I. The place of insecticides in tropical medicine: An introduction

216 I.

T H E PLACE OF I N S E C T I C I D E S IN

T R O P I C A L M E D I C I N E : AN I N T R O D U C T I O N BY PROFESSOR P. A. B U X T O N ,

C.M.O., F.R.S.

London School of Hygiene and Tropical Medicine

Available information This article is presented as an introduction to the group of papers which follow it. It should be explained that the writer was asked to organize a symposium at one of the Society's evening meetings and to select contributors. He proposed certain topics to the writers and discussed the papers in draft : the results are independent, individual studies of particular sides of the problem. It was necessary for the contributors to be brief and they were encouraged to be selective, both in the topics discussed in the papers and in the lists of references. The amount of work published on the synthetic insecticides, especially on DDT, is great, for knowledge has developed extremely rapidly : a considerable proportion of the work is of poor quality. For these reasons, it is most difficult for the reader to keep abreast of the rapid development of knowledge and to know what conclusions are justified at the moment. It will undoubtedly help if we direct attention to the main sources of information, particularly to recent publications. At the moment, much the most useful book on insecticides is the one recently produced by BROWN(1951). The author is a Canadian biologist with a training in forestry, but it is clear that he possesses a comprehensive knowledge of many sides of the subject : one notes, for instance, the interesting discussion on the relation between chemical structure and insecticidal effect. The planning of the chemical control of insects is well handled and the book contains an account of the application of insecticides from the air. The present writer, with some practical knowledge of that complicated subject, feels it is extremely well d e s c r i b e d : t h e chapter deals adequately with the size of droplets and other physical characters of air sprays: also with meteorological conditions , favourable or unfavourable : also with the procedure which must be followed if an air spray is to reach a target. BROWN'S account is up to date on such items as the rotary brushes used to control the size of spray droplets : the chapter concludes with more than 100 references : if few British contributions appear among the publications, that is because we have let too nmch of our work remain in files, circulated only to a limited number of people. (Other valuable references on the application of air spray are : KRUS~, PHILEN and LUDVIK, 1951 ; and MACKERRAS, RATCLIFFE, GILMOURand MULES, 1950.) BROWN'Sbook also deals with the chemical control of those insects and acarines that transmit infectionsto man and anima]s, givingan excellent summary with regard to each pest : the interesting Canadian work on the destruction of

P. A. BI3XTON

217

larvae of Simulium in running water is, needless to say, made available. This chapter runs to nearly 50 pages and contains nearly 250 references. The book by WEST and CAMPBELr.(1950), which has already reached a second edition, is alsomost useful. The authors, who approach the subject from the chemical side, are in a very good position to deal with the early development of this group of insecticides by the Geigy Company in Basle. From that they pass to the history of D D T and of its homologues and related substances, and so to the principles of formulating these insecticides. They deal also with D D T in such materials as textiles, paper and paint, and discuss the stability of thin films. In their biological chapters, the authors consider the effect of this insecticide on mosquitoes, ~ lice and many other types of insect : they discuss the agricultural uses of the substance; and call attention to the danger of destroying insects which are useful because they are enemies of pest insects : fortunately this complication is of small importance in relation to insects of medical importance. The final chapters of the book deal with BHC, chlordane, toxaphene, etc. One notes that the index of authors contains approximately 800 names : the main list of references contains few later than 1946, and even the supplementary list seems to have been made in 1948. Technical information on; certain aspects of work on insecticides is available in the reports published by the World Health Organization, through several channels and committees. The Committee on Insecticides has already issued two reports; (Expert Committee on Insecticides, 1950, 1951)and two further sessions have been held, in July and November 1951, the results of which are awaited with interest. In the first of the published papers, the Committee put forward proposals on the terminology of these substances, and on the standardizing of formulae ; technical and mechanical points in the construction of spraying apparatus were defined. Quarantine measures against insects, including the use of persistent insecticides, were defined. A panel of experts on particular sides of the subject was co-opted. In the second report these discussions were carried much further, many matters of international interest being defined. Among other publications of W.H.O., the bulletin by PAMPANA (1951) is invaluable as a review of what is known about t h e effect of modern insecticides upon adult Anopheles. The arrangement is geographical and the treatment full. The paper includes valuable demographic information on morbidity and mortality, including infant mortality, year by year, in certain malarious areas. Striking reductions in mortality, and also in spleen and parasite rates, have frequently followed the widespread use of D D T to control domestic species of ,4nopheles. The biologist will observe with interest that this method (and perhaps also a similar u s e of BHC) is very efficient in reducing or even exterminating certain species such a s .4. darlingi and .4. fluviatilis : in contrast, the adults of other species, generally less domesticated in their choice of resting places, are less easily controlled, for instance A. albimanus and probably `4. maculatus. It is possible that some of these latter species are not only protected by their habits and choice of outside

