Essays page 6

How is the excretory system of insects involved in the control of water balance?

Malpighian tubules lie loose in the haemolymph and move about the body cavity in most insects (some Tenebrio have a crypto nephridial arrangement to enhance water conservation with tubules closely associated with the rectum). The Malpighian tubules produce primary urine - it can be iso-osmotic or dilute but not concentrated.

Potassium is the driving force, and is actively pumped from microvilli to tubule lumen. This creates a pull on the basement membrane side where K+ enters from the haemolymph. Water follows the K+. Then the Malpighian tubule contents (primary urine) enter the hind gut.

The hind gut is very effective at absorbing water especially in insects like Tenebrio etc. It can transport water from the rectal lumen into the haemolymph even against a concentration gradient of 3X in locusts. It is lined with cuticle with pores of 7 nm in locusts, and this may act as a sieve against large molecules so protecting the rectal epithelium.

Rectal pads. These are large aggregations of epithelial cells with lots of mitochondria. The epithelial cells with their mitochondria are folded into stacks creating intercellular spaces. The stacks are rich in ATPase which is used in ion transportation. Movement of water from the rectal lumen to the haemolymph appears to occur without transport of ions - this is physiologically impossible, so how is it done?
1) There may be active secretion of ions from epithelial cells and/or haemolymph into the intercellular spaces raising concentration.
2) This would cause water (and possibly small molecules) to move from the rectal lumen to the intercellular spaces. These spaces are all interconnected so there could be a general flow into the infundibular space.
3) When sufficient pressure is created in the infundibular space the valve would open allowing the contents (water) to pass into haemolymph.
4) The ions can be recycled into the epithelial cells to start the process again.
So the active transport of ions into the intercellular spaces causes movement of water from the lumen into intercellular spaces, then a general flow to the infundibular space where pressure build up causes passage into the haemolymph - all powered by the large number of mitochondria.

The rate at which the fluid is lost depends on the rate of fluid secretion by the Malpighian tubules and the absorption in the rectum. By regulating these two processes insects maintain water balance.

A locust feeding on wet food produces faeces with a water content of 80%, but a water content of only 20% when feeding on dry food.

In Tenebrous all water from the rectal lumen returns to the haemopymph.

Hormones. Neurosecretory cells in the brain regulate the fluid produced by the Malpighian tubules. Generally feeding stimulus, e.g. stretch receptors - trigger neurosecretory cells to release diuretic hormone promoting water loss. The diuretic hormone causes an increase in Cl- permeability of the Malpighian tubules, decreasing the already negative potential of the tubules which is maintained during fast fluid secretion.

Anti-diuretic hormones may also exist to increase water uptake from the rectal lumen, or perhaps the absence of diuretic hormone is enough as the Malpighian tubules then secrete at very low levels in the absence of diuretic hormone.

Why is the cultivation of crops inevitably associated with pests?

It is estimated that without insect pests world food production would be increased by about a third. Thus in spite of all control measures we still lose a third of our crops to insects. Each insect is fairly small and eats only enough to fill its gut, but even so it only takes one insect to blemish a whole apple or transmit a disease to kill a tree. The most noticeable damage is done by large populations of insects. For example one hectare of oats may be home to 22 million fly larvae and 222 million black bean aphids can happily live on one hectare of beet. In the wild it is rare or never that such outbreaks occur. So why do they occur in crops?

1) By monocultural, or near monocultural cultivation man make an unapparent plant apparent. The theory of plant apparency was developed by Feeny, Rhodes and Cates. It states that unapparent plants (most wild relatives of crops) are relatively difficult to find, not available throughout the year, and invest little in chemical and physical defence. Their defence is that they won't be found. They breed rapidly and produce lots of seeds. Man has taken these plants and selectively bred them for seed, tuber, fruit etc. production, and densely planted them over miles of countryside while eliminating most other vegetation. What could be more apparent? In the wild if one plant was discovered it may have been badly eaten and died, but others would have lived to reproduce. With crop varieties the pest insect is surrounded by a sea of food, the next plant is the same as the one it is on, and so on. The situation might not be so bad as an insect cannot eat so much, but insects can breed.

