has developed. The soldiers are never far from the entrance holes of the nest and will bite any foreign object which enters. Traditionally, South American indians used these ants to ‘stitch’ open wounds by encouraging the soldiers to bite the edges of the wound and then twisting off the the animal’s body and leaving the head in position.

Although it is not a feature of all ant species, there is a considerable variation in size among the workers of leaf-cutting ants which range from about 2mm to almost 20mm. There is a division of labour between workers of different sizes, with the larger insects usually seen foraging for food and the smallest remaining in the nest where they can reach into the narrowest sections. In the genus Atta the queen may be the size of a small field mouse (Plate 1) and can survive for up to 20 years in captivity (Weber, 1972).

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Plate 1. A queen leaf-cutting ant Aftu cephulotes on the fungus garden attended by small workers. One of them (right) stands on her abdomen waiting for the next egg to be laid. The fluffy, white fungal mycelium growing on the plant fragments is clearly visible. D. J. Strudling.

ATTINES AND SYMBIOSIS The ant tribe Attini comprises 190 or so species and can be divided into three broad groups: primitive, transitional and higher attines (Weber, 1972). The primi- tive species largely collect insect drop- pings, for example from caterpillars, on which to cultivate their fungus and transitional species may also use some dead and decaying plant matter. Only the higher attines, of which there are about 40 species, actually cut pieces of living plants to supply their fungus with nutrients. Leaf-cutting and grass-cutting ants belong to this group. Their nests may contain up to seven million workers and occupy many cubic metres and several thousand nest chambers underground. They normally forage conservatively but in agricultural land may defoliate crop

plants and become serious pests (Cherrett, 1986).

Unlike other ants, the Attini have a unique symbiotic relationship with a fungus which has never been reliably iden- tified from any other source. The mycelia from most species of higher attine ants are virtually indistinguishable in their outward appearance but differ in their productivity (Stradling & Powell, 1986). The fungus benefits from the relationship by being transmitted and propagated by the ants, being supplied with food and being protected from competing fungi. In many ways these New World ants exhibit a parallel evolution with the fungus-grow- ing termites (Macrotermitinae) of Africa described by Thomas (1981).

The fungus produces clusters of swollen hyphae which the workers pick and feed

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Plate 2. A single football-sized fungus garden inside a cavity dug in the soil by the ants. The structure is often attached to living plant roots for support. D. J . Stradling.

to the larvae, queen and any mature 36 and which the colony contains. These structures provide the sole source of food for the larvae (Martin et al., 1969; Quinlan & Cherrett, 1979) and contain more protein than the plant tissues gath- ered by the workers (Cherrett, 1980). The workers consume a small amount of fungus themselves. Speculation has abounded as to the role of the fungus in the ants’ nests. Initial ideas were centred around the general role that microbes play in the digestive system of herbivores; that is, the fungus was thought to digest the cellulose of plant cells walls and make the carbohydrate available to the ants. However, the fungus is not actually able to break down cellulose effectively but has a strong capacity to digest starch and protein in the leaves (Powell, 1984). Research in the United States (Martin &

Boyd, 1974; Martin et al., 1973, 1975) revealed that the ants acquire a number of digestive enzymes from the fungus which break down starch, protein, chitin and pectin. These enzymes survive passage through the ants’ guts and appear in a concentrated form in the faeces. When the ants first obtain fresh leaf fragments, they cut them into tiny fragments, lick them to remove surface waxes (which normally inhibit fungal penetration), crimp them with their jaws to express juices, and defe- cate on them (Quinlan & Cherrett, 1977, 1978); the fungal digestive enzymes in the faeces react on the plant material and the fragments are then carefully placed in a fungus garden (Plate 2) and deliberately planted with a fungal inoculum. By this time the leaf fragment is already partially digested.

Examples of symbiotic relationships

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normally offered to biology students, such as the hermit crab and sea anemone, make the nature of the benefits to both partners quite clear. The symbiosis of Attini and fungus, however, illustrates a relationship which can be studied on a number of levels and provides a stimulating subject for discussion.

PLANT/HERBIVORE ‘ARMS RACE’ Leaf-cutting ant biology offers an insight into the relationships that exist between plants and the insects which feed on them. These relationships which have developed over millions of years are still evolving but this important biological concept is often neglected in the training of biologists. A colony of ants can be used to illustrate this idea.