218

INSECTICIDES IN TROPICAL MEDICINE

resting places, but also by resistance to larger doses of insecticides. But as to that we know nothing, because the elementary, fundamental work of defining the lethal dose under standard conditions, for a number of species of mosquitoes, has been neglected. A valuable summary of the use of D D T against mosquito larvae is given by FERGUSON, U P H O L T a n d SIMMONS (1949). The destruction of insects inside aircraft is important, in view of the risk of some insect of medical importance establishing itself in an area where it does not naturally occur. The most dangerous insects, generally speaking, are several species of mosquito ; one must also think of Glossina, and indeed of many other insects of importance both in medical, and also in agricultural, entomology. The complexity of the subject from the entomological side is emphasized by the work of HUGHES(1949), who states that in areas under U.S. control, 80,000 aircraft were examined in the 5 years ending 1947, half this number in the last 2 years. In these examinations, nearly 29,000 arthropods were found, of which 3,873 were mosquitoes : many of these were arriving, alive, in areas in which the particular species did not occur : the housefly and many other Diptera were also numerous. The total number of species of insects was over 500, so that it would be impossible to define briefly the ideal insecticide and dosage : in addition one has to take into account possible damage from solvents to a great variety of types of material, convenience of passengers and many other factors. On this complicated subject, it will be found that helpful papers are those of DUGUET(1949) ; and TEW, DAVID and BUSVlN'E(1951). If one turns from chemical application to biology, it will be found that most of the new insecticides with which we are concerned are solids, which act as contact insecticides : the problem is therefore how they penetrate the cuticle. The more serious worker should acquire a general knowledge of the physiology of the insect cuticle from WIGGLESWORTH(1950), and then turn to the more specialized book by RICHARDS(1951) which gives a full account of the chemical components and microscopic structure of the cuticle of insects, and of its permeability, both to insecticides and other substances. A related problem, the mode of action of organic insecticides, was discussed by METCALF(1948), who dealt with DDT, BHC, the o~ganic thiocyanates, and certain other organic insecticides with which we are not directly concerned, in each case summarizing current theories on their pharmacological action. In dealing with D D T he tabulated what was known of the relative toxicity of many analogues to a number of insects. In the use of new insecticides in medical entomology, there is no full general review except in the biological chapters of BROWN'S book. The paper by KINO (1951) provides valuable information on the newest materials (repellents and insecticides), including some that have not yet come into general use. Our Society may claim that a summary published in its pages (BUXTON, 1945) served a useful purpose for several years.

P . A. B U X T O N

219

T h e use of the lasting insecticides, particularly their domestic use, has directed attention to certain biological problems : for instance, there are now urgent practical reasons for enquiring about the resting habits, a n d resting places of certain mosquitoes. T o go m o r e deeply, there is need to enquire into the laws which govern the behaviour of these insects, indeed of insects m o r e generally. T h i s side of the subject, so far as it concerns mosquitoes, is extremely well served by the books b y BATES (1949) and MUIRHEAD-THOMSON (1951).

Notable results I t is now proposed to s u m m a r i z e in the briefest t e r m s some of the results obtained b y using m o d e r n insecticides against insects of medical importance. I have taken the responsibility of selecting those recent papers which appear to be most important. (

Pediculus, adults and nymphs. Body louse, perhaps in large groups of people : very unhygienic conditions. Application of 10% D D T dust blown underneath garments without undressing.

Satisfactory control of body louse, and break of typhus epidemics, in many places.

Various authors

et

al.

Extremely high resistance to D D T powder or impregnated cloth : not clear whether this is normal to strain, or acquired following exposure to DDT. Resulting failure to control over a period of months ; large field of experience in Korea.

HURLBUT

Head louse, in large groups of infested children or women. Small volume of thiocyanate (25 %) spread through hair.

