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PUBLIC RECORD OFFICE

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C.O. 885

24 PUBLIC RECORD OFFICE, LONDON

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Miscellaneous

No. 308.

SUGGESTIONS FOR FUTURE ENTOMOLOGICAL AND MEDICAL WORK IN CONNEXION WITH GLOSSINA.

By Mr. E. E. AUSTEN and Dr. A. G. BAGSHAWE,

(Appendix D to [Cd. 7350].)

In the course of their inquiry the Committee have had the opportunity of noting that some facts relating to its subject are fairly firmly established, while others rest on a less secure basis. Their views in this respect are indicated in the Report. It may safely be asid that of the experimental researches few have been on a aufficiently large scale or confirmed sufficiently widely over Africa to afford satisfactory support for a final scheme of preventive measures. It is not proposed to repent here what may be extracted from the Report, but it seems useful to indicate some lines of inquiry which may help in the elucidation of the general problem. These are given below under the heads Entomological Research and Medical Research.

Entomological Research.

In all work dealing directly with the insect carriers of trypanosomiasis the ultimate aim and object, namely, the elimination of the fly, must be kept promi- nently in view. When seeking to compass the local eradication of these insects, observations of both direct and indirect importance in connection with the bionomics of tsetse flies will almost certainly be made; yet it is none the less important that operations should not be commenced in desultory fashion, but that, so far as possible, each investigator should be provided with a definite scheme of work.

The following are among the subjects to which special attention should be directed :-

(i) Function of the sensory labyrinth in the second and third joints of the antenna of Glossina.-It is not yet known whether this is olfactory or auditory. Knowledge of the kinds of stimuli by which the organ is affected would be a useful aid in connection with trapping.

(ii) Influence of Odours.-Efforts should be made to determine whether tsetse flies, in choosing a breed- ing-place, are in any way influenced by odours; or whether, as Mr. Lloyd believes in the case of G. morsi- tans, the existence of a relatively dark spot "where the mother fly can hide during pregnancy" is the dominant factor. The odours by which insects are attracted are not necessarily perceptible to the human nostril, and consequently it does not follow that, because the breeding-places of G. morsitans and G. palpalis appear to human beings to have no dis- tinctive odour, such odour is not apparent to a pregnant taetse fly. In India it has recently been found by Mr. F. M. Howlett that Stomoxys calcitrans will oviposit freely "on cotton-wool soaked in valerianio acid, one of the acids present in the fermenting vegetable stuff in which the eggs of this species are Although Stomoxys naturally deposited. calcitrans, instead of depositing at intervals a single full-grown larva, lays egge in the ordinary way, the fact that it also is a blood-Bucking fly and somewhat closely related to Glossina perhaps affords some grounds for hoping that, if it be possible to analyse and separate the components of the humus in tsetse fly breeding- places, some substance or essence of a specially attra tire nature may be found. If discovered, this would of course be used in connection with-

(iii) Artificial Breeding-places-Every effort should be made to construct these, and to test their practical efficacy. If bird-lime or other sticky substance were applied to the under surfaces of the dead branches or other timber used in the construction of such breeding- places, the latter might form traps for the adult fies as well as for pupa. It is important to note that, in order that artificial breading-places may have a reasonable chance of success, all known or probable breeding-places must, so far as possible, first be destroyed or rendered useless.

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(iv) Range of Flight.-Definite knowledge on this subject is urgently required in connection with G. morsitans. Many of the statements on the subject made to the Committee in the course of the inquiry were mere guesses, or based on irrelevant or insuficient data. Important information on this head might, however, be gained in connection with experiments to determine -

(v) The Precise Effects of Clearing. At present we do not know whether clearing actually results in the death of the flies, or merely causes them to migrate. If it were possible, in G. morsitans country, to find a series of amall isolated patches of teetse, each separated by a different distance (400 yarda, half a mile, three-quartern of a mile, and so on) from the next patch of cover, the actual effect of clearing might be ascertained by marking and liberating a large number of G. normitans in each patch in succession, and then destroying the vegetation and noting the result. If possible, a method of marking which does not in any way impair the activity of the flies should be adopted. The desired end might be attained by collecting large numbers of pups, and breeding out the flies in cages so arranged that the insects on emerging become permanently marked with coloured powder.

(vi) Systematic Trapping and Catching continued for a considerable Period of Time (say One Year.)-This

should be given a thorough trial. In the Island of Principe & marked reduction in the numbers of Glossina palpalis has been effected by catching the flies by means of black cloths ameared with bird-lime and worn by natives. The number thus trapped was 95,000 in the last six months of 1912, or over 500 a day. When tried in German East Africa, however, in the case of Glossina morsitans, the method yielded but poor results. It is suggested that the failure may be due to the employment on the cloth of some substanco which is Botually distasteful to the flies and that further experi- ments with the same substance that is used in Principe would be of value. It is obvious that catching the adults must, relatively at any rate, produce a far greater effect on an exceptionally slow-breeding fly like Glossina, than on an insect such as the house fly, which

may produce six hundred eggs at one time. To this extent we are aided at the outset by nature. Correct conclusions as to the value of trapping and catching cannot be deduced from a trial lasting only two or three months, in which but a handful of natives are engaged; the value of limed cloths and of nets in the hands of expert fy-boys should be tested in a selected Some locality for at least a year, and on a large scale. hundreds of natives should be employed in the work, and

corps of, say, a dozen keen and energetic fly-boys should be established in each village in teetse ares. Payment should be by results, but small rewards would suffice, and the system should therefore prove inexpensive in working.

(vii) Insect Enemies.-In the case of a noxious insect, which exists in such numbers as to constitute a plague, It is useless to expect effective aid from endemic Were such enemies capable of controlling enemies. the harmful insect, the latter would never have become a plague, and if results of value are to be produced by this method enemies must be sought for elsewhere. In the United States of America attention has recently been drawn to the life-history and habits of a minute Hymenopterous (Chalcid) parasite known as Spalangia muscidarum, which has been bred in large numbers from the puparia of Slomorys calcitrane, and also attacks the pupe of other flies, including Musca domestica and Lyperosia irritans, Only one species of fruit fly) is at the genus Spalangia (parasitic on present known to occur in Africa, but in North America in addition to 8. muscidarum several other species are found; these include S. haematobias, which attacką Lyperosta irritans, and S, nigra and S. hirta, both of

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