Most herbivorous insects are restricted to one food plant or a small number of closely related ones; the caterpillars of butterflies are clear examples. Over millions of years of co-evolution and continuing competition between plants and the herbivores, mostly insects, that try to feed on them (Feeny, 1975; Rhoades & Cates, 1976) the former have become as unpalatable as possible, using many kinds of structural modifications (thorns, waxy or hairy leaves, sticky latex) or chemical toxins stored in the leaves in their own defence. The herbivores have adapted to these physical defences with modifications to the structure of their mouthparts and guts. The chemical plant defences pose the larger problem because about 30 000 types of defensive substances have been described (Harborne, 1977). For an insect to cope with all of these would require considerable biochemical versatility.

Most herbivorous insects can fly giving them the advantage that food plants can be located from the air and from a distance. These insects will have evolved structural and biochemical adaptations to breach their chosen food plant’s physical and chemical defences. They may even use the odour of the plant’s defensive chemi- cals to help locate and recognize it.

Colorado beetles Leptinotarsa decemli- neata, which feed on potato plants, have overcome toxic potato alkaloids. Simi- larly, white butterflies Pieris spp have overcome toxins such as sinigrin and other glucosinolates in cabbages (Edwards & Wratten, 1980).

The Attini are the only entirely herbi- vorous ants and no other ant group exploits fresh plant tissues (Stradling, 1987). However, unable to fly, they are forced to use food plants which grow in the vicinity of their nests. In a South American tropical forest this can amount to as many as 300 different species per 4000m2. This diversity of plant species would provide a huge variety of defensive chemicals even without the ‘blanket’ defence produced by many woody species in the form of tannins and other phenolic compounds which are aimed at herbivores in general. Cherrett (1968) found that leaf-cutting ants in a Guyanese rain forest utilized 30-50% of the plants around their nest. Similarly, Rockwood ( 1 976) found that two Atta species in Costa Rica exploited up to 31% of available plant species. Plants that are not utilized may possess physical defences such as sticky latex (Stradling, 1978) or nerve toxins which kill scouting foragers when they try to cut the leaves (Powell & Stradling, 1991). One particular tree is toxic both to ants and fungus (Howard et al., 1988). In general, however, the ants are capable of overcoming the defensive chemicals in the leaves they do cut.

The modern conception of the relation- ship between ants and their fungus is of an ‘unholy alliance’ whereby the fungus breaks down the chemical defences of plant leaves against herbivores whilst the ants remove some plant barriers against fungal penetration and growth (Cherrett et al., 1989). The most widespread of plant chemical defences against herbi- vores, especially in rain-forest trees, are phenolics (Harborne, 1977) which largely occur in the leaves in an inactive form, phenolic glycosides. When the leaves are damaged by herbivores or pathogens,

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active phenolics are released from the ruptured cells causing proteins and other large molecules to bind together thus interfering with the attacker’s digestive enzyme systems (Goldstein & Swain, 1965). To counter this defence, a few plant-feeding insects and pathogenic fungi have evolved a weapon in the form of polyphenol oxidase (PPO), which releases the molecules and counteracts the effect of the plant’s phenolics. It has been shown that the symbiotic fungi of leaf-cutting ants and other attines secrete PPO (Powell, 1984; Powell & Stradling, 1991). The enzyme is swallowed by the ant workers when they consume the fungus and is excreted together with the various digestive enzymes of fungal origin (Powell, 1984). As the leaf fragments pass through a fungus garden their phenolic content is decreased significantly as the ants defecate on them. The workers pre- sumably also use it to detoxify phenolic- laden plant sap that they drink when cutting leaves.

Some investigators have suggested that the ants act as ‘ecological vicars’ for their fungus, selecting plants that are not toxic to it and avoiding those that are (Hubbell et al., 1983). However, recent results presented by Powell & Stradling (1991) strongly indicate that this is not the case and that some leaf fragments collected are indeed toxic. In spite of this, the fungus garden remains healthy because the ants collect fragments from a huge range of plant species, the majority of which are harmless to their fungus, and so dilute the effects of any fungicidal ones. It seems unlikely that the ants could have evolved mechanisms for recognizing all of the chemicals in plants that are a potential threat to their fungus, especially in the immensely diverse tropical flora. What is more likely is that the selection of plant material is made on the basis of its pH and available protein content, which are directly linked with the phenolic content (Powell & Stradling, 1991) and are modi- fied by other leaf chemistry factors (Howard, 1987, 1988).