Highly satisfactory.

BUXTON (1950)

D D T emulsions (2 %) or BHC emulsion (0.2%)

Successful kill, little lasting power, so individual only protected for about I week.

BUXTON(1950)

Plague in rat and man in badly built tropical town. Free use of D D T dust followed by poisoning of rats.

80-90 % reduction of fleas on rats and in nests followed by end of epizootic.

MACCmAVELLO et al. (1946)

Pulex and several other fleas.

Very great reduction.

See BROWN (1951)

(1952)

Xenopsylla cheopis and other fleas.

D D T dust.

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INSECTICIDES I N T R O P I C A L M E D I C I N E

Cimex. Field trials in slum dwellings prisons, etc. Thorough spraying of walls etc. with D D T solution or emulsion. Textiles generally treated b y heat.

Complete dimination in several cases.

REID (1949) ;

D i t t o with B H C spray.

Less experience,' seems satisfactory.

GLrNN (1948)

Ditto with parathion, 0 . 0 5 % in water.

T w o sprayings given, perhaps less effective than 5 % D D T : some risks to operator.

STEINIGr~R

Careful, large scale comparison of 5 % and 2.5 % D D T , 0.35 % gammexane and 6 % 1ethane ; also two types of sprayer ; single treatments ; tested in 3,000 bedrooms, Kensington, London.

5 % D D T gave 97.2 % success, measured by repeated inspection up to 18 months : 6 % lethane the least successful, 70.8 %

Reviewed by Bvsvn,m (1948)

LANDERS(1947) ; G t r t ~ (1948) ; also references in BaOWN (1,951)

(1951)

. SUCCCSS.

Triatoma infestara. Infested houses, sprayed with high dose of dieldrin.

Successful kill ; surfaces remained insecticidal some months.

NEa~m (1949)

Similar conditions, aqueous suspensions of BHC at high dose.

Fair success, especially with BHC plus pyrethrum.

D,As and

et.

al.

I~LLEGRINO

(1948)

Anopheles, adults. Biological tests to determine whether a sprayed surface is still insecticidal : evaluation of spraying in terms of reduction in Anopheles, or of malaria. Domestic application of D D T , in many formulations and doses ; many parts of world; many species of Anopheles. Attempted eradication of malaria, by campaigns against adults.

PAMPANA (1948)

Result depending on circumstances, particularly on house haunting habit of adult insect. Frequently great reduction in insect and in sporozoite rate ; reduction in malaria (cases, spleens, parasites), in some cases reduction of infant mortality. Several almost successful results, especially in islands, or against particularly domestic mosquitoes, Disappearance of malaria.

Summarized by PAMPANA (1951)

P. A. BUXTON

221

Symposium on nationwide eradication of malaria, various methods, in the Americas. Eradication of A. darlingi from Brit. Guiana, and studies on its biology, of great interst.

(195I) for Brit. Guiana. Group of papers m same journal.

GIGLIOLI

Detailed description of m a j o r scheme : e x c e p t i o n a l epidemiological background. Main vectors A. darlingi and A. albimanus : house spraying with D D T . Venezuela.

Local eradication of A. darlingi (manhunter and domestic) but not A: albimanus (zoophil0us, not domestic). Almost cOm plete malaria control.

GABALDON (1949)

Use of D D T emulsion as residual domestic spray, against A fluviatilis and A. culidfacies, Bombay Province. Full studies on population epidemiology etc. H y p e r endemic malaria.

Great

VISWANATHAN a n d

Field work in Belgian Congo against A, gambiae and "A. moucheti ; analysis of anopheline behaviour : domestic BHC.

Control of Anopheles, indeterminate results on malaria.

DAVIDSON (1950)

Use of D D T in oil solutions : commonly 0.1 lb. D D T ] a c r e : difficult problem of even distribution often met by air spraying.

Generally a subsidiary to house spraying against adults.

Summary b y FER~USON et al. (1949)

Eradication campaign, mainly based on using oil larvicide (supplemented latterly by D D T ) . Cyprus.

Successful

AzIz (1950)

reduction

in

domestic

Anopheles and in malaria, measured i n several ways. very low.

Rao (1949)

Cost

Anopheles, larvae.

eradication

of

A.

elutus : _/1.superplctus not quite exterminated. ished.

