HARVARD UNIVERSITY LIBRARY OF THE Museum of Comparative Zoology tX>- Sc.79.7T VOL. 14 - 1 *- ' % a. "L )f PART 10 OF THE SOCIETY FOR BRITISH ENTOMOLOGY World List abbreviation : Trans. Soc. Brit. Ent. CONTENTS. Edward Broadhead The Biology of Psoquilla marginepunctata (Hagen) (Corrodentia, Trogiidae) Date of Publication, 30th November 1961 Copies may be purchased from the Publications Secretary, Department of Entomology, The Museum, Manchester 13 Price 7/- post free Published for the Society by the British Trust for Entomology Ltd. BRITISH TRUST FOR ENTOMOLOGY LTD., 41 QUEEN’S GATE, LONDON, S.W.7. LIST OF PUBLICATIONS FOR SALE (ALL PRICES ARE POST FREE) TRANSACTIONS OF THE SOCIETY FOR BRITISH ENTOMOLOGY GENERAL A New Chapter in Zoological Nomenclature : The Reforms INSTITUTED BY THE THIRTEENTH International Congress of Zoo¬ logy, Paris, July, 1948. By F. Hemming, 1950. 8 pp., Is. 6d. The Problem of stability in Specific Nomenclature, with special reference to cases where TYPE MATERIAL IS NO LONGER IN existence. By F. Hemming, 1951. 16 pp., 2s. Od. Some adaptations of insects to ENVIRONMENTS THAT ARE ALTERN¬ ATELY DRY AND FLOODED, WITH SOME NOTES ON THE HABITS OF THE Stratiomyidae. By H. E. ninton, 1953. 20 pp., 3 figs., 5s. Od. The terms “Larva” and “Nymph” in Entomology. A summary of the views of W. E. China, H. Henson, B. M. Hobby, H. E. Hinton, T. T. Macan, 0. W. Richards, T. Southwood, and V. B. Wigglesworth, followed by a review of The Terminology of Juvenile Phases of Insects by R. G. Davies, 1958. 10s. Od. ENTOMOLOGICAL FAUNA OF THE NEW FOREST SERIES Introduction by J. Cowley, and Part 1, Odonata, by Lt.-Col. F. C. Fraser, 1950. 12 pp., Is. 6d. Part 2, Neuroptera, by Lt.-Col. F. C. Fraser, 1951. 12 pp., Is. 6d. EPHEMEROPTERA Descriptions of some Nymphs of the British Species of the Genus Ba'etis. By T. T. Macan, 1950. 24 pp., 6 figs., 2 tables, 3s. Od. A Description of the Nymph of Ba'etis buceratus with notes and A KEY TO OTHER SPECIES IN THE genus. By T. T. Macan, 1957. 8 pp., 3s. *6d. The Life Histories and Migra¬ tions OF THE EPHEMEROPTERA IN a stony stream. By T. T. Macan, 1957. 28 pp., 12s. 6d. ORTHOPTERA, Etc. A Summary of the Recorded Dis¬ tribution of British Orthop- teroids. By D. K. McE. Kevan, 1952. 16 pp., 5s. Od. HEMIPTERA-HETEROPTERA Contributions towards an Ecolo¬ gical Survey of the Aquatic and Semi-Aquatic Hemiptera- heteroptera of the British Isles. Scottish Highlands and East and South England. By E. S. Brown, 1948. 45 pp., 7s. 6d. The Ribble Valley (Lanca¬ shire South and Mid). By E. J. Popbam, 1949. 44 pp., 1 map, 8s. Od. North-East Wales (Denbigh¬ shire and Merionethshire). By E. J. Popham, 1951. 12 pp., 2s. 6d. The Hemiptera-Heteroptera of Kent. By A. M. Massee, 1954. 36 pp., 7s. 6d. The Bionomics and Immature Stages of the Thistle Lace Bugs ( Tingis ampliata H.S. and T. cardui L. ; Hem., Tingidae). By T. R. E. Southwood and G. G. E. Scudder. 8s. Od. COLEOPTERA The Aquatic Coleoptera of North Wales. By E. S. Brown, 1948. 15 pp., 1 fig., Is. Od. The Aquatic Coleoptera of Wood Walton Fen, with some com¬ parisons with Wicken Fen and SOME OTHER EAST ANGLIAN FENS. By F. Balfour-Browne, 1951. 36 pp., 4s. 6d. TRANSACTIONS OF THE SOCIETY FOR BRITISH ENTOMOLOGY VOL. 14 NOVEMBER 1961 PART X The Biology of Psoquilla marginepunctata (Hagen) (CORRODENTIA, TrOGIIDAE) By Edward Broadhead (Department of Zoology, Leeds University) The genus Psoquilla Hagen 1865 is grouped by Roesler (1944) with Rhyopsocus Hagen and Eosilla Ribaga in the subfamily Psoquillinae of the Trogiidae. Two species have been described — - Psoquilla marginepunctata Hagen 1865 and a very closely related form P. infuscata Badonnel 1949. The literature on P. marginepunctata is very sparse and consists almost entirely of descriptions of the adults and of locality records. This species has clearly been widely dispersed by commerce and its country of origin is unknown. It has been reported from Paraguay (Ender- lein 1919), Brazil (Roesler 1940), Bermuda (Verrill 1902 under the name Heteropsocus dispar ), Hawaii (Williams 1932), Kuala Lumpur (Pearman 1935), England (Pearman 1931, Broadhead 1954) and from various parts of Africa (Belgian Congo, Gold Coast, Ivory Coast and Angola) by Badonnel (1949a, b, 1955). I can find no clear statement in the literature of its occurrence in North America, but it has no doubt been introduced there as well. Records of its habitat are very few. In England it is confined to stored products. Badonnel records the specimens from the Belgian Congo from a weaver bird’s nest and from the trunk of a diseased