2) Certain pest species breed enormously fast (r-seleceted) under favourable conditions. One aphid can give birth to 40 others in a few days, and some morphs are parthenogenic so don't even have to waste time on sex. When one plant gets crowded or begins to wilt they move. In a crop this move is just to the next plant. In the wild mortality is high during host transference. The winter moth larva balloons on a thread if it hatches before budburst. This is one of the factors that produces highest mortality. But if they are in an apple orchard in Nova Scotia the next tree in any direction is as far as they need to go. Studies showed that infections of sticky banded and unbanded trees were the same, i.e. had no relation to the number of eggs on a tree. Insects lay lots of eggs, often near or on the food plant. So the larva must colonise the food plant to survive and reproduce, but again if they are not food limited they have a much higher survival rate and may swamp predators and parasites.

3) Many crops are planted in the same field again and again. This is perfect for building up insect numbers as they may overwinter in the soil or stubble, then hatch and have to find food. How convenient of man to have planted some right next to the eggs. Watercress growers in Japan reported that the diamondback moth had become resistant to Bacillus thuringiensis (a bacterial insecticide). They had been growing watercress (a very fast maturing crop) in glasshouses continuously for 3 - 4 years, and in that time Bt had been applied 40 - 50 times! The moth was under such strong selection pressure no wonder resistance was the outcome.

4) Pest control. Insecticides etc. are never 100% effective, so there will always be a few escapees (see the diamondback moth above), and the escapees may have some mutation that makes them resistant, so they breed and the next generation are all resistant. The insecticide may have killed all the insects or even all arthropods, so now the new resistant generation are surrounded by a sea of food and most of their predators, e.g. spiders, carabid and staphylinid beetles are either dead or not yet adults. The pest control has led to pest outbreak such as has happened to rice leaf hoppers.

5) Many crops are introduced with their pest but without the pest's predator. For example the winter moth in apple orchards in Nova Scotia. The cotton cushiony scale insect in California. Both of these had happy endings for man, but for a while the insects came close to ruining an industry. Sometimes success is not so easy as just introducing a predator. For example tea in Sri Lanka is an introduced crop. A tortrix moth became a pest, s a parasitoid was introduced with marvellous success. Then a boring beetle became a pest on the crop, so dieldrin was used and was a greta success in reducing beetle damage, but unfortunately it facilitated outbreaks of two caterpillars which multiplied to become even greater pests that the beetle had been. Spraying of dieldrin was stopped, the damage lessened, and a new method of control is being searched for.

Discuss the role of true flies (Diptera) in the health of humans and their domestic animals.

Diptera parasitise vertebrates as larvae, and bite and transmit disease as adults.

Myiasis is the parasitism of the tissues of animals by larvae of Cyclorapha, these include the Muscoidea some of which suck blood. The Congo floor maggot, another bloodsucker is found only in humans. The screw worm fly which can enter through the smallest skin puncture then feed on the flesh, literally eating the animal alive. The point of control is the mating stage as the female mates only once. So sterile males are released in such great numbers as to swamp the normal males. This eliminated the fly from Libya where it was accidentally introduced in sheep. In America the fly is kept out of some areas by this technique. Strike in sheep is caused by the adult laying eggs in the soiled area around the anus. The maggots hatch and just eat into the flesh. These are the same maggots that are used medicinally to clean wounds. Bot flies of humans, sheep, cattle and horses. These enter through the skin, nasal passages etc. and lay their eggs in the nostrils in the case of the nasal bot fly. The larvae grow in the sinuses and are sneezed out. Sheep do not thrive in the presence of bot flies neither do cattle. The warble fly spoils leather by emerging at the side of the spine.

Ectoparasites in diptera are few in number. They include the deer fly of birds and the sheep ked which does not look like a fly.

Mosquito borne diseases kill millions of humans each year and infect many more. The diseases include malaria where the female mosquito transmits plasmodium spp. whilst taking a blood meal. Fliaraisis which involves the transmission of nematodes that cause elephantiasis. Yellow fever which is caused by a virus as is dengue.

Sleeping sickness is caused when certain species of tsetse (Glossina spp.) transmit trypanosomes.

Many other species of Diptera cause or transmit diseases. As far as humans are concerned malaria is probably the biggest killer among dipteran caused diseases. It was thought that DDT would eliminate the mosquitoes but they have proved resistant to most insecticides. Some new treatment for malaria is badly needed as there is some resistance to just about all the current medicines. Malaria not only kills but debilitates first. Some lessening of the effect would surely help the countries where it occurs as it puts a great strain on the health budget. There is also the spectre of the spread of malaria into the more prosperous nations caused by climate change.