Malaria abol-

Culicine adults. D D T at 200 mg. sq. ft. inside houses, against Culicine vectors of filaria. Virgin Islands.

Great reduction in C. fatlgans and in infection rate. Greater reduction in A. aegypti.

KOHLER et al. (1949)

Same dose of D D T as wettable powder. Malaya.

C. fatigans irritated and driven

WHARTON (t95I)

Similar work, BHC 40 mg. gamma/sq, ft.

Many C. fatigans killed for 5-7 weeks.

out for m a n y killed.

weeks:

few WHARTON (1951)

222

INSECTICIDES I N TROPICAL MEDICINE

Very large reduction ; infiltration after variable period.

References in BROWN (1951)

I n all cases, immense reduction.

HERTIG and FAIRCHILD (1948); HERTIG (1950)

Immense reduction of adults perhaps elimination from area.

WANSON et al. (1949)

Great reduction in adults (and mosquitoes).; rapid re-invasion in most cases.

Summaries by BROWN (1951)

D D T emulsion, generally giving 5 or more ppm. for 30 nun. Kenya.

Complete disappearance of adult S. neavei from heavily infested area with much onchocereal blindness. Fish killed in n u m bers.

GAmqHAM and McMAHON (1947)

D D T in oil from aircraft giving 0.13 ppm. for 36 min. Large river, Canada.

Destruction of larvae for 17 miles and some kill for 90 miles. Fish not killed.

Am~ASON et al. (1949) ; see also HADAWAY and BARLOW p. 236

BHC to small rivers, about 1.0 rag. of gamma/litre, or dispersible powder. Congo.

Larvae of S. damnosum killed ; small fish killed.

WANSON et al. (1950)

Culicoides, adult. Woodland and moorland, treated with D D T suspension or emulsion 2.5 lb. tech. DDT/acre, Scotland.

No reduction of midges, as measu r e d by sticky trap. Same t r e a t m e n t would have controlled salt-marsh mosquitoes.

KETTLE (1949)

Culicoides, larva. Wet soil, under bushes, gamma isomer at 100 mg./sq, ft. England.

Great destruction, larvae and pupae.

HILL and ROBERTS (1947)

Air sprays over vegetation ; large areas ; subarctic or salt marshes. Dosage about 0.5 lb. DDT/acre, or 0.1 lb. as aerosol or fog.

Ptdebotomus, adult. Residual spraying inside houses with D D T : against many slap. of Phlebotomus. Peru and several parts of Mediterranefln.

Simulium, adult. S. damnosum in rapids of river, too large to permit larvicidal attack. Air spray put down from tree ,top heights, against a d u l t s ; D D T at 20 mg./ sq. m., repeated daily. Onchocerciasis abundant. Congo. Armoying Canadian species, attacked by air spray or smoke.

Simulium, larva.

P° A. BUXTON

Brackish tidal swamps, heavy dose of D D T powder or emulsion. Caroline Islands,

223

Considerable reduction, presumably due to death of larvae.

Doas~

Many killed which would have escaped from trap without DDT.

MORRIS (1950)

D D T on screens ; on many treated cattle in fly belt. Tanganyika.

Large reduction.

WmTSSIDR (1949)

D D T smoke from aircraft, repeatedly. Follow up with bait cattle. Zululand.

Great reduction, final extermination 40 sq. miles.

du TOlT et al. (1950)

B H C smoke from canisters in thorn bush.

Never complete kill.

LEwis (1950)

B H C for trains in tunnel.

Good promise.

LEwis (1950)

Flies in buildings, deposit of 50-100 rag. sq, ft. of D D T .

Successful control, film lasting many months ; many countries.

References quoted by BROWN (1951)

After exposure to D D T flies often become resistant. Change to BHC, dieldrin etc.

Successful control. Resistance to dieldrin and often other insecticides may develop.

MARCH and MrrCALF (1951)

Glossina, adult. D D T , on sacking of t r a p : Gold Coast.

(1947)

Musca domestica, adult.

Change to D D T plus an analogue which seems to act as synergist.

SUMERFORD et al.

Change to pyrethrum or allethrin, as space spray ; use frequently.

M A R C H and M~rCALF (1951)

Flies in dairies,or muscids on body of cow. Small quantity of D D T found in milk, to which some countries object. Use insecticideoutside dairy or against larvae (below) ; resort to general hygienic methods.

