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Use of antihypertensive medications appears to preserve cognition in older African Americans, according to results of a study funded by the National Institute on Aging, the largest longitudinal study of [...]

The efficacy and safety of gabapentin as add-on therapy for refractory partial seizures in 237 children, aged 3 to 12 years were evaluated over a 6-month period. All children received gabapentin at 24 to 70mg/kg/day. Efficacy variables included the percent change in seizure frequency and the responder rate (defined as those patients who showed >50% reduction in seizure frequency). For all partial seizures, the median percent change in seizure frequency was –34% and the overall responder rate was 34%. Simple partial seizures showed a median reduction of –53%; complex partial seizures, –38%; and secondarily generalized tonic–clonic seizures, –35%. Thirteen patients (5%) withdrew during the 6-month period because of adverse events. Concurrent antiepileptic medication remained unchanged in 185 patients (78%), was decreased in 27 (11%), and increased in 25 (11%) patients. This 6-month follow-up study has demonstrated that gabapentin was well tolerated and appeared to show a sustained efficacy in a large population of children with refractory partial and secondarily generalized tonic–clonic seizures.

Dispersal of Larus novaehollandiae Stephens, from 10 colonies in South Australia, was studied during 1968-8 1 by means of bands designed for identification of free-living, uncaptured individuals. Dispersal patterns were characteristic of each colony, even for three colonies which were, at most, 10 km apart. Almost all dispersal records came from the area between Adelaide and Melbourne, and within 30 km of the coast. After breeding, the majority of gulls disperse eastwards; however, dispersal from each colony was correlated with a shift of gull population into areas where food was available from human sources such as rubbish dumps. From colonies 80 km south-east of Adelaide, a major human population, the predominant winter dispersal of these gulls was north-west, into the city and suburbs. The maximum direct-line dispersal distances recorded for 95% of the 3133 resighted gulls were <458 km. The greatest direct-line distance recorded was 1430 km. Overall, there was no significant difference in the mean dispersal distances of juveniles and adults, although at distances >480 km significantly more juveniles (<2y) were seen than adults (>2y). This involved only 2.5% of the total number of birds resighted. It is suggested that older, dominant birds maintain high status at preferred feeding places, and juveniles are possibly more erratic in their movements, as they search for food. This would account for the difference in the dispersal ofjuveniles and adults from a particular colony, and also for the significantly higher proportion of juveniles found at extreme distances from their natal colonies.

Daily light-trap collections of female C. brevitarsis were made at three localities along the northern coastal plains of New South Wales. Numbers increased during spring, were maximal in summer, declined during autumn and were minimal in winter. The generation time was about 3-4 weeks in the summer and several cohorts of nulliparous midges, probably representing different generations, were detected from spring to autumn. Some breeding continued throughout the winter. Summer abundance appeared to be associated with high rates of reproduction in late spring or early summer, and this occurred when rainfall was adequate for good pasture growth. Midge survival was better in the summer than in other seasons of the year, and numbers of parous females increased rapidly whenever it rained, probably due to their increased survival and longevity. At each locality, numbers fluctuated throughout spring, summer and autumn, with peaks and troughs of abundance which were often not obviously associated with concurrent climatic conditions or cattle movements.

Field surveys established that C. brevitarsis has a megathermic distribution. The GROWEST model of Nix was modified to reflect the temperature requirements of the midge, and a data bank was created of daily rainfall over 20 years, 1965-84, from 130 localities scattered across New South Wales. The environmental indices calculated were correlated with extensive field data on seasonal abundance of C. brevitarsis collected from 11 localities, and further checked against survey data collected from 1963 to 1984. The seasonal and annual distributions of potentially suitable environments for the midge, derived from the model, agreed well with field observations. Areas suitable for summer multiplication and winter survival were identified, and regions favourable for survival of breeding population, defined as being enclosed within 'brevitarsis lines', were determined for the spring of each year. In the wet years, 1973-78, these regions increased in size to the west and southwards along the coastal plains. In the drought, 1979-83, they conrracted to the upper Darling Basin and coast. The model enables extensions in the distribution in the summer to be analysed to determine whether they are due to local or long-distance dispersal, and has considerable application in analyses of epidemics of arboviruses of which C. brevitarsis is a vector.

