MINISTRY OF AGRICULTURE. EGYPT.

Technical and Scientific Service. —Bulletin No. 35.

The Egyptian Cotton Seed Bug ( hyalinipennh, Costa.). Its Bionomics, Damage, and Suggestions for Remedial Measures.

By T. W. KIRKPATRICK, B.A., F.E.S.,

ENTOMOLOGIST, MINISTRY OF AGRICULTURE, EGYPT.

Government Press, Cairo, 1923. To be obtained, either directly or through any Bookseller, from the GOVERNMENT PUBLICATIONS OFFICE, Ministry of Finance, Dawawin P.O., Cairo. Price - - - - - P.T. 10.

PREFACE.

The investigation of this cotton pest was begun in August 1921, and continued uninterruptedly until the end of 1922. Except where otherwise stated, all the experiments and observations recorded were made at the Laboratories of the Cotton Research Board at Gîza, or on the adjacent farm ; and with the two exceptions mentioned in the text, were all carried out by the writer personally. I wish to take this opportunity of expressing my sincere thanks to Dr. L. H. Grough, Mr. C. B. Williams, and the other members of the Entomological Section, for much kindly help and advice ; particularly to Mr. C. B. WiUiams for his ever ready suggestions regarding the experiments on the influence of temperature and humid- ity, and bio-climatics generally. Also to the several members of the Botanical Section for the time and trouble they have ungrudgingly taken in helping me in various matters connected with the botanical and agricultural aspects of the problem. The photographs which form Figures 21-23 are the work of Mohammed Efí. Mamoun Abdel Salam and those which form Figures 33-36 are from drawings by the late Hassan Efí. Raouf ; the remainder of the diagrams and drawings were done by myself. Temperatures are given throughout on the Centigrade scale, and the metric system is used for all measurements.

Gîza, February 1923.

CONTENTS.

PRELIMINARY :— 1. Introduction 1 2. A Short Summary of the more Important Literature relating to Oxycarenus spp 3. Geographical Distribution of the Species of Oxycarenus occurring on Cotton

II. IN EGYPT :— 1. Distribution in Egypt 2. The Quantity and Value of the Egyptian Cotton Crop...

III. DESCRIPTION OF 0. hyalinifennis :— 1. The Egg 9 2. The Nymphal Stadia 9 2a. Biometrical Method of checking the Number of Immature Stadia 11 3. The First Stage Nymph 12 4. The Second Stage Nymph 14 5. The Third Stage Nymph 15 6. The Fourth Stage Nymph 17 7. The Fifth Stage Nymph 19 8. The Adult Bug 21 8a. The Male 21 86. The Female 25 9. Note on the Characters and Distribution of the Different Types of Hairs 26

IV. LIFE-HISTORY AND HABITS : - 1. The Host Plants of the 28 2. The Life-history on Cotton : Breeding Season 29 (a) Copulation 29 (b) Oviposition 30 (c) The Incubation Period 33 id) Habits of the Nymphs 36 (e) The Duration of the Nymphal Stadia 37 (/) The Number of Generations 42 3. The Life-history on Cotton : The " Quiescent" Period 42 (a) Situations chosen by the Resting Bugs 44 (b) Habits and Reactions during the Early Part of the Quiescent Period 46 (c) Habits and Reactions during Spring and Early Summer... 18 4. The Approximate Numbers present on Cotton at Different Times of the Year 52 5. The Life-history on Bâmia 53 6. The Life-history on Til 55 7. The Life-history on mutabilis 56 8. The Life-history on Hollyhock 57 — VI —

PAGE . 9. The Life-history on mollis 57 10. The Life-history on Abutilón spp 58 11. The Life-history on diversifolia 58 12. The Life-history on the Eemainder of the Known Host Plants 58 13. The Percentage of Sexes 59 13a. The Effect of Adverse Temperature and Humidity Conditions on the Proportion of the Sexes 61 14. Tropisms or Forced Movements 64 15. Cannibalism 66 16. The Influence of Temperature and Humidity on the during the Period of Quiescence 66 {a) Experiments on the Eate of Mortality 67 (6) The Influence of Temperature and Humidity in stimulating the Quiescent Bugs to feed, and consequently to breed 68 17. The Decreasing Weight of the Bugs during the Period of Quiescence 70 18. General Conclusions regarding the Seasonal Life-history 71

V. THE NATURE OP THE DAMAGE :— 1. Damage to the Seed 73 (a) The Appearance of Cotton Seed attacked by Oxycarenus... 73 (6) The Loss in the Weight of the Seed 74 (c) The Extent to which Oxycarenus is responsible for the Non-germination of Cotton Seed 76 (d) Injury to the Embryo Eadicle, not so severe as to inhibit Germination 84 (ß) Injury to the Embryo Cotyledons 84 2. The Effect on the Ginning Out-turn of Damage to the Seed by Oxycarenus 86 3. Damage to the Lint 87 4. A Eefutation of the Theory that 0. hyalinifennis causes Bud and Boll-shedding 90

VI. CONTROL AND EEMEDIAL MEASURES :— 1. Natural Control 93 2. Discussion of Methods for Direct Control ... 94 {a) Attack on the Insect during the Winter Quiescent Period... 95 (6) Control during the Spring and Early Summer of those Bugs present on the Young Cotton 95 (c) Control during the Breeding Season 96 3. Methods of limiting the Damage :— {a) To the Seed 97 (6) To the Lint 97

SUMMARY 99

BIBLIOGRAPHY 105

EXPLANATION OF ARABIC TERMS USED IN THE TEXT 107 LIST OF ILLUSTRATIONS.

FIG. 1. Meso- and mela-thorax and first abdominal segment of third-stage nymph, to show rudiments of mesothoraeic wing-buds. 2. Meso- and meta-thorax and first abdominal segment of fourth-stage nymph, to show wing-buds. 3. Meso- and meta-thorax and first three abdominal segments of fifth- stage nymph, to show wing-buds. 4. Apex of the male abdomen. 5. Apex of the female abdomen (from beneath). 6. First stage nymph, apex of anterior femur. 7. Second stage nymph, apex of anterior femur. 3. Third stage nymph, apex of anterior femur. 9. Fourth stage nymph, apex of anterior femur. 10. Fifth stage nymph, apex of anterior femur. 11. Adult (male), apex of anterior femur. 12. The third stage nymph. 13. Fifth stage nymph, apex of anterior tibia. 14. The adult male. 15. The hemi-elytron. 16. Ditto, of a freshly moulted specimen, to show the venation. 17. Male genitalia, with penis extended. 18. Ovipositor of female, fully extended. 21. Quiescent bugs on the trunk of Ficus sp. 22. Quiescent bugs on the trunk of sunt (Acacia arabica), 23. Quiescent bugs on a leaf of Crotón eluteria, 33. An unattacked cotton seed. 34^. A slightly attacked seed. 35. A severely attacked seed. 36. A very severely attacked seed. 45. Cotyledon leaves of a seedling growing from a seed which has been attacked. LIST OF DIAGRAMS.

IflG. 19. The variation of the incubation period of the egg, according to the temperature. 20. The incubation period of the egg, calculated in terms of day efficiency. 24. Mortality of the quiescent bugs at different humidities, at a temperature of IP a ^ 25. Ditto, at normal winter shade temperatures. 26. Ditto, at normal Laboratory temperatures. 27. Ditto, at a constant temperature of 25^ C. 28. Ditto, at a constant temperature of 30^ C. 29. Ditto, at a constant temperature of 35^ C. 30. Ditto, at a constant temperature of 40^ C. 31 Ditto, at a constant temperature of 45^ C. 32 A comparison of the seasonal life-history on six of the more important and interesting host-plants. 37. A correlation of the average weight of 100 seeds, the percentage germination, and the Oxycarenus population per feddân. 38. Germination experiment No. 22. 39. No. 23. 40. No. 24. 41. No. 25. 42. No. 26. 43. No. 27. 44. No. 28. MINISTRY OF AGRICULTURE, EGYPT.

Bulletin No. 35.

THE EGYPTIAN COTTON SEED BUG {Oxycarenus hyalinipennis, Costa.). Its Bionomics, Damage, and Suggestions for Remedial Measures.

I.—PRELIMINAEY.

1. INTRODUCTION. The insect dealt with in the present Bulletin belongs to the Order Rhyncota, sub-order , which comprises the true sucking bugs. The great majority of this group of insects are, like the species here under consideration, feeders upon vegetable tissues, though there are numerous exceptions, as for example the predaceous species of the family Reduviidœ, which prey upon other insects : Triphleps (Anthocoridœ), well known in this country as feediDg upon the eggs of the pink boll worm, and the cosmopolitan bed-bug {Cimici- dœ)y only too familiar as a parasite of man. A very large number of Heteropterous insects are associated with the cotton plant in different parts of the world, and although certain of them are beneficial in destroying other pests, the good wrought by them is infinitesimal in comparison with the enormous destruction caused by the injurious species. Three groups of these insects stand out above the rest as regards their economic importance, namely, various species of Pentatomidœ, or shield-bugs, the genus {Pyrrhocoridœ), or cotton stainers, and the genus Oxycarenus {Lygœidœ) or cotton seed bugs. Of these the last named has, up to the present, received compar- atively little attention from entomologists ; indeed it is probably no exaggeration to say that of no other widespread and abundant pest of any such commercially important plant as cotton, has our knowledge of the bionomics, and the nature and extent of the damage caused, been so scanty and unreliable. The reason for this neglect is not far to seek. The injuries caused by Oxycarenus are not, as will be hereafter shown, in any - 2 - way conspicuous, and serious though they can be, cannot be compared with the colossal depredations caused by the boll-weevil in America, and the various boll-boring Lepidopterous larvae in all cotton-growing countries. Furthermore, the recent alarming spread of the Pink Boll Worm over practically all the cotton areas of the world has without doubt diverted the attention of entomologists from other less serious pests.

2. A SHORT SUMMARY OF THE MORE IMPORTANT LITERATURE RELATING TO OXYCARENUS SPP.

Kecords of the occurrence of the various species of Oxycarenus which are of economic importance are fairly numerous ; there are, however, but few references to the nature of the injuries they produce, and still fewer of these are based upon anything except conjecture. Further, there has been a tendency to confuse the damage caused by these insects with that caused by other Heteropterous cotton pests, in particular Dysdercus : these two genera, Dysdercus and Oxycarenus, being frequently alluded to collectively as '' stainers," whereas, as will be hereinafter shown, there is practically no similarity in their depredations ; the term " stainers '' should be limited to Dysderci, while '' seed bugs " is a suitable popular name for the genus Oxycarenus. So far as the writer has been able to ascertain, the first record of damage by Oxycarenus is a short note by Dr. E. Sickenberger (35, 1890). This reference is quoted by Morrill (28, 1910) as follows : '' These insects '' (referring to 0. hyalinipennis in Egypt) '' suck the sap from the base of the young pods and from the blossoms and thus prevent their development ; they attack also the seeds when they are tender, which results in a diminution of the germinative strength and consequently a diminution in the product of the plant. A staining of the lint is also mentioned, but the exact method by which this injury is brought about is unexplained.'' In the " Fauna of British India " (9, 1904) the following note occurs under 0. lugubris, Motsch : " In Ceylon this insect infests the ripe pods of the cotton, discolouring-and caking the cotton (Green)." The next paper of importance is also on the Egj^tian species, by Mr. F. C. Willcocks, Entomologist to the Sultanic Agricultural Society, Cairo (40, 1906). This article contains a description of the insect, an account of its life-history so far as then known, a guarded statement as to the probable injuries caused by it, and suggestions for control measures. As regards the nature of the damage, ~ 3 -

Mr. Willcocks writes : " Probable injury is caused in the following manner :— '' (1) The adults, by sucking the juices from the squares and young bolls, cause a certain amount of square and boll ' shedding.' " (2) The large colonies of stainers which live in the opened bolls dirty the fibre with their cast skins. The cotton is also stained by excrement, but not to a noticeable extent. The fibre may possibly be weakened by the excrement owing to a slight rotting. " (3) By sucking the juices from the seeds they cause a large proportion of ' light seed.' '' (4) By sucking the juices from the soft and immature seeds they may possibly cause weakening of the fibre. " (5) They may cause matting of the fibre to a slight extent. " (6) During the picking of the cotton the bodies of the stainers may be crushed, and the fibre stained by the contained juices. "(7) Seed cotton may contain stainers, some of which will possibly be crushed during the ginning process. The staining of the fibre from this cause, however, is probably much less in the case of the ' roller gin ' used in Egypt than in the ' saw-toothed ' gin of America. '' (8) The characteristic and very disagreeable odour of the insects is imparted to the cotton fibre.'' Altogether this is by far the most valuable paper hitherto published on this pest, and is almost alone in its absence of definite assertions unfounded on experiments or observations. Peacock (31, 1913-1914) writes of 0. dudgeoni, Dist., in Southern Nigeria : '' They feed and breed in the opened cotton bolls sucking the juices from the seeds. . . . There seems to be a decided preference for certain species of Hibiscus as food-plants, for in the Nursery at Ibadan the ripening plants were found to be black with these pests. The insects seem to be feeding on all parts of the plant, which is not the case with cotton. ... It is not safe at present to state the ex- tent of the harm done by these insects, but their abundance indicates that very real damage is being done to the seeds at least. Whether they stain the lint seriously cannot be said." Morstatt (30, 1914) reports the occurrence of 0. hyalinipennis in large numbers in (then) German East , and states that it is " scarcely a pest." This is of interest in view of the divergent opinions expressed concerning the economic status of this insect. Following upon this, a short note by Balls (7, 1915) gives the first well-founded account of the effects produced by the Egyptian species on the germination of cotton seed. The majority of the facts recorded in this paper are confirmed and amplified by the present writer. — 4 —

Fletcher (12,1917) writes of O. te¿^5 in India: " . . . . A minor pest of cotton, usually occurring on old open bolls and living on the extremely small amount of juice that they can suck from ripening seeds . . . The chief damage done is not so much to the plant itself as by the crushing of the bugs (chiefly nymphs) when the cotton is ginned, so that the lint is stained/' An article by Del Guercio (17, 1918) on the cotton Lygaeid of Somaliland, which with some hesitation is assigned to 0. hyalinipennis, does not, in the present writer's opinion, so far as can be ascertained from the description and drawings given, refer to the same species as occurs in Egypt. Nothing is definitely stated as regards damage done to cotton, but Del Guercio quotes statements by E. Schüler, studying the presence of Oxycarenus at Cairo, that it " . . . not only pierces and sucks the mature bolls, but also the young bolls and also the flowers . . . and it does not spare even the buds of the plant, ... it is found in large numbers in cotton bolls in Cairo, where it attacks also the flowers and may hinder their development.'' He also mentions a statement by Dr. Onor, also apparently referring to the Egyptian species, ''that it sometimes invades in destructive numbers the lint at the time of picking and in the stores." There are no references or dates appended to these quotations, and I have been unable to trace the originals. Del Guercio also describes in this paper two new species of Sporozoa, which he found in the viscera of this species of Oxycarenus from Italian Somaliland, but nothing is said as to whether any mortality is caused by them. Adair (1, 1918) writes of 0. hyalinipennis, '' . . . wrongly known as the stainer bug. Does much damage to buds and young bolls and is responsible for a great deal of the boll-shedding usually attributed to other causes." C. S. Misra, in a paper on cotton pests of North Bihar (25, 1919), writes that Dysdercus cingulatus and 0. lœtus, '' spoiled whatever little lint was left on the cotton plant." In the discussion following this paper (25, p. 561) some remarks on 0. Jiyalinipennis in Egypt are attributed to Dr. L. H. Gough, which I am informed by him were wrongly reported, and should therefore be neglected. Pomeroy (32, 1920-1921) describes 0. dudgeoni, as '' one of the chief cotton pests of Southern Nigeria." It is mentioned collectively with several species of Dysdercus as being a '' stainer." C. S. Misra, in a paper on 0. lœtus in India (26, 1921), in discussing the nature of the damage done to the cotton seed, states that "the bug not only injures the seed, but is the immediate cause of the reduction of the vitality of the seed through successive generations so as to render it more amenable to the attack of the insect pests, and possibly fungoid diseases." No experiments, however, are quoted in proof of this — 5 —

assertion. As regards the question of shedding, he writes '' The bug afîects the flowers and the buds and is the immediate cause of the shedding of these in enormous numbers." This somewhat sweeping statement is, however, considerably qualified by the following, a few lines further on : '' Of course, I have no doubt that this premature fall may be due to physiological causes, connected with subsoil moisture; soil aeration, drainage, manure, and the peculiar susceptibility of the particular variety or varieties of cotton to this cause.'' In the discussion which followed this paper the widest divergences of opinion were expressed concerning the injuries caused by this insect. A recent note by Willcocks (42, pp. 31-33, 1922) does not contain much information that is not found in his previous paper (40). The foregoing extracts show, if nothing else, the extremely unsatis- factory nature of our knowledge of this genus. The statements quoted vary from accusing Oxycareni of being responsible for nearly all the ills to which cotton is subject—bud and boll shedding, staining and weakening of the lint, deterioration of the seed and of the resulting plant—to almost if not entirely acquitting them of doing any damage of practical importance ; such widely divergent views being held even as regards a single species in one country. It is hoped that the experiments and observations which follow will be found to do something to settle this question, at any rate as far as the Egyptian species is concerned ; and while there is no doubt that the habits of the several species in different countries, or even of the same species under varying climatic conditions, may show considerable dissimilarities, it is not unlikely that subsequent research will prove that the injuries caused by the other species of this genus are not so very different from those of the one here under consideration.

3. GEOGRAPHICAL DISTRIBUTION OF THE SPECIES OF OXYCARENUS OCCURRING ON COTTON.

The following list, though doubtless by no means complete, will serve to give some idea of the geographical range of the various species which have hitherto been recorded from the cotton plant :— Africa :— Egypt, 0. hyalinipennis, Costa (1, 4, 28, 40, etc.). Sudan, 0. hyalinipennis (21). Italian Somaliland, 0. hyalinipennis (17). Uganda, 0. hyalinipennis (36). 0. exitiosus, Dist. (37). 0. albidipennis, Stäl. (37). 0. gossypinus, Dist. (36). — 6 —

Tanganyika Territory, 0. hyalinipennis (29). Zanzibar, 0. albidipennis (2). Nyasaland Protectorate, 0. hyalinipennis (23). Transvaal, 0. albidipennis (8). Angola, 0. hyalinipennis (18). Nigeria, Southern Provinces, 0. dudgeoni, Dist. (31). Asia :— India, 0. lœtus, Kirby (24). Ceylon, 0. lœtus (9). 0. luguhris (33.) Mesopotamia, 0. tot^5 (43)., Australia :— Queensland, 0. luctuosus (39). Victoria, 0. arctatus (19). Äot^iÄ Ameriea :— Brazil, 0. hyalinipennis (27).

Species of Oxycarenus have also been reported from plants widely removed from the Order Málvales. Among these may be mentioned : 0. lectularis on Opuntia and also on strawberries in New South Wales (15, 14), 0. amygdali, on peaches in the Transvaal (10), and 0. eollaris on cut grasses at Stavropol, Russia (44). This species has also been taken in Egypt by sweeping, at the Barrage, and at Ezbet el Nakl (20). 7 —

IL—OXYCARENUS HYALINIPENNIS IN EGYPT.

1. DISTRIBUTION IN EGYPT.

The Egyptian cotton seed bug has been known to occur in Egypt at least since 1860 (4) and there seem to be no grounds for supposing that it is not indigenous to the country. No doubt long before the introduction of cultivated Malvaceous plants, it existed on wild species of both in the Nile Valley and delta, and in the desert, where the writer has found it at the present time, some twenty kilometres or more from the nearest cultivation. Being free from parasites and predatory enemies, the introduction of cotton cultivation, providing it with abundance of food and more favourable conditions, would rapidly effect its increase from a compar- atively uncommon insect—as it still is in the desert—to the position it holds to-day, that of the numerically most abundant Egyptian cotton pest. This insect appears to be abundant throughout Lower and Middle Egypt, ix. as far south as Minya. Foaden (13) states that it is found most extensively near the sea coast; at the present time, however, it is as far as can be judged equally common everywhere, if anything it is most numerous round Cairo. In Upper Egypt it rapidly becomes scarcer ; occurring in moderate numbers at Asyût, less frequently at Sohag, and being practically non-existent at Luxor. The Inspector of Agriculture at Luxor has also informed the writer that it is not found in the neighbourhood of Qena, Armant, or Kom Ombo, from which latter place it was, however, recorded by Willcocks (40) in 1906. It is an abundant pest in the cotton growing areas of the Sudan (21). The factors controlling its distribution are undoubtedly climatic : from the somewhat incomplete meteorological records available, it appears that the insect is not found where the average mean temper- ature for any month exceeds 32°-5 C. Thus at Qena, the mean temperature for June and July exceeds 33° C, at Aswan it is over 32°-5 C. in May, over 34° C. in June and August, and over 35° C. in July. At Wad Medani in the Sudan, where Oxycarenus occurs, the highest mean monthly temperatures are 32°-2 C. for May and 31°-2 C. for June (during both of which months there is a considerable amount of cloud). At Asyût and further north no month has an average temperature above 30° C. The atmospheric humidity has apparently — 8 — little or no connection with the distribution ; at Wad Medani, for instance, the mean relative humidity for the months of February to May is below that of any month either at Asyût where the insect also occurs, or at Qena and Aswan where it does not. This is hardly surprising, as there is little doubt that the humidity of the air in close contact with a growing plant is both high and constant, and bears very little relation to the figures obtained by ordinary meteorological methods.

2. THE QUANTITY AND VALUE OF THE EGYPTIAN COTTON CROP.

Taking the average figures* for the five years 1910-1914 (as being more stable than recent years) the area planted with cotton in Egypt was as follows :— Lower Egypt 1,347,000 feddâns. Middle Egypt ..., 308,000 „ Upper Egypt ,/. 56,000 „

Consequently nearly 97 per cent of the total crop is grown in areas where Oxycarenus is abundant. The average annual value of the cotton harvest during those years was L.E. 25,707,000 for the lint and L.E. 4,299,000 for the seed. If the loss in value to the lint is estimated at only 2 per cent, and the loss in weight to -the seed at only 2| per cent, figures which, though difficult of verification, are probably on the conservative side, then the annual loss to the country is upwards of L.E. 600,000, a loss which, as will be shown in Part VI, is almost entirely preventable ; and insignificant though it may appear in comparison with the damage done by the Pink Boll Worm, should not on that account be neglected.

* Figures taken from Annuaire Statistique de VEgypte, 1919. 9 —

III.—DESCRIPTION OF 0. HYÄLINIPENNIS.

1. THE EGG.

The egg is oval, somewhat more pointed at the posterior end, the average size being 0-95 mm. long by 0-28 mm. in diameter at the broadest part. Among the numerous eggs measured, the greatest length—1-01 mm.—and the smallest diameter—0-26 mm.—occurred in the same specimen, as also did the shortest length^—0-88 mm.—and the greatest breadth—0-30 mm. The shell has about twenty-five longitudinal corrugations, giving it a markedly striated appearance, which is most obvious before the embryo becomes visible through the shell. At about 0*05 mm. from the anterior end (i.e. where the head of the contained embryo lies) are six small semi-spherical protuberances, arranged in a circle round the end of the egg. The diameter of each of these protuberances is approximately 16 fx. The area contained by them, i.e. the anterior extremity of the egg, is smooth and unstriated. When first laid, the egg is of a pale straw colour ; about half way through the period of incubation, it becomes orange marked with pink, owing to the embryo becoming visible through the thin, colourless, transparent shell. The eyes of the embryo are readily distinguishable, as also are the antennae, rostrum, and legs, towards the end of the incubation period. The eggs are not attached to the cotton fibre in any way, and may readily be shaken out ; where, however, they are laid on a green boll {vide page 31), they are loosely fixed to it, and when they are laid in batches of two or more together, they adhere to each other. When the young nymph emerges, the shell splits at the anterior end, and the insect makes its way out head first.

2. THE NYMPHAL STADIA.

After emerging from the egg, the young bug undergoes five ecdyses before attaining maturity. The first three stages are very similar to one another, except as regards size and the number of facets m the compound eyes. The fourth stage is characterized by the rudimentary wing-buds which conceal the side margins of the meta- — 10

tí ^-A. : I I QJ lO • A ei i.ä^ • • • CO ce ^ pH . . 4< HH CÔ 3-+3 * O Ü '^ M 3 . < -+3 • <1 : - tí c6 Oí .- s r—1 ¿ : r-H 8"! 00 o ^ .^ 4^ : ^ 1< laIs «lie 1 4^ : rJD tí ce qp Cß Ù a ^^_^ Ê • ^y tíO^n o O 1 • ^ s T-H t- ►H 1 có M : tí |co tí 1 O : tí S ^ Ecj 4-3 — • ? pH rO tí 5« ce 0^ ce ë

a c:0 M1 4S 00 ti) • •rH (M 1 i .a §^ O '" tí

> tí sili 4^ O O

4^ •rH^ ''''~^' 4-3 '$ '^ tí o no rtí O ce ö a t ^ 'S 1—1 1 tí 2 ë s 1tí ^ 1 -3l 11 thorax (Fig. 2), while in the fifth and last immature stage the wing buds are more fully developed, extending to the third abdominal segment (Fig. 3). In all the immature stadia there are only two tarsal joints on all legs, and no trace of ocelli. The table on the preceding page may assist in the determination of the various stages.

2a. BiOMETRiCAL METHOD OF CHECKING THE NUMBER OF IMMATURE STADIA.