Yellow fever and sleeping sickness both rely on having a reservoir of disease in the wild hosts - primates for yellow fever, and just about any vertebrate for trypanosomes. This makes elimination of the disease virtually impossible. It also means that previously cleared areas can become reinfested. The presence of the tsetse fly has limited the colonisation of many parts of Africa by cattle farmers. Others lose a proportion of their cattle each year, in cattle the disease is called nagana or ngana. Sleeping sickness kills only a few thousand humans each year, so now is no longer seen as a real danger.

Filariasis affects humans and one type can cause heart worm in dogs. There are about one hundred million cases of elephantiasis in the world. It is a debilitating disease transmitted by Culex quinquefasciatus which lives in and around human dwellings, so it should be possible, with education, to limit the amount of stagnant water left lying around. River blindness is caused by filarial nematodes transmitted by black flies (Simulium) it does not kill, it just blind making people unable to work.

Most dipteran caused diseases occur in the developing world, they have been eradicated or occur only sporadically in the developed world. So the people affected can least afford to pay for treatment. And the dissemination of information on lifestyle changes to limit the spread of disease is perhaps more difficult in these countries. This, plus the ling time before drugs are approved limits the years a company will have a patent on a new treatment. So research into new drugs or control methods has been decreasing while the pests and vectors have been developing resistance to the drugs and treatments currently available.

Describe the role of the insect gut and its symbionts in overcoming the biochemical barriers to herbivory.

Plants, apart from pollen, seeds and nectar, are not very nutritious, though they are plentiful. The cell walls are fairly indigestible as they contain cellulose, hemicellulose and lignins; proteins and lipids are low. Also most plants have allelochemicals usually both constitutive and induceable. Many insects have modified mouthparts to deal with the physical barriers to herbivory. The biochemical barriers are mainly overcome in the insect's gut.

The gut pH in most insects is quite high. In caterpillars (gut pH 8.8) which eat large quantities of leaf with minimal chewing this high pH further breaks down the leaf parts.

Cellulose digesters. To digest cellulose requires both exo- and endo-glucanases.
1) Hind gut flagellate protozoa are found in some termites. The termites chew up the wood and the protozoa break down the cellulose. The lining of the hind gut of insects is cuticular, and this is lost when moulting. So termites would lose their symbionts if it were not for the habit of feeding from the anus and faeces of nest mates. This may be one of the causes of eusociality in Isoptera. Roaches (non-social) retain their hind gut protozoa by anti-peristaltic movements of the gut prior to moulting to bring glucose into the mid gut for absorption.
2) The higher termites, wood-boring beetles, crane flies and cockroaches have bacteria, these operate in a similar way to the hind gut protozoa.
3) Fungal enzymes break down cellulose and are taken in along with the wood by some beetles, e.g. Ambrosia beetles, and also by wood wasp larvae. In the fungus growing termites the enzymes are ingested when the termites eat the fungal fruiting bodies.
1, 2 and 3 are all examples symbiotic relationships enabling cellulose digestion. Nasutermes spp. and one cockroach species have their own cellulases so can digest cellulose without symbionts.

Aphids tap straight into the phloem of the plant. Phloem is rich in water and sugars, but relatively low in nitrogen. So the aphid must process a lot of phloem to meet its nitrogen requirements. The water is quickly excreted by by- passing most of the mid gut, as the fore gut has a connection to the rear part of the hind gut so excess water takes this route.

Dealing with allelochemicals.
Sequestration. Some insects actually depend on the so-called defensive chemicals for their survival. They do not digest them, but sequester them and use them to protect themselves against predation, e.g. the cinabar moth eats ragwort which contains cyanide. The antibiotic properties of some allelochemicals may also provide protection against pathogens.