C. brevitarsis 'rested' in the ground herbage during the day and flew just before dusk and during the evening and night, when air temperature was above 18C and wind velocity was below 8 km h-'. More females were caught in light traps with 6-V 18-W globes than with 7.2-V 3-W globes. Only the light ventral to the traps played a part in catching this biting-midge. More were captured with the 120-traps, which illuminated a 10-m circle of herbage beneath, than with 40-traps, which illuminated a 2-m circle. Covering up to 20 by 20 m of the ground beneath 40-traps with opaque plastic or setting these traps in ploughed paddocks, 40 m from any ground herbage, gave collections of females similar in numbers and population structure to nearby collections over grass. Nulliparous and parous females, empty, blood-fed and gravid, were captured at 2, 4 and 6 m above the ground. Females were shown to congregate around cattle to feed, to oviposit, and to maintain contact. Dispersal in the wind is an integral part of the biology of C. brevitarsis.

An investigation was undertaken to determine the species of blood-sucking flies which feed on sheep. Engorged insects were collected by a number of methods and their blood meals were identified by precipitin and haemagglutination inhibition tests. Sixteen species of mosquitoes attacked sheep, and of these Anopheles annulipes and Culex annulirostris dominated. Twelve species of biting midges in the genera Culicoides, Leptoconops and Lasiohelea were shown to bite sheep; the dominant species were C. marksi and C. breuitarsis. The simuliid Austrosimulium pestilens and the muscid Stomoxys calcitrans also fed on sheep. Some of these species also fed on other hosts-eight on ox, five on marsupials and one on horse. Four of the most widespread Culicoides species, C. brevitarsis, C. dycei, C. marksi and C. victoriae, fed on both sheep and ox, a factor of epidemiological significance in their potential role as vectors of arbovirus diseases of livestock.

Aspects of the reproductive ecology of silver gulls, Larus novaehollandiae Stephens, were studied in South Australia during 1968-78. Some 15 950 pulli and 597 breeding adults were banded on 15 colonies, using numbered and coloured leg bands designed for identification of free-living individuals without the necessity of recapture. Nine colonies were on marine islands, four were on lacustrine islands, one was on a port breakwater, and one was on causeways in a saltworks complex. Fidelity to colony, mate and nest-site, and timing of breeding are considered in detail. The spatial relationship of adult and immature gulls, on the colony studied in greatest detail, and reproductive longevity of the gulls are also discussed. The gulls nested from June to December inclusive, although the commencement and length of breeding seasons varied between colonies and between years. There was a marked absence of 1-year-old gulls on breeding colonies. Of 3530 pulli banded on the major study colony, Penguin Island (3730''S., 14001''E.) at Beachport, in 1968, 950 were known to be alive in the 1970 breeding season. Almost 40% of these 2-year-olds were seen on breeding colonies, and mostly on the natal colony; however, only 0.3% were known to raise pulli, and a further 0.7% to produce eggs. Significant breeding activity therefore did not commence until the end of the third year, or later. The older, previously established breeders on Penguin Island were significantly more successful, and had significantly earlier laying dates, than younger birds. Potential reproductive longevity appears to be at least 11 breeding seasons. In this study, silver gulls showed considerably less fidelity to nest-sites and colonies than has been suggested previously. Significant shifts of nest-site, or change of colony, with or without the previous mate, were not uncommon. Of gulls banded on nests as established breeding aduls, 7-44% of gulls found breeding in subsequent years were at colonies other than the one where banded. In 1970, over 80% of 2-year-old gulls recorded present on any colony were only recorded on the natal one. Of the pulli banded on Penguin Island in 1968 and 1969 and later found actually nesting or breeding, 18% were recorded on other colonies. A small percentage of gulls were seen to have high fidelity to nest-site and to mate over 3 or 4 seasons, but it is suggested that, for some colonies, over 50% of silver gulls which eventually breed may do so at colonies other than natal. Significant spatial separation was found on Penguin Island between areas generally occupied by established breeders, which were known to be at least 4-year-olds, and by the 2-year-olds. The older birds may select and hold the territories most suitable for nesting, where vegetation or topography minimise intraspecific aggression which often leads to high mortality rates of eggs and pulli, and assist protection of eggs and pulli from extreme weather. Non-breeding gulls associating with the colonies occasionally move into the nesting areas, but are aggressively forced away and tend to congregate on the periphery of the colony or on exposed areas not suitable for successful breeding.

