IN TOUCH WITH NATURE

Otago Witness, Issue 3890, 2 October 1928, Page 5

IN TOUCH WITH NATURE

BEETLES CULTIVATE PLANTS.

By

J. Drummond, F.L.S., F.Z.S.

Bees, wasps, ants, and the termites, or “ white ants,” dealt with by Maurice Maeterlinck in his characteristic way, are proverbial for their social organisation, rivalling the most highly organised human civilisations, but other insects have their social lite. New Zealand has members of a family known as the ambrosia beetles, which, it is believed, show a very definite social organisation by cultivating special fungi, using them as food, and bequeathin'' them to succeeding generations. They tunnel the bark of trees. The tunnels, in many ■cases, radiate from one centre. Each set of tunnels usually is the work of the progeny from a single batch of eggs. The only New Zealand species of the group whose habits have been observed is the ambrosia Platypus, that is, the broad-footed ambrosia. What little is known about it has been disclosed by Mr D. Miller, an able entomologist on the staff of the Cawthron Institute. It is less than a quarter of an inch long. Its legs and feelers are yellow, its head and thorax are light brown, its wing-cases blackish-brown. It has been found boring through bark into the heart of living mountain-beech. Roundish, pearly white eggs are laid by the female in the main tunnel. Each grub, as soon as it s hatched, makes a tunnel for itself. The fungus it cultivates —if it does so —has a long name, Lasiosphaeria. This leaves a deep purple stain on the wood around the tunnel. Another New Zealand member of the family, the kauri Platypus, is believed to cause pin-holes seen in dead kauri trees. The holes are made in living trees. The slender Platypus, reddishbrown, narrow-bodied, broad-headed, less than a fifth of an inch long, tunnels into living silver pine. It bores through the bark into the tree’s heart, leaving at the entrance to the tunnel white accumula tions of shredded wood it ejected. Doue s Platypus attacks the sap and the heart of living mountain-beech, and has ex tended its operations to the bluegum.

Ambrosia beetles are called ambrosia beetles because in other countries they cultivate fungi that bear the name of the fabled food of the ancient Greek gods, which conferred immortality on those who used it. , Coming down from food for gods to drink for men, there is a 'species in the tropics known as Tippling Tommy because it bores into the staves of beer and rum casks, and makes them leak The females of two American species prepare fungus-beds in pits in their tunnels. The young are no sooner hatched than they begin to eat the fungus. The mothers are in constant attendance on their young during development. They guard them with care. The mouth of each cradle is closed with a plug of the fungus. As fast as it is consumed by the young, the supply is renewed. From t'me to time the young clean out their cradles hygienically, pushing pellets jf material through an opening they make in the plugs. The mothers remove the material." and again seal the openings with fungus.

The true ambrosia beetles now are separated from the Platypus beetles, which have a family of their own, represented by eight species in New Zealand. A North American species. Platypus compositus. has the walls of its tunnels blackened by the fungus it cultivates. A female of this species often is accompanied 4>y several males. As they are savage fighters, fierce sexual contests arc The tunnels are strewn with fragments of the vanquished. Projecting spines at the ends of the wing-cases are the weapons. With them a beetle attacked in the rear can make a good defence. By a lucky stroke, it may dislocate its enemy’s outstretched neck. The young, wandering along the tunnels, feed in company' on the ambrosia that grows on the walls. Each species of ambrosia beetle, and of Platypus, a? far as is known, grows its own, special fungus in a pure culture. Platypus females in other countries carry the spores of the fungi from tunnels, in which they spent their early stages of life to new tunnels they make for their own progeny. For this, each has a kind of crate or basket, made of several dense tufts of long, curve* hairs on the top of the head or on the mouth parts. Female ambrosia beetles, carrying the fungi in the forepart of the stomach, infect the walls of their new tunnels.

Six groups of social beetles, at least four of them represented in New Zealand, one with no fewer than 152 species, are known. Their food is remarkably diverse. It ranges from dung and wood in different stages of decay to the living tissues of plants, the honey- dew produced by mealy-bugs, and delicate fungi. These food" supplies, abundant, but not verynutritious, which the grown-up beetles seek and use primarily for their own consumption, enable them tcr attain a fair longevity. In each group, the parents show an interest in their young, a much deeper interest than might be expected, and feed them directly, or, at least, place them in close contact with food, and guard them. The male helps the female in providing for the young, but his help maybe slight. Unlike ants, bees, and termites, which rank higher than beetles, social beetles have no castes.

Longevity is regarded as an important consideration in insects. The adult life of the parents must be jirolonged to cover the juvenile development of the progeny. Social life is made possible by the lengthening of the adult stage. Brevity of adult life prevents solitary- insects from developing the social habit. Length of life in the juvenile stages does not count m this respect. Some solitary insects have juvenile stages that extend over months or years, but their adult stage may be only a few day’s or a few hours. Amongst the higher social insects, fear has been seen in all its manifestations, from abject cowardice and shamming death to panic rage. It has been pointed out that . they make elaborate nests, build fortifications, and develop powerful jaws, hard skulls, pungent secretions, and deadly stings. Some, going further than others, do not wait for their

ei-emies, but sally forth to meet timm before they reach the strongholds. The earwig is classed as a sub-social insect because the female takes particular care of her eggs, and remains with her young for a time after they are hatched. One female earwig, immediately she had laid her eggs, picked them up in her mouth parts, one by one. and wiped them all over. The eggs were left clean and glossy. She placed them in a neat pile, and stood gua-d ovei ihcm. Some earwigs have refused to couch food from the time they laid until the yonn-' were hatched. Others have left their eggs to get something to eat. The weba group of insects unrepresented 111 New Zealand, which make galleries on the ground or under stones and rocks, are as solicitous as the earwigs. The female takes up her position close to her eggs, and tries to conceal them. She gathers her young about her in the same way as a hen gathers her chicks. There is so much in common between the highest insect societies and human societies, that matter of fact men of science have failed to detect really fun damental biological differences between them. Real estate, in the form of nests, pastures, and hunting grounds, are bequeathed by social insects. When weaving the silken walls of nests, some ants use their own grubs as shuttles. This is equivalent to the use of tools by primitive humans. Articulate speech lias been developed by humans, but members of insect societies communicate with one another by movements of the body, and or the feelers, by- sounds, and by odours. The behaviour of ants often is regulated by future dontingencies more than by the needs of the hour. Individual ants may sink their own interests in guarding the interests of the community. 1 hey maygive all their activities, all their aims, all they have, to the defence of their community. completely sinking their individuality, losing even the power of feeding and cleaning themselves, and depending for these offices on the services of slaves. The value of communal action is recognised to a greater degree by ants and bees than by any other creatures in thS world. A spirit of self-sacrifice, of service, has raised the higher insects from obscurity and lo.wliness to a position of dominion in which they menace man himself.