It was shown by Dyar (11) that, if measurements are taken, during the successive immature stages of an insect, of some part of its anatomy which is not subject to growth during a stadium, the increase in size follows an almost exactly regular geometrical progression. By this means it is possible to ascertain whether a moult, and consequently a stadium, has been overlooked in the breeding experi- ments or not. Thus, the total length of the antennae of 0. hyalinipennis was found to be :— First stage 0-68 mm. Second stage 0-85 Third stage 1-09 Fourth stage 1-38 Fifth stage 1-70 By dividing 0*85 by 0*68, ix. two successive members of the series, the factor 1 -25 is obtained, and by multiplying the length in any one stage by this factor, the theoretical length of the succeeding stage is found, thus :— 0-68X1 •25=0-85=theoretical second stage. 0-85X1-25=1-06=theoretical third stage. 1-06x1-25=1-33=theoretical fourth stage. 1-33X1-25=1 •66=theoretical fifth stage. These calculated results agree with those actually found sufficiently to preclude the possibility of an instar having been overlooked. Similarly, the length of a single antennal joint may- be taken, e.g. the terminal joint :— Actual lengths of fourth antennal joint found by measurement :— First stage ... 0-27 mm. Second stage 0-32 Third stage 0-39 Fourth stage 0-455 Fifth stage 0-545 — 12

Factor 32/27, or approximately 1-2. O- 27XI•2=0-32 ^calculated second stage. 0- 32X1-2=0•384=calculated third stage. 0-384x1-2=0-46 =-calculated four stage. 0- 46Xl-2-:0-55 -^calculated fifth stage. It appears also that the number of ommatidia in the compound eye follows the same rule, thus : Approximate number of facets counted was :— (Calculated numbers.) First stage ... 25X{ii=)l'6-= 40=second stage. Second stage 40 40 XI-6= 64:-= third stage. Third stage ... 60 64 X1 • 6-:102=fourth stage. Fourth stage 100 102xl-6=163=fifth stage. •Fifth stage ... 180

3. THE FIRST STAGE NYMPH. Head brownish olivaceous, brightly shining, with a pale yellow curved line running backwards and inwards from each eye, these lines meet on the posterior margin of the occiput, forming an U-shaped marking. The head is thinjy covered with fine white truncate hairs, which terminate in a corona of usually* five very minute teeth. Antennae with the basal three joints pale orange or pinkish, the fourth brownish magenta, and somewhat thicker than the others. They are thinly clothed with fine hairs, which are least numerous on the basal joint, somewhat more numerous towards the apices of the second and third, and considerably more so on the whole of the fourth. The hairs are in length about two-thirds the breadth of the middle joints, slightly longer at the apices of the second and third joints, and on the fourth. On the first three joints the hairs are truncate, or slightly capitate terminating in a corona of minute teeth, which are even smaller than those on the hairs of the body : on the terminal joint the hairs are simple and tapering ; there are also a few simple hairs towards the apex of the third joint, especially on the inner side, and one on the first joint on the inner side near the base. The lengthf of the antennae is as follows :—

Average. Maximum. Minimum. Millimetres. Millimetres. Millimetres. 1st joint 0-100 0-11 0-09 2üd „ 0-159 0-175 0-15 3rd „ 0-163 0-175 0-155 4th „ 0-275 0-28 0-27

TOTAL LENGTH 0-687 0-715 0-65

* Vide note on the coronate hairs, section 9. t AH the measurements of antennae and rostrum are the average, maximum, and minimum, of fifteen specimens of each instar. — IS —

Tlie labrum (upper lip) is straw-coloured, and bears a pair of coronate hairs near its base and a few more exceedingly minute hairs. It is slightly longer than the first joint of the labium. The labium bears a few very short hairs, and a tuft of minute bristly hairs at its apex ; it is of the same colour as the labrum. The setse, the outer pair of which are homologous with the mand- ibles, and the inner pair with the maxillae, of other insects, are pale yellow ; they are exceedingly fine, their diameter towards the apex being in the neighbourhood of 2 to 3 microns. In newly hatched, or starved, nymphs of the first instar, the rostrum projects slightly beyond the apex of the shrunken abdomen. The length of the rostrum is :—

Average. Maxinaum. Minimum.

Millimetres. Millimetres. Millimetres.

1st joint 0-200 0-21 0-19 2nd „ 0-244 0-26 0-23 3rd „ 0-271 0-29 0-26 4th „ 0-243 0-255 0-24

TOTAL LENGTH ... 0-958 0-99 0-94

The eyes are dark red, appearing brighter round the circumference ; oval, the greater (vertical) diameter being about 0-07 mm,, they are composed of approximately twenty-five facets. Prothorax and meso-thorax brownish olivaceous, and brightly shining like the head, with a pale yellow median stripe. The posterior margins of both pro- and meso-thorax are also pale yellow. The meta-thorax is white, and contrasts conspicuously with the remainder of the body. The thorax bears hairs similar to, but slightly shorter than those of the head, except on the pale median line, which is bare. The pleurae and sternum are yellowish brown, tinged with a varying amount of pink coloration. The legs are pinkish to brownish, trochanters and apices of all femora paler, all tibiae, more especially the mid and posterior pairs, somewhat more reddish on the basal two-thirds ; the tarsi are straw- coloured. The legs are sparsely clothed with short hairs, which are truncate and toothed on the femora and tibiae, except a few short simple hairs on the inner side of the femora, and towards the apices of the tibiae ; on the tarsi all the hairs are simple. — 14 —

The anterior femora are rather stout, bearing on the inner side {i.e. that which lies in apposition to the tibia when the leg is folded) about three-quarters the distance from the base, two small strong slightly curved spines, which are close together, the apical one being rather less than half the size of the other (Fig. 6). The mid and hind femora are less thickened than the anterior pair, and simple, one subapical hair on the outer side is slightly longer and stronger than the rest. All the tibiae, in addition to the usual hairs, have three or four short stoutish apical spurs. The anterior tibiae are gradually dilated towards the apex, where their breadth is about If times that at the base. They have a small subapical wart on the inner side, which bears three hairs somewhat stronger than the rest, stout at the base, and abruptly attenuated on the apical half. They also have an apical comb of short stifï regular hairs. The mid and hind tibiae are simple, and normally haired. Tarsi with the second joint about twice the length of the first ; the hairs are more numerous on the underside of the metatarsus. Claws long, curved almost in a semi-circle. The abdomen is shining orange-yellow, except the first segment, the anterior two-thirds of which is bright pink, and two pinkish red round spots in the middle of the fourth and fifth segments. The anterior margin of the fifth segment is also pinkish, except in the median area, between the two spots. The distribution of the pink coloration is, however, somewhat variable and towards the end of the stadium the abdominal colour tends to become more pink and less orange. It is sparsely clothed with short hairs similar to those on the thorax. Venter shining brownish-orange, tinged with pink on the first and fifth segments. The basal segments are bare, there are a few fine hairs towards the apex. The anal process is dark brown. The average length, excluding the antennae, and measured when the abdomen is distended with food, is 1 • 2 mm.

4. THE SECOND STAGE NYMPH.

This is very similar to the preceding instar, except as regards size, the average length being 1-53 mm. The U-shaped marking on the head is somewhat less conspicuous, being of a darker brown colour. - 15

The antennae are similar, the length of the jomts being :-

Average. Maximum. Minimum.

Millimetres. Millimetres. Millimetres.

1st joint 0-135 0-14 0-13 2nd „ ... 0-21 0-22 0-195 3rd „ 0-21 0-225 0-20 4th „ 0-32 0-34 0-305

TOTAL LENGTH ... 0-875 0-92 0-84

The rostrum is also the same except in size, its length being as follows :—

Average. Maximum. Minimum.

Millimetres. Millimetres. Millimetres.

1st joint 0-272 0-28 0-25 2nd „ 0-338 0-365 0-32 3rd ;, 0-381 0-405 0-36 4th „ 0-289 0-305 0-27

TOTAL LENGTH ... 1-279 1-34 1-19

The approximate number of facets in the compound eye is 35-40. On the front femora, in line with and nearer the apex than the two thorns, there is a longish simple hair. The characteristic hairs arising from the small wart on the inner side of the anterior tibiae are rather more conspicuous, as also is the apical comb of about 14 short stiff hairs. The third and fourth abdominal segments are rather lighter m colour than the remainder of the abdomen ; the round red spots on the fourth and fifth segments are as a rule well defined. The abdomen often becomes dark reddish brown by exposure to the air.

5. THE THIRD STAGE NYMPH. (Fig. 12.) This again is somewhat like the two earlier instars. The average length is 2-25 millimetres. Head and thorax rather more pinkish brown, contrasting more strongly with the white meta-thorax. The pale lines on the head running backwards from the eyes are fainter and less curved inwards, the base of the U-shaped marking thus being broader. The pale median line on the pro- and meso-thorax much fainter. Inconspicuous — 16 —

slightly paler swellings on the sides of the meso-thorax indicate the first traces of the mesothoracic wing-buds (Fig. 1). The antennae have one long and about two shorter simple hairs on the inside of the first joint near the base, a very few simple hairs towards the apex of the second, and rather more towards the apex of the third joints : the fourth joint is slightly less densely hairy than in the preceding stages, otherwise the arrangement of hairs is the same. The length of the antennae is :—

Average. Maximum. Minimum.

Millimetres. Millimetres. Millimetres.

1st joint 0-170 0-18 0-15 2nd „ 0-281 0-30 0-26 3rd „ 0-264 0-28 0-25 4tli „ 0-395 0-41 0-37

TOTAL LENGTH ... 1-100 1-15 1-05

The length of the rostrum, which in other respects is similar, is

Average. Maximum. Minimum.

Millimetres. Millimetres. Millimetres.

1st joint 0-336 0-37 0-31 2nd , 0-45 0-47 0-41 3rd „ ...... 0-47 0-52 0-425 4tli „ 0-349 0-37 0-32

TioTAL LENGTH ... 1-605 1-70 1-50

The compound eyes are composed of approximately sixty facets. On the anterior femora (Fig. 8) there are rudiments of a third thorn nearer the apex than the two which were also present in the earlier stadia. This apical thorn is rounded instead of pointed at the tip, and bears a fine simple hair. The thorn nearest the base of the femur is at least twice the length of the next, and considerably directed forward, they are brownish with darker tips. There is also a very inconspicuous tubercle near the middle of the femur in line with the other thorn. In the later stages this also becomes a well defined thorn. The subapical wart on the inner side of the anterior tibiae is scarcely visible, but the three strong hairs arising from it are conspi- - 17 ^

cuous, and of the same characteristic shape as before. The anterior tibiae are somewhat less dilated at the apex, but the apical comb of short regular hairs is as conspicuous or more so. All the tibiae have at their apices four spurs, as well as a few rather strong pointed hairs. The colour of the legs is somewhat darker, all the femora being brownish magenta, paler at the apices, and similarly all the tibiae except the posterior pair just at their apex, where they are lighter brown. The trochanters and tarsi also are light brown. Abdomen more generally unicolorous than in the second stage nymph, being bright pinkish, becoming darker red after exposure. The two median spots are as a rule only readily discernible in newly moulted specimens.

6. THE FOURTH STAGE NYMPH.

This stadium differs conspicuously from the preceding by reason of the wing-buds, which cover the side margins of the meta- thorax (Fig. 2). When newly moulted, the head, pro- and meso-thorax, including the meso-thoracic wing-buds, are olivaceous brown, the head being slightly darker than the thorax : the two faint curved lines on the head as in the third instar, but generally obscure. The median line on the pro- and meso-thorax is also obscure, and somewhat pinkish. Abdomen almost unicolorous bright pink, except for the two darker median spots on the fourth and fifth somites, which are fairly distinct. After exposure to the air, the head, pro- and meso-thorax become dark reddish brown, and less brightly shining ; rather paler on the median line. The pale lines on the head as a rule become scarcely visible. The coronate hairs are as in earlier stages, except that the posterior median area of the head, behind and between the eyes, is bare. The mesothoracic pair of wing buds only just extend beyond the anterior margin of the first abdominal segment, they overlap the metathoracic pair, except for a narrow strip on the inner margin (Fig. 2). These latter, like the whole of the metathorax, remain white throughout this stadium. The average length of this instar is 2-86 millimetres. The antennae are reddish brown, the first joint, apical half of the third, and the fourth except at the extreme tip, rather darker. Some- times nearly the whole of the third joint, and the apical two-thirds of the second, are also dark. The distribution of the simple and coronate hairs is the same as in the third stage. — 18

The length of the antennae is :-

Average. Maximum. Minimum.

Millimetres. Millimetres. Millimetres.

0-21 0-22 0-20 1st joint 0-375 0-415 0-345 2nd „ 0-34 0-365 0-325 3rd „ 0-455 0-48 0-43 4th „

TOTAL LENGTH ... 1-38 1-44 1-31

Rostrum light reddish brown, except the apical two-thirds of the fourth joint, which is darker. Length :—

Average. Maximum. Minimum.

Millimetres. Millimetres. Millimetres.

1st joint 0-445 0-475 0-41 2nd „ 0-57 0-62 0-52 3rd „ 0-62 0-67 0-565 4th „ 0-408 0-43 0-39

TOTAL LENGTH ... 2-038 2-15 1-91

The eyes consist of approximately 100 facets. Legs brownish red, trochanters, apices of all femora, and of mid and hind tibiae, and all metatarsi, paler. The anterior femora have the blunted, piliferous, apical thorn, which first became apparent in the preceding stadium, larger but still inconspicuous. There is also a trace of another thorn situated near the middle of the anterior femora, on the inner side in line with the other three near the apex. This basal thorn is sharply pomted like the two larger ones (Fig. 9). The tibiae, in addition to the coronate hairs, have several simple hairs, especially on the inner side and towards the apex. They have four apical spurs as in the third stage. Abdomen almost unicolorous reddish sometimes with traces of more yellowish markings on the basal segments ; the short coronate hairs rather more numerous. The venter is also rather more abundantly provided with fine hairs. 19 —

7. THE FIFTH STAGE NYMPH.

This, the last immature stadium of the insect, when just moulted, has coral pink antennae and legs, transparent whitish wing-huds, and a brilliant red abdomen with some traces of pale coloration on the basal segments. After a few hours this appearance is lost, and the characters become as follows :— Head, pro- and meso-thorax, including wing-buds, dusky reddish black, punctate, scarcely shining, covered with short white erect coronate hairs, which are longer on the fronto-clypeus, and shorter and less numerous on the posterior of the head, and the median area of the thorax. On the middle of the occiput there is a completely bare area. There is a paler red very fine line on the head running almost straight back from the anterior margin of the eye, so that the two lines do not, as in the early stages, meet at the back of the head. Pro-and meso-thorax with a median dull reddish line. Mesothoracic wing-buds slightly longer than and overlapping the metathoracic pair (Fig 3) except on the inner margin ; extending as a rule nearly to the posterior margin of the third abdominal segment, but in starved specimens considerably further. The metathoracic wing-buds are transparent white with a dark border. Metathorax broadly concealed at the sides by the wing-buds, it has a pale brown median spot in line with the central stripe on the pro-and meso-thorax, but towards the end of the stadium this also becomes darker. Pleurae reddish, black above coxal cavities, with a few short white truncate hairs. Sterna reddish, shining, bare in the central line (where the rostrum rests when not in use) but with a few short white simple hairs at the sides near the inner margins of the coxal cavities. Antennse dark red, shining ; the whole of the second joint and the basal half of the third light brown at first ; but prolonged exposure causes the whole antennae, especially the third and fourth joints, to become almost black. On the basal joint the hairs are all coronate, except for the three or four simple hairs near the base on the inner side, of which one is much longer than the others. On the second joint they are mostly coronate, with a few simple near the apex, while on the third the simple hairs are more numerous, especially towards the apex. The fourth joint is entirely clothed with simple hairs; except for two or three truncate or very minutely coronate hairs on the outer side, these are not invariably present. — 20

The simple hair^ are rather less erect than the coronate ones. The length of the antennal joints is :~

Average. Maximum. Minimum.

Millimetres. Millimetres. Millimetres.

1st joint 0-265 0-28 0-245 2nd „ 0-496 0-57 * 0-45 3rd „ 0-425 0-48 * 0-40 4'li „ 0-540 0-56 * 0-50

TOTAL LENGTH ... 1-699 1-88 * 1-595

The labrum has a single pair of longish coronate hairs near the base, but is otherwise almost bare. It has numerous transverse grooves, which give it an annulated appearance. Eostrum dull reddish, paler at the junctions of the first and second and second and third joints, almost black on the apical half of the fourth ; sparsely clothed with fine short tapering hairs. Length :- -

Average. Maximum. Minimum.

Millimetres. Millimetres. Millimetres.

1st joint 0-578 0-65 t 0-525 2nd „ 0-677 0-82 t 0-59 3rd „ ... 0-697 0-85 t 0-58 4tli „ 0-450 0-50 t 0-415

TOTAL LENGTH ... 2-400 2-82 t 2-145

The eyes are dark red, and are composed of about 180-185 facets. Legs dark reddish black, shining ; coxse (which are less brightly shining), trochanters, and apices of femora more reddish ; tibige slightly darker; apex of posterior tibiae and all metatarsi paler; second joint of all tarsi nearly black. Sometimes the legs become entirely almost black. Anterior femora much swollen, with the four thorns well defined (Fig. 10) ; the one situated in the middle of the femur is of the same size as the apical thorn, this latter being rounded at the tip and bearing

* These appear to be somewlmt exceptional lengths, which all occurred in the same mdividual. t These also appear to be exceptional lengths, and were found in the same individual as the one with abnormaUy long antennae. — 21

a hair, as in the previous instar ; the subapical thorn is about three times the length of these, and the third from the apex about twice the length of the latter. The mid and hind femora are somewhat dilated, but much less so than the anterior pair. The anterior tibiae have the curious subapical hairs similar to those in the fourth stadium, and conspicuous, as also is the apical comb (Fig. 13). They have four or five apical spurs, as well as a few rather strong tapering hairs near the apex. The mid and hind tibiae have, in addition to a few similar strong hairs, five or six apical spurs. Abdomen dull red,* slightly darker on the middle and paler on the posterior margins of the segments, especially on the three basal ones ; covered rather more thickly than in the earlier stadia with the usual white coronate hairs. The two orifices of the stink glands are clearly visible as small brownish slits in the median line of the abdomen, in the sutures between the fourth and fifth, and fifth and sixth segments. Venter emarginate, reddish like the dorsum of the abdomen, but somewhat more shining, with a few very fine simple hairs, some of which are three times as long as the rest. Anal process black, in females the rudiments of the ovipositor are visible as a pale yellow or greyish oval area showing through the integument of the venter. The length of this stage varies from about 3 • 28 to 4 • 27 millimetres, the majority of those longer than 3-65 millimetres being females.

8. THE ADULT BUG.

When the adult first emerges from the final nymphal stage, it is of a beautiful coral pink colour, both on the body and on the antennae and legs; the wings have a silvery iridescent appearance. After a very few hours, the period being shorter when the weather is warm, the coloration is entirely changed, and the insect assumes the following form.

8a. THE MALE (Fig. 14).

Head blackish, punctate, clothed with white coronate hairs, which are almost erect, but slightly directed forwards. Among these there are some less erect, somewhat curled simple hairs, which arise from the punctures. The median area of the occiput bears only simple

* Sometimes when replete with food the abdomen assumes a greenish tinge. — 2^1 — hairs. At the side of the head in front of the eye there is a single coronate hair considerably longer than, but otherwise similar to, the rest ; there is also a pair of somewhat longer such hairs towards the apex of the fronto-clypeus. The under side of the head (gula) with short flat-lying simple hairs, except in the groove where the rostrum lies, which is bare. The antennae have the first joint black, except for a yellow spot at the apex on the outer side ; the second joint is black on the basal tenth and apical third, except the extreme apex, the remainder being light brown ; occasionally the whole joint is dark brown. The third joint with the basal fifth or less and the extreme tip brown, sometimes dark brown, the rest black. Fourth joint all black except at the base and sometimes also at the apex, where it is brown. On the first antennal joint the hairs are all white, semi-erect and truncate with an inconspicuous corona of teeth, except for two or three short and one somewhat long simple hair on the inner side near the base. The second joint bears similar coronate hairs, and also a few simple ones towards the apex ; the third mostly simple hairs, but also some coronate ones especially neai* the base ; whereas on the fourth joint all the hairs are simple. The fourth joint is considerably, and the third somewhat more densely hairy than the first and second. The length of the joints is :—

Average. , Maximum. Minimum.

Millimetres. Millimetres. Millimetres.

1st joint 0-275 0-285 0-245 2nd „ 0-563 0-625 0-470 3rd „ 0-472 0-500 0-440 4th „ 0-545 0-580 0-520

TOTAL LENGTH ... 1-849 1-980 1-750

It will be observed that the range of variation is considerably greater in the adult than in the immature stadia. The labrum is slightly longer than the first segment of the labium, it has numerous transverse grooves, and is bare except for a single pair of erect truncate hairs at its base. The rostrum is brownish to blackish, often quite black, rather paler at the junctions of the joints ; and at the tip of the fourth joint always quite black : it is thinly clothed with short fine hairs, and at the apex of the fourth joint there is a tuft of minute bristly hairs. 23

Its length is as follows :-

Average. Maximum. Minimum.

Millimetres. Millimetres. Millimetres.

1st joint 0-565 0-61 0-51 2nd „ 0-676 0-69 0-65 3rd „ 0-672 0-72 0-64 4th „ 0-421 0-46 0-39

2-46 2-23 TOTAL LENGTH ... •2-344

The diameter of one of the setae near the middle was carefully measured, and found to be between 3-75 and 3-89 [x. The compound eyes project out considerably from the head, they are dull red, slightly oval in shape, the vertical diameter being the longer. The ocelli are brighter red, somewhat shining during life ; they are situated above and behind, close to, the compound eyes. Prothorax and scutellum of mesothorax (the only part of the mesothorax visible externally) punctate, black, the anterior and posterior margins of the prothorax somewhat brownish. Hairs as on the head, except that the coronate hairs are slightly less numerous, particularly on the middle line of the thorax, and directed somewhat backwards, instead of forwards as on the head. Propleurge black, coarsely punctate, and haired like the dorsum, but more shining ; posterior margins brown, whitish pruinose above the coxae. Episternum of mesothorax black, shining, similar to propleurae ; the epimeron whitish pruinose, bare except for a few exceedingly minute hairs. Episternum of metathorax black, minutely punctate, and bare. From the base of this sclerite, just anterior to the hind coxa, arises the orifice of the stink glands, which consists of a trans- versely elongate vulviform chitinous valve, whitish or pink in colour, projecting forwards and upwards, the upper end being free, i.e. not in apposition with the episternum. The metathoracic epimeron is whitish pruinose like that of the meso-thorax. The posterior margin of the metapleura projects backwards over the side of the basal segment of the abdomen as a whitish hard chitinous plate, marked with greyish spots and bearing very minute hairs. The sterna of all three thoracic segments are brownish black, shining, with fine white flat-lying hairs. — 24 —

Legs shining, with the coxae and trochanters brownish, all femora black, brown at their apices. Anterior tibiae with the basal third black, remainder brown ; mid and hind tibiae with the basal quarter and apical third black, except the extreme apex which is brown, the middle portion straw-coloured or almost white. Tarsi three-jointed, all metatarsi brown, the second joint rather darker and the third black. The anterior femora are considerably incrassated, with four tooth- like spines on the inner side ; these are dark brown with black tips. The third from the apex is the longest ; the basal one, situated on the middle of the femora apart from the other three, is of about the same size as the subapical one, while the apical and smallest spine is rounded instead of pointed at the tip, where it bears a longish very thin simple hair. With the exception of this latter spine, they are all distinctly two-jointed, there being a curved suture just before the point (Fig. 11). The front tibiae have the apical third somewhat dilated and bear four curious subapical hairs on the inner side ; these hairs are stout on the basal half, somewhat curved, and abruptly tapering towards the tip. There are about eight apical spurs, and an apical comb of about twenty-four fine but stiff short regular hairs. The mid and hind femora and tibiae are simple, the hind femora being about one-eighth, and the hind tibiae one-third as long again as those of the middle pair of legs. The mid and hind tibiae have about twelve short stoutish apical spurs. All the femora bear truncate coronate hairs, also a few simple ones on their inner sides ; the tibiae coronate hairs and also some simple, especially on their inner sides towards the apex, while those on the tarsi are all simple and especially numerous on the underside of the metatarsi. At the apex of the last joint of all tarsi, there are also two particularly long hairs, which reach almost to the end of the tarsal claws. The fore wings, or hemi-elytra (Fig. 15), are hyaline, brownish at the base, with a small brown spot at the apex of the clavus, and a larger brown mark at the apex of the embolium. The anterior margin of the clavus has a row of about twenty-two or twenty-three circular pigmented pits, and another row of thirteen or fourteen along the posterior margin. There is also a median row of pits, which are very variable in number, usually about twelve but ranging from seven to fourteen. From these pits arise very fine sim.ple hairs, which are somewhat curved. Along the hind margin of the embolium there is a row of about thirty-three rather similar but smaller pits, some of which are crescent-shaped, being incomplete on the anterior side. 25 —

The cía vus and the basal quarter of the cuneus and embolium are rather denser than the rest. Membrane very thin, hyaline, with traces of five inconspicuous longitudinal veins. In the freshly emerged adult, the venation of the membrane is more clearly seen, and can be traced also in the basal part of the wing (Fig. 16). With the exception of the membrane, which is bare, the hemi-elytron has a few coronate hairs of the type found on the body, but bearing rather more conspicuous teeth. Besides the curved simple hairs springing from the pits, there are also a few very minute straight simple hairs, more particularly on the anterior margin of the embolium. On the under surface of the wing, the base of the vein that forms the posterior margin of the embolium is very conspicuously keeled ; it is possible that this vibrates against the projecting process of the metasternum, causing the faint buzz made by the insect during flight. The hind wings are exceedingly thin, hyaline, with a silvery appearance during life when seen through the hemi-elytra. Venation of the type normal in the family. Abdomen orange brown, darker at the side and in the middle of the basal segments. The orifices of the stink glands are still visible as in the nymph, though it is probable (34, p. 541) that they do not function in the adult, the odoriferous substance being emitted through the structure on the metathoracic episternum described above. The abdomen is bare on the disc, where it is covered by the wings when they are not in use. Venter brownish, blacker at the sides, shining : showing pale rings between the segments when the abdomen is distended. It has a few fine pale hairs, of which some are about three times the length of the others. On the median area of the two terminal segments (excluding the genitalia) there is also a thick row of very fine white simple hairs, except at the sides and on the central line. Genitalia (Fig. 17) black, terminal segment with a tuft of about ten longish simple hairs on the rounded outer apical corners, as well as some shorter hairs. Terminal pair of claspers strong sickle shaped, minutely haired. The penis consists of a yellowish brown rod-shaped organ terminating in a fine coiled tube, the total length when fully extended being over 1-1 mm. The average length of the adult male is 3-8 mm.

86. THE ADULT FEMALE.

The adult female is very similar to the male except in size, the average length being 4-3 mm., though specimens of 4-8 mm. may be found. — 26

The antennal joints have the following length :—

Average. Maximum. Minimum.

Millimetres. Millimetrea. Millimetres.

1st joint 0-326 0-335 0-300 2nd „ 0-671 0-740 0-580 3rd „ :. 0-527 0-550 0-470 4th „ 0-598 0-620 0-570

TOTAL LENGTH ... 2-115 2-190 1-950

The length of the rostrum, which is also greater than that of the male, is :—

Average. Maximum. Minimum.

Millimetres. Millimetres. Millimetres.

