PUBLIC RECORD OFFICE
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Reference :-
C.O. 885
24 PUBLIC RECORD OFFICE, LONDON
ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH-NOT TO
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environment. On the contrary, most of the roving flies behave toward man and (in the experiments) cattle almost precisely as do all of them toward the umbrella or other strange and conspicuous but stationary and inanimate object.
PROTECTION.
A.-Breeding Grounds as Protection to Puparia.
25. The bionomics of any insect is a subject of some complexity at the best, but it expands to unwieldy proportions whenever it is attempted to study its natural enemies individually. To be consistent theirs must be studied too, and there is no end. A line must be drawn somewhere, and in the case of Glossina it has appeared practicable to draw it well in, and to limit investigation to the features of its environ- ment which protect it against inimical influences, with small regard as to the nature of these.
26. The larva of Glossina is nourished to maturity by its mother, and its inde- pendent existence is momentary. Within a few minutes of its birth it loses power of locomotion, its body contracts, and its skin hardens and changes colour to form the "puparium."* During the short period of activity it must bury itself in the soil or run the gravest risk of being found and destroyed by wandering predators. and its mother must have selected a spot where it is physically able to do this. Some- times she does not, for on various occasions puparia have been found exposed on the surface in localities which were excellent as breeding grounds in all other respects than the impenetrable nature of the soil. Localities where miscellaneous predatory foes so rarely stray as to permit the puparia to remain thus exposed for more than a few days (or hours) are relatively rare (as experiment has shown), so that it is impos- sible to ascertain the real extent to which the mother is at fault in this respect.
Sometimes she selects 27. She may be at fault in other respects as well. localities wholly suitable except that they are shaded by vegetation of such ephemeral They are character that it withers and dies before the puparia have hatched. properly buried in the soil and safe from animate foes, but the sun striking directly upon the surface overheats and kills them. In the first-mentioned instance an ant or beetle may have been the agent of destruction, in this it is the sun's rays; but is the maternal instinct which was at fault on both occasions, and "good breeding grounds" would have protected equally against both destructive agents. severely practical standpoint it does not seem necessary to differentiate between animate and inanimate destructive agencies, much less between the innumerable species of animate foes.
From a
28. It would be otherwise if any among these were specifically inimical to Glossina and sought its puparia wherever they might be found, in preference to other insects. But no such specific foe has been discovered, nor has any observation Protection thus comes to be a question of been made suggestive that it may exist. location with reference to other insects and their enemies.
29. It is not unusual, in particularly attractive spots, to find hundreds of There can be no doubt puparia and hatched shells in the space of a square yard.
that such spots are sought by the gravid females with deliberate intent.
30. The most attractive spots are such as are particularly avoided by insects in general and their enemies. In consequence they actually do afford the puparia a degree of protection which, in many instances, approaches the absolute.
It is
31. Puparia have been collected in such places and planted in others where they are not naturally found. Usually they have been promptly destroyed. certain that, if the mother did not use some discretion in placing them, so many would be destroyed that the distribution of the species would be much more restricted than at present.
32. It was also discovered that there were places (the tufts of a certain species of grass, for example) in which puparia were never found naturally, but in which These would serve excellently as breeding they appeared to be perfectly safe.
grounds, but for some reason have not come to be recognised as such by the flies.
33. As far as physical environment is concerned, any locality not exposed to the sun and not too wet (it may be damp, and frequently is, but must not be con- tinually water-soaked) will serve. Proximity to water is oftentimes a temporary
* Within the puparium it passes through various stages and sub-stages, of which the pupa, strictly
speaking, is only one.
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disadvantage, for puparia may be destroyed by the rising of the lake level due to continued rains or by an unusual storm. After the water has subsided the fly may benefit, for its safest breeding places are in the clean washed sand and gravel just beyond the reach of the waves.
34. There appears to be a correlation between the host preferences and favoured breeding grounds. The crocodile, a preferred host, deposits its eggs in sandy beaches, and thereafter until they hatch the mother comes daily to haunt the spot and guard them. At such times she is freely fed upon by fly, and it is but a natural incidence that the largest deposit of puparia ever discovered should be at or near a spot actually selected by a crocodile for nesting, or at such a spot as a crocodile might select. Varanus frequently basks in similar localities, but as frequently on the top of rocks, just in or out of the shade of overhanging herbage, grass, or fern. In the course of time a mass of dry vegetable débris comes to accumulate in such spots, and here also large quantities of puparia have been found, not necessarily near the water, but on one occasion on the top of the highest hill on a considerable island. These two represent the known extremes in the types of breeding grounds, and hardly resemble each other except in the two essential points-both are avoided by insects and the enemies of insects in general, and both are associated with a most favoured host.
35. A third type, falling between the two, is represented by the sunning spots kept open by antelope in thick bush or forest. Perhaps a tree, has fallen, bringing with it a mass of vines. Ordinarily other trees would quickly spring up to take its place, and the vines clamber back upon them, but the antelope nibble back and break or trample down up-springing vegetation, or pull the vines to the ground and The thick defoliate them, until they may actually enlarge the size of the opening. layer of leaf mould that may formerly have carpeted the soil is dried by the sun and trampled and ground beneath the feet of the antelope until it may become an excel- lent medium for the incubation of puparia. Miscellaneous woodland insects avoid the spot, and under the shade of the prostrate log or of a tangle of dying vines large numbers of hatched shells as well as of healthy puparia have been found.
36. It is believed to be significant that certain potential hosts, common but not fed upon, such as cormorant and other "shore birds," should be dissociated from any locality which would likely serve as breeding ground; and, conversely, that several types of potential breeding ground where puparia would be safe, but where they have not been found (page 33), are dissociated from any potential host.
37. The hosts may not only lead the fly to good breeding places, but may do something towards preparing them for the reception of its young.
In one instance
From
more puparia were found in a sunning spot of antelope in thick forest than could be The soil was found at any one point on the shore some hundreds of yards distant. sandy, but everywhere in the vicinity of the opening (except actually in it) was covered by a thick layer of leaf mould matted together by interlacing rootlets. what has been observed of the depth to which the larvae of Glossina penetrate below the surface in various media, it was judged that very few, if any, would pass through the leaf mould to the soil beneath. Large numbers were planted in the vicinity, beneath stumps, logs, tangled vines, etc., in places most nearly like those in which they were found in the open spot. Invariably, unless they were buried in the sand below the leaf mould, they disappeared in the course of two or three days, and usually overnight. It was concluded that in this particular locality the antelope was no less a friend to the fly in providing it with breeding grounds than as a source of food. Varanus plays a similar rôle not infrequently, and crocodile less frequently but occasionally.
38. The fact must not be overlooked that, however the choice of breeding places came originally to be made, the habit is now become fixed. Even though all the crocodiles should be driven from a reach of sandy shore by too close proximity to human habitation, the fly might feed on men or cattle (if it found them acceptable as hosts) and carry its larvæ to the sand beds just the same.
39. Crocodile, varanus, and antelope frequently abound in localities where It is the rule that if "shelter" is shelter or breeding grounds, or both, are absent.
at all distant fly is absent, irrespective of food supply or breeding grounds. But it shelter is good and hosts plentiful the roving habit of the fly may lead it to the Its own immediate wants are spot from breeding grounds several miles distant. fairly met in such localities, and such localities are lightly or heavily infested depending on distance from populous breeding places.