One aspect of an intensive study of arboviruses and insect vectors at Beatrice Hill, N.T., was to determine the hosts of the insects by identifying the source of their blood meal. The collection methods included buffalo bait, calf- and chicken-baited Magoon traps, truck traps, light traps and collecting from insect resting places. Blood meals were identified by precipitin and haemagglutination-inhibition tests. Fifteen species of biting midges, mostly Culicoides spp., and 24 species of mosquitoes were represented in the collections, and the blood meals within 75% of some 11,000 insects were identified. The majority, 97.7%, of the blood meals were mammalian in origin, 76% being bovine and 17% marsupial. A significant proportion of the blood-fed mosquitoes from Magoon traps had fed on hosts other than the bait animal or collector. Double feeds were detected in 1.1% of the insects in which the source of the blood meal was identified. It was possible to draw conclusions about the feeding habits of most of the insect species.

The life cycle of Psororgatos ovis is completed in 5-6 weeks, and there are six stages : the egg, larva, protonymph, doutonymph, tritonymph, and the male or female adult. All stages are found under the stratum corneum, but adults and occasional tritonymphs are also found on the surface of the skin. Only the adult is motile and is responsible for the spread of infestation over the body of sheep. Adult mites transferred most readily to cloths which were placed next to the skin, which indicated that they primarily are responsible for transference of infestation from sheep to sheep. Adults did not leave the skin rapidly; at 20C, they survived away from sheep for only 24-48 hr at R.H. 92 and 100% and they died of desiccation within 24 hr at R.H. 54 and 75%. These findings suggest that natural transference of infestation is mainly by adults when the fleece is short, which would explain the slow spread of infestation which has been observed in the field.

A collection of sera from 81 species of Australasian marsupials and 65 antisera to them, prepared in rabbits, chickens, or various species of marsupials, was examined to devise a scheme to identify the blood of marsupials imbibed by blood-sucking insects. The precipitin test was of limited value but established that the blood was marsupial. With the haemagglutination inhibition test, however, it was possible to identify the family, subfamily, genus, and species. Thus a procedure could be devised to identify the donors' blood based principally on serological methods supplemented by data on the geographical distribution of the various marsupial species.

The numbers of D. ovis decline in the spring, remain low during the summer, and increase during the winter. A density of two lice per square inch is necessary in the autumn if numbers are to increase during the winter to 200 per square inch, the density found on heavily infested sheep in the early spring. The time needed for this increase has been calculated using the deterministic matrix model ofpopulation increase described by Leslie (1945), and 4-5 months are required when there is only a small mortality. Thus, when the favourable winter period lasts only 3 months, the increase in louse numbers may be insufficient to sustain the losses which occur in late spring, summer, and early autumn. The factors responsible for these losses determine the density of the louse population at the commencement of winter. Should the winter period last c. 6 months there is usually a direct relationship between the number of lice on a sheep in the late autumn and in the following spring. However, should winter last 9 months it is suggested that other factors become increasingly significant, and determine the eventual size of the louse population.