Mixed function oxidases (MFO) are memberane-bound enzymes that detoxify a wide variety of allelochemicals. MFO are usually found in the fat body or the mid gut. Their characteristics are:
1) They catalyse oxidative reactions resulting in polar products that are easily excreted.
2) They are non-specific, accepting many chemical substrates.
3) They are easily induced by exposure to novel toxins.
MFO are especially valuable to polyphagous insects as they eliminate the need to maintain a wide variety of specific protective enzymes. The detoxification is as follows:
1) Primary degradation in which a toxic molecule receives a chemical group, e.g. OH which makes it water soluble.
2) Conjugation with sugars, amino acids, sulfates, phosphates etc, bound for excretion.
3) Excretion.
For example nicotine becomes cotinine and is excreted.
MFO activity can appear within minutes of exposure to novel chemicals, e.g. the armyworm (Spodoptera eridania) chews a new leaf, waits a few minutes, then starts to eat the leaf. The few minutes' wait is all that is required to induce MFO activity. As the hours pass the caterpillar becomes increasingly efficient at digesting the food source. MFO activity varies among species, and even among individuals within species. Lepidopteran larvae that are polyphagous have higher MFO activity than mono- or oligophagous larvae. So generalists are better adapted. MFO has preadapted many insects for developing resistance to pesticides, e.g. DDT and kelthane.

RECONCILING THE NEEDS OF NATURE CONSERVATION AND THE BENEFICIAL USE OF A NATURE RESERVE BY PEOPLE

Introduction
One of the main interests at Sands of Forvie National Nature Reserve is the birds that arrive in spring to breed and then leave at the end of summer.  The main species are common, little, Arctic and sandwich terns, eider ducks, shelducks and oystercatchers.  The sandwich terns usually arrive first in April, and start breeding in May.
 
The Reserve is used by people throughout the year for a range of activities, three of the main ones being:

  1. Wildfowling.  This takes place from September to February, and is open to the public.  Only certain species may be shot, there are some occasions when protected species are shot, but prosecutions are generally not successful.  The disturbance caused by shooting is localised in time and place.
  2. Fishing on the river.  The anglers do occasionally disturb terns on their nests; this can lead to desertion of the nest.  Small boats moving up and down the river also cause some slight disturbance.  However on the whole the disturbance caused by fishing is not excessively damaging.
  3. Visitors and locals walking, sometimes with dogs.  Dogs certainly seem to cause the most human-induced damage to the reserve.  Owners should keep dogs on leads, and there are signs asking them to do so, but they rarely do.  There have been no prosecutions, nor does it seem that there is any intention to prosecute.

The reserve is also used by wind-surfers, educational parties of children from local schools, and for academic research.

A study of the effects and frequency of disturbance on eider crèches done in 1988 and 1989 found that disturbances affected the activity of the crèche for up to 35 minutes.  Also that most disturbances were shore-based, and of these the most frequent (70%) cause of disturbance was people with dogs (Keller, 1991).

The reserve and the locals
It is well known that reserves cannot be successful without the goodwill and/or help of the locals.  This fact seems to be realised by the Site Manager at Forvie.  However it is the locals who use the reserve most for dog walking, so they are the ones causing the most damage to the reserve.  This fact also seems to be recognised; but apart from handwringing, it seems that nothing is going to be done about it.

The locals of Newburgh and Collieston are probably the same as most other people, and would not knowingly allow their dogs to do harm.  When a dog does disturb a few birds out of many, they probably see it as an isolated incident, scold the dog, and regret the damage.  They probably do not realise that this damage can be multiplied many times over for other dogs, and cumulatively can cause population losses, or failure to breed successfully.  In their defence they would say that they have always walked their dogs there, and so has everyone else for as long as they can remember.  They may feel that they have a right to walk their dogs there, and ignore the signs because for a large part of the time the terns, duck and oystercatchers, etc., are not there.  
The problem

  1. Dogs, not on leads, owned by locals are causing damage to populations of nesting birds, one of the most important interests in the reserve.
  2. The locals have always walked their dogs on the area covered by the reserve.
  3. For much of the year the terns, eiders, etc. are not nesting, in crèches, moulting or otherwise at risk, or are not present.
  4. Most of the locals probably do not intend to do any damage, or are aware of the cumulative effect of the damage.
  5. SNH want to keep the goodwill of the people.
  6. It is the policy to allow dogs into NNRs providing they are kept on a lead.