1st joint 0-623 0-650 0-600 2nd „ 0-798 0-850 0-760 3rd „ 0-778 0-860 0-720 4th „ 0-478 0-500 0-450

TOTAL LENGTH ... 2-677 2-770 2-560

The abdomen is truncate at the end (Fig 5), the folded ovipositor as a rule slightly projecting, which affords a ready means of distinguish- ing the sexes at sight. The ovipositor (Fig. 18) is two-jointed, doubly folded back on the ventral surface of the abdomen, and covered by the penultimate ventral sclerites. When fully extended it projects about 1-8 millimetres from the apex of the abdomen. It is yellow in colour, the first joint bare, the second with a few exceedingly fine short simple hairs, and with about four to six rather longer fine hairs at the apex. The venter is without the rows of long fine white hairs on the two apical segments.

9. NOTE ON THE CHARACTERS AND DISTRIBUTION OF THE DIFFERENT TYPES OF HAIRS. (i) The coronate hairs. This type of hair is found on the head, thorax, abdomen, antennae (rarely on the terminal joint) legs (except on the tarsi) and hemi- elytron. -•^

— 27 —

They are always erect or sub-erect, dilated slightly at the tip, and terminating in a corona of usually five, sometimes four or six, and very occasionally seven, small teeth. The size of these teeth varies greatly, they are largest and most conspicuous on the hairs of the hemi-elytra, while on the antennae they may sometimes be almost non-existent, in which case the hairs appear to be slightly capitate and truncate. (ii) More or less straight simple tapering hairs. These are in all respects normal hairs, and are found on the antennae, especially the third and fourth joints, with a few at the apex of the second and two or three at the base of the first joint on the inner side : also on the femora (inner side only) tibiae towards the apex, and the tarsi ; and on the venter and genitalia. (iii) Very fine curved tapering hairs. These are always more or less flat lying,f and are only found arising from the pits on the head, thorax, and ^ wings of the adult insect. — 28 —

IV.—LIFE-HISTORY AND HABITS.

1. THE HOST PLANTS OF THE INSECT.

Oxycarenus hyalinipennis has up to the present been found to breed in Egypt on the following plants :— Cotton ...... spp. (C). Barnia ...... Hibiscus esculentuSy L. (C) Tîl „ cannabinus,, L. (C) „ mutabilis, L. (G) „ trionum, L. (W) Khobbiza ... Malva parviflora, L. (C, W) ,, sylvestris, L. (W) Hollyhock ... Althœa rosea, Cav. (G) spinifer, Cav. (G) Sida mollis. (G) „ rhombifolia, L. (G) Sphœralcea miniata, Spach. (G) ,, umbellata. (G) . Abutilón fruticosum, Guil. (G) „ Thompsonii, Veitch. (G) „ venosum, Lern. (G) Sterculia diversifolia, Don. (G) (C) signifies cultivated plants. (W) „ wild plants of frequent occurrence as weeds. (G) „ plants found in gardens.

With the exception of the last, all the plants in this list belong to the family . The family Sterculiaceae, of which the tree Sterculia diversifolia is a member, is, however, very closely allied to the Malvace^ ; both families belonging to the order Málvales. The one essential to enable Oxycarenus to breed is the presence of seeds of a Malvaceous or closely related plant. It is not necessary that the seeds should be ripe, though in the case of the majority of the plants enumerated above, e,g. Cotton and Bâmia, the carpel walls enclosing the unripe seeds are too thick to allow of the insect penetrating to the seeds until they are ripe and the carpel wall splits : in such case the bug can only breed on the ripe seeds, unless the im- mature seeds have been rendered available by, for instance, the hole made by a boll worm. ^m

— 29 —

The influence of other factors, such as temperature and the lapse of time since the last breeding season, will be discussed after the seasonal life-history on each of the known host plants has been described. It will be most convenient to describe in detail the life-history of the insect as it occurs on cotton, as being the most important plant from an economic point of view, and consequently the one that has been most fully studied : comparisons and contrasts will then be made with the seasonal life-history on the other host-plants.

2. THE LIFE-HISTORY ON COTTON: BREEDING SEASON.

Immediately on the opening of the earliest bolls, the bugs present in the cotton—which at this time are adults only—congregate in these bolls and commence feeding on the seeds. {a) Cofulation^ Copulation takes place very soon ; copulating pairs have been found in a boll less than forty-eight hours after it had opened, the scarcity of open bolls at this time making it improbable that the individual had come from another boll that had opened previously. Copulating pairs may be found both inside the bolls between the locks, inside the epicalyx, and also walking about the leaves of the plant. They are, however, only rarely seen in exposed positions, at any rate in the middle of the day, during the early part of the boiling season ; later on, when the weather is cooler, they are more frequently met with outside the bolls. Copulation takes place at any hour of the day or night, at any rate in the Cairo District, where the minimum night temperature up till the middle of October seldom falls below 14^ C, which temperature does not appear to inhibit the sexual act. Indeed, pairs which had been in copula, but which had separated, were observed to reunite after fifty-six hours at temperatures as low as 8°-4 C. and 10°-2 C. Copulation seems, however, to be most frequent during the forenoon and again just before sunset, but no definite figures on this point have been collected. Coitus may last for certainly four hours, probably longer, conti- nuously ; there is then frequently a period of separation lasting for from one to three hours, followed by one or more repetitions of coitus, not by any means necessarily with the same individuals, i.e. the males are polygamous and the females polyandrous. The female sometimes deposits a few eggs during the interval between two periods of coitus. Out of eighteen pairs collected actually in copula in the early morning, six remained in copula for four to four and a half hours, five for about three and a half hours, three for about two and a half hours, one for about two hours, and three for one and a half hours or less — 30 — and after an interval of one and a half to three hours, copulated again for periods of one to one and a half hours. During the hot weather of August and September, copulation appears as a rule to be completed within twenty-four hours ; during cooler weather it extends over two or more days ; but the only records on this point are from laboratory experiments under necessarily unnatural conditions, and consequently m.ay not be of much value. The extreme cases recorded may be cited, though it is impossible to say what would have happened under natural conditions. 1. Bugs reared on cotton seedfromeggs(parents had fed on Althaea). Became adult May 19, 1922. First noticed in copula 8 a.m. May 22, 1922. In copula at intervals almost every day until June 8, 1922, i.e, extending over eighteen days. No eggs laid until June 8, 1922. The daily maximum temperature of the room during the period over which copulation extended varied between 31° C. and 26"^ C, and the minimum between 25° C. and 21° C. Mean for the whole period about 25° C. 2. Pair (fed on Althaea) taken in copulation May 4, 1922. Again noticed in copulation on May 6, 10, 11, 13, 14, and 20, 1922. Both insects died between May 26 and 31. Eggs were laid on an undeter- mined date before May 13, and none after. The daily maximum temperature of the room during the above period ranged between 28° C. and 23°-5 C, and the daily minimum from 23°-5 C. to 21° C. The actual average for the whole time was about 24°-4 C. When preparing to copulate, the male mounts upon the back of the female, but they quickly assume the usual back-to-back attitude. During the act of coitus, the ovipositor is extruded from beneath the chitinous sheaths which normally cover it, but it is not extended, i.e. it is still bent double. The penis is inserted far up the ovipositor, at least as far as the first joint. The pair frequently walk about while in copula, the female invariably leading. Copulation not seldom takes place even after the female has laid all her eggs, as proved by subsequent dissection ; the reason for this seems obscure, possibly it is analagous to the infertile coitus that may sometimes occur in spring and early summer {vide p. 51).

(6) Oviposition. The first eggs appear to be laid on the same day as the first copulation, at any rate during hot weather, though this again is difficult of absolute verification under natural conditions. It is deduced, however, from the following : of thirty-two copulat- ing pairs brought into the laboratory in the early morning on different — 31 — dates during August and September 1922, twenty-two laid eggs on the same day, before 8 p.m., and none subsequently ; five laid eggs both on the same day and the day following, and five laid no eggs at all, their ovaries being empty. It would be expected that some would have laid eggs on the second day and not on the first, if oviposition did not normally occur the same day as the first copulation. The above refers only to cotton fed bugs; in the case of those fed on hâmia, the results are somewhat different {vide Section 5). Oviposition may be completed in one day, often it extends over two, and rarely over three days ; this again does not apply to bugs fed on all other host plants. The eggs are normally laid in the lint ; when the boll has been ripe some time and the lint has fuzzed out, they are generally placed close to the seed ; in the case of newly open bolls they may be placed on the lint either in the central cavity or on the outer side of the lock next to the inner side of the carpel wall. Other positions chosen are between the calyx and the base of green bolls, and occasionally between two contiguous lobes of the epicalyx. The habit of laying the eggs anywhere except in an open boll appears to be far less common at the beginning of the breeding season, indeed before September it is decidedly rare, but becomes more frequent later, even making allowance for the large increase in the numbers of eggs to be found in a field as the season advances. It is conceivable that this partial change of habit has some connec- tion with the longer incubation period consequent upon the cooler weather later in the year, as only large green bolls which will shortly become ripe appear to be chosen, and it is decidedly rare, though not unknown, for eggs to hatch on a still unopened boll. When this does happen either the young nymphs must move to an adjacent open boll, or run the risk of starvation ; for although they have been ob- served by Willcocks (42) very occasionally to feed on the outside of green bolls they do not appear to be able to subsist for long on such a diet. In this connection it is perhaps worthy of mention that in the case of females enclosed in muslin sleeves on green bolls in August 1921, in several cases the eggs were laid in folds of the muslin, the bolls being neglected. The same thing was observed in the case of a laboratory experiment, in which females were put on green bolls inserted in a test tube of water the mouth of which was plugged up with cotton wool : the eggs were laid in the cotton wool. Finally, the eggs are sometimes laid inside holes made by the larvae of the common boll worm {Earias insulana, Boisd.) in green bolls. In such cases only can reproduction take place apart from the - 32-

presence of open bolls. The writer has not observed any instance of either eggs or young nymphs being found within the exit holes made by the larvae of the pink boll worm {Gelechia gossypiella, Saund.), though there appears to be no reason why, if the hole is sufficiently large, this should not occasionally occur. One instance has also been noticed of eggs laid on a small deformed prematurely opened boll (the work of either Creontiades palUdus, Ramb., or Nezara viridula, L.) ; such bolls may sometimes be found before the usual date of opening, and would thus afford facilities for earlier breeding, though the case in question was observed after the date on which bolls had begun to ripen normally. Owing to the difficulty of obtaining virgin females and keeping them under conditions which could not possibly interfere with fertility, and at the same time would admit of accurate observation, the average number of eggs laid cannot be stated with absolute certainty. The following figures give the numbers laid by forty-eight females fed on cotton. In each case copulating pairs were obtained early in the morning and brought into the laboratory. The numbers are arranged m order of magnitude, the dates range from August 16 to October 23. 26, 24, 22, 22, 19, 19, 18, 18, 18, 17, 13, 12, 10, 9, 9, 8, 8, 8, 7, 7, 7, 7, 7, 6, 5, 5, 5, 4, 4, 3, 3, 3, 2, 2, 2, 2, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0. It will be noticed that none of these forty-eight females laid either fourteen, fifteen, or sixteen eggs. It is suggested therefore that the numbers of seventeen and above represent the total number laid, while those females which laid thirteen or less had previously, before they were collected, laid some of their eggs, some no doubt earlier in the same morning, some the day before. The true average is therefore probably to be arrived at from the mean of the numbers of seventeen and higher, namely approximately twenty. The above figures should be compared with the very striking differences obtained from females reared on hâmia {vide Section 5) and Sterculia (Section 11). There is no evidence of any increase or decrease of the numbers laid, as the season advances, due either to the successive generations or the cooler weather. Oviposition has been observed to occur at almost any hour of the day, and, in the laboratory also by night. It has not been noticed in the field at night, but this may be due to the difficulties of accurate observation. The eggs may either be placed singly or in groups of any number up to the total number laid. Single eggs and small groups of two to four are the general rule when they are laid in the lint ; in other situations large groups are commoner.. The eggs are laid loose in the lint, but if two or more are laid side by side they are attached to each other. ~M

When laid in other situations they are both attached to each other and to the surface on which they are placed. During the act of oviposition the female raises herself upon the legs, and the ovipositor is extended vertically downwards, and is used as a probe to find a suitable position. The antennae and often the rostrum as well are in constant motion, and are directed downwards, feeling the surface on which the insect is standing. The passage of the egg down the ovipositor only occupies three or four seconds ; and the ovipositor is usually withdrawn and folded after the deposition of each egg. The writer has observed three eggs deposited at intervals of fifteen seconds ; whether this rate is kept up when large numbers are placed in one batch cannot be said. The length of time for which the adults survive after oviposition depends largely if not entirely on the temperature. Normally, in the case of bugs breeding on cotton in the comparatively hot weather of August to October, it does not exceed two or at most three days. Often they die the same day that the eggs are laid. They have,however, been kept alive for as long as two weeks after oviposition, in a cool incubator at temperatures of 20° C. and below.

(c) The Incubation Period, The sole factor which determines the period of incubation of the egg is the temperature. Three other factors which it was considered might conceivably have some influence in this direction, namely the relative humidity, whether the eggs were kept in light or darkness, and the food-plant of the parent, were tested and found to exercise no effect. In the case of the relative humidity it is perhaps somewhat surprising that the eggs should hatch successfully and, given the same temperature, after the same length of time, in relative humidities of 1, 20, 40, 60, 80, and 100 per cent. The experiment was, however, repeated twice with the above percentage humidities and twice more with humidities of 1 per cent, 100 per cent, and the normal varying humidity of the room, and though the mortality was somewhat greater in dry atmosphere no variation of the incubation period was ever found. In the low relative humidities, as was to be expected, the young nymphs died almost immediately after hatching. Seeing therefore that, as far as could be ascertained, the temperature alone determines the period of incubation, the effect of this was studied in some little detail. This was greatly facilitated by the use of a specially constructed graduated incubator which gave any desired temperature at intervals of approximately 0°-6 C. with a daily variation at each temperature of under 1°C. and an average for the incubation period probably correct to less than 0°-2 C. of error. — 34 —

Results were also obtained by keeping the eggs both in the laboratory and outside, and calculating* the average temperature ... 1 n 1 . Max.+Min. , ,, during the period, but these figures being are probably subject to considerable error. It will be seen from Figure 19 that the period of incubation varies from just under four days at temperatures between 36°-2 C. and 34° C. to forty-three days at a temperature of 14°-6 C. Figure. 20 shows the incubation period in terms of day efficiency. It will also be seen that there is some indication of an increase in the period at temperatures just below the fatal point. This is more clearly observed from a consideration of single experiments in the graduated incubator, in which the times of oviposition and hatching were carefully noted to within two hours. In the following case all the eggs were laid between 11 -0 a.m. and 1.0 p.m., October 17, 1922.

Temperature 38-3 37-5 36-8 36-2 35-5 33-3 32-0

Hatching Never 6-0-70 11-0 10-0 9-0a.m. 11-0 10-0 p.m. a.m.- a.m.- a.m.- p.m.- 12.30 12-30 12-30 Oct. 21 p.m. p.m. p.m. to 7-0 Oct. 21 Oct. 21 Oct. 21 Oct. 21 Oct. 22 a.m. Oct. 22

Period (days) — 4i 4 4 3| 4 4i-4|

On another occasion, the following results were obtained

Temperature 37-5 36-8 36-1 35-5 34-7 34 Period 4| 4i 3| 4| 4i ^

Temperatures of 37°-8 C. and above invariably proved fatal, with the exception of a single egg in one batch at SS^'-e C, which completed its development and half emerged from its shell, but died before completely free, in a period of five days. This is further evidence that warmth above the optimum, which appears to be about 34° C- 35°-6 0., retards emergence. At temperatures between 37°-8 0. and about 40°-5 0. a certain amount of development takes place, as shown by the eggs turning pink before the death of the embryo ; above 41 "" 0. no apparent change can be noticed. '^

~ 35 —

As regards abnormal temperatures for short periods, the following results were obtained :-—

Temperature. Period of Exposure. Result.

50° C. 30 minutes Eggs hatched. 50 60 „ Death. 60 2 „ Eggs hatched. 60 3 „ Death. 2 25 days Eggs hatched. —120 rising to 0° 30 hours Death.

Eggs that were just on the point of hatching were transferred to temperatures of 11° C. and 2° C. and actually hatched while still subject to these low temperatures. Eggs exposed to the sun for four hours on a July morning failed to hatch. , The white bulb thermometer during this time rose approximately to 48 T., and the black bulb to 64° C. It must always be remembered that insect's eggs are not normally laid in incubators at a constant temperature. Field observations, however, where the exact times of oviposition and hatching are known, and the eggs are not in any w^ay disturbed, are well-nigh impossible to make. Only one such with any likelihood of accuracy was obtained, namely, a period of five days in the last week of August, and even in this case it cannot be absolutely guaranteed that the eggs which were observed being deposited were the ones which were seen to hatch five days later. Furthermore, little or nothing is known of the climatic conditions existing within the lint of an open cotton boll, except that they prob- ably have very little relation to the ordinary shade readings taken at the same place. Some attempt in this direction was made by enclosing the bulbs of thermometers within bolls actually containing the eggs of Oxycarenus, the bolls chosen being within twenty yards of a thermometer in a louvred screen, the temperatures of which are given for comparison.

Air Shade Temperature Day. Time. Boll No. 1. Boll No. 2. Boll No. 3. in Louvred Screen.

Aug. 10, 1922 1-0 p.m. 36-0 33-8 37-5 34-5 „ 10, 1922 5-30 p.m. 35-8 29 32-7 30-5 „ 11, 1922 7-0 a.m. 25-5 27 26-5 26 Fog ; no sun- (minimum for previous light night =25°) „ 12, 1922 11-0 a.m. 33-0 29 — 39*

* Boll in full sunlight. — 36 —

It appears from the above that the temperature within an open boll per day tends to be lower than the shade temperature, even when the sun is almost vertical, provided it does not actually strike the boll. When the sun is low down, the difference is even greater; at night, however, the minimum within a boll appears to be above the minimum air temperature. The above figures are only given for what they are worth, and to emphasise the fact that for purposes of Entomology, temperatures as ordinarily recorded are of comparatively little value.

(d) Habits of the Nymphs,

The first part of the young nymph to emerge from the egg is the rostrum, which may be pushed out and withdrawn several times before the head and finally the whole insect gets clear of the shell. The process takes albout ten minutes to a quarter of an hour. In the case of large groups of eggs laid on the outsides of bolls, the nymphs, which usually hatch within a short time of each other, may often be seen clustering together round the empty shells before dispersing to look for food. The length of time that elapses before they begin to feed is not known, but is certainly at most a few hours. The immature bug undergoes five moults or ecdyses before attaining maturity {vide Part III, Section 2a) the habits of all five nymphal stages being very similar. For about twelve to twenty-four hours before and after, at any rate the last two, and probably all, the ecdyses, the insect ceases feeding. At the beginning of the breeding season in August, nymphs are very rarely to be found anywhere except in open bolls, unless just before or after dawn, when they may sometimes be seen on leaves, etc., jiear open bolls. Later on, in October, they are more commonly found outside bolls, not only at dawn and dusk, but even in the middle of the day ; this applies particularly to the fourth and fifth stages ; at no time are the earlier stages often seen outside bolls. In making this statement allowance has been made for the very large increase in number in October over those present earlier. This change in habit may be due to the cooler weather and dimi- nished evaporation later in the year. The sole food taken by the insects consists of the juices of the ripe or almost ripe seeds, which they pierce with their extremely minute setae (in Phytophagous the whole rostrum is never, so far as is known, inserted into plant tissues) with the resulting damage that is described in detail in Part V, Section 1. Very occasionally the later stages may be seen sucking at the gland on the under side — 37 — of the midrib of the leaf, near the base ; but in the writer's opinion this is merely a means of obtaining moisture, in the absence of dew. Mr. Willcocks (42) states that he has very rarely observed the nymphs feeding on the outside of green bolls. This probably only occurs when eggs laid in such a position hatch before the opening of the boll. Experiments tend to show that the nymphs cannot survive for long, or complete their development, without a diet of seed. When the boll is only recently opened, and the lint has not yet fuzzed out, the insects are to be found in the cavity between the locks and consequently feed only on the inner sides of the seeds. In the case of riper bolls, the cotton of which has dried and opened out, they penetrate the lint, getting as close to the seed as possible on all sides. The radicle end of the seed is the more favourite point of attack, but, especially when large numbers of bugs are feeding on one seed, all parts may be fed on. About dawn, whenever, as is generally the case at Giza during the months of August to October, there is dew on the cotton plants, numbers of the bugs of all stages may be seen drinking it, either on the bolls or the leaves near them. The extent to which free moisture is necessary is difficult to determine ; the bugs cannot be bred in captivity without giving them water, which they readily drink, unless the atmosphere is artificially maintained at a high relative humidity approaching saturation point. As suggested above, in the absence of dew they may be able to obtain moisture from the leaves. It may be mentioned that in Upper Egypt, when dew is probably a rarity, the insect becomes rapidly less common as one goes south ; whether this is due chiefly to moisture or temperature conditions is undeter- mined.

{e) The Duration of the Nymphal Stadia.

Considerable difiiculty was experienced in collecting accurate data, under anything approaching natural conditions, concerning the duration of the immature stages. Simple observations in the field are practically useless, owing to the impossibility of being certain whether all the nymphs, except the one under consideration, have been removed even from an isolated ripe boll ; and also to the difficulty of determining the time of moulting of the first three instars, unless the cast skin can be found. Further, muslin bags on a boll (which in any case mterfere very considerably with the normal climatic conditions), in order to prevent — 38 — the young nymphs escaping, have to be made of such fine material as to be quite opaque. Consequently it was found necessary to fall back upon laboratory experiments, under admittedly highly artificial conditions ; and even then the mortality of the nymphs was very great. The method adopted for breeding the bugs was to put the nymphs, immediately after hatching, separately into glass-bottomed pill-boxes inverted and standing on a filter-paper. One cotton seed for food was put in each pill-box. A bell jar was placed over a number of the pill-boxes, inside which was also a dish containing a solution of KOH of such a strength as to keep the air within at a relative humidity of about 95 per cent. In addition a drop of water was put daily on to the filter papers, to provide free moisture, which in most cases was readily drunk. The following results were obtained by this method of rearing. (a) Six eggs laid by one female on August 22, 1921.

Duration in Days of No. Egg. bex. Egg.

1st 2nd 3rd 4th 5th Total.

Stage. Stage. Stage. Stage. Stage. Excluding

0^ 1 i 3 3 4 2 11 23 2 4 5 2 3 2 5 17 3 4 5 2 3 1 3 14

4 4 5 3 2 2 7 19 ? 5 4 5 3 3 3 5 19 6 4 5 3 3 3 7 21 Approx. Average... 4 5 3 3 2 6 19

The actual average temperatures of the room during the above period were unfortunately not kept, but approximately ranged between a minimum of 25^ C, and a maximum of 32° 0.-33° 0, 39

(b) Nine eggs laid by one female on April 8, 1922.

Duration in Days of ^f No. Egg. |1 ^ Sex. 1st 2nd 3rd 4th 5th ígPí Stage. Stage Stage. Stage. Stage, H 1 12 5 4 4 5 10 28 rí^ 2 12 5 4 4 6 11 30 î 3 12 5 4 4 7 10 30 r/ 4 12 5 4 4 7 10 30 5 5 12 5 4 4 8 10 31 6 12 5 4 4 8 11 32 7 12 5 4 4 10 9 32 rí" 8 12 5 4 4 10 11 not 34 recorded. 9 12 5 4 4 (15*) — — Approv. Average 12 5 4 4 8 10 31 Approx. average Temp. ... 210-3 21° 220-3 230 230-5 240-5 230-2 — (c) One egg laid on August 12, 1921.

Duration in Days of Total Egg. Excluding 1st Stage. 2nd Stage. 3rd Stage. 4th Stage. 5th Stage. Egg.

4 3 3 3 .2 3 14 Temperature not recorded. {d) Three eggs laid by one female, hatched April 13, 1922.

Duration in Days of Total. 1st and 2nd Stages. 3rd Stage. 4th Stage. 5th Stage.

( 2 Died 19 5 11 40 ( 6 14 44 Approximate average temperature during the whole period 23°-0 C. (e) Three eggs hatched April 20, 1922.

Duration in Days of Total 1st and 2nd Stages. 3rd Stage. 4th Stage. 5th Stage.

(7 7 Died 14 ]9 6 (9 8 11 or 12 42 or 43 Average temperature about 23^^-2 C.

* Died soon after moult to 5th instar. 40

It will be seen that there does not appear to be any difíerence in the development period of the two sexes. (/) The following incomplete records were also obtained, under the conditions outlined above :—

No. of Stage. Duration. Average Temperature. Days. 1st 3 29 (2 records) 1st 4 26 1st 5 22 2nd 6 24

(g) In addition, a considerable number of incomplete life-histories were recorded under somewhat difierent conditions, the insects being kept out of doors in the shade, in muslin-topped pill-boxes resting on filter-paper, both the paper and the muslin being damped daily. The exact temperatures were not recorded accurately enough to be of value. The month in which the observations were made is given in the following summary.

Approximate Number of Length of Each. No. of Instar. Records. Average.