Croton tree and Roesler’s Brazilian specimens were found under bark. On 7th November 1952, I received from the inspectors of the Ministry of Agriculture and Fisheries a single micropterous female of P. marginepunctata, which lived for a week and laid 25 eggs. Three generations were reared and many hundreds of specimens obtained. The present study was carried out on this living material and was brought to an end by the rapid decline of the cultures during the fourth and fifth generations, apparently the result of increasing infertility. The animals were reared initially in observation cells made from aluminium strips 1 mm. thick bored with holes 1*5 cm. in diameter. The floor consisted of black bolting silk fixed to the strip by means of a solution of celluloid in amyl acetate and a glass cover slip secured by paraffin wax served as a roof. Several strips were supported on glass rods about 2 cm. above saturated sodium chloride solution in a shallow glass dish fitted with a plate glass lid and sealed with vaseline. In this way a constant relative humidity of 76% was maintained and the animals could be observed without disturbing the humidity, if so desired. The food supplied 224 [November throughout was a mixture of crushed dried yeast (“Aluzyme” tablets) and a little tropical fish food consisting chiefly of dried Daphnia. Oviposition The ovipositing behaviour of a female in one of the cells already described was observed under a binocular microscope. The female walked around the cell and on several occasions stopped and moved backwards slightly, so pushing the tip of the abdomen into the angle formed by the wall and floor of the cell, and at the same time raising her thorax and thus allowing the abdomen to be more effectively bent downwards to bring the genital opening into contact with the substratum. The gonopods were moved relative to the subgenital plate by means of a backward move¬ ment of the lateral portions of the sclerotized last abdominal tergum, to which the gonopods are attached. The gonopods, which in this species consist of only a single pair of hairy lobes, also moved up and down and their long hairs came in contact with the substratum on which the egg was subsequently laid. The egg was now extruded, its blunt end being the first to appear. Since the gonopods could be seen lying dorso-laterally along the egg, it appears likely that they play an important part in forcing the egg firmly down on the substratum to which it adheres. Immediately afterwards, the female moved backwards over the egg and scattered debris on to its still wet and sticky surface by vigorously kicking with its hind legs, a process which has also been observed in Embidopsocus enderleini (Ribaga) (Broadhead 1947). All these events took place in less than five minutes. The Egg The egg (fig. 2) is ovoid, elongate and bilaterally symmetrical. Its anterior pole tapers and is slightly upturned, the posterior pole being rounded. Three prominent longitudinal ridges are present, one median (mid dorsal), the others dorso-lateral, which, viewed in profile, are seen to carry a series of very short denticles. The chorion is white, semi-transparent and sculptured with regular hexagonal areas. The eggs take on a pale brownish tinge within a few days. Their dimensions are: length, 0-39-041 mm. (7 eggs); breadth, 0T9 mm. (1 egg). The eggs are laid singly. In observation cells they were always laid either in the angle between the side and floor or in crevices provided by the particles of food. No silken threads are ever produced by this species in the nymphal or the adult stage. The duration of the egg stage at 25° C. (40 eggs) is 8-11 days, and averages 9-6 days. Pearman (1927) has described and figured the eggs of three species of Trogiidae, Trogium pulsatorium (L.), Lepinotus inquilinus Heyd. and Cerobasis guestfalicus Kolbe, all belonging to the subfamily Trogiinae. The eggs of Psoquilla show the distinctive Trogiid features of an acutely pointed anterior end, bilateral symmetry and sculpturing of the chorion. The demarca- 225 1961] tion of the rupture line, also mentioned by Pearman as a characteristic feature, is not obvious in Psoquilla. The chorion is cut by the egg burster along the prominent mid-dorsal ridge, but the anterior and posterior limits of the rupture, indicated in fig. 2b, are not marked by any structural feature. The Psoquilla egg differs from these others in the presence of only three longi¬ tudinal ridges and in the finer sculpturing of the chorion. The sculpturing into regular hexagonal areas resembles that in T. pulsatorium, where