Possible solutions
Do nothing, or very little
This will keep the goodwill of the people, it is cheap, and it appears to be the current practice.  However in the long term the reserve may suffer, and the birds certainly will suffer some population loss.  This has been the situation for a number of years, so it would be difficult to change things.  Perhaps the volunteers that help patrol the reserve could be asked their opinion on the matter.  They probably know many of the locals. The volunteers may try a period of asking every dog owner to put their dog on a lead.  This might work if it is done by local volunteers during the time when the nesting birds are clearly visible and the dog owners are most aware of the potential damage.
There is no incentive for a dog owner to put her dog on a lead if she has never done so in the past, has never seen other dogs on leads, and is unaware of the full damage a dog can cause.  This solution is easy to implement, costs nothing, and if successful will please everyone, except perhaps the dogs.

The reserve has a boardwalk in places to prevent sand erosion, and to keep human impact minimal.  Dogs cannot walk, or find it difficult to walk on such a boardwalk.  What is the point of having such an expensive structure if the dog owner must either carry the dog, take it off the lead, or walk off the boardwalk on the sand.  If dogs are to be allowed in such areas, and owners are expected to keep them on a lead, and to follow a path, then the path should be suitable for dogs too.

Ban all dogs
This will certainly solve much of the problem caused by dogs, though I feel sure that the ban would not be 100% successful.  Before dogs were banned there would have to be a period of education and information dissemination.  Articles in the local newspapers and leaflets to the two communities outlining the reasons for the drastic measures would be sufficient to give initial warning.  On-site signs well in advance of the proposed ban would also be necessary.  If the problem is explained carefully and the media used skillfully this solution might succeed, however it would need manpower and possibly a few prosecutions before the ban would be fully observed.  It would be unlikely that this would not anger the locals, and if their goodwill is lost and the manpower to police the ban is insufficient, it might lead to even greater damage and vandalism.  This solution should only be considered when all else has failed, but if decided on it should be maintained rigorously.

The compromise - ban all dogs some of the time, in some areas, or in all areas
This would mean banning dogs from nesting areas from some time in April, when the first terns, arrive, until September, when they leave.  The ternery in the south of the reserve already has a barrier fence.  An additional fence might follow the Rockend track, so keeping people off the estuary altogether, but still allowing them access to a large part of the reserve to the north of the path.  Any barrier would have to be dog-proof, this might not be easy to construct or maintain, but there would be the added advantage that it might also serve to keep foxes out to a certain extent.

As the eiders do not really have a defined nesting area a decision must be taken to either allow dogs on part of the eider area, or to ban dogs from the reserve during the whole of the nesting period.  If dogs were banned for the whole of the nesting period then there would not need to be any additional expenditure on a barrier.

To enforce the ban would require the help of local volunteers; these already do help in some capacity during nesting time.  Local volunteers would be invaluable as there is bound to be a period before and during the first few years of the ban when there will be misunderstandings.   The situation might be better accepted if the explanation came from a local rather than from an outsider.

What are NNRs for and should dogs be allowed on all of them?

I think it is questionable that dogs should be allowed on all NNRs.  The rules state that they must be kept on a lead, if this is a short lead and the dog is reasonably well behaved then it will probably do little damage.  However this relies on dog owners to abide by the rules, from what I have seen few do. 

Nature reserves are there to protect and preserve the flora and fauna in the reserve. Human activity has made the surrounding area such a dangerous place that the plants and animals need a protected place where the only human intervention will be beneficial.  Because human intervention has been so limited these places are often attractive.  On some reserves I am sure that dogs off the lead would cause practically no damage, and in these reserves dog walking might be allowed.  In other reserves perhaps even the occasional bird watcher may cause more damage than the reserve can tolerate, so they should be excluded. 

The first priority must be the protection of whatever the reserve was set up to protect, if this is not done then the reserve has no right to exist.  It should be recognised that each reserve has its own unique set of characteristics, therefore should have its own level of allowable human impact.  This level can and should be reviewed with each management plan.   We must recognise that reserves are not there for us, but to protect the plants and animals from us.  Also it is a duty of SNH, etc. to try to educate the general public so that they look on these reserves as places of refuge for flora and fauna, and not just nice places created for them to take the dog for a walk.  

Reference

Keller, V.E.  (1991).  Effects of human disturbance on eider ducklings Somateria mollissima in an esturine habitat in Scotland.  Biological Conservation.  58: 213-228.