THE FUNGUS Although apparently unique to the leaf- cutting ants, the symbiotic fungus is not rare. On the contrary, given the abun- dance of leaf-cutting ant colonies, it is possibly the dominant fungus exploiting living plants in the New World tropics (Cherrett et al., 1989). The fungus, whether from the nests of Atta or Acro- myrmex spp looks very similar and has been given the name Attamyces bromatij- cus (Kreisel, 1972). It forms a glistening white mat on the surfaces of all the leaf fragments in the fungus garden. Its micro- scopic structure reveals that it consists of a fine, branching mycelium of which the hyphal tips are swollen into spheres, the gongylidia. A cluster of these is called a staphylus (from the Greek: bunch of grapes) (Plate 3). It is the staphyla that are consumed by all members of the colony but mostly by the larvae.

From an educational point of view Attamyces is of considerable interest. It is not in fact so dependent on its ant partner that it cannot exist on its own, although this does not seem to occur in nature, and it can be isolated from the nests of leaf- cutting ants and cultured on a simple mycological media (Plate 4). Powell & Stradling (1986) have described the isola- tion and exact requirements for the culture of the fungus in the laboratory and the methods would not be beyond the capabilities of most advanced biology students. From this point of view it could form the basis for many simple projects. Studies on growth rates and the produc- tion of gongylidia when grown on media in which the carbohydrate varied would be an example. The fungus is not a human pathogen and so presents no health hazards. It is a fairly typical ‘white rotter’, that is it is not good at digesting the cellulose in woody plant tissues but can digest the other components of wood, leaving the white cellulose intact. It possesses a number of specialized enzymes, including PPO. The addition of tannic acid to the medium causes a striking colour reaction (the Bavendamm

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Plate 3. A cluster (staphylus) of swollen fungal hyphae (gongytidia) of Attamyces bromatifcus, the symbiotic fungns of leaf-cntting ants. The gongytidia are about 0-05 mm in diameter. Staphylae are about 0.5 mm across and are fed to tfie ants’ larvae providing their entire nutritional requirements. R. Powell.

__ - _. -__-- --- .-- __---- --11_____1______

Plate 4. Attamyces bromatificur isolated from the fungls gardens and cultured on Potato Dextrose Agar in a Petri dish. Staphylae are clearly visible as spots evenly distributed over the mycelium. R. Powell

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reaction) offering a clear evidence of the presence of this enzyme; a simple demon- stration which can be carried out by students.

In a zoo situation, with competent tech- nical assistance it would not be difficult to display living cultures of the ant’s sym- biotic fungus growing in Petri dishes within an ant exhibit. If the equipment is available, microscope slide preparations of some of the mycelium would add an extra dimension but if this is not possible the features could be displayed in photo- graphs on interpretative panels.

OBTAINING COLONIES The feasibility of importing colonies of leaf-cutting ants from Central and South America depends upon local regulations. In the United States permits must be obtained from the Federal and State Departments of Agriculture. In the United Kingdom the ants are on the Ministry of Agriculture’s restricted list but at the time of writing this is under review. At present a collection wishing to keep the ants must obtain a licence from the Ministry and the colonies are usually inspected. Clearly the ants’ status as pests (Cherrett & Peregrine, 1976) in the native habitat causes concern but in temperate regions neither ants nor fungus would survive the climate. In tropical or sub- tropical regions outside their country of origin, however, escaped ants could become a serious threat to agriculture.

Few zoos are in the position to collect their own leaf-cutting ant stock but colonies may be obtained through profes- sional entomologists or often as surplus stock from ant-pest research programmes. Researchers take a few newly mated queens from the thousands that are released from each nest annually at the beginning of the rainy season. In the wild many of the prospective queens fall to predators and only a small proportion actually establish colonies. A successfully mated queen loses her wings and digs a small cavity in the ground where she deposits a small piece of fungus garden

which she has carried in her mouthparts from the parent nest. She will nurture the new garden until her first eggs produce workers to take over its care.

MAINTENANCE IN CAPTIVITY Most of the requirements of a leaf-cutting ant colony relate to the natural habitat. They live in dark cavities dug in the soil of the tropical forest floor where the temperature is a constant 25°C and relative humidity never drops below 70%. Powell & Stradling (1986) concluded that allowing conditions to vary far from these limits will do more harm to the fungus, which is sensitive to light and tempera- ture, than to the ants themselves. Lethal conditions for the fungus are exposure to low humidity, temperature above 30°C or ultraviolet light, that is, direct sunlight.

In a well-designed exhibit many of the aspects of the ants’ behaviour can be displayed to the public. The smaller workers can easily be seen engaged in all of their gardening activities and the fate of a leaf fragment can be followed from the parent plant to its incorporation into the garden planted with fungus.