the areas are however larger. In the sub¬ family Psoquillinae, the egg is known in only one other species — Rhyopsocus bentonae Sommerman. This is figured by Sommerman (1956) and shows a closer resemblance to the Psoquilla egg than do these other Trogiids. The median ridge is well developed but the lateral ridges with their denticles are evident only towards the anterior end and the sculpturing is represented by a wrinkling of the chorion. Nymphal Instars The presence of 6 nymphal instars was established by daily examination of isolated individuals in observation cells from the egg to the adult stage and by the application of Dyar’s Law to measurements of the width of the head capsule. Colour (fig. 1) The 2nd-6th instars all have a characteristic and striking colour pattern, which is very different from that of the adult. The body is yellowish with an extensive brown area on each side of the head postero-laterally, with blackish brown patches laterally on the meso- and meta-thorax, and with reddish brown pigment on abdominal terga 2-7 laterally, this pigment progres¬ sively extending medially until it forms a complete or almost complete transverse band across the mid line on the 5th tergum. Brown patches are also present on the last abdominal tergum and the wing pads in the last two instars are dark brown with a whitish tip. The legs are pale yellow to whitish with a broad annular brown band on the proximal half of the 1st tarsal segment and another on the distal half of the tibia. The markings of the 2nd and 3rd instars, particularly on the head and legs, are paler and less extensive than those of the later instars but the charac¬ teristic abdominal pattern is clearly visible. First instar nymphs have a whitish, semi-transparent body and a pale brown head with orange brown pigment laterally on the thorax and on the vertex of the head but with no abdominal colour pattern. Structural features In the nymphs observed, which developed into micropterous males and females, wing pads (of the forewings) first became recognisable in the 4tli instar (fig. 1), and in the last instar nymph they projected backwards over the first 3 abdominal 226 | November Figs. 1-2. — Egg and nymph of Psoquilla marginepunctata. (1) 4tli instar nymph to show colour pattern. (2) egg (a) dorso-lateral, (b) dorsal and (c) lateral view, (d) the sculpturing of the chorion, linear magnification of 3 times figs, (a)-(c); mr, median ridge, lr, lateral ridge, e, extent of rupture along mid dorsal ridge at hatching. terga. In last instar nymphs of macropterous forms, the developing hindwings are almost as large as the forewing pads and extend backwards as far as the 5th tergum. The number of antennal segments increases gradually during nymphal life by subdivision of the segments at ecdysis. There are 9, 14, 16, 18 and 21 antennal segments in the lst-5th instars respectively and 22 in both the 6tli instar and the adult. The ten nymphs of each stage examined, which were reared in isolation, showed no variation in this feature. The adults examined, which were taken from crowded vial cultures, showed considerable variation, many of them having fewer than 22 segments. Since the terminal segment appeared normal, this was probably due to damage of the antenna during nymphal life. The nymphal instars can be distinguished from each other by measurement of the width of 227 1961] the head (including the eyes), since the ranges of variation of this character (Table 1) do not overlap in successive instars. Head width is greater in females than in males for all instars except the first, the difference increasing as growth proceeds. Table 1. — Width of head capsule (mm.) of micropterous females and males of Psoquilla marginepunctata Instar 1 Mean (N = 15) females Observed extremes Mean (N = 15) Males Observed extremes 1 0-185 0-174—0-191 0-186 0-183— 0'-189 2 0-223 0-212— 0-228 0-221 0-216—0-225 3 Of 263 0-256—0-267 0-259 0-253—0-264 4 0-309 0-304— Q-314 0-300 0-295—0-305 5 0-362 0-354—0-367 0-341 0-333—0-347 6 0-418 0-408—0-432 0-388 0-378—0-394 Achilt 0-476 0-459—0-489 0-425 0-417—0-434 Duration of instars Newly hatched nymphs were reared separately in observation cells on the dried yeast /dried Daphnia food mixture at 25° C. and 76% R.H. and the moults were recorded by daily examina¬ tion. The mean durations of each stage in days (15 individuals of each sex, all micropterous) for females and males respectively are: 1st instar 3-6, 3-4; 2nd instar 2-6, 2*7; 3rcf instar 2-5, 2-4; 4th instar 2-9, 2-7; 5th instar 2-8, 2-7; 6th instar 4-2, 4T, and total nymphal