August 1921 :— Ist ...... 8 3,3,3,5,5,5,5,5 4 2nd 4 2,2,3,3 H 3rd 1 3 3 4th 1 2 2 5tli 1 3.. 3 September 1921 (1st half):— 1st 4 3,3,4,5 4 2nd 5 3,3,3,3,4 3 3rd 8 2,3,3,3,3,4,5,6 H 4th 6 1,2,2,2,3,3 2 5th 6 3,5,5,7,11 6 October 1921*:- 1st 2 8,9 &h 2nd 4 6,8,8,9 8 3rd 7 7,9,9,12,12,13,15 11 4th 9 8,8,9,12,13,13,16,17,17 ... m 5th 9 12,13,15,16,16, 17,17, 18, 18 16 November and Dec. 1921:— 3rd 1 7... 7 4th 2 11,13 12 5th 4 16,19,20,21 19

Majority of records made in latter half of month. - 41 —

The very long periods recorded from mid-October onwards are no doubt due to the insects being kept in complete shade, as stated above. They were on several occasions noticed apparently not to be feeding for days on end. When breeding late in the year, whether on cotton or any other plant, the bugs normally chose situations to " which a certain amount of sun penetrates. At the risk of repetition it must again be insisted upon that the foregoing records (which represent only a fraction of the breeding experiments attempted, so great was the mortality) can, for the reasons already stated, only be taken as giving a slight indication of the duration of the various instars under natural conditions. It is deduced from numerous fragmentary and in themselves inconclusive observations in the field, that the normal duration of the nymphal stages from the hatching of the egg to arrival at maturity, approximates to the shortest times recorded in the laboratory experi- ments, namely fourteen to twenty days in the warm weather of August and September. Very possibly the development may be completed in even less than two weeks. Further, the writer's opinion is that cooler weather does not lengthen the developmental period by anything like so long as would be inferred from the above records, owing to the insects choosing situations more fully exposed to the sun ; partly of course through necessity, the majority of the open hoUs after the first picking has been taken, being on the upper bra^nches of the tree. The interval of time elapsing between the final moult and copula- tion is also difíicult of absolute verification. The only laboratory experiments gave this period as six days (two records in August) and three days (two records in May under artificial conditions of temperature and moisture). However, a number of bugs that all became adult on September 1, 1922, were enclosed in a sand-fly- netting sleeve with an open boll (which had previously been carefully examined to see that no eggs were already laid in it). When examined on September 18, 1922, a number of eggs half-way through the incubation period were found, which subsequently hatched on Sep- tember 20, and which were probably laid on September 15 and at the very latest on September 16. This figure of two or at the outside three days is almost certainly much nearer the mark. The number of generations during the breeding season cannot be estimated directly, as a very short time after the opening of the earliest bolls, all stages of the immature bug may be found in a field, and indeed in one boll. It appears that under normal conditions, as well as in the laboratory experiments, nymphs hatching on the same day from the same batch of eggs may vary considerably in the time taken to reach maturity. - 42 —

In the writer's opinion, based on all the foregoing evidence, the following is a fair summary of the life-cycle under natural conditions :— Egg 4- 8 days. Nymphal stages 14-22 days (perhaps somewhat,but not much, longer towards^ the end of the season). Arrival at maturity to co- pulation 2-3 days. Copulation to oviposition 0- 2 „ Total 20-35 days.

(/) The Number of Generations. The breeding season may be taken as lasting just about three months from the opening of the first bolls (for a further discussion on this question, vide Section 18). It is assumed therefore that there are at any rate three complete generations, and almost certainly a partial and very possibly complete fourth. This deduction agrees very fairly with the observed rate of increase in the Oxycarenus population of a cotton field from July to October {vide Section 4). During the breeding season, the males fly but little, and the females apparently seldom or never ; being too heavy for flight before oviposition, and too exhausted afterwards.

3. THE LIFE-HISTORY ON COTTON : THE "QUIESCENT'' PERIOD.

With the adults of what, as indicated above, are probably the fourth generation descendants of those bugs present in the cotton-field before the .first bolls ripened, there occurs a remarkable change of habits. Little if any food is taken, as deduced from the fact that the excreta of such bugs is generally quite transparent and colourless, whereas that of bugs feeding during the breeding season is thick and of an opaque greenish brown colour.* Sometimes a little coloured excreta may be voided by bugs that have only just assumed the resting condition, but later on it is invariably colourless. No breeding takes place, as the insects for the time being are sterile and on dissection of the females no eggs can be found in the ovaries. The failure to breed, as has been already pointed out (p. 28) is a corollary of the abstinence from food consisting of the seeds of a Malvaceous plant. The gregarious habit, always more or less present, becomes very marked, the insects congregate in enormous numbers in old bolls, under the dried carpel walls of bolls of which the cotton has been picked, and within the epicalyx of any still green bolls and buds that may be — 43 — present, in this respect their behaviour is exactly parallel to that in the months of May to July, before the breeding season starts. They may at this time frequently be seen drinking dew in the early morning or sucking at the glands on the underside of leaves or the outside of the epicalyx, but they have not been observed ever to feed on seeds once the breeding period is over. The nature of the stimuli which induce this change of habit, which as will be shown is in no way con- nected with hibernation, is further discussed in Section 18. It must not be inferred that the breeding season suddenly comes to an end about three months from its commencement ; at the end of October and beginning of November there are still many immature bugs left, which given the opportunity, i.e, if the cotton sticks are left standing with some seed cotton still on, will slowly complete their development. A very small proportion will also, in these circumstances, go on breeding throughout the winter and early spring ; in the case of a small area of cotton left standing from the 1921 season until June 1922, an increasingly small number of nymphs could be found up till the end of April. It is probable that such bugs are the descendents of those that remain quiescent long after the opening of the earliest bolls {vide p. 49) and do not start breeding until late in September. There is no doubt that in the case of these bugs which continue breeding during the winter, the immature period is of much greater duration than it is during the breeding season proper, probably for many days on end the temperature is often so low that no feeding and consequently no growth takes place, as observed with the nymphs kept in captivity in the shade in cool weather (p. 41). This prolongation of the breeding season may also occasionally be observed, but to a still lesser extent, in old bolls containing seeds on stacks of pulled cotton sticks. For the majority of tie bugs, such places as have already been men- tioned as chosen by them for their resting period, are only temporary. Soon, about a fortnight, after, they begin to leave the cotton fields and seek for suitable situations in which to pass the winter. At the close of the 1922 cotton season, on a field the earliest bolls of which had ripened early, in mid-July, the bugs were first observed congregating in bolls, buds, etc., on October 10, and were first noticed leaving the cotton on October 22. Doubtless many of the final generation, on attaining maturity, leave the cotton at once, and some also, if the sticks are left standing, remain on it all the winter ; but judging from the fact that the apparent numbers of quiescent bugs on the cotton sticks increased rapidly between October 10 and 25, and then slowly decreased, or at least did not increase, although the sticks were not pulled till November 9, while during this time the — 44 — numbers in the situations shortly to be described were continually being augmented ; many of them spend a short period of quiescence on the sticks before migrating to a more favourable location.

(a) Situations chosen hy the Resting Bugs. The situations finally chosen by the insects are of a very varied character, but the main factor which dominates their choice is undoubt- edly positive thigmotropism, which forces them to place as much of their body as possible in contact with a surface. Sometimes lateral contact is only obtained by apposition to other individuals. The following list gives some idea of the places where the semi- quiescent bugs may be found. Tree trunks (for details of species of trees selected and positions chosen, see below) (Figs. 21, 22). The undersides of leaves of trees, both green and dead leaves being selected (the former especially if somewhat curled from some cause or other (Fig. 23). The pods of leguminous plants to which access is possible through a hole made by a lepidopterous larva. Cracks in telegraph poles or wooden posts and fences, or under the bark. The old nests of Polistes. The crevices between the strands of barbed wire. The dried flower heads of plants growing on canal banks, e,g, Erigeron crispum. Among the roots of grasses, etc., growing at the edges of fields and on canal banks. Under the sheath-leaves of and sugar-cane ; when the stalks are pulled the bugs leave such situations and go elsewhere. Also, as mentioned above, if cotton is left standing throughout the winter, many remain on it in old bolls or in the leaves distorted by mealy-bugs, and a few will also remain in the bolls on pulled and stacked cotton sticks. Finally, artificial traps {vide Part VI, Section 2) such as old sacks placed in hedges or on poles in or near cotton fields, will collect incredible quantities of the insects. Of the above list, which though by no means complete includes the more usual and interesting situations which have been observed, the most attractive appears to be some situation or other on a tree. Not all trees, however, are equally sought after ; in general it may be said that rough-barked trees are more frequented than those with smooth bark, but this is subject to numerous exceptions. Willows and poplars, although they have rough bark affording numerous crevices, even if growing in the most favourable situations, are apparently always neglected. A band of sacking on a specimen of Salix babylonica had collected,'in November 1922, less than twenty bugs, and those in — 45 — folds of the sack, not touching the bark, whereas on a tree of Ficus sp., growing within less than five yards of the willow, there were perhaps 20,000 in the sacking band, as well as incalculable numbers elsewhere on the tree. Date-palms and mulberries are among others that appear to be relatively unattractive, though a few bugs may sometimes be found on them. Of the commoner trees which are particularly sought after, may be mentioned various species of Ficus, Sunt (Acacia arabica) and other members of the same genus, and to a lesser extent Eucalyptus. It is possible that some chemical constituent in the bark, as for instance salicin (C13 H^g O7) in the bark of willows may act as a deterrent to the insects. It should, however, be mentioned that an extract of willow bark, obtained by prolonged boiling with water, was not found to have any deterrent effect. The bugs fly to their resting-places ; at this time of the year they are.more active on the wing than at any other. The distance which they will travel from a cotton field has not been accurately determined ; the writer has found quiescent bugs over fifty yards from the nearest cotton or other Malvaceous plants, but it is probable that they often go very much further than this. They have not been observed to fly by night, and a light-trap in a direct line between a tree on which the numbers of quiescent bugs was steadily increasing by day, and the field from which they were coming, did not attract a single individual. They are most active in flight during the warmth of the day ; between eleven and twelve o'clock on a warm November morning the bugs were observed alighting on a favourite tree trunk at the rate of probably over 100 a minute ; they were apparently flying direct from the cotton field about thirty yards distant in an easterly direction, the wind at the time being moderate from the north ; the writer is almost certain that he has also observed them flying from the same field to the same tree when there was a gentle south wind, but unfortunately no actual note was made of this at the time. Having alighted on a tree, they walk, mostly upwards, until a crevice is found, or in the case of smooth-barked trees, a colony of the bugs is formed, and then settle down. A small proportion have been seen to fly off again from a suitable tree after having alighted for a short time ; and should a colony be disturbed they readily take to the wing. The northerly sides of a tree are the most favoured, as being not exposed to the sun, but they will take up positions on the southerly faces equally readily if such are shaded by leaves or overhanging branches, or the cracks in the bark are sufficiently deep. On a smooth-barked acacia, where the south side was shaded and the north side very much — 46 — exposed to the prevailing wind, the insects were noticed to be almost entirely congregated on the southern aspects. Colonies have been observed on a large tree up to a height of six or seven metres, but they may equally well be found quite close to the ground. In the absence of suitable trees, hedges, or fences, the bugs take refuge among the roots of the coarse herbage growing on canal banks, etc. They may be found right on the ground, and even actually under dry clods of earth, in such situations, but are far less conspicuous than when in enormous masses on tree trunks. Indeed considerable search was necessary before anything approaching a large colony was found among the vegetation of a canal bank ; but taking into account the large areas occupied by the banks of small misqas as well as larger canals, all of which are generally covered with coarse grass and thus afford ample protection, there is no doubt that enormous numbers do take refuge in such places. In the case of all resting places within a reasonably short distance of a cotton field, an extremely small number of fifth stage, and a still smaller number of the earlier stage, nymphs may occasionally be found in company with the quiescent adults and apparently them- selves quiescent. It is difficult to imagine a reason for this, as there is no evidence to show that such nymphs can survive ; after a short time they appear shrunken and starved, and after about a month none can be found. It would have been thought that they would remain on the cotton sticks even if these have been uprooted, as indeed the vast majority of them do, and take their chance of being able to complete their develop- ment on the remaining bolls.

(6) Habits and Reactions during the Early Part of the Quiescent Period. The term quiescent or semi-quiescent has been used to denote the state of the insect after the breeding season is over. It is by no means a suitable word, and is only used in default of a better. Under certain circumstances the bugs may be as active, and as regards flight even more so, during this " quiescent '' period than during the breeding season. Sexually, however, they are completely dormant, consequent on their not feeding ; furthermore, food in the shape of malvaceous seeds, which is a necessity to enable them to breed, has absolutely no attractive powers for them in the earlier months of quiescence except in conjunction with the added stimulus of artificial warmth. The bugs are never all completely inactive, except at night and on particu- larly cold days. On warm sunny days they walk about near their resting places, and frequently fly away to neighbouring plants. — 47 -

Only a small proportior of a colony ever appears to leave at any one time, thus even on warm days large numbers are still to be found remaining motionless. Whether they take it in turns to leave, or whether the bugs that show activity are always the same individuals, is difficult of accurate determination, but it appears probable that the latter is the case, at any rate when the colonies are well protected from evaporation. In captivity, when kept at normal winter temper- atures, and at a high percentage humidity, they will survive success- fully without any signs of diurnal activity. Some attempt was made, during January 1922, to determine the nature of the stimuli causing activity. The number of bugs showing movement on a given area of a tree trunk which afforded a resting place to large numbers, was counted at different times of the day during a period extending over about a fortnight, and at each observation the temperature, humidity, direction and strength of the wind, etc., was recorded. Unfortunately the humidity which, it is considered, is the most important, was taken from a recording hygrometer which was afterwards found to be entirely inaccurate ; the results are not therefore worth recording in detail. It may be said, however, that activity only once was noticed before 10 a.m. and ceased shortly before sunset. The lowest temper- ature at which movement took place was 15° C, and in general it increased with a rise in temperature, and possibly also with a fall in the percentage humidity. Sunshine was not essential, if the temper- ature on a cloudy day was sufficiently high, but strong winds curtailed movements. Judging from the above very incomplete data, from the fact that the bugs which have temporarily left their resting places may some- times be seen drinking dew or sucking at the veins of various plants, and from the laboratory experiments on the effect of temperatures and humidity on the semi-quiescent bugs, it is with some hesitation deduced that a high rate of evaporation is the stimulus which induces the insects to leave their resting places in order to find some form of moisture. It should be said, however, that for the first month or so after the commencement of the semi-quiescent state, in spite of comparatively high temperatures, there appears to be rather less activity than later, indeed the amount of movement seems steadily to increase during the winter, although until the end of January the temperature is tending to fall. Those bugs that are passing the winter in masses on the undersides of green leaves, where there is probably less evaporation than on the trunk of a tree, are less frequently seen active ; on the other hand, of those that are seeking shelter among the roots of grasses on canal banks, where it would be thought evaporation was at a minimum, — 48 — many may be found on warm days crawling up the stems of grasses or any wheat or berseem that may be in the vicinity. Willcocks (40, pp. 20-21) quotes an observation that the insects sometimes change their position on a tree trunk according to the direc- tion of the wind. The present writer has not actually noticed this to occur, but colonies are constantly changing in numbers and new ones being formed throughout the winter, by bugs which have been active during the day returning in the evening to somewhat different positions. With the warmer weather of February and March, the numbers of bugs on such situations as tree trunks, etc., begin to diminish; probably many of those which fly away by day do not return, but seek temporary shelter from the cold nights among the roots of grasses and berseem. During all this time, cotton seed has absolutely no attraction for the insects ; during the winter of 1921-1922 seed cotton was placed on trees covered with the semi-quiescent bugs ; they used it as a shelter, but to no greater extent than any other material, such as old sacking, that afforded them crevices into which to squeeze their bodies ; but no single case of feeding on the seeds was observed, nor was any coloured excreta voided, and no breeding took place. For the influence of cotton seed combined with artificial warmth on the semi-quiescent insects, vide Section 16 (6).

(c) Habits and Reactions during Spring and Early Summer. Cotton is normally sown in middle Egypt during the first half of March. When it is well up, with several leaves, i.e. towards the end of April, numbers of the bugs migrate to the cotton and remain there. At first they are chiefly confined to the edges of the fields, but soon spread all over. It seems doubtful whether chemotaxis is chiefly, or even at all, the stimulus, as they are not attracted to the cotton before is has grown to a height of 20 centimetres or so. Furthermore, the migration to the cotton is gradual, many of the bugs remaining in their former situations, on trees, leaves, etc., during all the early summer, and even long after the bolls have begun to open {vide p. 49), Again they do not feed any more than before ; they may frequently be seen sucking at the glands on the midrib of the leaves, but this is almost certainly solely in order to obtain moisture. As soon as the first formed buds have attained a fair size, i.e. the epicalyx with a diameter of fifteen to twenty millimetres, practic- ally all the bugs present in the field congregate within the epicalices : from one or two to fifty or more may be found within a single bud. At this time there is considerably less activity noticeable than before the buds become available; they still sometimes suck at the glands, ~ 49 ^ both on the leaves and at the base of the epicalyx outside, but much less than formerly. They have never been observed actually to feed on the bud itself, a point which, as will be seen later when the nature of the damage is discussed (Part V, Section 4), is of paramount importance. Furthermore, what little excrement is voided by those bugs which at this time of the year are congregated in buds or green bolls, is invariably clear and colourless, as it was when they were quiescent in other situations where there was no possibility of food being taken. From the end of April onwards, the numbers of bugs in a cotton field increases at the expense of those still remaining in their former resting places ; in which latter, however, a considerable proportion stay until the end of July, or when the bolls open and breeding begins. It was noticed, however, during the summer of 1922, that only those colonies on the green leaves of trees remained inactive until July and after ; from more exposed situations such as tree trunks, they had almost all gone by the end of May. In the case of two trees of Crotón eluteria, the undersides of the leaves of which, earlier in the year, contained numerous colonies of fifty to 300 individuals each, a considerable number of these remained until the first week of August, or a fortnight after the neighbouring cotton had begun to ripen, while one colony, judged to consist of perhaps 100 to 150 individuals, actually persisted until between September 22 and 26. It was considered possible that there might be some radical and important difference in the subsequent behaviour of those bugs that migrated to the young cotton plants in spring, compared with those that remained stationary in their old resting-places ; that perhaps for instance not all were destined to become the parents of the new generation when the cotton ripened. The following experiment was therefore undertaken to test this point. Seven cages of muslin on a wooden frame were erected over young growing cotton plants at the end of April, the greatest care being taken to ensure that no Oxycareni, other than those put in, were left on the plants or could gain access to the interior. They were stocked as follows with between two and five hundred bugs each. No. I.—^A colony inactive at mid-day on April 29, 1922. No. II.—Bugs actively moving (on a tree containing inactive colonies) at midday on April 29, 1922. Nos. Ill and IV.—^Bugs taken from the buds of young cotton on May 15 and 16, 1922. — 50 — No. V.—^A colony still resting on the underside of a leaf on June 10, 1922. No. VI.—Ditto on July 20, 1922. No. VII.—Ditto on July 21, 1922.

The behaviour of each of these sets of bugs was the same, and exactly similar to that of the bugs present on young cotton under normal conditions, i,e, they all congregated within the epicalices of buds or, later, small green bolls. In each case they remained thus until the first bolls within the cages opened, when feeding followed by breeding immediately occurred. It is considered probable, therefore, that the movement to the young cotton plants in spring is, like the daily movement earlier in the year, stimulated by excessive evaporation. As has been mentioned, those bugs which persisted in their old quarters for a very long time were the ones congregated on green leaves, where the evaporation must undoubtedly be less than on, for instance, an exposed tree trimk ; and also they may be able to obtain a certain amount of moisture from the sap. This theory also meets the case of those which, having passed the winter (when evaporation is in any case low) in exposed situations, are stimulated to activity by the increased evaporation of the warmer and drier spring days, and alighting on the young cotton (whether by the influence of chemo-taxis is uncertain) crawl into the epicalices of buds and young bolls, on account of their strong thigmotactic tendencies, and, once in this position, where, even on hot dry days, the evaporation must be very low indeed, their activity ceases until it is re-stimulated by chemotropism to the ripe seeds. In additional support to this theory, one instance was noted on April 21, 1922, of a colony moving from the trunk of a tree to the leaves on the same tree ; the maximum temperature on this day reached 39'" C. and the minimum humidity fell below 12 per cent. The temperature for the past few days had also been considerably above the normal. As previously mentioned, the insects do not invade a bud the epicalyx of which is less than about fifteen to twenty millimetres in breadth. This is an important point, as will be seen later in view of the accusations that have been made againt this pest with regard to bud and boll shedding (Part V, Section 4). The majority are to be found in those with an epicalyx measuring about twenty-five to thirty millimetres. Many of the colonies undoubtedly remain in a bud once selected during the whole course of its development to flower and boll; but others, especially when as sometimes happens, the divisions of the epicalyx open out and thus afford inadequate protection, move to a more suitable bud or boll. ~ 51 -

At this period of the year, although of course none is normally available, if unginned cotton or cotton seed is placed in the vicinity of the resting bugs, it excercises a certain attractive power ; the bugs feed on it, and consequently breeding commences. At the beginning of April 1922, a number of pieces of seed cotton were fastened to various trees harbouring numerous bugs. By April 8 several bugs were seen to be feeding on the seeds, though many more appeared to be using the cotton solely as a shelter. By the 18th there were a number of copulating pairs on and around the cotton, several eggs were laid in the lint, and two first stage nymphs were found. By the 25th there were several first stage arid one second stage nymphs, two of the former were found on the trunk of a tree thirty centimetres away from the seed ; but on trees on which no cotton had been placed, there were adults only and no signs of breeding. About the middle of April three petri dishes full of ginned cotton seed were placed at the base of the same trees, and left until May 20, 1922, when 127 adults were collected from them, and numerous nymphs of all stages. Similar experiments were carried out at intervals until the bolls normally began to open, and in all cases a few bugs, but only an infinitesimal proportion of those present even in the immediate neighbourhood, were attracted to the seed and started feeding and reproduction. The chemical attraction of the seed, for such it must undoubtedly be, appears to be felt over only a very short distance ; in the case of some seed-cotton tied to cotton trees at the beginning of July, many of the bugs even on the same tree were not attracted to it, but remained inactive on the green bolls. This limited range of attraction may explain why, as stated on page 49, some bugs remained quiescent long after there were plenty of open bolls readily available. Two instances only of nymphs (both first stage) being found on young cotton before any bolls were ripe, were recorded. In both cases they were within two or three yards of the seed-cotton tied on to the trees, as mentioned above, for experimental purposes ; and it seems that the only explanation is that the parent bugs had fed on this seed, but had oviposited a short distance away. Careful search was made in several fields of young cotton where no seed had been placed, and none of the immature stages were ever found. Copulating pairs may, however, be found, especially on warm days, both on cotton and non-malvaceous plants, any time from April on- wards, and in the complete absence of the seeds of any malvaceous plant. Such copulation never results in oviposition, the female being invariably sterile. Details of laboratory experiments to confirm this, in which copulation was successfully induced by the right degree of warmth and humidity alone, but was never followed by oviposition unless food was also available, are given in Section 16, - 52 —

Sexually, therefore, the bugs remain completely dormant until with the ripening of the earliest bolls at the end of July or the beginning of August, food becomes available and the breeding season com- mences.

4. THE APPROXIMATE NUMBERS PRESENT ON COTTON AT DIFFERENT TIMES OF THE YEAR.

The following figures can only be taken as giving an extremely rough idea of the numbers of these insects to be found in a cotton field. The method of estimation used was as follows : On young cotton, before the breeding season started, a number of plants, equi- valent to the one-thousandth part of the approximate number per feddân, were chosen at random, and the bugs on these plants counted and the total multiplied by 1,000 to give the number per feddân. During the breeding season, the numbers being very much greater, this method was found impracticable ; the number of bugs (of all stages excluding eggs) was therefore counted on five open bolls on each of eight or ten trees, and the approximate population calculated from the average number of open bolls per tree, and trees per feddân. In some cases the probable error of the mean was roughly cal- culated, but it is very likely that the real error is in considerable excess of the figure arrived at. (1) Ashmûni, at Gîza, numbers calculated at 11 a.m. on May 5, 1922: 94,000 ±12 per cent per feddân. (2) Sakellarides, at Gîza, in close proximity to several trees on which enormous quantities of bugs had been, and many still were, quiescent. Estimation on May 20, 1922 : 232,800 per feddân. (3) Ashmûni, at Sanhûr, Faiyûm, somewhat irregular and back- ward crop. On May 28, 1922: 54,000 ±25 per cent per feddân. (4) Good forward crop bordering on above the same date, 210,000 ± 10 per cent per feddân. *(5) Sakellarides, at Gemmeiza, on June 2, 1922: 75,000 ±10 per cent per feddân. *(6) Assili, at Gemmeiza, on June 2, 1922: 96,000 ±15 per cent per feddân. (7) Ashmûni, at Gîza (same field as 1. above) on July 30, 1922. Breeding season had just started, but, in this case adults only are estimated. 30,000-60,000 per feddân. (8) Very heavily infested Zagora, at Gîza, unpicked up till Sep- tember 29, 1922, on which date the population was estimated at thirteen millions per feddân. *(9) Very heavily infested Sakellarides, at Gîza, on October 7,1922 (a first picking had been taken about five weeks previously). Estim- ated population, twenty-two millions per feddân. -sa-

ín the case of the three examples marked*, the estimaiion wavS not made by the Avriter personally. In any case none of the figures can be taken as more than the barest indication of the real Oxycarenus population at any time. As an indication of the large numbers of these insects which may be found within a single open boll, or feeding on the seeds of a single lock, the following may be taken. . (1) A single lock, most of the seeds with some bugs feeding on them. çf(ç/( 2. ?$ 0. Nymphs 61. (2) A single lock, most seeds heavily infested. ^X^X 15. $$ 13. Nymphs 144. (3) One boll, fully open, many seeds being fed on^

o o 6. ÇÇ 7. Nymphs 247. (4) One boll, lint not fully fuzzed out, bugs in the centre cavity only. O o 5. ?$ 8. Nymphs 66. (5) Ditto, slightly infested. ÇJ'.X X. $? 4. Nymphs 43. (7) A single open boll, examined four days after the second picking on October 9, 1922. (It therefore contained large numbers left behind in the field when the cotton was picked.)

ADULTS. NYMPHS» TOTAL. o^o-^ ?? 1st Stage. 2nd stage. 3rd Stage. 4th Stage. 5th Stage. 68 72 18 68 75 170 278 749

In the light of these figures, and considering that often practically all the open bolls in a field may contain the insects, the figures arrived at of 13 and 22 millions per feddân do not appear so impossible as might at first sight have been thought. It is probable that an ordinarily badly infested field in the district round Gîza contains by the time of the second picking a population of somewhere between seven and twelve millions of bugs per feddân.