(1951)

Successful control, or avoidance of insecticide in milk.

KNIPLING(1949)

Emulsion of chlordane or B H C more effective than toxaphene or D D T .

References given by WgST (1951)

Musca domestica, early stages. Treat ~breeding place with ininsectmidal emulsion.

224

INSECTICIDES I N TROPICAL MEDICINE

Larvae of normal strain compared with those of one resistant strain : D D T added to culture medium. A C A R I N A , general. Variety of problems.

Some evidence that larvae of this resistant strain were themselves resistant to D D T .

PIMENTEL and DEWEY (1950)

BHC much more successful than DDT.

Trombicula, larvae. F o r garments and person, light smear of dimethyl phthalate.

Successful kill, even after repeated washing.

Benzil impregnation.

Adequate kill, and great resistance to washing.

CROSS and SNYDEa (1948)

F o r control on surface of ground, BHC dust, 8 lb./ acre ; or lower dose as emulsion ; or chlordane emulsion.

Successful "area control" against several species of mite.

SMITH and GOUCK (1947)

New insecticides not in use (BHC of great value i n veterinary problems).

BROWN (1951)

Complete eradication.

HOCKING (1946)

Less successful.

HOCKING (1946)

Floors of huts dusted with 3 to 4lb. per 1,000 sq. ft. of B H C (0.5 % gamma). Tanganyika.

Successful economic control of vector of relapsing fever, important local disease.

JEPSON (1947)

O. crossi similar in biology ;

Effective control, t o b e repeated after 3 weeks.

KALRAet al. (1950)

~arcoptes. H u m a n scabies.

Ornithodorus spp. O. moubata burried in dust in floor of hut. BHC at 1.25 gamma/sq, ft. (about 100 mg./sq, ft.) T w o applications. E. Africa. Same conditions, 1.25 D D T (? crude)/sq, ft.

g.

vector of relapsing fever. D D T or BHC dusts. Kashmir.

REFERENCES ARNASON, A. P., BROWN, A. W. A., F R E D - - , F. J., HOPEWRLL,W. W. & REMPEL,J. G.

(1949). Sc/. Agr/c., 29, 527. Cyprus Annual Medical & Sanitary Report, 1949.

Aziz, M. (1950). p. 13.

Appendix A and B.