life 18-60 ± 0-23, 18-00 + 0*30, the difference between these means being only doubtfully significant. It may be noted here that adult life is relatively long compared with nymphal life, the maximum duration of adult life (4 females) under these conditions being 75 days. Bisexual Reproduction Fourteen freshly emerged virgin females were enclosed separately in cells for a period of 13 days, during which time each female laid between 3 and 23 eggs. A total of 161 eggs was laid. All these unfertilized eggs collapsed within a few days. Mated females under the same conditions laid many eggs and these fertilized eggs all hatched within 11 days. Facultative partheno¬ genesis does not, therefore, occur in this species. Mating Behaviour and the Spermatophore The following account is based upon observations of the mating behaviour of 13 pairs, eight being micropterous females with micropterous males and five being macropterous females with micropterous males. No differences in behaviour were found between these two types of cross. Virgin individuals 2-7 days old were selected. The male was introduced into a cell containing the female and the subsequent events observed through a binocular microscope. 228 [November Male and female met and often touched one another while walking round the cell before the characteristic courtship behaviour started. After two or three such accidental meetings the male became more active, moving about more rapidly and more abruptly, and frequently stopped to carry out a series of flicking movements of the wings. The wings were raised over the abdomen at an angle of about 45°, moved rapidly up and down many times through an arc of about 20° for 2-3 seconds and were then returned to the normal resting position lying flat over the abdomen. In the intervals between this flicking of the wings, the male usually resumed his short darting movements around the female. Occasionally both male and female remained quite motionless for a minute or more. This behaviour was repeated many times. As courtship proceeded, the wing flicking was carried out more frequently and more vigorously, the wings not now being restored to the normal resting position in the intervals but held slightly raised at an angle of about 30° to the abdomen and slightly extended laterally. The last stage of court¬ ship was marked by a continuous and vigorous flicking of the wings which were directed almost vertically and moved through a much wider arc. The male, usually at this time in front of the female, then turned round and moved backwards beneath her, his upraised wings being displaced into a forwardly directed position lying flat over his head. Coitus was then effected. The female accepts the male by keeping her ground and slightly raising her body as the male moves back beneath her. In one of the pairs observed, the male carried out the last series of wing vibrations behind the female. She turned round to face him and he then turned round and moved backwards beneath her. Courtship lasted from 3 to 22 minutes. Neither sex flicked the antennae, and the females were never observed to flick their wings during courtship. Almost immediately after genital contact, the male twisted round through 180°, sometimes to the left and sometimes to the right side of the female, so that the animals faced in opposite directions, the tip of the male abdomen having rotated through at least 90°. Orientated thus, the female often walked about, dragging the male behind her. During the whole period of coitus, which lasted 25-48 minutes, continuous distending and contract¬ ing movements of the abdomen of the male took place, involving a separation and approximation of the basal rods of the male genital armature. This armature, easily seen through the semi¬ transparent sterna, is protruded only slightly during coitus, its distal end being inserted between the female gonopods. The separation of the sexes after coitus was observed in 8 pairs. In three of them, a spermatophore was projecting from the tip of the male abdomen as the sexes separated. It was quickly extruded and left behind on the floor of the cell. From its lack of opacity it appeared to be empty. In the other five pairs, no spermatophore was visible at the apex of the male 229 1961] abdomen when the sexes separated, but the male extruded a spermatophore within half a minute. In one case a meniscus appeared and passed quickly down it as it was extruded. The concavity of the meniscus indicated that the contents were being withdrawn into the body, so that when the spermatophore was finally shed it