5. THE LIFE-HISTORY ON BâMIA {Hibiscus esculentus, L.). As regards the main facts of the insect's life-history, the differences when bâmia is the food-plant are not very striking. In the case of a plot of bâmia sown early in February 1922, the first capsules split on June l,.and breeding immediately started. The number of ripe capsules was, however, not large for another three weeks. — 54 —

Copulating pairs are very much more frequently seen on the leaves than is the case on cotton, even in the middle of a hot day ; this is also true of the nymphs, especially the two final stages, which often undergo ecdysis on the leaves, a fact which has never been observed on cotton leaves. It is possible that the reason for this is to be found in the roughness and corrugations of bâmia leaves, which, besides exercizing a thigmotactic influence, also keep the insects cool by checking evaporation. The eggs, besides being laid within ripe capsules, near the seeds, are very often laid on the outside of green ones ; they are almost invariably placed on the north side, protected from the sun, but even so several cases were observed when the plant having bent over, the. eggs became exposed to the direct midday sun and failed to hatch. A few batches of eggs were also noticed in the folds of young leaves.* One of the most striking points is the very much greater number of eggs laid compared to that when the parents have fed on other food-plants. The following figures give the total eggs laid by seventy-six copulating pairs, collected on different dates between July 23, 1922, and September 20, 1922 (it should be stated that no appreciable variation in the numbers laid at different times during the breeding season could be detected) :— 41, 35, 34, 34, 33, 32, 32, 29, 29, 29, 28, 27, 26, 26, 25, 25, 24, 24, 24, 23, 23, 22, 22, 22, 21, 21, 21, 20, 20, 19, 19, 19, 18, 18, 18, 17, 17, 17, 17, 17, 16, 16, 16, 16, 16, 16, 14, 14, 14, 14, 13, 12, 12, 12, 9, 9, 9, 9, 8, 6, 6, 6, 6, 5, 3, 3, 2, 1, 1, 0, 0, 0, 0. 0, 0, 0. In the case of the female which laid forty-one eggs, twenty-three were produced during the first twenty-four hours after capture, and the remaining eighteen during the next twenty-four hours. The female that laid the next highest total, viz, thirty-five, laid them all within twenty-four hours. On the other hand oviposition often extended over three days and in two observed instances over four days. Of fifty-seven copulating pairs, twenty-five laid eggs only on the day they were brought into the laboratory, sixteen both on the same and the following day, five on the same and each of the two following days, while six laid no eggs the first day, but did on either the second or third day ; finally five laid no eggs at all. These figures should be compared with those in Section 2 (6) for similar observations in the case of cotton-fed bugs.

* Dead first stage nymphs have often been seen on green capsules, presumably having failed to find in time ones containing available seeds. • - 55 —

It is somewhat difficult to arrive at the true average from the above figures, but it is probably in the neighbourhood of twenty-seven to thirty. In addition to the above figures, it may also be mentioned that thirteen copulating pairs collected at noon on a day in August laid an actual average of 19-2 eggs each, while twenty more collected at 5 p.m. on the same day laid an average of 13-4. This greater fertility leads to a rapid rate of increase, and towards the end of the breeding season incredible numbers of the insects are to be found within a single dry capsule. The post-breeding quiescent stage was first definitely observed on October 5, 1922, when several colonies formed on the under sides of green bâmia leaves, or four months after the opening of the very earliest capsules, but it must be remembered that the majority of the capsules had b)^ this date not been ripe for much over three months. There is no doubt also that quiescence had started at least three weeks previous to this, judging from the enormous numbers of adults collected within old ripe capsules, of which the majority were certainly not breeding; but owing to the necessity of opening the capsules and consequently disturbing them before they could be seen, it cannot be definitely asserted that they were quiescent. At the close of the breeding season, the adults appear to leave bâmia for other situations to a much lesser extent than they leave cotton, as judged from the comparatively small numbers which took refuge in traps consisting of old sacking tied round stakes in a bâmia plot. The great majority remain in the old capsules which if left until November may be packed full of the insects. When the old stalks are removed they doubtless attempt to find other resting places for the winter. The adults migrate to a certain extent to the young bâmia plants in the spring, as is the case with cotton. In 1922 they were first observed doing this on May 5 ; they collected in colonies chiefly on the young curled leaves, and remained quiescent until the capsules ripened.

6. THE LIFE-HISTORY ON TIL {Hibiscus cannahinus). This does not possess any points of marked interest. In 1922, on a plot of early sown til, fertile copulating pairs were first noticed on June 17, a week later first-stage nymphs were also observed. It appears that the bugs are able to penetrate to the seeds of unripe capsules, and that breeding therefore commences before the capsules are actually ripe. The eggs are chiefly laid within the involucral bracts,, both on ripe and green capsules. The following are the numbers of eggs laid by twenty-two copul- ating pairs: 23, 23, 16, 16, 14, 13, 11, 11, 10, 8, 8, 7, 6, 6, 4, 3, 2, 2, 1, 0, 0, 0. -^se-

it appears therefore that the average number is the same or somewhat less than is the case on cotton. At the end of the breeding season large numbers of the adults collect on the heads of the til plants when these are distorted by mealy-bugs ; numbers of nymphs may also be found with them which probably under favourable conditions complete their develop- ment. In the case of some late-sown til, which the writer was informed was not ripe until the middle of November 1921, breeding certainly continued throughout the winter, and was still in slow progress when the sticks were removed at the end of February 1922.

7. THE LIFE-HISTORY ON Hibiscus mutabilis, L.

This host-plant is of interest because at Giza it does not flower until October or November. In 1921 the earliest capsules ripened towards the end of November; by December 6 there were numer- ous copulating pairs and eggs in all stages of development. By the first week in January 1922 nymphs of all stages were common. Towards the end of February the plant under observation was unfortunately pruned, all the capsules being removed, together with almost all the breeding bugs ; it cannot therefore be definitely said how long breeding would have continued. Of the few which remained on the stalks and leaves, the nymphs gradually disappeared, presum- ably being killed by starvation, and the adults became practically quiescent. Quiescent adults have also been noticed on this plant before the breeding season started, from August to November, and are probably present throughout the year. In the case of one plant of this species, on which a few dried capsules containing seeds was left over from the previous year, breeding on a small scale was noticed in these capsules in September and October. This is doubtless analogous to those bugs which, on cotton, will start breeding in April and May if seed is provided for them. It is noteworthy that within a few days of the new crop of seeds becoming ripe, in November, these old capsules were deserted. The eggs are usually laid on the exterior of the capsule, often exposed to a certain amount of sunlight. Although a good many were observed not to hatch, possibly having been killed by excessive heat, no doubt this exposed position materially shortens the incubation period during the cold weather of the winter months. The approximate average number of eggs laid appears to be much the same as when cotton is the food plant, judging from the numbers laid by seventeen copulating pairs collected on November 21, 1922, viz. : 25, 24, 23, 16, 14, 12, 12, 11, 11, 9, 8, 7, 6, 3, 3, 0, 0. — 57 —

8. THE LIFE-HISTORY ON HOLLYHOCK (Althœa rosea).

This provides an example of a host plant on which breeding takes place in the spring. The bugs are able to feed on the seeds before they are quite ripe, although, as in all other cases, ripe seeds are preferred when available. Copulating pairs were first observed at Gîza on April 7, 1922, and by April 27, 1922, there were many eggs and first stage nymphs and one or two second stage nymphs. Breeding continued until the beginning of July ; by the last week in July no nymphs were to be found and the few adults left were quiescent in the old capsules ; the majority of the adults left the plants for other situations. Although capsules containing seeds in all stages of ripeness were present on the plants throughout the summer and autumn, none of the bugs remaining on the plants showed any signs of starting to breed again.

9. THE LIFE-HISTORY ON Sida mollis.

On this plant also the breeding season starts about the end of March. Eggs and first stage nymphs were abundant by April 6, 1922. The adults at any rate can feed on the green capsules, and have been observed with their heads closely pressed to the outside of the capsule, and their setae apparently deeply inserted so as to reach the seeds. The nymphs appear to feed mainly if not entirely on the ripened seeds. The eggs are laid both on the outside of green capsules and within ripe ones ; one instance was observed of eggs laid on the stem, which in this plant is thickly covered with soft hairs. By July 22, 1922, breeding had entirely ceased, and no nymphs were left. The majority of the adults were packed in enormous numbers within old ripe capsules, but no feeding was taking place, the small amount of excrement voided being clear and colourless, whereas while the bugs were feeding it was thick and of a brown colour. One large colony was also noticed on this date on the underside of the leaf of a tree {Pterospermum acerifolium) which had almost certainly come from the adjacent plants of Sida mollis. Towards the middle of October a very small proportion of the large number of the adults remaining on the plants started breeding again. The explanation of this is no doubt the same as that suggested before for the second minor breeding season in the case of bugs on H. mutahilis (Section 7) and cotton (Section 3 c). It is, however, possible that the nymphs observed in such cases are the offspring of — 58 — parent bugs which have migrated from some other host-plant, e.g. Hibiscus mutahilis, on which the breeding season has not yet begun.

10. THE LIFB-HTSTORY ON ABUTILóN SPP. {fruticosum, Guil. Thornf- sonii, Veitch, and venosum, Lem.). The only point of interest in connection with these plants is that, at Gîza, the fruits always appear to be shed before they become ripe. Notwithstanding this the bugs feed on the immature capsules about the beginning of April, and breeding takes place. Only nymphs of the first two stages have, however, been observed on these plants. It is probable that they seldom if ever manage to complete their development owing to the lack of food as stated above.

11. THE LIFE HISTORY ON Sterculia diversifolia, Don.

The capsules on this tree begin to split about the middle of July, affording the insects access to the ripe seeds. On July 22, 1922, numerous copulating pairs and eggs were observed ; the eggs appear invariably to be laid within the capsules, generally on the inner wall. The number of eggs laid is considerably smaller than has been recorded in the case of bugs feeding on any other host plants on which such observations have been made. Nineteen copulating pairs collected on August 22 and 30 laid the following numbers : 11, 11, 11, 11, 7, 6, 4, 4, 3, 2, 1, 0, 0, 0, 0, 0, 0, 0, 0. The average number is probably therefore no more than ten or eleven, as against about twenty when cotton, and about thirty when bâmia is the food plant. By November many of the adults were obviously quiescent in the capsules, though a few nymphs of the later stages were still to be found at the beginning of January. The bugs may at times be seen on the trunk or branches and leaves, but the majority appear to spend all the non-breeding period within the old capsules. Doubtless the excellent protection afforded by these ensures a low mortality, which compensates for the reduced fertility during the breeding season, when compared with that of the bugs which have fed on other plants.

12. THE LIFE-HISTORY ON THE EEMAINDER OF THE KNOW^N HOST PLANTS. As regards these, but little of interest has been recorded. On Hibiscus trionum, in the Faiyum, breeding was observed to be just starting at the end of May 1922 ; breeding bugs were also seen near Cairo on this plant on November 20, 1921, — 59 —

On Malva parviflora, breeding starts about March ; a single final stage nymph was found in October by sweeping herbage contain- ing this plant, in the desert about ten miles south-east of Cairo. In the desert during the non-breeding season, the adults may be found by sweeping almost any plant, especially perhaps Stachys œgyptiaca. The breeding season on Malva silvestris also commences about the same time. On both species of Malva, the seeds are available for food before they are ripe. On Pavonia spinifer, Cav., all the nymphal stages were abundant on May 5,1922 ; by the middle of July the reproductive season was over. Breeding on Sida rhombifolia, L., takes place from September to December ; it is probable but not certain that the unripe seeds of this plant also are available. On Sphceralcea miniata, Spach, breeding has only been observed during June and July. Comparatively few of the flowers of this plant appear to set their fruits. On Sphceralcea umbellata, the reproductive season occupies approximately the months of May, June, and July ; at other times the adults may be found resting in the old capsules or among leaves distorted by mealy-bugs, and at times are seen active on the plant.

13. THE PERCENTAGE OF SEXES.

The percentage of the sexes at different times of the year and on different host plants shows several curious features of some little interest. All the figures obtained will therefore be given categorically.

Percentage. Number Date. Situation. examined. Males. Females.

(i) Breeding bugs on cotton :— (a) Oct. 5, 1921 200 35-5 64-5 (b) July 30, 1922 117 44-4 55-5 (c) Sept. 20, 1922 87* 46-0 54-0 (d) Oct. 8, 1922 3231 39-9 60-1 (e) Oct. 9, 1922 140 48-5 51-5 Average for the tour records during 1922 867 41-5 58-5 (ii) Bugs attracted to cotton seed placed in petri dishes during May 1922 and breeding thereon (vide p. 51) :— May 20, 1922 127 60-6 39-4

* All the adults from five bolls. t All the adult» from about eighteen bolls. — 60 —

Percentage. Number Date. Situation. examined. Males. Females.

(iii) Bugs quiescent after the 1921 breeding season on cotton :— (a) Nov. 7, 1921 Trunk of Ficus sp 366 33-6 66-4 (b) April 1, 1922 Ditto (same tree) 353 33-7 66-3 (c) Jan. 20, 1922 Bark of a sunt tree...... 151 33-0 67-0 (d) Feb. 1, 1922 Bugs showing signs of activity on a warm day 126 39-0 61-0 (e) „ 5, 1922 Bugs quiescent in old bolls on still standing cotton 200 34-5 65-5 (/) March 2, 1922 A small colony in an old sunt pod 45 24-4 75-6 (l) May 20, 1922 From the buds of young cotton 147 36-7 63-3 (m) June 2, 1922 Ditto (at Gemmeiza) 67 48-0 52-0 (n) „ 14, 1922 Ditto (Gîza) 189 48-0 52-0 (9) „ 19, 1922 Bugs still quiescent on the leaves of Crotón eluteria 227 38-8 61-2 (h) Aug. 15, 1922 Ditto 100 49-0 51-0 (k) „ 19, 1922 Ditto ... 63 36-5 63-5 (o) June 24, 1922 From the buds and green bolls of young cotton 130 44-0 56-0 Average for those in original resting places 1,505 35-35 64-65 Average for those that migrated to young cotton plants 533 43-9 56-1 (iv) Bugs quiescent after the 1922 breeding season on cotton :- (a) Oct. 9, 1922 Still green buds and bolls ... 230 40-4 59-6 (6) „ 28, 1922 A trap of sacking on a pole in a cotton field 1,000 42-2 57-8 ± 0-9 Average of above 1,230 41-87 58-13 (v) Breeding bugs on bâmia :— July 25, 1922 f 204 I 48-5 51-5 (vi) Quiescent bugs on a bâmia leaf :- October 8, 19221 103 I 41-7 58-3 (vii) From old Til sticks, the breeding season being almost finished :— Dec. 28, • 19211 — ] 194 I 49-5 50-5 (viii) Breeding bugs, on Hollyhock :— May 20, 19221 | 267 I 53-5 46-5 (ix) Breeding bugs, on Sterculia diversifolia :— October 5, 19221 105 66-6 33-3 Nov. 21, 19221 Bugs mostly quiescent ... . 500 48-0 52-0 ± 0-6 (x) Breeding bugs on Hibiscus muiabilis :— Nov. 21, 19221 — 212 I 51-8 48-2 — 61 —

The most obvious deduction from the foregoing facts is that the percentage of the sexes cannot be accurately ascertained from an examination of small numbers of the insects. The following inferences, however, appear to be justifiable :— (i) The percentage of sexes among the quiescent bugs (which it must be remembered are the adults of the final generation only) have a close relation to the percentage among the earlier generations. Thus, the only figure obtained for the breeding bugs during 1921 (probably consisting mainly of the penultimate generation) gave the percentage of males as 35-5, while the average for the ultimate generation, during the period of quiescence and excluding those that migrated to young cotton, was 35-35. For the 1922 cotton season, these figures (based on still larger numbers) were 41-5 and 41-87. The writer is unable to offer any satisfactory explanation of the undoubtedly significant differences in the proportions for 1921 and 1922. (ii) Possibly a comparatively greater proportion of males show signs of activity on warm days during the early period of quiescence. (iii) The males to a slightly greater extent than the females leave their original resting places for the young cotton plants in spring. This is possibly due to chemotropism, vide (v) below. (iv) The percentage of males tended to rise during the non- breeding season April-July 1922, owing to a greater mortality among the females ; this almost certainly depends on climatic conditions and may vary from year to year. (v) The males are very much more positively chemotropic to cotton seed in spring than the females. (vi) As regards the influence of other food plants on the proportion of the sexes, the figures for bâmia and til are too small to be conclusive, but it appears that the proportion of males is greater than on cotton, while this is almost certainly the case when hollyhock, Hibiscus mutahilis, and StercuUa, are the host-plants.

13a. THE EFFECT OF ADVERSE TEMPERATURE AND HUMIDITY CONDI- TIONS ON THE PROPORTION OF THE SEXES.

The following experiments to ascertain whether either of the two sexes have a greater chance of survival from one breeding season to the next, were carried out on cotton-fed bugs taken from the situations on which they were quiescent during February and March 1922. ~ &2 — 1. Experiments with the sexes separated. (In order to separate the two sexes with accuracy, it was found necessary to anaesthetize the insects with ether. From a control experiment, this treatment, when expeditiously carried out, did not appear to have any adverse effect on their vitality.)

(a) Temperature 11° C, humidity 1 per cent:— Number of Time (hours) 20 30 44 54 67 78 92 102 115 127 150 164 190 215 bugs used

QX ^/f 30 / I 3 13 17 20 50 53 80 90 93 100 > Percentage dead < $ $ 44 ^ / 0 2 2 5 9 27 34 39 59 64 86 91 93 100

(6) Temperature 17"" C, humidity 10 per cent:— Number of Time (hours) 21 30 55 69 79 92 102 Í05 117 126 bugs used ^X ^ 27 ^ ( 0 4 19 44 66 81 96 100 / Percentage dead } Ç $ 37 ^ ^ 0 0 13 43 57 78 92 92 97 100

(c) Temperature 17° C, humidity 40 per cent:— Number of Time (hours) 30 55 69 79 92 102 117 126 141 bugi used ^ ^ 27 ) ( 0 11 22 48 63 78 92 100 > Percentage dead \ $ $ 40 ^ ^ 0 7 22 32 62 77 92 98 100

{d) Temperature 30° C, humidity 80 per cent :— Number of Time (hours) 30 44 54 67 78 92 102 115 127 150 169 190 215 bugi used ^ ^ 28 ) ( 0 7 18 36 64 82 93 93 97 100 / Percentage dead \ $ Ç 41 ^ ( 0 2 15 29 44 60 80 85 92 96 96 98 100

(e) Temperature 35° C, humidity 50 per cent :— Number of Time (hours) 21 30 65 bugs used ^ ^ 2l) Í 52 95 100 / Percentage dead \ $ $ 24 ^ ^ 25 75 100

(/) Temperature 40° C, humidity 80 per cent :— Number of Time (hours) 7 21 31 46 93 117 140 bugs used ^ ^X 49 ) Í 0 22 29 56 98 98 100 > Percentage dead \ $ $ 62 \ / 0 69 92 100 - 63 — (2) Experiments with the sexes not separated, the proportion of sexes among the dead and the surviving bugs being ascertained at the end of a period of exposure to the given conditions.

(a) After fifteen minutes' exposure to a temperature of —8° C. (humidity uncertain, probably near 80 per cent). Dead, 50 per cent: ^^o^ H P^^ ^^^*' 2? ^^ P^^ ^^^*- Alive, 50 per cent: ^^^f^ 24 per cent, ?? 26 per cent.

(6) After two hours' exposure to a temperature of —6° C. :— Dead, 79 per cent: ^-^c/ 28 per cent, ?? 51 per cent. Alive, 21 per cent: o-^c^ 12 per cent, ?? 9 per cent.

(c) After twenty-two hours' exposure to a temperature of 35° C. and humidity 20 per cent:— Dead, 86 per cent: ^^^^^ 32 per cent, $? 54 per cent. Alive, 14 per cent: ^^^/^ 1-5 per cent, ?? 12-5 per cent.

{d) After twenty-two hours' exposure to a temperatue of 35° C. and humidity 40 per cent:— Dead, 32 per cent: ^^^r^ 20 per cent, ?$ 12 per cent. Alive, 68 per cent: ^/^^ 18 per cent, $$50 per cent.

(e) After four and a half hours' exposure to a temperature of 45° C. and humidity 1 per cent, the dead numbered 32 per cent, of which only 6 per cent were Ç? ; and after six and a half hours under the same conditions, the 16 per cent still alive were all $$. (The total proportion of sexes in this case was almost exactly 2 ?$ to 1 ^/^.)

(/) After six hours at a temperature of 45° C. and humidity 90 per cent, 11 per cent of the females, and only 4 per cent of the males, were dead.

{g) After four and a half hours' at a temperature of 45° C. and humidity 100 per cent, 24 per cent of the females, and only 6 per cent of the males, were dead. — 64 —

Summarizing the above

Temperature. Humidity. Resistant Sex.

°C. Per cent. —8 (?) 90 Males . Very much more resistant. —6 (?)90 ÎÎ j> j> >) 11 1 Females . 17 10 . Slightly more resistant. 17 40 30 80 . Very slightly more resistant. 35 20 . Considerably more resistant.

35 40 J5

35 50 >5 . Slightly more resistant. 40 80 Males . Very much more resistant. 45 1 Females . . Considerably more resistant. 45 90 Males 45 100 5, . Very much more resistant.

It is therefore clearly observable that the males are more able to resist extremes of temperature, both high and low, while the females are more resistant to unfavourable, i.e. low, percentage humidities. As previously mentioned, there was a slight increase in the comparative number of males during the spring and early summer of 1922, before the commencement of the breeding season, and, though it is unsafe to draw conclusions from a single year, it may be noted that during this period the temperature and the relative humidity were, on the whole, slightly above normal, conditions which would favour the survival of the males to a greater extent than the females.

14. TROPISMS OR FORCED MOVEMENTS.

(1) Phototropism.—This insect is at all times during its life-history positively phototropic, but not very strongly, and this reaction is often masked by its very marked positive thigmotropic tendency. It is not attracted to light at night, and its phototropism can only be demonstrated by laboratory experiments in which other stimuli are eliminated. (2) Thigmotropism.—This is the most characteristic tropism, at all times the bugs being very strongly positively thigmotropic. (3) Chemotropism.—The bugs are positively chemotropic to the seeds of Malvaceous plants, but, after the breeding season is over, it appears that for a period such seeds have no attraction. Possibly they are positively chemotropic to young cotton plants in spring, — 65 — but this is not by any means certain {vide p. 48). They may be negatively chemotropic to some substances in the bark of certain trees (p. 45). (4) Geotropism.—Like most insects, they are negatively geotropic, but not to any marked extent. (5) Thermotropism,—The resting bugs were found, by means of an apparatus devised by Mr. C. B. Williams, to be thermotropic to a temperature of 36° C. This is a surprisingly high figure, in view of the results from the experiments on the rate of mortality, but there seems to be no doubt about their decided preference for such a temperature. (6) Hydrotropism,—It is probable that, in the absence of free moisture to drink, and except perhaps at very high temperatures, the bugs are hydrotropic to a relative humidity approaching saturation point. The following experiment intended to test this was almost entirely unsuccessful owing to the difficulty in eliminating the effects of thigmotropism. Bugs were put into a long wide glass tube closed at each end with wire gauze, and outside the gauze at one end a chamber containing strong sulphuric acid, and at the other water. This was found to give a gradation of relative humidity down the tube from saturation to almost complete dryness. The bugs, however, which at first were distributed the whole length of the tube, soon took up positions on the gauze (which afforded a rough surface) at both ends irrespectively. Those that had gone to the dry end, after about two days showed some signs of activity, and some of them moved* down the tube to the wet end, but the majority made no attempt to move and were mostly dead at the end of three days : whereas those at the damp end lived for a long time.

Comparative Values of Different Tropisms. For this experiment about three or four hundred bugs were placed in a glass tube of about two centimetres internal diameter and one metre in length, the ends being closed by smooth corks. {a) One-half of the tube was darkened with brown paper—all the bugs came to the light end under the influence of phototropism. (6) The tube was reversed, the brown paper moved to the end where all the bugs had now congregated, and cotton wool placed at the light end : all the bugs went to the light and crept in among the cotton wool. (c) Tube reversed again, so that the bugs among the cotton wool were again in darkness, only two or three per cent now left the — 66 — cotton wool and came to the light, i.e. thigmotropism is very much stronger than phototropism. When a brilliant electric light was used instead of daylight, about half the bugs were attracted to it from the cotton wool. Similarly it was found that thigmotropism was very much more powerful than negative geotropism.

15. CANNIBALISM.

It is doubtful whether cannibalism is a natural phenomenon with this species. The following instances all occurred with bugs being bred under laboratory conditions. (1) A newly emerged first-stage nymph was seen to suck dry two recently laid eggs within five minutes : two others had also apparently been sucked previous to the observation being made. In this case no seed was available as food. (2) A first and a third stage nymph were both seen destroying freshly-laid eggs, although these eggs were actually on a cotton seed, upon which the nymphs could easily, and afterwards did, feed. (3) A first-stage nymph was seen to be sucking another first stage nymph, which was, however, dead when first noticed. (4) A newly emerged adult male was seen to be killed by being sucked by a fifth-stage nymph. It may be mentioned that eggs which have the appearance of having been sucked have been noticed in the field, and that no other insect predaceous on the egg has yet been recorded in this country.

16. THE INFLUENCE OF TEMPERATURE AND HUMIDITY ON THE INSECTS DURING THE PERIOD OF QUIESCENCE.

These experiments were carried out during the early months of 1922, under the following conditions. The bugs were obtained from trees and sacking traps, where they were resting after the 1921 breeding season on cotton. Between one and two hundred bugs were used for each individual experiment ; they were enclosed in wide specimen tubes the mouths of which were covered with fine mosquito-netting. The percentage humidity was controlled by keeping the tubes in small desiccators with sulphuric acid or caustic potash of various strengths ; and the temperature by immersing the desic- cators in water-baths kept constant by thermostats. Experiments were also done at ordinary room temperatures, ordinary outside shade temperatures, and abnormally low temperatures. No food was 67 given in the case of the experiments on mortality, as it was found either to be neglected, or, if taken, caused breeding to start {see b below) which in general hastened the rate of mortality. The results of most of the experiments are best shown by means of curves (Figs. 24-31). Many of the minor irregularities in these are no doubt due to experimental error, which was necessarily some- what high, owing largely to the difficulty of making a rapid and accurate count of the dead or living bugs in a glass tube. {a) Experiments on the Rate of Mortality. (1) Low temperatures (humidity uncertain, probably about 70-90 per cent).

Temperature. Duration. Percentage killed.

°C. Per cent.