TERMITE ECOLOGY

Introduction

There are about 2200 species of termite in the world (Wilson 1971), occurring mainly in the tropical and sub-tropical areas, where they may surpass the earthworm in the activity of breaking down organic matter (Brady 1990).  All termites are eusocial and together they form the Order Isoptera.  Though they have many similarities to the Hymenoptera, termites are actually more closely related to the cockroaches, and the similarities between Isoptera and Hymenoptera are usually described as examples of convergent evolution.  Termites have a caste system that consists of larva, nymph, worker, soldier, and reproductive; the different species may have some intermediate castes, but the main castes are the same in all species.

The termite colony

Food
Termites feed on cellulose or cellulose products, to digest the cellulose they have a symbiotic relationship with protozoans and bacteria that live in their hind guts, these digest the pulp that the termites have chewed up (Wilson 1992).  They eat dead wood, leaf litter, live wood, green vegetation, lichen (Brian 1983); and also dead or surplus nest mates, and the soil itself (Golley 1983).  The most primitive termite alive today is Mastotermes darwiniensis, it lives in the northern part of Australia, and is considered to be a very destructive pest.  It has been observed to eat wood in any form, even wood soaked in oil; salt, ivory, billiard balls and the plastic coating around electric cables (Wilson 1971).

Nest construction
Nest construction begins soon after mating which takes place after the wings have been broken off in some species but in others during the nuptial flight.  Although Mastotermes darwiniensis is considered the most primitive termite its nest construction and connecting passageways are lengthy and elaborate.  Passageways can extend for 100m from the nest and may be either subterranean or covered passageways constructed on the soil surface, the subterranean passages can extend as deep as 4m, though most are within 50cm of the soil surface (Wilson 1971), they usually extend from the nest to a food source.

Surface passageways are constructed for two main reasons: 1) as protection from predators, 2) as protection from the desiccating effects of the outside air, termites have a delicate exoskeleton and require high humidity.  The only time that termites will break through the outer wall of the nest or mound to reach the outside air is to let the reproductives out for their nuptial flight, the walls are then quickly repaired.

The most advanced termites belong the family Termitidae, which consists of about 75% of the known species (Wilson 1971).  Some species in the Termitidae family cultivate fungus gardens in their nests.  They hollow out a chamber and build a comb resembling a sponge, of partially digested faeces.  A symbiotic basidiomycete breaks down the lignin, cellulose and other litter that the termite supplies, and the termites eat the conidiophores of the fungus (Brian 1983). The fermentation heat coming from the fungus causes a convection current which helps to aerate the nest (Wilson 1971).

There is some debate among entomologists as to the true nature of the termite-fungus relationship.  Some say the fungus is used solely as a heat generator to provide a convection current, and it is true that there are species of termite that do not appear to eat the fungus, e.g. Pseudacanthotermes spiniger (Wilson 1971); there are other species that do not exist symbiotically with a fungus until the spores are brought back, presumably accidentally, by workers on foraging trips; whilst other species, e.g. Odontotermes badius, will die if it is supplied with only sterile fungus (Wilson 1971); so perhaps only certain species have a truly symbiotic relationship with the fungus.  The size and shape of fungus gardens vary considerably.

An advanced termite nest may contain as many as 2 million individuals, with a queen that lives for over ten years, laying as many as 84,000 eggs a day, a colony may have a life of over 80 years, though in this time the queen would have been replaced by other queens (Wilson 1971).   Nests can reach a great size, over 5.5m above ground, they are cemented with saliva, excreta and plant material (Golley 1983). 

The walls of the nest are strengthened and lined with a mixture of saliva/excreta/silt (Brian 1983), this makes the tunnel smooth to speed up traffic. Nests are usually found on and below ground but some species nest in trees.  The nest has 3 main functions; protection of the chamber occupied by the king and queen, as a refuge and defence of the whole colony, and a shelter where the correct temperature and humidity can be maintained.  The compass termite orients its mound so that the long axis faces north-south this reduces heat gain during the hottest part of the day whilst maximising heat gain during the cooler times.

Communication and navigation
Some termites are blind others have eyes and can navigate using the sun, but all lay down pheromone tracks of varying durability when foraging, and it seems that they do not rely on their eyes very much (Brian 1983).  It is said that termites cannot hear sound travelling through the air (Wilson 1971), but can communicate alarm by vibration, by banging their head or abdomen on the nest wall.  Most communication seems to be by pheromones, which are used in trail marking, mate signalling after the nuptial flight, and during trophallaxis when the general condition of the nest is communicated to all individuals.  Soldiers are fed by workers, they can feed themselves, but don't, trophallaxis passes on gut symbionts as well as pheromones.