was empty. In the other cases, bubbles appeared in the distal end as it emerged from the abdomen and quickly increased in number. Four of these females were used in the oviposition experiment described below. They laid fertile eggs from which nymphs were obtained. Since this species cannot reproduce parthenogenetically, sperms were transferred from male to female during these copulations without the transference of the spermatophore and this appears to be the normal condition in this species. The spermatophore here may be a vestigial structure or perhaps may function as a delivery tube through the narrow end of which the sperms are forced into the spermathecal orifice of the female. Discharged spermatophores, many of them partly eaten, were found in numbers in the vial cultures of this species, but I have never observed any in vial cultures of many Liposcelis species, of Lepinotus patruelis Pearman, L. inquilinus Heyd. and L. reticulatus End., of Trogium pulsatorium (L.) and of Myopsocncma annulata (Hagen). The deposition of the sperma¬ tophore by the male after coitus has, however, been recorded by Sommerman (1956) in Rhyopsocus bentonae and in Psoca- tropos lachlani Rib. as well as in Psoquilla marginepunctata. The spermatophore is an elongate, colourless, transparent tube, smooth externally, pointed at the end which is first extruded from the abdomen of the male, and rounded at the other end. Length 0-43 mm., width 0*12 mm. The similarity of wing colour and pattern in both sexes suggests that this colour pattern has no significance in courtship, and moreover, mating takes place successfully in complete dark¬ ness. Vigorous flicking of the wings is a characteristic feature of courtship in many species of winged psocids. In apterous species, such as Liposcelis , these are replaced by a similar pattern of flicking of the antennae (Broadhead 1952), so that females are probably receptive to the vibrations produced by these rapid movements rather than to any visual stimulus. Oviposition Rate Four micropterous virgin females 2-7 days old were enclosed with males. Copulation was observed. The males were then removed and the females enclosed separately in observation cells at 25° C. and 76% R.H. with dried yeast and dried Daphnia as food. Thev were transferred each day into other cells with fresh food and the number of eggs laid was recorded. All these eggs were incubated until the fertilised ones hatched and the infertile ones collapsed. [November 230 Fig. 3. — Oviposition and life span of four micropterous females of Psoquilla marginepunctata . (a) two females mated once; (b) two females mated twice; first mating on day zero, the arrows indicate second mating. The total number of eggs laid is plotted, for each female, against the number of days from the initial mating in fig. 3. In two of the females (fig. 3a), oviposition resulting from the one mating was observed throughout life. Within 4 days the oviposition rate had increased to a level (8-9 eggs per female per day), which 231 1961] then remained constant for the next 14 days. All these eggs were fertile. The rate then abruptly declined to zero over a period of 3-4 days, when some unfertilized eggs were laid, which soon collapsed. A fairly long post-reproductive period followed (10 and 19 days respectively). These two females lived for 30 and 38 days. In the other two females (fig. 3b), oviposition resulting from the first mating followed a very similar pattern. A few days after egg laying ceased, a male was introduced to each. Oviposition started again immediately, although now at a lower rate, this latter falling off gradually to zero, when again some unfertilized eggs were produced. These two females lived for 61 and 68 days. Together, they laid 304 eggs as a result of the initial mating and a further 269 after the second. The second mating appears, therefore, to have prolonged the female life span considerably and almost doubled the number of eggs laid. More¬ over, since fertilized eggs were laid up to the end of each oviposi¬ tion cycle, living sperm must have been stored by these females for 18-27 days. The oviposition of a single macropterous female under the same cultural conditions was very similar to that of the micropterous females up to the 20th day after mating when records were discontinued. Sex Ratio and Polymorphism Progeny were reared from micropterous males and females under two cultural regimes to find out whether environmental factors play any part in determining the ratio of the sexes and the proportions of the four polymorphic types. In both