—12 20 minutes 95 —12 30 „ 100 — 7 15 „ 55 — 7 30 „ 60-70 — 6 2 hours 79 0 72 „ 0 0 120 „ 1 0 9 days 18 0 1 month 95

It appears from the above that the fatal effect of low temperatures is due to sudden shock. Probably if the temperature were to fall gradually (as it would under natural conditions, if the bug were to inhabit a cold country) the resulting mortality would be very much less. (2) Temperature iV ; humidities of 1, 20, 40, 60, 80, 90, and 100 per cent of saturation. Vide Figure 24. (3) Outside shade temperatures; humidities of 1, 20, 40, 60, 80, 90, and 100 per cent of saturation. Vide Figure 25, on which the approximate average daily temperatures are also given. (4) Normal laboratory temperatures (average l?"" C, daily varia- tion seldom exceeding 4"" C.) and humidities of 1, 10, 20, 30, 40, 50, 60. 70, 80, and 90 per cent. Vide Figure 26. (5) Temperature 25'' C, and humidities of 1, 20, 40, 60, 80, 90, and 100 per cent. Vide Figure 27. (6) Temperature 30° C, and humidities the same as in the previous series. Vide Figure 28. (7) Temperature 35"" C, and humidities of 1, 20, 40, 60, 80, and 100 per cent. Vide Figure 29. (8) Temperature 40° C, and humidities of 1, 20, 40, 60, 80, 90, and 100 per cent. Vide Figure 30. ~ 68 —

(9) Temperature 45° C, and humidities of 1, 20, 40, 50, 60, 70, 80, 90, and 100 per cent. Vide Figure 31. (10) At a temperature of 47-5-48° C. 95 per cent of the bugs were dead within one and a half hours irrespective of the humidity. (11) At 50°-54° C, 95 per cent died within ten minutes at any humidity. These experiments are at the least sufficient to show the very great importance of the relative humidity on the length of life of the insect. At the same time it must not be supposed that because, at a temperature of 35° C. and humidity of 20 per cent, for instance, 90 per cent of the bugs were found to die within 24 hours, a corre- sponding mortality occurs among the resting bugs during the summer, when such conditions, as recorded by the ordinary meteorological methods, may frequently be experienced, for at any rate several hours on end. Not until there are instruments capable of the accurate measurement of the temperature, humidity, and evaporation, in the exact situations inhabited by insects, will such experiments be of any great value ; meanwhile they are by no means entirely useless, provided that their limitations are not forgotten. It will be seen from the mortality curves that the optimum humidity for survival is 100 per cent of saturation at temperatures of 30° C. and below, but this becomes rapidly less favourable as the temperature rises, until at 45° it causes death at about the same rate as an almost completely dry atmosphere, while 90 per cent is also well above the optimum. It must be remembered that in these experiments no free moisture was available for the insects to drink : under natural conditions, as has been previously explained, it is probably a high rate of evaporation which stimulates the quiescent bugs to activity, and to seek situations for the remainder of the quiescent period where moisture is available.

(b) The Influence of Temperature and Humidity in stimulating the Quiescent Bugs to feed, and consequently to breed.

In these experiments, cotton seed was enclosed with the bugs which were otherwise kept under the conditions previously out- lined. The following results were obtained :— No feeding took place at temperatures of 20° C. or below, or 40° C. or above. At 25° C, feeding followed by oviposition occurred at a humidity of 90 per cent, but not at 80 per cent or less. At 30° C, feeding and oviposition occurred at humidities of 90 per cent and 100 per cent, but not at 80 per cent or less. At 35° C, it occurred at a humidity of 80 per cent, but not at 70 per cent or less, nor at 90 per cent or above. — 69

Much more data are required in connection with this very in- teresting matter. It is possible that a greater stimulus is necessary at the beginning of the quiescent season than later on. The above experiments were done during February-March 1922, i,e. after about four months' quiescence, but in November 1922 a temperature of about 28° C. and a humidity of 90 per cent stimulated breeding, i.e. after only five to six weeks of quiescence. The most difficult problem is to reconcile the above results with the fact that in October 1922 the main breeding season on cotton finished, and quiescence started, during a period of excep- tionally warm weather, also with the fact that those bugs which breed on Hollyhock, Sida, etc., in early summer, cease reproduction (in spite of a continued abundance of food) just at the time when the temperature conditions are ideal, and the bugs on cotton commence their breeding season {vide Fig. 32). It should be mentioned that bugs quiescent after breeding on Sida mollis were taken in August and kept at suitable humidities (70, 80, and 90 per cent) in the laboratory, the temperature of which averaged about 28°-30° C, seeds of both cotton and Sida being provided, but no breeding took place. In November, however, similar bugs kept at about 28° C. and 90 per cent humidity, started breeding within a few days of the food being given to them. The only explana- tion which the writer can ofEer—an admittedly unsatisfactory one- is that after breeding for four generations, the adults of the last brood cannot reproduce again till either a period of rest has intervened, or there is a stimulus of temperatures above the normal, which in the case of those which finish breeding at the hottest part of the year would probably be impossible, as fatal temperatures would be approached. Copulation in the absence of food, which as has been stated is never followed by oviposition, was observed during the experiments on mortality to occur under the following conditions :—

Time of Exposure Temperature. Humidity. after which Copulation first noticed.

°C. Per cent. Hours.

25 90 90 30 90 44 30 100 21 35 80 21 35 90 21 35 100 47 40 80 67 40 90 89 — 70 —

As has been mentioned (p. 51) similar infertile copulation may often be observed among the bugs present on young cotton in spring and early summer, on warm days when the temperatures are within the aforesaid limits. Although at such times the humidity of the air, as ordinarily recorded, is very much below the lowest at which copulation occurred in these experiments, it is highly probable that could the humidity of the air in close contact with the leaves of growing cotton plants be determined, it would be found to approach the experimental figures of 80 per cent and upwards.

17. THE DECREASING WEIGHT OF THE BUGS DURING THE PERIOD OE QUIESCENCE.

As additional evidence (for what it is worth) that the bugs do not take any food to speak of except during the reproductive season, the weigh£ of a large number was taken at four different times during the resting stage. The method used in each case was to collect the insects in a weighing-bottle, which was weighed, the bugs then killed, removed, and counted, and the weight of the bottle plus any other matter that had accidentally got in when collecting the bugs, was subtracted from the total. (1) Bugs on a tree, November 22, 1921. 1,646 weighed. Average weight per hundred, 0-2163 gramme. (2) Bugs on a tree, April 4, 1922. 909 weighed. Average weight per hundred, 0-1940 gramme. (3) Bugs on a tree, June 19, 1922. 229 weighed. Average weight per hundred, 0-1834 gramme. (4) Bugs in the epicalices of cotton buds and green bolls, June 24, 1922. 130 weighed. Average weight per hundred, 0-1785 gramme. (3) and (4) are not as they stand strictly comparable, owing to a slight difference in the percentage of sexes, in (3) the females being 61-2 per cent and in (4) 56-0 per cent. However, it was ascertained that the weight of a female is to a male as 137 to 100 ; in order to make a comparison of the weights it is therefore necessary to calculate what would have been the weight in (4) if the percentage of females had been 61-2 per cent ; and this is found to be 0-1812 gramme per 100. It is therefore seen that the weight steadily falls during the period of quiescence ; in the case of the bugs that remained on trees the loss amounted to 10 per cent after 132 days and 15-2 per cent after 209 days ; nor is the loss checked when the insects migrate to the young cotton plants : in their case it amounted to 16-2 per cent after 214 days 71 —

18. GENEEAL CONCLUSIONS REGARDING THE SEASONAL LIFE-HISTORY.

In the foregoing pages, the life-history of this insect has been treated separately on each of its known host-plants. This has been done purely as a matter of convenience, and it must not be inferred that, as is the case with some insects, the species has developed into a number of biological races, each capable of breeding only on its particular host-plant. A considerable number of combinations of food-plants were tried to prove that this is not the case, and in every instance individuals partially reared on the seeds of one species were able to continue their development on the seeds of another, even in the case of Sterculia, which, as has been said, is of a different, though closely related, family to the rest of the host-plants. Notwithstanding, under natural conditions there is almost certainly very little transference from one host to another during the course of the (probably) four generations of a single breeding season. This statement is based chiefly on the following facts. A plant of Sida mollis was grown at Gîza with cotton surrounding it on three sides : on one side at a distance of less than a metre. Breeding started on this plant in April, and continued until July, when the adults of the last generation all became quiescent within the old capsules, and made no attempt to move to the adjacent cotton, which began to ripen at the end of July. Further, although throughout August, September, and October, this cotton was swarming with breeding bugs, they did not migrate to the Sida, as no nymphs could be found thereon during these months, although there was an abundant supply of capsules containing seeds in all stages of ripeness throughout the summer and autumn. Again, a plot of tfl was grown, with cotton adjacent to it on three sides. On October 9, 1922, about nine-tenths of the tîl was cut down, the stalks being left on the ground for some days. Judging from the sudden increase in the Oxycarenus population of the still standing one-tenth, on October 16 (especially as regards adults and the two last nymphal stages) the bugs formerly present on the cut-down tîl migrated to that still standing, rather than to the cotton which, on two sides at any rate, was actually nearer to the cut sticks than were the growing til plants. Furthermore, under natural conditions, the adults of the final generation on any host-plant cannot be induced to breed either on their original or another host, until a certain period of quiescence has intervened. Experiments to prove this have only actually been carried out in the case of bugs that had finished breeding on cotton, bâmia, and Sida mollis ; but there is no reasonable doubt that the statement would hold for the other host-plants as well. — 72 —

Exactly what is the minimum necessary period of quiescence in each case could only be ascertained by a long series of experiments, thetime for which has hitherto not been available ; it is known, however {vide the experiment detailed on p. 51), that bugs reared on the previous year's cotton crop are capable of breeding by April, although they normally do not start reproduction until July or August. From a comparison of the life-history on the various host plants, therefore, it is shown beyond all possible doubt that the phenomenon of comparative quiescence is in no way connected with either hiberna- tion or aestivation.* Given suitable food plants, both breeding and quiescent bugs may be found at any time of the year ; nevertheless, the descendants of bugs breeding, for instance, on cotton, cannot continue breeding throughout the year by migrating to other plants. In other words, a period of rest is necessary between the breeding seasons, the adults of the final generation of one breeding season being unable to continue reproduction immediately, however favourable the other conditions of food and temperature. A similar phenomenon was found to exist by Tower (38), in the case of beetles of the genus Leptinotarsa, which require a period of rest after two generations, before reproduction can start again.

* Vide Figure 32, where the life-history on six different host-plants at Gîza is represented graphically, together with the maximum and minimum shade temperatures in five-day means, for the thirteen months over which the observations extend — 73

v.—THE NATUEE OF THE DAMAGE,

1. DAMAGE TO THE SEED.

As during the whole of the breeding season all stages of the insect feed solely on the cotton seed, it is obvious that some injuries must result. Judging from the millions that are often present in a cotton field at the time of the second picking, it might be thought that no seed whatever would be left. In point of fact, however, this insect, like most seed-feeders, is very economical, in marked contrast to most leaf-eating insects. Bruchus pisi, for example, completes its whole development by eating a portion of a pea scarcely larger than the full-grown insect, whereas many Lepidopterous leaf-eating larvae require a weight of food five hundred or more times as great as the full-fed larva. Notwithstanding, the damage done by Oxycarenus is by no means trivial, and will consequently be treated in some little detail. Although the injuries are, of course, all effected in one way, by all stages of the bug piercing the testa of ripe seeds with their setae and extracting the juices of the embryo, it will be convenient to describe them under the following four heads :— Damage to tugâri {ix, seed used for oil extraction and the manufacture of cake) by direct reduction of the weight of individual seeds, and consequently of the total crop. Damage to taqawi {i.e, seed used for sowing). By causing non-germination Injuries to the embryo radicle not so severe as to inhibit germination. Injuries to the embryo cotyledons.

(a) The Appearance of Cotton Seed attacked by Oxycarenus. From an external examination, it is not possible to tell whether a seed has been attacked by this pest or not, as their extremely minute setae—^less than 0-004 millimetre in diameter—leave no visible hole in the testa. If, however, an attacked seed be cut open longitudinally, a characteristic brown discoloration will be observed over a greater or lesser part of the embryo. When the attack is not severe, this discoloration is generally, but not quite invariably, confined to the radicle ; but when a seed has been subjected to an ^ 74: — intense attack, the whole embryo will be discoloured and considerably shrivelled ; vide Figures 33-36, which show a sound seed compared to those which have been attacked in varying degrees of intensity.

(6) The Loss in the Weight of the Seed. The following experiments were made to ascertain to what extent the weight of cotton seed is diminished by this pest. In the 1921 cotton season, four plots of about ten metres square were chosen in each of which the cotton was regular and similar. No. I was picked every day, thus giving Oxycarenus no opportunity to feed on the seeds. No. II was picked once every week. No. Ill twice only, in the second week of September and the third week of October, and No. IV left unpicked until the first week of November. The whole of the cotton from each plot was ginned and well mixed before sampling. The percentage of boll worm damaged seeds was ascertained, and fortunately found to be not only small, but almost exactly the same in each plot; thus the loss in weight cannot be attributable to the diminution caused by boll worm attack on unattacked seeds in the same boll {vide Gough, 16). All the boll worm damaged seeds were removed, and samples of 1,000 apparently sound seeds from each plot were carefully weighed by hundreds. The results were found to be as follows :—

Average Weight of Number of Plot. Percentage of 100 apparently Sound damaged Seeds. Seeds (Grammes).

I 10-5 11-233 ±0-053

II 11-5 11-209 ±0-004

III 11-5 10-923 ±0-007

IV 11-0 9-748 ±0-020

The differences between I and II are, as was to be expected, immaterial, but III shows a loss or 2| per cent and IV of over 13 per cent from the original seed weight. A somewhat similar experiment was carried out in 1922, though in this case the cotton was somewhat irregular, and the attack of pink boll worm increased considerably during the picking period, not, however, to such an extent as to interfere seriously with the results. On this cotton the number of Oxycarenus were large even for the Gîza District, — 75 ~

1. Picked twice a week :-

Percentage of Weight of 100 Seeds. damaged Seeds.

(a) Between July 15 and Aug. 27 7 ll-230±0-028 (6) „ Aug. 30 and Sept. 11 18 10-475±0-039 \c) „ Sept. 14, and Sept. 23 ... 23 10-031 ±0-030 (d) „ Sept. 27 and Oct. 16 28 9-997 ±0-036 (e) Approximate actual average of above 10-667

It is thus seen that, quite apart from Oxycarenus, there was a progressive decrease in the weight of apparently sound seeds, partly no doubt due to indirect damage by boll worms, and partly perhaps due to a weakening of the plant consequent upon the production of bolls. The loss in weight caused by Oxycarenus can be estimated from a comparison of the foregoing with the following :— (2) Picked once only.

Percentage of Weight of 100 Seeds, damaged Seeds.

(a) Picked on August 27 8 ll-408±0-057 (b) „ September 23 ... 13 10-526±0-034 (c) ,, October 16 17 8-665±0-064

Thus, when Oxycarenus had not fed on the seeds the weight of those produced at the end of the season was found to be 89 per cent of the weight of those produced at the beginning, while when the seed was left open to the attack of the bugs until October 16, the average weight of all the seed produced up to that date was found to be only 76 per cent of that produced during the first month in which the bolls began to ripen. Or, again, 2 (c) may be compared with 1 (e), when the loss is found to be over 18 per cent. 76 —

Thé great extent to which delay in taking the pickings, especially the second, diminishes the seed weight if Oxycarenus is numerous, is shown from the figures obtained from another plot, on which the average weight of 100 apparently sound seeds of the first picking, on September 23, was 10-526 ±0-034, and of the second picking, on October 16, 8-980±0-084. The cotton on this plot was adjacent to, and so far as could be judged, equally as good as that which gave a weight of 11-408 ±0-057 for an early picking on August 27; therefore, allowing for the decrease from other causes previously explained, this represents a loss due to Oxycarenus of approximately 3-5 per cent for the first picking and 10 per cent for the second. ' It must be remembered that the whole of this loss in weight is from the kernel of the seed, the testa being unaffected. Balls (6) gives the relation of the weight of the kernel to the testa as approximately 57 to 43 ; the loss in the valuable part of the seed is therefore more than double that shown by the total weight. The extent to which different intensities of attack affect the weight of individual seeds is clearly shown by Figures 38-44, in which the proportion of seeds classified in 10-milligramme weight-groups is given of a number of samples having varying percentages attacked by the bug.

The financial loss incurred by reduction in seed weight due to Oxyca- renus,—From the foregoing figures, a loss of weight equal to 2-5 per cent of the total possible crop appears to be a very conservative estimate. It is true that in Upper Egypt the bug is practically absent, but the cotton grown there is a very small percentage of the whole Egyptian crop, and it must be remembered that even a short delay in taking the second picking, such as often occurs, will enormously increase the loss, as at this time the insects are to be numbered by millions per feddân. 2| per cent appears at first sight negligible, yet, taking the average crop for the years 1910-1914, and excluding the seed used for sowing, it represents a loss to the country of almost exactly L.E. 100,000 annually, a figure which would be somewhat greater at the present time, owing to the increased price of cotton seed.

(c) The Extent to which Oxycarenus is responsible for the non-germina- tion of Cotton Seed.

The factors which may cause cotton seed to fail to germinate may be classified as follows :— Externally visible damage, which includes direct attack by Gelechia and Earias, and attack on the immature seeds in the green — 77 — boll by plant-bugs such as Creontiades palUdus (Capsidae) and Nezara viridula (Pentatomid-se), {vide 22). Under this head would also come obvious causes such as mecha- nical damage during the. process of ginning. Externally invisible causes of non-germination comprise :— (1) Hollow seeds, consisting of testa only : these are seldom as much as 5 per cent of the total, and apparently arise from physiological causes, as they have been found in cotton screened by a cage from all insect pests. (2) Seeds with the embryo malformed, for reasons also uncon- nected with insect damage. These form an even smaller percentage in caged plants, and in normally growing cotton may very possibly be non-existent ; in any case it is not possible to distinguish them from (3) seeds with the embryo malformed, presumably from starvation, owing to attack by Gekchia on other seeds in the same boll. This type of damage has been discussed in detail by Gough (16). Finally, and by far the most important (4) the effect of Oxy- carenus. That a correlation exists between seed weight and percentage germination has long been known, vide Balls (5), and Gough (I.e.). The following experiments will show that, except where there has been a heavy attack by Gelechia, when the damage mentioned in (3) above assumes prominence, this is almost entirely due to the effect of Oxycarenus. The method adopted in all the germination experiments, except those where the seeds were weighed out singly, was as follows. The seed to be tested having been mixed, a sample estimated to contain rather over 1,000 apparently sound seeds was taken, from which all those visibly damaged by boll worms, Creontiades or Nezara, were removed, and their percentage counted as '' damaged seeds.'' Similarly all the obviously hollow ones were removed and counted. Of the remainder, consisting of apparently sound seeds, ten groups of 100 each were counted and weighed, to ascertain the average weight, and probable error of the mean weight of 100 seeds. These thousand seeds were germinated in shallow earthenware dishes, 16-17 centi- metres in diameter, holding about 250 seeds each, between thick felt discs, for four days at a temperature of 30° C. The stale water was drained off and fresh added at intervals of 24 hours during the four days. Those that had germinated healthily were removed after two days, to the number of which was added any subsequent healthy germinations at the end of the period, and their percentage calculated. In most samples, a small proportion of seeds was found which produced a short radicle, under one centimetre in length, but failed to grow any more. These are shown as '' partially germinated/' s

— 78 —

Finally, those which failed to germinate were examined to see if any hollow seeds, or seeds directly damaged by boll worms, had been overlooked in the preliminary examination, and if such were the case, their percentage added to the figures previously obtained. The number of such overlooked damaged seeds was found to be very small, rarely exceeding one per cent, and not such as to affect appreciably the average weight of the apparently sound seeds. Excluding such, all those which did not germinate were classed as '' failed." In a few cases, the probable error of the mean germination of 100 seeds was calculated, but as the probable error seldom exceeded 0-5 per cent, and it involved considerable extra labour and calculation, it was not thought necessary in all samples. The only deviations from the above technique were that in the earlier samples hollow seeds were counted among the apparently sound, and consequently among the failed, and the " partially germinated '' were not estimated, being classed among the ''healthily germinated.'' Neither of these, however, is of much importance, and in practice would generally balance each other. Where less than 1,000 seeds were germinated, either because the sample was not considered sufficiently important, or through absence of enough seed, the number is stated, though it appears from the probable error that a sample of about 500 is amply sufficient. In the following experiments on the seed from the four plots described on page 74, in addition to the germination testa, a further 500 apparently sound seeds were cut open and examined for signs of visible damage by Oxycarenus as described on page 73.

Visible Oxy. Germination Expt. No. Germinated. Failed. Damage. Per Cent. Per Cent. Per Cent.

(1) I (picked daily) 92-8 7-2 1-1

(2) II (picked weekly) 92-3 7-7 3-0

(3) III (two pickings) 85-5 14-5 15-3

(4) IV (one picking) ...... 44-5 55-5 56-6

The following germination tests were made on seed* from the 1922 crop, which was, as has been stated, somewhat irregular and more heavily attacked by pink boll worm than the 1921 experimental plots. The numbers of Oxycarenus present were, however, very large, especially towards the end of the season, and their damage is clearly reflected in the germination.

* Variety Sakellaridis. ^79 —

Germination.

I-sig O g 02^ CO 'U 1^ Failed. Nature of Sample. o $ ^ O ■ > '^ c. tí ft W Per Cent Per Cent Per Cent Per Cent Per Cent

(5) Picked twice a week, thus practically avoiding damage by 1-4 2-8 Oxycarenus, July 15 to Aug. 27 7-0 3-5 11-230 95-8 ±0-028 ±0-3 84-75 4-0 11-25 (6) Ditto Aug. 30 to Sept. 11 ... 18-0 3-9 10-475 ±0-039 4-0 16-3 (7) Ditto Sept. 14, to Sept. 23 23-5 5-4 10-031 79-7 ±0-030 6-0 26-0 (8) Ditto, Sept. 27 to Oct. 16.., 28-2 5-0 9-997 68-0 ±0-030 (9) Approximate actual average of above four, allowing for varying total quantity of seed 10-667 86-4 3-2 10-4 in each 15-5 4-1 88-2 2-3 9-5 (10) First picking seed, on Aug. 27 8-0 3-7 11-408 ±0-057 ±0-5 (11) Second picking of same, on 66-5 5-0 28-5 September 23 27-0 2-4 10-885 ±0-020 (12) Third picking of same, on 24-4 3-3 72-3 October 16 (500 seeds) 23-2 3-0 8-642 ±0-070 (13) First picked on September 23 60-0 7-8 32-2 (500 seeds) • 13-1 2-5 10-526 ±0-034 ±0-7 (14) Second picking of same, on 26-4 4-1 69-5 October 16 (500 seeds) ... 26-7 2-6 8-980 bO-084 2-5 75-7 (15) First picked on October 16 17-0 4-0 8-665 21-8 bO-064

These results clearly show the loss to both weight and germination which ensues from allowing cotton seed to remam exposed to the attack of Oxycarenus, and how this loss rapidly mcreases towards the end of the picking season, in correlation with the mcrease m numbers of the bug. A graphical representation is given m figure 37 The following experiments on Zagora cotton ot the 19^^ crop give similar results. The numbers of Oxycarenus present were agam very large. — 80

Germination. Nature of Sample. O o J3 Failed. ce cü ai Tí P CÔ O n'a pH Per Cent Per Cent Per Cent Per Cent Per Cent (16) Sound green bolls free from boU-worni, enclosed in muslin sleeves just before ripening, therefore no attack by Oxycare- nus. Picked September 23 (366 seeds) 0-0 1-6 10-060 97-25 2-2 (17) Cotton grown in a muslin 0-45 cage, free of all pests, but plants rather weak and straggling. Picked September 23 (361 seeds) 0-0 3-0 10-400 97-2 1-5 1-3 (18) Similar cage containing nu- ±0-038 merous Oxycarenus. Picked September 23 (239 seeds) ... 0-0 0-0 7-930 33-5 4-2 62-3 (18a) Ditto, picked October 14 (138 seeds) 0-0 0-0 7-610 23-9 4-3 71-8 (19) A normal late first picking, on September 24 (900 seeds) 10-5 1-5 9-672 61-0 3-8 35-2 ±0-058 (20) 250 seeds picked individually on September 21 each with Oxycarenus actually feeding on them when picked 0-0 0-0 8-048 6-4 5-6 (21) Ditto, not being fed on when 88-0 picked, and no bugs present in the lint 0-0 0-0 10-204 68-0 9-6 22-4

The foregoing results show clearly enough the adverse effect oi Oxycarenus on the weight of cotton seed,"and consequently on Its germmative powers, in bulk samples. In order to gain a more complete knowledge of the effect of the reduction of weight on the vitality, the following experiments were carried out, in which everv apparently sound " seed of each sample was individually weighed on a specially constructed micro-balance, each sample being thus divided mto weight-groups at ten-milligramme intervals, which were germmated separately. (In these experiments hollow seeds are counted among the "apparently sound" and "partially germi- nated seeds among the " healthily germinated.") The results are best shown by means of graphs. (22) (Fig. 38). Sound bolls picked between August 10 and August 21 1921 just after ripening attack by Oxycarenus consequently nil. Damaged rÄtr^lötrair • ''' ''-'' "^^^'^'- ^--^^ W per cfnt, - 81 ~

(23) (Fig. 39). Sound bolls picked between August 30 and September 2, 1921, just after ripening, attack by Oxycarenus consequently nil. Damaged seeds 9-8 per cent. 1,000 seeds weighed. Average weight per cent, 10-312±0-020 grammes. It will be seen from the graphs of the above two samples that the average germination of each is practically the same, m2;. 95-4 per cent and 96-8 per cent, in spite of the considerably lower weight of the second sample, which actually gave slightly the better germina- tion. It therefore appears that within reasonable limits of weight, i.e. when the seed is not starved by poor growth of the plant, and in the absence of Oxycarenus, and with only a slight attack by Gelechia, there is no correlation between germination and seed- weight, as an almost perfect germination is reached by seeds having a weight considerably below the maximum possible. (24) (Fig. 40). Seed from - Plot No. Ill " {vide p. 74) in which 15-3 per cent of the apparently sound seeds were, on being cut open, found to be visibly damaged by Oxycarenus. 500 seeds weighed. (25) (Fig. 41). Seed from. Plot No. IV (56-6 per cent visibly damaged by Oxycarenus). 750 seeds weighed. (26) (Fig 42). Seeds picked individually on October 22, 1921, actually being fed on by Oxycarenus when picked. 300 seeds weighed. The percentage in each ten-milligramme weight-group alone is given ; the germination was affected by the failure of the incubator, and was probably unreliable. It would almost certainly have been under 10 per cent. (27) (Fig. 43). Seed from cotton left unpicked until the middle of November 1921, Oxycarenus attack very heavy, 80 per cent showing signs of damage. Damaged by boll worms, 12-5 per cent. Average weight of 100 seeds, 8-790±0-037. 428 seeds weighed. (28) (Fig. 44). Seed from Ashmûni cotton grown in a-large wire gauze cage. Boll worm attack nil, but Oxycarenus numerous, 41 per cent showing signs of attack. Average weight of 100 seeds 10-363±0-006. 500 seeds weighed. From Nos. 22 and 23 of the foregoing (Figs. 38 and 39) it is seen that in the absence of Oxycarenus and the almost complete absence of indirect Gelechia damage (consequent upon the small percentage of seed with direct Gelechia damage) very nearly complete germination is obtained from all seeds weighing over 80 milligrammes. With the increasing intensity of attack by Oxycarenus (Nos. 24-28, Figs. 40-44) not only is the proportion of lighter seeds increased, as is natural, but the germination of the heavier seeds is also affected, as many of the seeds which now weigh, for instance, lOO-llO milligrammes,''would have weighed perhaps 120-130 milligrammes, had they not been sucked by the bugs and their vitality consequently destroyed. The following germination experiment, No. 29, shows how quickly the vitality of a seed may be destroyed if it is fed upon by large numbers of the bugs even for a short time. A plot of cotton - 82 — very heavily infested with Oxycarenus was entirely cleared of ripe cotton on October 5, 1922. The day following a boll was noticed to have opened, and, four days later, this was picked and found to contain over 700 bugs. Of the 17 seeds in it, none of which had been attacked by boll worms, only one—equivalent to 5-9 per cent— germinated. Seeds that have been killed by Oxycarenus* usually harbour the spores, and sometimes traces of the mycelium, of a fungus, Rhizopus nigricans (which in Egypt is almost universally present on suitable media). In this case, however, it appears to be a saprophyte, and in no way affects the germination of healthy seeds, as is shown by the following germination experiment. No. 30, in which a sound sample, known to give approximately 90 per cent germination, was used. (a) Control, germinated as usual between clean felt discs previously sterilized in a solution of CUSO4:— Per Cent. Healthy germination 90-3 Partial germination 4-0 Failed 5-7 (h) Bottom felts covered with a thick blanket of Rhizopus mycelium growing on bug-destroyed seeds, and bearing numerous sporangia, top felts taken straight from use on a badly attacked sample : Per Cent. Healthy germination 90-6 Partial germination 3-1 Failed 6-3 Germination under Field Conditions.—As the percentage germ- ination under optimum conditions in an incubator might not neces- sarily have any relation to the percentage capable of producing a seedling when sown in the normal way in the field, the field germination of certain samples was tested with the following results. " Apparently sound " seeds only were sown, ten in each hole. Samples from' 1921 crop (sown Mayf 1922) :-^ (a) Unattacked by Oxycarenus, weight 11-996 grammes per hundred. Optimum germination, 95-4 per cent. Field germination 90-7 per cent = 95-1 per cent of optimum. (&) Unattacked by Oxycarenus, weight 10-312 grammes per hundred. Optimum germination, 96-8 per cent. Field germination, 85-1 per cent = 87-9 per cent of optimum.