Many D. ovis are found more than 1/4 in. from the skin of the sheep, and 30-50% of a louse population may be lost when the sheep is shorn. The lice near the tip of the fleece come to the tip quickly when it is shaded and warmed, particularly when the fleece is short, and consequently lice, mainly adults and stage III nymphs, spread rapidly from sheep to sheep which are in close contact. All nymphal and adult stages of D. ovis were killed when exposed to 48C for 60 min, 50C for 30 min, or to 55 or 60C for 5 min. Some lice died when exposed to 45C for 4 hr but the main effect was on oviposition, and females exposed for only 2 hr laid fewer eggs. Most eggs were killed when exposed to 45C for 4 hr, 47C for 2-4 hr, or 49C for 4-1 hr. The intensity of solar radiation during the summer in Australia can result in a temperature gradient within the fleece of sheep from c. 45C near to the skin to 65-70C at the tip of the fleece within 5-10 min of exposure. Many lice in the distal parts of the fleece are killed as lethal temperatures develop, and the number of eggs laid by survivors may be reduced. On newly shorn sheep even lice and eggs near the skin may be killed, as the temperature near the skin can rise to 45-52C. Reasonably heavy infestations may be maintained on sheep kept permanently in the shade, and it appears that the cumulative effect of repeated mortalities due to solar radiation prevents an increase in numbers of D. ovis during the summer.

On Macquarie I. it rains daily and abundantly; whether the habitat is flooded or not determines whether the tick Ixodes uriae and the flea Pavapsyllus magellanicus heardi can survive and breed. The principal hosts of these ectoparasites are penguins; the degree of infestation of the four species of penguins that breed on Macquarie I. differs because of differences in their breeding and moulting behaviour. Royal penguins, Eudyptes chrysolophus schlegeli, form large colonies which are surrounded by tussock, Poa foliosa. Rock stacks covered with vegetation may be within the colony. The drier conditions within the tussock and on the rock stacks are necessary for oviposition and egg development of I. uriae although larvae, nymphs, and adults can survive submersion in water for many weeks. Royal penguins are present in the colony from September to April, and consequently a blood meal is readily available close to the breeding area of the tick for half of the year. In these circumstances the life cycle of I. uriae can be completed within 2 yr. The other penguin species do not afford such favourable opportunities for population growth of I. uriae. Only the rockhopper penguin, Eudyptes chrysocome, nests in sheltered situations such as caves, or under overhanging rocks. In these drier nests the larval and adult flea, P. magellanicus heardi, can survive, and the larvae can overwinter.

The Weddell seal, Leptonychotes weddelli, which lives around the shores of Antarctica, is infested with the blood-sucking louse Antarctophthirus ogmorhini. Infestations spread solely from female seals to their pups by the transference of adult lice, and are frequent and heaviest on yearling and immature seals but are less frequent and lightest on mature seals. Few mature bulls are infested. Lice are usually restricted to the tail, ankle, hip, and hind flipper, but the margins of the anal and penile orifices of males may be infested, and occasionally the axilla of the fore flipper. The skin temperature of these sites of infestation varies with the thermoregulatory requirements of the seal, thus providing more opportunities than elsewhere on the body for lice to reproduce when the seal is ashore, and to feed when the seal is at sea. The number of lice is largely determined by the behaviour of the Weddell seal, and numbers are greatest on those age groups which haul out of the sea most frequently throughout the year. The principal physiological adaptation of A. ogmorhini for survival on the Weddell seal is the ability to become active and to reproduce at 5-15C. Eggs can develop and hatch at constant temperatures as low as 0-4C.

Although the southern elephant seals, Mirounga leonina, that breed on Macquarie I., come ashore for only 3-5 weeks twice a year, the hind flippers of most of them are infested with the blood-sucking louse Lepidophthirus macrorhini. L. macrorhini does not oviposit, and eggs do not hatch, in water. Reproduction occurs when the elephant seal is ashore on the beach or in the adjacent tussock. The life cycle can be completed in c. 3 weeks and, because 6-9 eggs are laid daily, multiplication can be rapid. Temperatures greater than 25C are required for rapid multiplication, and these temperatures occur more frequently on the hind flippers than elsewhere on the body. The number of L. macrorhini on a hind flipper however rarely exceeds 100. The principal causes of mortality of the lice are failure to survive the seal's prolonged stay at sea, the moult of the seal, and transmission to unfavourable sites on the seal. When an elephant seal goes to sea its skin temperature falls to nearly that of the sea. The reduction in the metabolic rate of the louse at low temperatures results in the amount of oxygen obtained from the sea by cutaneous respiration being sufficient for survival. The lice do not enter into a state of complete suspended animation, and a blood meal is required at least once a week to enable sufficient to survive to repopulate the seal. The skin temperature of a seal at sea rises more frequently on the flippers than elsewhere on the body because of the increased rate of blood flow to the flippers after diving and whenever it is necessary to dissipate heat. Consequently, there are more opportunities for the lice on the hind flippers to feed. L. macrorhini burrows into the stratum corneum, thus reducing losses to the population when the elephant seal annually sheds the outer layers of the stratum corneum attached to the hair, because only the roof of the burrow is lost. Lice do not reproduce on the older seals that moult in muddy wallows, and consequently fewer lice are found on these animals. Pups are infested within a few days of birth, and the gregarious habits of the elephant seal spread infestations through the seal population. Lice transfer to all parts of the bodies of seals but it is the multiplication of those on the flippers that maintains the louse population. The abundance of L. macrorhini is determined largely by the frequency and duration of opportunities to reproduce when the elephant seal is ashore, and to feed when the elephant seal is at sea.