Zoos have tended to follow fairly similar designs for leaf-cutting ant display. Typically an exhibit consists of a large glass tank which acts as the foraging arena for the ants, beneath which the fungus garden is housed. In many cases the fungus garden is not on-exhibit but since much of the activity of the colony takes place here, it should really be an integral part of the display. It is not tech- nically difficult to display the fungus garden; it can be shown with a low level of illumination, possibly using a red-light source with a timed release switch oper- ated by the visitor for short periods of viewing. Light will not disturb the ants but care has to be taken not to expose the fungus to excessive amounts.

The fungus garden is contained in transparent boxes; for example, clear polystyrene ‘lunch boxes’, which have been cut and drilled to provide entrance holes. If the garden expands more boxes

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are added linked via the pre-drilled holes. Thermostatically controlled heating pads in the vicinity help to maintain the constant 25°C required and a fine mist spray into the foraging tank daily helps to maintain high humidity.

The ants can be prevented from escaping from the foraging arena, by painting the inside top rim of the tank with a band of Fluon, a non-stick agent which prevents the ants from walking on the painted glass. Some exhibits have used completely enclosed foraging arenas connected to the fungus garden by long transparent plastic tubes through which the ants lay foraging trails and can be observed carrying their colourful plant burdens.

A large range of plant material can be offered although extreme care must be taken to avoid plants which have been sprayed with pesticides or fungicides. The ants will readily cut flower petals, citrus peel and the leaves of a huge range of trees and shrubs. In winter useful sources of leaves are privet Ligustum and Rhodo- dendron and leaves collected and frozen in the summer are also acceptable. However, the ants should be offered a variety since feeding the same material over a long period may result in a decline in foraging and, should the plant material contain toxic chemicals, may eventually poison the fungus. In spite of its amazing bio- chemical powers, it is unable to detoxify everything (Mullenax, 1979; Powell & Stradling, 1991).

As a guide to the quantity of material a leaf-cutting ant colony can consume, Weber (1972) reported that an Atta fungus garden of 1.2 litre and weighing 130 g was built from 1 kg of fresh leaves. Probably only about 10 g of this garden is accounted for by the weight of the ants. Weiss (1990) reported that a captive colony of Atta cephalotes isthmicola reached a maximum size of 54 litres and consisted of many interconnected fungus gardens. It survived for nine-and-a-half years and used a total of 139 kg of plant material (largely red oak Quercus rubra

and oatmeal flakes) with a maximum of 2.66 kg per month.

After stripping off the fungal mycelium for use, the ants remove spent plant frag- ments from the fungus garden usually dropping them in heaps well away from the garden. In the wild this may be above ground or in middens, special nest cavi- ties, which are eventually sealed off. The material looks rather like used tea leaves and in an exhibit must be cleared away to prevent the formation of moulds.

PRODUCT MENTIONED IN THE TEXT

Fluon: polytetrafluoroethylene (PTFE), non-stick fluid, manufactured by ICI plc, Slough, Great Britain.

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KREISEL, H. (1972): Pilze aus pilzgarten von Atta insularis in Kuba. Z . allg. Mikrobiol. 12 643-654. MARTIN, M. M. & BOYD, N. D. (1974): Properties, origin and significance of the fecal proteases of the fungus-growing ants. Am. Zool. 14: 1291. MARTIN, M. M., CARMAN, R. M. & MACCONNELL, J. G. (1969): Nutrients derived from the fungus cultured by the fungus-growing ant Atta colombica tonsipes. Ann. ent. Soc. Am. 6 2 11-13, MARTIN, M. M., GIESELMANN, M. J. & MARTIN, J. S. (1973): Rectal enzymes of attine ants. Alpha- amylase and chitinase. J . Insect Physiol. 19

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SILVER, R. G. (1975): Activity of faecal fluid of a leaf-cutting ant toward plant cell wall polysaccharides. J. Insect Physiol. 21: 1887-1892. MULLENAX, C. H. (1979): The use of jackbean (Canavalia ensiformis) as a biological control for leaf-cutting ants (Atta spp). Biotropica 11: 313-314. POWELL, R. J. (1984): The influence of substrate quality on f i g u s cultivation by some attine ants. Unpublished PhD thesis, University of Exeter. [Available from BLDSC; ref. no. D51730184.1 POWELL, R. J. & STRADLING, D. J. (1986): Factors influencing the growth of Attamyces bromatificus, a symbiont of attine ants. Trans. Brit. mycol. Soc. 87:

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Manuscript submitted 23 January 1991