cases the same food mixture of dried yeast and dried Daphnia was used, and both were maintained at 25° C. and 76% R.H. In the first cultural treatment the eggs, laid by the four micropterous females in the oviposition experiment described above, were reared to the adult stage in observation cells, the food being renewed every few days. Densities wTere not controlled, 1-10 adults being obtained from each cell. 468 adults were obtained. In the second treatment, cultures were set up in 3" x 1" glass tubes covered at the top with bolting silk. The food was spread over the circular floor of the vial to a depth of about 2 mm.; a strip of filter paper 2 cm. x 6 cm. was introduced and each of the 7 vials was supplied initially with 2-8 pairs of animals. The food was not renewed and the vials were disbanded after 7-8 weeks (about one generation), when the sex and type of the 1772 adults and last instar nymphs present were recorded. The 215 nymphs of earlier instars were discarded. The results are set out in Table 2. The sex ratios ( 9 : 6 ) among the progeny are the same in both treatments — for the cell cultures TO and for the vial cultures 0-95, which does not differ significantly from unity (X2 = T093, P = 0*30). The proportions of macropterous and micropterous forms show a striking difference. In the cell cultures, micropterous forms predominated 232 [November with only a small proportion (4-3%) of fully winged individuals, all females, this proportion varying in the replicates from 0-8%. In the vials 42-9% of all individuals were fully winged, the proportion varying from 25-50%, and these, moreover, included a small number of macropterous males. There is no doubt that crowding and contamination of the food were eventually much greater in the vials than in the cells, so that the appearance of macropterous forms, the majority of which are females, seems to be related to progressively more unfavourable conditions. The adaptive nature of this population response is evident. It is likely that this species in nature lives under bark or in birds’ nests, that is, in habitats which are both ephemeral and highly circumscribed, so that the population will sooner or later exhaust, as well as contaminate, the food supply, and new habitats must be found. Under such adverse conditions, winged females will be produced in large numbers and, since females are able to mate very shortly after emergence, the majority will probably mate before leaving the colony, and thus the number of fully winged males required would be very small. Table 2. — Sex and type of offspring reared from micropterous individuals of P so quit la marginepunctata under two cultural regimes (a) Numbers of individuals of the four types in Macropterous Micropterous total cells female male female male individuals 1 2 0 35 51 88 2 0 0 47 47 94 3 11 0 61 67 139 4 7 0 71 69 147 Total 20 0 214 234 468 in vials 1 19 0 13 44 76 2 41 2 4 32 79 3 72 2 9 98 181 4 102 2 41 126 271 5 138 2 13 164 317 6 161 2 30 211 404 7 212 5 9 218 444 Total 745 15 119 893 1772 (b) Proportions of the four types expressed as percentage Culture Macro] pterous Micropterous method female male female male cells 4-3 0-0 45-7 50-0 vials 42-1 0-8 6-7 50-4 1961] 233 Variation in Wing Length Psoquilla marginepunctata is the only psocid so far known which has a well defined wing dimorphism with no intergrades in both sexes. The existence of these four types of individual in this species was first recognised by Roesler (1940) from pre¬ served material collected in Brazil. A biometric study of the variation in length of the forewing in each of these four types has been carried out on the specimens reared in the laboratory. From the original single micropterous female, four females and four males were reared and these four brother-sister pairs gave a second generation of adults, all short-winged, from which the measurements of the micropterous males and females were obtained. The macropterous specimens measured were all derived from the third generation of adults. All these individuals were, therefore, highly inbred so that the variation recorded here may be greater (than that occurring in any single wild population. Only 17 macropterous males were available for study, but measurements of the forewing length of 150 individuals were made of each of the other three forms. The frequency distribution of wing length is recorded graphically in fig. 4 and the mean lengths and coefficients of variability with their standard errors are given in Table 3. The coefficient of variability V = — — , where M is the mean and