No development of the egg within the female Damalinia equi (Denny) occurred at 16C. Most eggs were laid at 36C at R.H.'s of 75% or less, but after an exposure to 44.5C for only 1 hr females did not lay eggs. Morphogenesis proceeded to an advanced state from 27-39C, but its completion and the subsequent hatching of the embryo only took place from 31-39C provided the R.H. was less than 90%. A R.H. of 90% prevented hatching of the eggs. Exposure of eggs to 49C for 2 hr was lethal. The skin temperature of the horse is influenced considerably by atmospheric temperature. The abundance of D. equi on the bodies of horses in early spring is probably due to the temperatures near the skin of the body being continuously favourable for reproduction of D. equi during the winter. Exposure to the sun can cause the temperatures within the hair coat on the upper aspects of the body to become higher than 44.5C for more than an hour and thus can retard reproduction. The accumulative effect of repeated high temperatures could prevent an increase in the numbers of D. equi during the summer.

Exposure of nymphal and adult Damalinia ovis (L.) to 100% R.H. at 37C did not increase the death rate but immersion for 6 hr in water followed by exposure to 40% R.H. was sufficient to kill all nymphs and adults. Immersion of only 1 hr was fatal for 50-100% when followed by exposure of 7.5-24 hr to 90% R.H. Eggs continued to develop under water at 37C and an appreciable mortality occurred only after 7 days immersion. Exposure to relative humidities of over 90% killed hatching eggs. When the fleece of a sheep infested with D. ovis is soaked by rain it may take many hours to dry and there is a resultant mortality of nymphal and adult lice and hatching eggs. In the region where the experiments were carried out, sheep were soaked periodically by thunderstorms in the autumn. The irregular mortalities of lice on different sheep was reflected 6 months later, when the lousiest sheep were shown to be those which were not soaked in the previous autumn.

Linognathus ovillus has been found on all regions of the sheep except the lower aspects of the limbs, but populations are maintained throughout the year only on the parts of the body covered with hair, particularly the face. The inability of L. ovillus to multiply below a constant temperature of 30C, or to survive prolonged exposure to cold temperatures, probably prevents maintenance of populations on the lower parts of the legs. Only adult lice were transferred from sheep to sheep, and fewer were required to establish a population on the hairy face than on the parts of the body covered with wool. The greasiness and length of the wool caused females to lay eggs less densely, required a greater density of males and females for fertilization, and resulted in a greater mortality of nymphal and adult lice. Lice disperse continually from the face into the surrounding wool, and the consequent density of lice in this wool frequently becomes sufficient for the population to maintain itself, thus resulting in a swarm of lice in that area. Shearing removes few lice from the parts of the body covered with hair, but many from those parts covered with wool. Thus, whereas the density of lice on the face is little affected by shearing, that on the body is reduced considerably. When a sheep is exposed to atmospheric temperatures of c. 28C the temperature next to the skin rises to over 38.5C. Few eggs develop and hatch at this temperature. These two factors probably account for the disappearance of L. ovillus from the body after shearing in the spring, and during the following summer. The occurrence of lethal temperatures within the fleece during the summer may also be a contributory factor. Observation of an infested flock over a period of a year showed that the sheep which were most heavily infested in the autumn were also the most heavily infested in the subsequent spring. This indicates that the size of a louse population on a sheep in the spring may frequently be directly dependent on its size at the commencement of the previous winter.