* Seeds damaged by boll worms are also generally affected. t The high temperatures prevalent during these experiments minimized, and possibly precluded, any error due to attack by the " sore-shin " fungus {corticium vagum) which is only severe in cool weather. - 8¿ -

(ó) Seed showing upon examination 15 per cent visibJv attacked by Oxycarenus, weight 10-923 grammes per hundred. Optimum germination, 85-5 per cent. Field germination, 71-6 per cent = 83-6 per cent of optimum. Samples from 1922 crop (sown October* 1922) :— (d) Same seed as in germination experiment No. 5, no attack by Oxycarenus, weight 11-23 grammes per hundred. Optimum germination, 95-8 per cent. Field germination, 81-5 ± 0-7 per cent = 85 per cent optimum. (e) Same seed as in No. 10, Oxycarenus attack slight, weight 11-23 grammes per hundred. Optimum germination, 88-2 per cent. Field germination, 70- 7 ± 0- 8 per cent —80 per cent of optimum. (/) Same seed as in No. 13, moderately severe Oxycarenus attack, weight 10-526 grammes per hundred. Optimum germination, 60-0 per cent. Field germination, 40-4 + 1-2 per cent =67 per cent of optimum. (g) Same seed as in No. 15, Oxycarenus attack very severe, weight 8-665 grammes per hundred. Optimum germination, 21-8 per cent. Field germination, 16- 35 ± 1 • 5 per cent=75 per cent of optimum. The percentage of seeds which germinate under field conditions therefore appears to fall slightly in correlation with reduced weight, apart from attack by Oxycarenus ; and rather more so in correlation with the severity of attack by this bug. ' The following experiments were done on the weight and germina- tion of bâmia seed attacked to different degrees by Oxycarenus. The same method as for cotton seed was used, except that at least eight days were found necessary to secure complete germination. (a) 250 seeds from capsules picked green on October 10, 1922, and ripened off in the sun, thus securing complete immunity from Oxycarenus (though possibly affecting the germination in other ways) :— Weight per hundred 6-968 grammes. Germinated ... 82-4 per cent. Failed 17-6 (b) 190 seeds picked September 22, 1922, having only been open a few days, therefore only slightly attacked :— Weight per cent 7-29 grammes. Germinated 77-9 per cent Failed 22-1

* The high temperatures prevalent during these experiments minimized, and possibly precluded, any error due to attack by the "sore-shin" fungus (Corticium vagum) which is only bevere in cool weather. - 84 -

(c) 140 seeds moderately attacked, picked September 22, 1922:— Weight per hundred 7-54 grammes. Germinated 48-6 per cent. Failed 51-4 (d) 400 seeds very badly attacked, picked September 22, 1922. Weight per hundred 5-16 ±0-06 grammes. Germinated 19-25 per cent. Failed 80-75 ^ „

(d) Injury to the Embryo Radicle, not so severe as to inhibit Germination. A slight attack on the radicle end of the seed, while probably being responsible for a certain proportion of the seeds that show a '' partial " germination and then die, does not by any means in- variably cause the death of the seedling. This is obvious from experiment 20, where a healthy germination of 6-4 per cent was obtained from seeds all known to be attacked, and from ^3 and 4, where the percentage of failures was found to be slightly less than the percentage showing on examination visible signs of attack. The radicle produced by such a slightly attacked seed is almost always blunt instead of tapering, and at the end of four days germina- tion at 30° C. will only be about 30-50 millimetres long, or about half the length of a sound radicle. It commences, however, to produce lateral rootlets very much earlier than* a normal seedling, and though it no doubt receives a temporary check for a short time,- it appears able to recover and produce as good a plant eventually. Ten seeds were grown in water-cultures : in five cases the radicle had been slightly attacked, and the normal tap-root replaced by several lateral roots taking a downward course; in the other five the seeds were sound and a normal root system developed. The number experimented upon is of course insufficient for a definite judgment to be pronounced; but, as regards the above ground growth of the plants, none of the ten showed any appreciable variation, actually the one that appeared to grow slightly the best was from an attacked seed.

(e) Injury to the Embryo Cotyledons. Although the bugs generally direct their attention to the radicle of the seed, not infrequently the embryo cotyledons are also pierced. If such a seed has not also been attacked at its radicle sufficiently to kill it, when the cotyledons appear above the ground they always bear one or more pairs of spots of dead tissue, which are symmetrical on each cotyledon (Fig. 45). — 85 —

To ascertain the correlation between the percentage of seeds with this type of damage, and the percentage entirely killed by Oxycarenus, the seedlings growing from the field germination experi- ments (d), (e), (/), and (g) detailed above were carefully examined to find the numbers showing damaged cotyledons, with the following results :—

Percentage Field Percentage (of germ- Germination. inated seeds) showing damaged Cotyledons.

(d) 81-5 8-5 (e) 70-7 13-75 (/) 40-4. 33-8 (g) 16-35 56-8

Such*"dead patches in the cotyledons might cause damage to the plant in two ways, firstly by direct reduction of food material, and secondly by reducing the assimilative area of the young seedlings. In (d) and (e) above, two healthy seedlings showing no signs of attack were left in each hole, the remainder being removed ; while in (/) and (g) the two showing the largest dead areas (which seldom were as much as 20 per cent of the total area of the leaf, and in most cases very much less) were left, all the sound seedlings being removed. After a month's growth, each plant was cut off just above the cotyledon leaves, in order to secure uniformity, and the dry weight of the two lots compared. Those which had had sound cotyledons gave an average dry weight of 0-1516 gramme per plant, and an average for 40 plants of 6-045 ±0-121, and those which had had damaged cotyledons an average of 0-1565 gramme each, and for 40 plants 6-183 ±0-188. It should also be mentioned that though just after thinning the sound seedlings had a more healthy appearance than the damaged ones, no apparent difference in the look of the plants could be detected after a month's growth. Although the dry weight of a plant may not be an absolute measure of its vigour, yet it certainly seems probable that the slight initial set-back that may be caused by the damage to the cotyledons is entirely recovered. Again, out of a large number of seeds ^each known to have been attacked by Oxycarenus in 1921, which were sown in 1922, five germinated and all five produced plants apparently healthy in every way, though as they were widely spaced consequent upon the small percentage of germination, a strict comparison as to yield, etc., could — 86 - not be made. The seed from these five plants was, however, collected and compared with that from plants grown from similar but known to be unattacked seeds, growing in the next row to them. The germination of both was somewhat affected by the 1922 attack of Oxycarenus (the cotton was not, as should have been done, picked frequently, within a few days of the bolls opening), but the results are at any rate sufficient to show that the seeds produced by a plant grown from a slightly attacked seed are not in any way affected. (a) Seed from five plants grown from seeds known to have been attacked in 1921 :— Damaged by boll worms ... 23 per cent. Average weight per hundred... 10-50 grammes. Germination, healthy 81-25 per cent. ,, partial 7-5 ,, Failed 11-25 (6) Parent seeds unattacked :— Damaged 14 per cent. Average weight per hundred.. 10-55 grammes. Germination, healthy ... .. 82-2 per cent. ,, partial 4-8 Failed 13-0

2. THE EFFECT ON THE GINNING OUT-TUKN OF DAMAGE TO THE SEED BY OXYCARENUS.

It is obvious that as the bug causes a reduction in the weight of the seed, while the lint, which is fully formed before the insect has access to it, remains untouched, the ginning out-turn, or proportion of lint to seed cotton, will increase in relation to the severity and duration of the attack. The following results from the plots of cotton used for germination experiments 6, 7, 8, 13, 14, and 15, give some idea of the extent to which this occurs. For commercial purposes the ginning out-turn is usually expressed as rotls of lint obtained per qantâr of 315 rotls of seed cotton. Following the general custom in scientific work, however, it is here given as the percentage lint to total seed cotton. (1) Twice weekly pickings (==no damage by Oxycarenus) :— Percentage lint. (a) Between August 30 and September 11 28-15 (6) „ September 14 and 23 28-25 (c) „ September 27 and October 16 28-70 {d) Actual average of above 28-30 — 87 —

(2) Two pickings during season : Percentage lint. (a) On September 23 29-02 (6) On October 16 30-41 (c) Actual average of above 29-60 (3) One late picking only:— On October 16 32-76 However desirable to the buyer of seed cotton a high ginning out-turn may be, it is quite obvious that if it is attained by the reduction in weight of the seed owing to the attack of Oxycarenus, it is most prejudicial to the growers' interests, as the extra price that might be paid for a cotton with a high out-turn would not compensate for the reduction in the total weight of seed cot.ton produced ; for instance, taking (1) (d) and (2) (c) above, the rise of 1-3 per cent in the percentage of lint is due solely to a loss of 4-4 per cent in the total weight of seed cotton.

3. DAMAGE TO THE LINT. It has been explained that this bug only commences feeding on the seeds of cotton when the bolls have split, by which time the lint is fully formed ; there is therefore no damage done to the lint resulting from the puncture of green bolls, such as occurs when cotton is attacked by '' stainers '' (Dysdercus spp.) or by such bugs as Creon- tiades pallidus and Nezara viridula, which are responsible for a certain amount of such damage in this country (22). Possible damage could consequently only be effected in the following ways :— {a) Staining by the squashing of the bugs during picking. (6) Staining from the same cause during ginning. (c) Staining from their excrement. {d) Dirtying of the fibre by the dried dead bodies and the cast skins of the insects. {e) The bugs might impart their exceedingly unpleasant smell to the lint.

{a) Staining during Picking, As regards {a) the bugs are practically never squashed sufficiently to cause any staining, during the process of picking. The cotton from a heavily infested field was examined immediately after having been picked, and the only traces of staining that could be found were on locks of " scarto'' cotton, no doubt because^ such locks are more compact and less resilient than sound cotton which has fuzzed our properly. Even then, squashed bugs were by no means frequent, and, " scarto *' cotton being in any case of low value, it can confidently be stated that staining from this cause is for all practicable purposes absolutely negligible.

(h) Staining during Ginning. If seed cotton containing living Oxycareni is ginned, a certain number of the bugs will be squashed and stain the lint a conspiciious reddish colour, sometimes with traces of green, though it is surprising how many of the insects pass uninjured through the gin ; but this only occurs if the bugs are still alive ; very soon after death their bodies become dry and brittle, and no staining whatever then results. The time for which the bugs are able to survive in the seed cotton after it has been put in a sack consequently assumes some importance. Probably it depends on the temperature and humidity, chiefly no doubt on the latter, as the cotton immediately after picking is usually spread out in the sun before being put in sacks, and thus becomes very dry. In the case of a sack of second picking cotton containing large numbers of bugs, after six days scarcely any, and after twelve days none at all, were found to be still alive. This was then ginned, and no staining could be observed. Through the kindness of Mr. H. C. Thomas, of the Nile Cotton Company, the writer was able to inspect a number of samples sent for grading. In only one, an otherwise clean sample of Sakel of high quality, could any staining from squashed bugs be detected. Although the exact interval was not known, this cotton had almost certainly been ginned very soon after picking, as Mr. Thomas had received it very early in the season. Inquiries from several ginners revealed the fact that very seldom is cotton ginned within less than a week or ten days of its being picked ; this only occurs when cotton of the first picking (which never contains very large numbers of Oxycarenus) is urgently required for the market. Although therefore such staining might easily be so severe as to lower the "value of the lint by four or five dollars per qantâr, in practice it' seldom occurs, and furthermore is entirely avoidable {vide Part VI, Section 3 6). It should be mentioned that a similar pinkish stain on the lint is sometimes caused by the crushing in the gin of pink boll worms {vide Willcocks 41, p. 45). Staining caused by Oxycarenus can always be distinguished from this by the presence of fragments of the crushed insect. {c) Staining from the Excrement. This is an absolutely negligible form of damage. The majority of the excrement is not deposited on the lint at all, but on the epicalyx, — 89 — leaves, etc., near the boll. Such as is voided on the lint is sometimes just noticeable as a small faint yellowish brown discoloration; but in the case of the lint from a boll which had contained several hundred bugs, only one or two such spots could be detected, and then only with the aid of a pocket lens ; to the naked eye the lint appeared perfectly clean. It was noticed that traces of excrement were some- times just visible on the fibre of open bolls in the field, in the early morning when they were wet with dew, but that the discoloration was no longer apparent when the lint had dried. Careful examination completely failed ever to find the slightest indication of the excrement in ginned cotton.

{d) Dirtiness of the Lint from the Dead Bugs and Cast Skins. As has been said, by the time that seed cotton is normally ginned, that is to say after a lapse of at least a week, and generally much longer, after picking, the bugs are all dead and brittle. During the pre-ginning processes, emptying the cotton out of the sacks and mixing it, many of these dead bugs are shaken out ; the majority, however, remain in the cotton and pass through the gin. Of these a further quantity are left behind with the seed; but some of them, as also some of the cast skins of nymphs, and a few eggs that have been injured and therefore have not hatched, can always be found in the ginned lint. Traces of dead bugs have been found in practically all the samples examined, except some of those from Upper Egypt. There is, however, even in the cleanest samples of cotton, always a certain amount of dirt, chiefly fragments of dead leaves, etc. When this amount becomes excessive, it lowers the value to the extent of as much as five or six or even more dollars per qantâr. The amount of such dirt also tends to be greater in cotton of the second picking, which from other causes such as lesser strength, is also lower in value. Mr. Thomas informed the writer that all dirt from whatever cause is classed together in estimating the value of a sample, and in none of the samples that have been examined has the dirt arising from the presence of these bugs been anything more than a small fraction of the total. As is to be expected, it is only considerable in second picking cotton, which, as has been mentioned, is almost invariably much dirtier, and lower in value, from other causes. It may therefore be concluded that dirt arising from the presence of Oxycarenus would only be of economic importance in the case of high qualitj/ cotton, carefully picked to ensure almost complete absence of fragments of leaves, which would otherwise be perfectly clean. If the measures suggested in Part VI are carried into practice the amount of dirt consisting of fragments of this bug left in the lint after ginning, always trivial, will be so small as to be of no importance whatever. . — 90 —

(e) Unpleasant Smell. Although this bug, especially when squashed, emits a peculiarly unpleasant smell, this is never imparted to the lint with lasting effects. The mere presence of the insect does not cause the lint to smell at all; in the lint from a number of bolls which had con- tained large quantities of Oxycarenus no odour whatever could be detected. If the bugs are crushed in the lint, which as has been shown seldom occurs, the smell persists for a short time only, and does not impart a permanent odour to the cotton.

4. A REFUTATION OF THE THEORY THAT Oxycarenus hyalinipenms CAUSES BUD AND BOLL-SHEDDING.

A glance at the summary of previous literature (Part I, Section 2) will show that this pest, as well as others of the same genus, has been accused of causing the shedding of buds and young bolls. This impres- sion, which it will be shown is entirely erroneous, at any rate as regards this species in this country, no doubt arises from the fact that in spring and early summer large numbers of these insects may be found within the epicalices of buds and small bolls, many of which are shed. '' Post hoc, ergo propter hoc.'' Also there are in Egypt two little known and not very conspicuous insects, Creontiades pallidus, Ramb., and Nezara viridula, L., which though apparently seldom abundant, are yet responsible for a not inconsiderable proportion of the total shedding of buds and small bolls. These two pests have been discussed by the writer in a separate bulletin (22). The following is the evidence for the innocuity of Oxycarenus in causing shedding. (1) In the account given of the life-history (Part IV), it was shown that many of the adults remained throughout the non-breeding season, i,e. (for cotton feeding bugs) from November till the following July, in a state of semi-quiescence in situations where no food was available, and that the behaviour of these when the breeding season started was found to be exactly similar to that of those which had left such situations in April or later, and spent the early summer months on the young cotton plants. This shows that at this time of the year food is at any rate not essential to the insects. (2) Those that do spend the early summer on cotton plants have never at any time of the day or night been observed actually to feed on either buds or green bolls. They may, it is true, be seen especially on warm dry days, sucking at the glands at the base of the mid-rib of the leaves and at the base of the epicalyx, in order — 91 ^

fco obtain moisture ; however, large numbers of other insects, especially ants, frequently do the same thing, and it is quite inconceivable that the loss of a very small amount of moisture—from glands that apparently often exude moisture naturally—could in any way cause shedding. (3) It has been mentioned that these bugs do not congregate in buds the epicalices of* which are under about 20 millimetres in diameter, and that for the most part they favour still larger ones ; yet the great majority of the shedding that occurs is of small buds with an epicalyx of 10 millimetres or less ; and the chances of a bud being shed become rapidly less as it grows older. (4) Three individual buds harbouring very large numbers of Oxycarenus in May were kept under observation, and all of them produced perfectly sound bolls, although the bugs did not leave them until they were half grown, and in one case remained until the boll ripened.

(5) A shedding experiment that was attempted, the cotton plants being grown under muslin cages, gave no positive results, owing to the un-uniformly deleterious effect of the cages on the plants. Actually, the only two cages in which the cotton happened to grow at all normally contained large numbers of the bugs, and in these the shedding was less in proportion than in the control cages. Several individual buds harbouring the insects within these two cages were watched, and most of these—^including one which for six weeks had been black with bugs, and which when picked just before ripening was found to contain over 120 within the epicalyx—^produced sound bolls. (6) It has already been mentioned (Part IV, Section 17) that the weight of the bugs decreases throughout the non-breeding period, both in the case of those that remain in their original resting-places, and those that live on the young cotton in the early summer, which affords additional evidence that no food is taken at this time of the year.

(7) The results of the following experiment on shedding and the possible causation of " mabroum " bolls is given for what it is worth ; it was started in August 1921, before the writer had definitely discovered that the only food of the insect during the breeding season consists of ripe seeds. A number of green bolls and buds were enclosed in muslin " sleeves," with some of them Oxycarenus were put, about 30-80 bugs per sleeve^, others being kept free of bugs as controls. \

92 —

The result of the examination oi the sleeves, during the first week in November, was :—

Sleeves with Control Sleeves. Oxycarenus.

Number of buds enclosed 78 148 „ bolls enclosed 111 179

Total, buds and bolls ... 189 327

Sound bolls 69 = 36-5 per cent. 129 = 39-7 per cent. " Mabroum " bolls 45 = 23-8 79 = 24-2 „ Shed bolls ... 23 = 12-2 32 = 9-8 Shed buds 42 = 22-2 67 = 20-5 Still green sound bolls 10 = 5-3 20 = 6-0 „

If the shed buds, the large number of which was without doubt due to the action of the sleeves, be neglected, the following figures are arrived at :—

Control. With Oxycarenus.

Per. cent Per cent.

Sound bolls ... 53 54 "Mabroum" bolls ... 34 33 Shed bolls 13 13

The results are so nearly identical as completely to exonerate Oxycarenus from causing either shedding or '' mabroum '' bolls, even were it not now known that the only food taken by them is the juices of the ripe seeds. (8) At the end of the breeding season, and before the cotton sticks are removed, numbers of the adult bugs again take shelter within the epicalyx of the few remaining buds and green bolls, and remain there quiescent, behaving exactly as their ancestors did in the early summer. This is an additional indication that they congregate in the epicalyx solely because it afíords a suitable shelter where the evaporation is at a mimmum^ and not for purposes of obtaining food, - 93 -

VI.—CONTKOL AND REMEDIAL MEASURES.

1. NATURAL CONTROL. As far as has been ascertained, this species is entirely free from the attack of any insect parasite : this immunity is enjoyed by a very large number of Ileteroptera, and it is unlikely that any parasites on Oxycarenus occur, at any rate in this country. It also appears to be remarkably free from predatory enemies, due no doubt to its unpleasant smell : birds have never been observed to eat them, nor would a Mantis that had been without food for several days take any notice of them. On one or two occasions ants have been seen carrying off dead nymphs; whether they actually killed them or not is uncertain. In India, Triphleps tantilus was once seen to attack the nymphs of 0. lœtus, at Pusa (26) ; a species of Triphleps is common on cotton in Egypt, but has never been observed naturally, and could not be induced in the laboratory, to attack any stage of 0. hyalini- pennis. The question of cannibalism has already been discussed (Part IV, Section 15) and shown to be of very limited extent; and it is quite certain that none of the foregoing can have any appreciable effect in keeping down the numbers of this pest. The only factors responsible for checking the rate of reproduction during the breeding season appear directly or indirectly to be connected with the weather. It has been mentioned that direct sunlight for even a short time causes the death of the eggs, though on cotton the number so killed appears to be small. More important is the mortality among the newly-hatched nymphs, possibly through lack of moisture or inability to penetrate through the lint to the seed sufficiently soon ; but though a certain number of first-stage nymphs do die, it is not an uncommon thing for all the eggs of a batch to hatch, and arrive suc- cessfully at maturity. When the cotton is picked, large numbers of the bugs are either shaken out and drop to the ground, or else are carried off the field. The majority of those that are shaken out in the field appear to find their way back to remaining bolls with ripe seeds available, at least in the case of adults and the later stage nymphs. Nymphs of the first two stages are either not so readily shaken out of the lint, or, if they are, perish before being able to find a boll containing ripe seeds, ^ 94 — judging from the population of the few open bolls left after a picking has been taken, which as a rule swarm with adults and the older nymphs, but contain comparatively few of the younger. Those which are removed from the field with the picked cotton probably only survive if the seed-cotton is placed on the ground near the growing crop, and they are able to crawl to it. Some of the males doubtless fly back, but, as has been mentioned, the females at this time of the year fly but little. Very little feeding if any appears to take place once the cotton has been picked, and those bugs which are put into the sacks and are unable to escape, perish within a week or ten days. The causes of the enormous decrease in numbers which takes place between the end of one breeding season and the beginning of the next are also probably in the main climatic. Many of those bugs which leave their resting-places on warm days in winter and spring do not return to the same or similar situations, and it is certain that large numbers of them fail to find suitable places in which to pass the remainder of the non-breeding season, and sooner or later succumb to adverse weather conditions, of which a high rate of evaporation is probably the most important. Heavy rain also appears to be responsible for a considerable mortality; it was noticed that the more exposed branches of a tree, which had previously been almost black with the bugs, were nearly free of them after some sharp showers at the end of December 1922, and though there was some increase noticeable in the number on the most sheltered parts of the tree, it was not such as to compensate for the disappearance of the others. It may be mentioned that in laboratory experiments in which the bugs were kept at high percentage humidities (90 per cent and above) a fungus (apparently Aspergillus flavus) sometimes made its appearance on dead bodies of the insects. Although the presence of this fungus was found to hasten very considerably the rate of mortality, it appeared that this was due not to its being parasitic, but to the numerous minute spores which clogged up the spiracles of the living bugs, and caused death by suffocation. It has not been observed under natural conditions, and would probably only be of any effect when the insects, being confined in a small space such as the bottles used in these experiments, would quickly become covered with the spores.

2. DISCUSSION OF METHODS FOR DIRECT CONTROL.

The following are the possible methods of direct control which have either been tried by the writer or suggested by others. _ 95 -

(a) Attack on the Insect during the Winter Quiescent Period. This should take the form of elimination of those situations chosen by the bugs, in which it is difficult or impossible to kill them, and the encouragement or provision of those where they can readily be destroyed. The method whereby the first of these requisites can be largely secured is obvious : clean cultivation, and especially the destruction of all weeds and coarse grasses growing on the banks of canals and irrigation channels, etc. A reduction in the numbers of Oxycarenus will be one of the least of the benefits accruing from such a course; yet either through apathy or ignorance or the idea that it is better to save a piastre this year than gain a pound next, clean canal banks are a rare sight in Egypt. As regards destruction of the insects in situations where it is practicable, it is suggested that from the trunks of large trees which may sometimes be almost black with the bugs, they could be brushed or beaten off without difficulty : this should be done for preference early on a cold morning, when the insects, being inactive, would fall to the ground, and could be stamped in. Where this method would be difiicult, as for instance on a Sunt hedge, traps consisting of pieces of old sacking tied on to the bushes will be found to collect vast numbers. Similar traps may be put on stakes in or at the edges of cotton fields ; they should be put in position in October, before the breeding season finishes : it will be found that old, coarse-meshed, torn sacking is the most effective. One such trap at Gîza, collecting bugs from probably less than a qirât of cotton, was found to harbour upwards of 25,000 of the insects. The chief disadvantages are the large number of such traps that would be necessary, at least one every ten metres round the edge of a cotton field, and the fact that however old and dirty may be the sacking used, it has a high value among the fellahin as clothing or bedding, and would almost certainly, as proved to be the case at Gîza, be largely stolen. The bugs in such traps may easily be destroyed by shaking them or dipping the whole piece of sacking into a pail of water with a film of paraffin on its surface.