Termites as food

The staple diet of the aardvark and pangolins are termites, the aardvark is a strong digger and destroys most of the nests it visits, the giant pangolin takes only part of the termite colony so does not completely destroy the nest, the long-tailed pangolin feeds on arboreal nests, and the tree pangolin is more of a generalist feeding on both ants and termites on the ground and in the trees (Golley 1983).  In Brazil anteaters and armadillos eat termites (Oliveira-Filho 1992), in the African tropical forests termites can be an important source of nutrients to the forest-dwelling people (Sayer et al.  1992). Probably the greatest predator of termites is the ant, and in a contest between ants and termites it is usually the termite that comes off worse.  In arid areas the termite is a valuable source of moisture to almost any animal that crosses its path.

The effect termites have on the outside world

Termites as agents in soil forming processes
Termites are major decomposers of organic material and may amount to as much as 10% of the animal biomass in the tropics (Wilson 1992), this can be as much as 3 -4 kg m-2 wet weight (Brian 1983), they have been found to consume as much as 570 g m -2 annually in Zaire, this amounts to about half the annual litterfall (Golley 1983).  This initial breakdown of litter and wood makes it available for other decomposers.

The "campo de murundus" in Brazil are earthmound fields in the savanna region of central Brazil.  The earthmounds are found in areas that are seasonally flooded, and are islands during the wet season colonised by shrubs and trees (Oliveira-Filho 1992).  The smaller mounds, <0.8m diameter, consist almost entirely of termite nests of the species Armitermes euamignathus, which tends to construct relatively small nests and is more tolerant of waterlogging than Corntermes spp. whose nests were found on larger mounds (Oliveira-Filho 1992).  Oliveira-Filho postulates that Armitermes spp. nest construction facilitates the construction of the larger Cornitermes spp. nests.  These larger nests raise the mounds enabling the more water tolerant vegetation to colonise, this vegetation provides protection against erosion, during the rainy season these islands, which can be 1 m high and 250 m in area Oliveira-Filho 1992) are the only dry land available to wildlife.  Repeated nest building and erosion changes the soil properties.  Similar alteration of soils has been found in Kenya (Pomeroy 1983) and in Sierra Leone (Miedema and Van Vuure 1977).

However termites do not always have a beneficial effect on all the soil.  The rapid decomposition of litter in savanna or scrub regions may enrich the N and P content of the termite mound and its surrounding area, but that may be at the expense of areas further away from the termite mound (Jones 1990).  It has also been suggested that this rapid decomposition may take the C out of the soil system altogether releasing it as CO2 and CH4, adding to the greenhouse effect (Jones 1990).

Termite mounds used by other animals
In the Kruger National Park most wild dog dens are in old termite nests, hyenas and other animals also use termite nests for shelter.  As mentioned above, the soils in termite nests have different properties to the surrounding soil, and may contain minerals that are in short supply elsewhere.  Elephants are known to break down termite nests and eat some of the soil, it is believed for the minerals they contain.  Once the elephant has broken up the nest other animals can obtain the minerals too, so the remains of the nest is used like a salt lick.
 
Termites as pests
Wood is the food of many termites, and because wood is widely used by man termites can be considered a pest.  They eat wood used in construction, paper, cloth, furniture, anything made of wood unless it is protected.  They also cause some damage to living trees, and it has been reported that some damage has been done to growing cotton in some parts of Africa (Cloudsley-Thompson 1977).  The termites that build the larger nests can cause problems during road building etc.,  in Zaire termites nests held up the building of a railway, bulldozers couldn't shift them so dynamite had to be used (d'Entreves and Zunnio 1976).

Conclusion
 
Termites are commonly seen only as pests, and it is true that they do cause a lot of damage whenever they build nests near buildings, but like the earthworm, they are invaluable in soil forming, and their nests are truly wonderful constructions.  In Nottingham a new office belonging to the Inland Revenue was opened recently, the air conditioning system was designed to operate in a similar way to the ventilation in compass termite nests.  It is estimated that this building will use between 1/3 and 2/3 of the energy of a similar, conventional building.  It is no longer just entomologists that find termite nests interesting.

LITERATURE CITED
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