P. A. BUXTON

225

BATES, M. (1949). The Natural History of Mosquitoes. New York : The Macmillan Co. BROWN, A. W. A. (1951). Insect Control by Chemicals. London : Chapman & Hall. BusvI~m, J. R. (1948). Bull. Hyg., 23, 344. BUXTON, P. A. (1945). Trans. R. Soc. trop. Med. Hyg., 38, 367. (1950). The Louse. 2nd Ed. London : Edward Arnold. CRoss, H. F. & S ~ E R , F. M. (1948). J. econ. Ent., 41, 936. DAVIDSON, G. (1950). Ann. trop. Med. Parasit., 43, 361 ; 44, 1. DIAS, E. & PELLEGmNO,J. (1948). Brasil-med., 62, 185. DORSEY, C. K. (1947). ft. econ. Ent., 40, 805. DuctmT, J. (1949). Bull. WorldHlth. Org., 2, 155. Expert Committee on Insecticides (1950). Rept. 1st session, 1949. (W.H.O. Tech. Rept.4.) ~(1951). Rept. 2ndsession, 1950. (W.H.O. Tech. Rept. 34.) FERGUSON, F. F., UPHOLT, W. M. & SIMMONS, S. W. (1949). J. nat. Malar. Soc.,'8, 32. GABALDON,A. (1949). Trans. R. Soc. trop. Med. Hyg., 43, 113. GARNHAM,P. C. C. & MCMAHON, J. P. (1947). Bull. ent. Res., 37, 619. GmLIOLI, G. (1951). J. nat. Malar. Soc., 10, 142. GUNN, W. C. (1948). Med. Offr., 80, 251. HEaTI~, M. (1950). Bull. World Hlth. Org., 2, 621. & FAIRCHILD,G. B. (1948). Amer.07. trop. Med., 28, 207. Hmn, M. A. & ROBERTS, E. W. (1947). Ann. trop. Med. Parasit., 41, 143. HOCKINa, K. S. (1946). E. Afr. reed. J., 23, 50. HUOHES, J. H. (1949). Publ. Hlth. Rpt. Wash. Supplement 210. 1. HURLBUT, H. S., ALTMAN, R. M. & NIBLEY, C. (1952). Science, 115, 11. JEPSON, W. F. (1947). Nature, Lond., 160, 874. KALRA, S. L., JACOB,V. P. & RAO, K. N. A. (1950). IndianJ. med. Res., 38, 457. K~TTLI~,D. S. (1949). Ann. trop. Med. Parasit., 43, 284. KINa, W. V. (1951). J. econ. Ent., 44, 338. KNIPLINO, E. F. (1949). Soap., 25, 107 ; 131. KOHLER, C. E., BROWN,H. W.& WILLIAMS,R. W. (1949). Publ. Hlth. Rpt. Wash., 64, 857. KRus~, C. W., PHILEN, E. A. & LUDVIE, G. F. (1951). 07. nat. Malar. Soe., 10, 23. LANDERS, J. J. (1947). 07. Hyg., 45, 354. LEwis, E. A. (1950). East African Tsetse and Trypanosomiasis Research and Reclamation Organisation Ann. Rept, for 1949. 36. MACCHIAVELLO,A., MOSTAJO, B. & MOSTAJOh]jo B. (1946). Bol. Ofic. sanit, panamer., 25, 1097. MACKEREAS, I. M., RATCLIFFE,F. N., GILMOUR, D. & MULES, M. W. (1950). Commonwlth Sci. Ind. Res. Org. Australia. Bull. No. 257. MARCH, R. B. & METCALF,R. L. (1950). Soap., 26, 121. METCALF, R, L. (1948). Chemical Biological Coordination Centre. Review No. 1. Nat. Res. Council. Washington. MoRms, M. G. (1950). Bull. ent. Res., 41, 259. MUIRHEAD-THOMSON, R. C. (1951). Mosquito Behaviour in Relation to Malaria Transmission and Control.in the Tropics. 2nd. Ed. London : Edward Arnold. NEGHM~ A., SmvA, R., Vme h'~s, R. & ALFARO, E. (1949). Bol. inform, parasit. Chilenas., 4, 36. PAMP~A, E. J. (1948). Bull. World Hlth. Org., 1, 253. --(1951). Ibid., 3, 557. PIMENTAL, D. & DEWEY, J. E. (1950). 07. econ. Ent., 43,105. REID, E. N. (1949). Hlth. Bull. Scotland., 7, 13. Ric~mDS, A. G. (1951). The Integument of Arthropods. Univ. Minnesota Press (and Oxford Univ. Press). SMITH, C. N. & GOUCK, H. K. (1947). J. econ. Ent., 40, 790. STEINIGEn, F. (1951). Z. Tropenmed. u. Parasit., 2, 544. SUMERFORD,W. T., GOETTE, M. B., QUARTERMAN,K. D. & SCHENCK, S. L. (1951). Science. 114, 6. TEw, R. P., DAVID, W. A. L. & BUSVINE,J. R. (1951). Mon. Bull. MiD. Hlth. and Pub. Hlth. Lab. Ser., 10, 30.

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du TOlT, R., KLrOGE, E. B. & FIEDLER, O. G. H. (1950). Tsetsefly and Tryp. Permanent Inter-African Bureau. Biblio. Bull., No. 7, 249. VISWANATHAN,D. K. & RAO, T . R. (1949). Indianff. Mal., 3, 269. WANSON, M., COImTOlS, L. & LEnlED, B. (1949). Ann. Soc. beige Mdd. trop., 29, 373. , - & BERVOETS, W. (1950). 1bid., 30, 629. WEST, L. S. (1951). The Housefly, its Natural History. Medical Importance and Control. Ithaca. N.Y. : Comstock Pub. Co. - & CAMPBELL, G. A. (1950). D D T and Newer Persistent Insecticides. 2nd Ed. London : Chapman & Hall. WHARTON, R. H. (1951). Nature, Lond., 167, 854. WHIamSlDE, E. F. (1949). Bull. ent. Res., 40, 123. WlGGLESWOBTH, V. B. (1950). The Principles of lnsect Physiology. 4th E d . London : Methuen & Co.