(6) Control during Spring and Early Summer of those Bugs present on the Young Cotton. Hand-picking of the insects at this time has been suggested, but as the writer has found when desiring to obtain them for experimental purposes, it would be quite impracticable. The bugs are almost entirely to be found within the epicalyx of buds and green bolls, from which it is often impossible to dislodge them without damaging the plant. The only method of trapping which is possible at this time of the year is the provision of cotton seed among the young - 96 - growing plants. As has been said, such traps attract only those bugs in the immediate vicinity ; apart from this drawback their use would in any case be undesirable, as if neglected, the insects start breeding on them, and there would be larger instead of smaller numbers ready to enter the first opening bolls. Early sown bâmia and tîl have also been suggested as trap crops, under the idea that, ripening before the cotton, they would attract the insects to breed on them, where they could be destroyed. The limited attractive power of seed applies, however, equally in this case ; and it was found that although the bugs present on the young bâmia started breeding as soon as its fruit ripened, in June, yet those quiescent on cotton only a metre away were not attracted to the bâmia seed, but remained until the cotton ripened some six weeks later. It has also been suggested that the presence of early ripening bâmia or til near cotton may be deleterious, as tending to increase the number of bugs before the cotton ripens, some of which might leave the bâmia for the cotton seed, when the latter becomes available. It has, however, already been stated 'that there is apparently very little migration from one host-plant to another during the course of one breeding season : and although a plot of cotton was grown next to some bâmia which had ripened some six or seven weeks before the cotton, and by that time was heavily infested, no greater numbers were noticeable on this plot than on any other far away from any bâmia.

(c) Control during the Breeding Season.

Although this is the only period of the year at which the insect is either increasing in numbers or doing any damage, it does not appear possible to effect any control at this time. It has been sug- gested that at the time of the first picking, all those bolls which have been so damaged by boll worms as to contain no lint worth picking, and which are normally left on the trees, should be removed. Although such bolls almost invariably contain large numbers of seed-bugs, the writer's opinion is that such a course, apart from the expense ojf the extra labour involved, might actually be harmful from the point of view of damage done by Oxycarenus (though it might help in some small measure to control the pink boll worm). Some of the bugs contained in such bolls could no doubt be carried off the field and destroyed, but the majority would certainly fall out in the field, crawl up the plants, and wait a day or two until the next sound bolls ripened, which would then be far more heavily infested than if these bugs had remained harmlessly in useless bolls. In other words, though the total numbers of seed-bugs would be reduced, the damage would be intensified. ~ 97 —

3. METHODS OF LIMITING THE DAMAGE.

(a) To the Seed. It has been clearly shown (Fig. 37) that the loss in weight of the seed (and consequently the reduction in yield of seed-cotton) and the diminution of its percentage germination is directly proportional to the numbers of Oxycarenus present and the length of time for which they have access to the ripe seeds on the standing cotton plants. It is therefore obvious that the earlier the pickings are taken, the smaller will be the loss : especially is it important that the second picking should not be postponed in the hope of a few more bolls opening, as the numbers of bugs being very great at this time, the total yield of seed-cotton is diminishing rapidly with the delay. It is tentatively suggested that it would be financially advanta- geous to take three pickings instead of the usual two : the extra cost— about L.E. 1 per feddân—would be repaid by, taking average figures, an increase of five per cent in the yield per feddân. It is true that, ex- cept where the attack of Oxycarenus is exceedingly severe, limitation of its damage by this method would probably not secure such an increase ; but on the other hand the cotton from the first and second pickings, being taken earlier than would be the case if the second picking were the final one, would be cleaner and of a higher grade. Seed used for sowing (taqâwi) should, as is the usual practice, be of the first picking, to ensure a high rate of germination. The ordinary taqâwi at the present time rarely gives a germination higher than 85-90 per cent ; if it were taken from an early first picking of three, instead of from a late first picking of two, the germination would be found to approach or exceed 95 per cent. It may be mentioned that if, as might be the case in experimental work on new varieties, all the seed from a small plot is required for resowing, the cotton should be picked several times during the season at frequent intervals. The same precaution about the selection of seed for sowing applies to bâmia ; especially is it important when bâmia is used as a " nurse '' for cotton seed, that a high rate of germination should be secured by using seed from capsules which have not been left ripe on the plant for any length of time.

(6) To the Lint. What little damage is done to the lint may be almost entirely eliminated by the observance of the following precautions, which demand the expenditure of nothing but a certain amount of care. If, as is generally done, the cotton is placed in heaps on the ground as it is picked, and not put directly into sacks, large numbers of the bugs craw] or fly away from the heaps, and their chance of survival — 98 - depends on their finding growing cotton. If therefore the cotton as it is picked is spread out in small heaps, some ten yards or more from the nearest standing cotton, and left for an hour or two in the sun, most of the bugs will leave it, and few if any of the nymphs will survive. Of those which are still left in the cotton, and are put with it into the sacks, a further number will effect their escape if the material of which the sack is made is of a coarse texture, such as to allow of their egress through the meshes. The use of such sacks is therefore recommended. Finally, at least ten days should elapse between the picking and the ginning of the cotton, in order that those few bugs still left may be dead, and all danger of their causing discoloration by being crushed may be avoided. If for any reason it is urgent that the cotton should be ginned sooner, leaving the sacks exposed to the sun as much as possible would doubtless hasten the death of the buys. 99

SUMMARY.

Part. I.—Attention is called to the paucity of knowledge of the bionomics of, and damage caused by, species of this genus. They have frequently been classed together with Dysdercus spp. as cotton stainers, whereas the genus Oxycarenus should be known as ''seed- bugs.'' A short summary is given of literature dealing with the injuries caused by them, which shows the widest possible divergences of opinion. Various cotton-feeding species of the genus are recorded from Africa, Asia, Australia, and South America, the majority being from Africa. A few species are mentioned that have been recorded as injurious to plants other than those of the family Malvacese.

Part. II.—0. hyalinipennis occurs throughout Lower and Middle Egypt abundantly. In Upper Egypt it becomes rapidly less common going south. It is also abundant in the cotton growing districts of the Sudan. The limiting factor is probably high temperatures. Nearly 97 per cent of the Egyptian cotton crop is grown in areas where the insect is numerous.

Part III.—The egg is oval, about 0-95X0-28 millimetre in size. It has about twenty-five longitudinal striations, and six small protuber- ances at the anterior end. It is pale yellow at first, becoming pink as the embryo develops. There are five nymphal stages : Dyar's bio- metrical method of checking the number of instars is shown, to apply very closely to this species. All the immature stages are wingless, have only two tarsal joints, and no ocelli. The first three instars are very similar except in size, their respective average lengths being 1-2, 1-53, and 2-25 millimetres. The head and thorax are brownish olivaceous, and the abdomen pinkish. The fourth instar is rather darker brown on the head and thorax, and the wing-buds are distinct, overlapping the sides of the white metathorax. The final nymphal stage has conspicuous wing-buds, considerably overlapping the abdomen. The adult when first emerged is pale pink, but rapidly turns almost black. The male is somewhat smaller than the female, the abdomen terminates in a round lobe, whereas that of the female is truncate. They have three tarsal joints, and a pair of ocelli is present. The hemi-elytra are hyaline, the clavus and base of the cuneus and embolium being rather denser than the rest. The hairs on this insect are of three different types, more or less erect, stiff hairs. — 100 — blunt at the tip, where they terminate in from four to seven small teeth ; normal straight tapering hairs ; and very thin curved flat- lying tapering hairs.

Part IV.—A list is given of the seventeen plants on which the species has so far been found to breed in Egypt, the most important of which are cotton, barnia {Hibiscus esculentus), and til {H, cannahinus). All belong to the family Malvaceae except one, Sterculia diver si folia, a member of the closely allied family Sterculiacese. Breeding can only take place when the seeds of one of the host-plants are available for food ; on cotton it commences as soon as the first bolls open. Copulation lasts for four hours or longer, not always continuously ; in warm weather it is as a rule completed within twenty-four hours. The eggs are laid very soon after copulation, usually in the lint, sometimes on green bolls. The average number laid by one female which has fed on cotton is about twenty. The bugs die very shortly after oviposition. The period of incubation varies with the temper- ature from just under four days at the optimum of about 35° C. to forty-three days at 14-6° C. : there is an indication of a slight increase in the period between the optimum and the maximum temperature of 37-8° C, above which they fail to hatch. All stages of this insect feed solely on the seeds, except that they often drink dew, and occasion- ally suck at the glands on the leaves, in order to obtain moisture. The duration of all five nymphal stages is two weeks upwards, but there is considerable variation, apart from that caused by temperature. The whole cycle, egg to egg, may probably be completed in as short a time as twenty days. There are certainly three, and almost certainly four complete generations during the course of one breeding season. At the end of the breeding season, the adults become quiescent, some at first on the cotton, in bolls, etc. : and all subsequently away from the cotton in such places as the trunks, branches, and leaves of various trees (certain species although apparently suitable are neglected) and coarse grass and weeds ; to which situations they fly in large numbers on warm November days. They are never all completely inactive throughout the winter, on warm days many fly away to neighbouring plants, of which they sometimes suck the sap. At this time of the year they are not attracted to, and will not feed on cotton seed. In April, when the young cotton is well up, many of the bugs leave their former resting places and take refuge on the young cotton plants. They are nearly all to be found within the epicalices of buds, and later, of green bolls. They do not come to the cotton to obtain food, as at most they occasionally suck at the glands on the leaves and they spend the greater part of their time completely quie- scent. Also many of them do not leave their old situations until — 101 - the cotton bolls are ripe, in July or August, and a few even persist in a state of quiescence long after the breeding season has begun. Experi- ments showed, however, that there is no difference in the subsequent behaviour of those which migrate to the young cotton and those which wait until the bolls are ripe. It is considered that all movement on the part of the so-called " quiescent '' bugs during the non-breeding season is stimulated only by climatic conditions, probably a high rate of evaporation being the most influential in causing activity. In the warm weather of April onwards, if the seeds of a Malvaceous plant are provided, breeding will start; but the attractive range of seed is very limited, and cannot therefore be used as a method of trapping the insects. In the absence of food, copulation is sometimes noticed on warm days in the early summer, but it is invariably sterile. The numbers of Oxycarenus which occur in a badly infested cotton field are enormous, seven to twelve million per feddân probably not being an unreasonable estimate for the end of the breeding season. As many as 749 adults and nymphs have been found within a single boll. On bâmia breeding commences as soon as the capsules are ripe : the eggs are more often laid on the outsides of green capsules than is the case on cotton. The average number laid is about thirty, or one- half as many again as when cottdn is the food-plant. On tîl the bugs appear able to penetrate to the seeds of unripe capsules; breeding may therefore be started before the seeds are actually ripe. On Hibiscus mutahilis breeding takes place during the winter, as the plant does not come into flower at Gîza until October or November. On Hollyhock and Sida mollis the breeding season is from April to July ; by the end of July quiescent adults only can be found. On three cultivated species of Abutilón (fruticosum, Thomp- sonii, and venosum) breeding starts about April, the adults feeding on the unripe seeds. At Gîza, however, these plants apparently seldom if ever ripen their fruits; consequently the breeding season on these plants comes to an abrupt close, when the capsules are shed. On Sterculia diversifolia breeding lasts from July to November; during the remainder of the year the adults remain quiescent in the old capsules. The average number of eggs laid is much smaller than observed when the bugs have fed on any other food-plant, being at most ten or eleven. The proportion of sexes is in the neighbourhood of forty males to sixty females, but shows some very remarkable variations according to the time of the year and the habits of the bugs, and the different food plants, which are discussed in detail. — 102 —

Laboratory experiments show that the males are more able to resist extremes of temperature, both high and low, and the females are more resistant to unfavourable, i.e. low, relative humidities. The various tropisms of the insect, of which thigmotropism is the most characteristic, are discussed. Cannibalism has occasionally been observed in the laboratory, both by the nymphs on each other and on the eggs. The results are given of laboratory experiments on the influence of temperature and humidity on the quiescent bugs ; from the point of view of longevity, at temperatures of 30° C. and below, a humidity approaching saturation is the optimum, but above that temperature a drier atmosphere is more favourable. When provided with food, the quiescent bugs in winter can be induced to breed at temperatures of 25° C. to35°C. and humidities of 80-90 per cent. It appears that the bugs of the final generation of a breeding season are unable to reproduce until either a considerable period of rest has intervened, or there is a stimulus of temperature well above the normal : in the case of those bugs which finish their breeding season at the hottest time of the year, e.g. those breeding on Sida or Hollyhock, such a stimulus is impossible, as fatal temperatures would be approached. Sterile copulation in the absence of food can also be induced by high temperatures. The weight of the bugs is shown to decrease steadily from the end of one breeding season to the beginning of the next, this decrease not being checked in the case of those bugs which migrate to the young cotton plants in spring. Although there is normally •little if any transference from one host-plant to another during the course of a single breeding season, the species has not developed into biological races, and an individual which has started its development on one food-plant can readily continue it on another. A study of the life-history on the different host plants has shown that the quiescent period is not connected with either hibernation or aestivation, but is merely a period of rest between breeding seasons, which are influenced only by the time of year that the seeds on the different plants are available.

Part V.—Cotton seeds cannot be recognized externally as having been damaged by Oxycarenus ; but if cut open, an attacked seed will be found to have a discoloured and somewhat shrivelled embryo. The direct loss in weight to the seed is estimated at, at the least, 2-5 per cent under normal conditions : seed of a delayed second picking may have lost as much as 15 per cent or more of its weight. — 103 —

L.E. 100,000 annually is a very conservative estimate of the loss from this cause alone. The extent to which this pest causes non-germination of cotton seed is discussed in detail. In severe cases of attack, and when the picking has been delayed, the vitality of three-quarters of the seed may be destroyed. Experiments on the germination of seeds weighed separately show that, in the absence of damage by Oxycarenus, almost complete germination should be obtained from Sakel : seeds weighing over 80 milligrammes each, but with increasing intensity of attack by this bug, the proportion of lighter seeds is increased, and the germina- tion of the heavier ones is affected. A fungus is frequently present on seeds the vitality of which has been destroyed by Oxycarenus ; but it is of no importance, being purely a saprophyte. Under field conditions the germination, calculated as the percent- age of the optimum germination in an incubator, falls slightly in correlation with reduced weight apart from attack by Oxycarenus, and more so in correlation with the amount of damage by this pest. The germination of bâmia seed is shown to be similarly affected by the attack of Oxycarenus. Slight attack on the radicle, insufficient to kill the seed, does not appear to be deleterious, as the seedling makes up for an initial set- back to its main tap-root by the earlier production of numerous side- roots. If the cotyledons of the seed are pierced by this bug, and the radicle is not at the same time destroyed, the resulting seedling will show S5niimetrical dead patches on the cotyledon leaves. An experi- ment showed that these dead patches, which are never large in area, do not appear to result in any permanent damage to the plant. The ginning out-turn may be raised considerably by the attack of this bug, owing to the reduction in weight of the seed. Possible damage to the lint is discussed, and shown to be of secondary importance. Staining only occurs if cotton is ginned very soon after picking, and there are still living bugs present. If the seed- cotton is left ten days after being picked, all the bugs will be dead and dried up, and no staining can then result. Staining from the excrement is non-existent. A certain amount of dirtiness to the lint results from the dead bodies and cast skins of the bugs, but it is only a small proportion of the dirt usually present from other causes: fragments of leaves, etc. The smell of the bugs is not permanently imparted to the lint. Evidence is given to prove that 0. hyalinipennis does not, as it has been accused of doing, cause either shedding of buds or young bolls, or " mabrouma '' bolls. — 104 —

Part A^L—Tliis bug appears to be immune from either parasites or predatory enemies ; weather conditions are probably the only natural means whereby its multiplication is checked. A fungus has been found growing on the dead bugs, the presence of which does increase the rate of mortality, but apparently only by choking up the spiracles. The most obvious method of control is the elimination of those places in which the insect spends the winter, where it is difficult to destroy it. This would largely be secured by the destruction of weeds on the banks of canals and irrigation channels, a measure which, though it would confer numerous other benefits, is seldom practised. From the trunks of trees and other places where the bugs are collected in large numbers and are easily accessible, they could be brushed on on a cold morning and stamped into the ground. Traps made of- pieces of old sack-cloth tied on to stakes and put round the edge of a cotton field will collect vast quantities of bugs, but the number of such traps necessary for a large field is a disadvantage. Other methods of control, viz. hand-picking, traps of cotton seed in early summer, trap crops of bâmia or til, and the removal of all totally damaged bolls at the time of the first picking, are discussed, but considered either useless or impracticable. The damage to the seed can be curtailed by early picking ; it might conceivably be financially advantageous to take three pickings instead of the usual two. Any damage to the lint can be entirely eliminated by spreading the cotton in the sun, and the use of loose-meshed sacks, to enable as many as possible of the bugs to escape ; and the postponement of ginning for about ten days after picking, so that none of the few bugs still left may be alive, and cause any staining by being crashed. BIBLIOGKAPHY.

(1) ADAIR, E. W.—A Preliminary List of the Insects associated with the Cotton Plant in Egypt. Agrie. Journ. of Egypt, Vol. VIII, 1918. (2 ADERS, W. M.—Zanzibar Protectorate Med. and Sanit. Report, 1913. (3 ADERS, W. M.—Bull. Entom. Research, Vol. X, Part 2, 1920. (4 BALLOU, H. A.—West Indian Bull. Barbados, XVII, No. 4, 1919. (5 BALLS, W. L.—^The Eñect of Seed Weight on the Field Germination of Cotton Seed. Cairo Scient. Journ., No. 47, pp. 185-187, 1910. (6 BALLS, W. L.—The Cotton Plant in Egypt. MacMillan and Co., 1912. (7 BALLS, W. L.—Notes on an Internal Disease of Cotton Seed. Agrie. News, Barbados, 1915. (8: BRAIN, C. K.—Union S. Africa, Dept. Agrie. Pretoria, Loc. Ser. No. 59, 1918. (9; DISTANT, W. L.—Fauna of British India, Rhyncota, Vol. II, 1904. (lo; DISTANT, W. L.—Bull. Entom. Research, Vol. V, Part 3, 1914. (11 DYAR, H. G.—The Number of Moults of Lepidopterous Larvae. Psyche, Vol. V, pp. 420-422, 1890. (12 FLETCHER, T. B.—Rept. Proc. Second Entom. Meeting, Pusa, p. 116, 1917. (13 FOADEN, G. P.—Insects and other Pests Injurious to Cotton in Egypt. Journ. Khediv. Agrie. Soc. and School of Agrie, Vol. I, No. 1, pp. 85-96. (14; FROGGATT, W. W.—Agrie. Gaz. New South Wales, No. 2, 1915. (15; FROGGATT, W. W.—Agrie. Gaz. New South Wales, XXVIII, No. 6, 1917. (16 GouGH, L. H.—On the Effects produced by the Attacks of the Pink Boll Worm on the Yield of Cotton Seed and Lint in Egypt. Agrie. Journ. Egypt, 1919. (17 DEL GUERCIO, G.—Agrie. Colon., Florence, XII, No. 3, 1918. (18 GUERREIRO BEATRIZ, M.—Bol. Agrie. Pecuaria e Fomento, Loanda, 1919. (19 HILL, G. F.—Dept. External Affairs, Melbourne. Bull. Northern Terr., No. 13, 1915. (2o; HORVATH, G.—^Bull. Soc. Entom. d'Egypte, 3me fase, 1910. (21 KING, H. H.—Sudan Entom. Bull., No. 4, 1917. (22 KiRKPATRiCK, T. W.—Preliminary Notes on two Minor Pests of the Egyptian Cotton Crop. Min. of Agrie. Egypt. (In the course of Publi- cation.) (23 MASON, C.—Dept. Agrie. Nyasaland Protect., Zomba, 1915. (24 MAXWELL LEFROY, H.—^Agriö. Res. Inst. Pusa. Occasional Bulletin, No. 2, 1905. — 106 —

(25) MiSRA, C. S.—Kept. Proc. 3rd Entom. Meeting, Pusa, 1919. (26) MiSRA, C. S.—Kept. Proc. 4th Entom. Meeting, Pusa, 1921. (27) MoREiRA, C.—^Entomologia Agrícola Brasileira, 1921. (28) MoRRiLL, A. W.—Plant Bugs injurious to Cotton Bolls. U.S. Dept. of Agrie, Bull. No. 86, 1910. (29) MoRSTATT, H.—Der Pflanzer. Dar es Salaam, IX, No. 5, 1913. (30) MoRSTATT, H.—^Beiheft zum Pflanzen. Dar es Salaam, X, No. 1, 1914. (31) PEACOCK, A. D.—Entomological Pests and Problems of Southern Nigeria- Bull. Entom. Research, Vol. IV, Part 3, .1913. (32) PoMEROY, A. W. J.—Ann. Rept. Agrie. Dept. Southern Provinces, Nigeria. 1920-1921. (33) RUTHERFORD, A.—Rept. Ceylon Dept. Agrie, 1913. (34) SHARP, D.—The Cambridge Natural History. Insects, Part 2, p. 541, 1899. (35) SiCKENBURGER, E.—Insect Life, Vol. Ill, p. 68, 1890. (36) SMALL, W.—^Ann. Rept. Dept. Agrie, Uganda, 1915. (37) THEOBALD, F. V.—Proc. Assoc. Econ. BioL, Vol. I, Part 2, 1905. (38) TOWER, W. L.—Evolution in Chrysomelid Beetles of the Genus Leptino. tarsa. Bull. Carnegie Inst., No. 48, 1906. (39) TRYON, H.—Queensland Ann. Rept. Dept. Agrie, and Stock. 1916-1917. (40) WiLLCOCKS, F. C.—Notes on the Egyptian Cotton Bug or Cotton Stainer. Year-book Khed. Agrie. Soc, Egypt, 1906. (41) WiLLCOCKS, F. C.—The Insect and related Pests of Egypt. Vol. I, Part I, The Pink Boll Worm. 1916. (42) WiLLCOCKS, F. C.—A Survey of the more Important Economic Insects and Mites of Egypt. Bull. No. 1, Suit. Agrie. Soc. Cairo, Egypt, pp. 31-33, 1922. (43) WiMSHURST, C. R.—Admin. Rept. Agrie. Div. Mesopotamia, 1919. (44) ZoLOTAREVSKY, B. N.—Prelim. Rept. on the Work on Entomology in 1914. Stavropol-Caucasian Agrie. Exper. Station, Stavropol, 1915. '\0*

EXPLANATION OF ARABIC TERMS IN THE TEXT.

Bâmia Hibiscus esculentus, a Malvaceous plant extensively used as a vegetable. Bersîm Egyptian clover, Tri folium alexandrinum. Feddân 24 qirâts= 1-038 acres. Fellahîn .. Egyptian peasants. L.E Pound Egyptian=£ 1 Os. 6d. Mabrouma. Lit. twisted, used of cotton bolls that have failed to fuzz out properly, or have dried prematurely and contain no pickable lint. Misqa Small permanent irrigation channels. Qantâr Of ginned cotton : 100 rotls=:99 lbs. Of unginned cotton: 315 rotls=312 lbs. Qirât 2^4 of a feddân=209-3 square yards. Rotl ... . 0-99 lb. Taqâwi Seed for sowing. Tîl Hemp, Hibiscus cannabinus. Tugâri Of cotton seed, that which is sold for commercial purposes. \oS-

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S- of £. 2.3/336. FIG. 33.—An unattacked cotton seed.

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/ \ Probable tot&/ germinst/on \ /cas than 10 % , / \ \ \ / \ ; ^¿7 - / >^\-J^JÏl/^^>^v3V^'5i;, ^o\^\ / \ / \ / \ ■ / \ / \ / \ / / / V /1 \ ~ / \ \ /1 \ I / \ so / \ / / \ / \ / \ / \ / \ / \ - / \ / \ o \ cu • \ 0) 1 \ t \ 1 \ 1 \ 1 1 \ 1 \ 1 \ / V / / \ c: / \ / \ O / t. / / \ / \ \ \ \ 1^ 1 1 1 1 -1 1 1 ! liJ I \ . t'i^^ 51-60 ei-70 7Í-80 ai-90 9t-100 W1-11Q 111-120 IZt'I^O 131-1^0 l'élise Í51-1GO Weight -groups, (Miifigrammes.)

GERMINATION EXPERIMENT N? 26. YV ¿>-;oU^3^^^ 3^>i;t_JJÜL\,jj J.—J|\ iijj o'-t\ T•<>^ v.--v\ ^.-v\ s-i\\ \—\\ \\-\-\ \\-\\\ \t-\^ M-vt» \»-»i\ \-v--\o> 7Oí;

■*í-3o sr-eo ei~7o VI-BO ai-90 91-100 101-110 tii-120 1Z1-130 isi-i'ho iti-iso 151-ieo Weight-groups, (Milligrammes ) GERMINATION EXPERIMENT N°27. Tig^. 43 0"i\ V-oS V..n\ A.-W i\.-M \..'\\ S\.'\-\ \\.'\\\ Nt'-NtN \ï-\r\ »»•-\t\ M- -N0\ 100 1 1 1 1 1 ( i 1 1 i 1 ■ 1 >••:

r-x v - so h - / - \ \ î / "'. \ / di' / \. 1 ao ■•>. : / J / / y ,7 / V.. - 7 o Í / .3 / / / ,60 / ■\" / / / 20 0 ..- - 50 ■V' f'

■ // / / / / 1- fô ->o 1

Í • 30 < r-- o I / / ; v^ 10 -V • S. / / r—-^ \ / / r-- o / / / / \ 5 -o / / \ / / w ^» - /O ^ c; / y O t. ,>-' •-■' ' /

a , / i ( 1 1 1 1 1 1 1 . ■ ^7-30 S1~GO 37-70 7730 8790 91-700 707-710 777-720 7Z1-13Q 137-7^0 14-1750 15/-/60 Weight-groups (MHIîgnam mesJ

GERMINA TI ON EXPERIMENT N? 28.

S.or E.23/336. Fig. 45.