Linognathus pedalis, which is found on the legs of sheep where the temperature near the skin can fluctuate greatly, was able to survive prolonged exposure to cool temperatures, whereas L. ovillus, which is found particularly on the face, and to a lesser extent on the body, could not. L. pedalis is more sedentary, congregates into clusters, and is most numerous on the parts of the leg covered with hair, whereas L. ovillus disperses, never forms clusters, and its populations are usually densest in the region of mergence between hair and wool on the face.

The number of Polyplax serrata (Burm.) on the mouse Mus musculus L. is determined by the efficiency with which the mouse grooms itself with its mouth. The efficiency with which the accessible hindpart of the body is groomed is such that normally the majority of all stages of the life cycle are found on the forepart of the mouse with the exception of the stage I nymph which is distributed over the whole body. The principal requirements for self-grooming to control the number of lice are that the technique is efficient, that sufficient time is spent grooming, that an adequate area of the body is groomed, and that lice move readily into the accessible area. Any factor which influences adversely any one of these requirements causes the efficiency of grooming to decrease, and thus permits lice to increase in numbers and to populate the whole body.

Female Linognathus pedalis (Osborne) were exposed to temperatures of 22, 25, 30, 36, and 40C. Nost eggs were laid at 36C but none at 22C. Eggs were exposed to 22, 25, 30, 33, 36, 38, and 40C and hatched only at 33, 36, and 38C. Most eggs hatched at 36C. At 36C, however, few eggs were laid at 100 per cent. R.H. and the majority of eggs exposed to even 92 per cent. R.H. failed to hatch. Thus, high humidities could reduce the number of eggs which are laid and which hatch on the legs of sheep even if the temperature near the skin is favourable. When sheep were exposed to atmospheric temperatures near 28C the temperatures near the skin of the body were higher than 38C, and conditions cool enough for the maintenance of L. pedalis populations were found only on parts of the legs. On exposure to cold, the temperature near the skin of the legs fell and remained too cold for oviposition and egg development during several hours of exposure. However, it was also found that the resultant temperatures near the skin of the legs of the same sheep and of the legs of different sheep could differ greatly. Thus, those legs on which temperatures near the skin are above 30C for the longest periods may become most heavily infested. These findings offer a possible explanation of observed differences in the numbers of L. pedalis on the legs of sheep.

The temperature and humidity requirements for the development and hatching of the eggs of Damalinia ovis (L.) were determined. Morphogenesis of the eggs of D. ovia was completed only within the temperature range 30-39C but the most favourable range was 33-39C. When development was completed eggs hatched from 22-42.5C. The majority of embryos within eggs incubated at 33-39C and maintained at R.H.'s of 7-92 per cent. completed their development but those exposed to 92 per cent. R.H. failed to hatch. An exposure to 92 per cent. R.H. for only the last 24 hr of their development was sufficient to prevent hatching.

The eggs of Damalinia equi (Denny) and Haematopinus asini (L.) are attached to the hairs close to the skin with the end of attachment nearest to the skin. The oviposition behaviour of D. equi is similar to that of D. ovis (L.). The only observable differences are that the gonopods are not used at the time of egg laying and the fibre is grasped by the claspers. Temperatures between 32 and 38C are required for the maximum number of lice in a population to oviposit. Skin temperature can determine the lateral distribution of the eggs in the natural environment. A fibre of suitable diameter is also necessary. D. equi cannot attach its eggs to the coarse hairs of the face, mane, tail, and legs whereas H. asini is able to do so. As the coarse hairs of the mane, tail, and legs are not shed with the fine hairs of the coat at the beginning of summer and winter the shedding of the coat effects a more severe reduction of the population of D. equi than of H. asini.

The eggs of Damalinia ovis (L.) are attached to the wool and hair fibres of the sheep and have a vertical and lateral distribution, i.e. they may be laid at different distances from the skin and their distribution over the body of the sheep may vary. The vertical distribution of the newly laid eggs of D. ovis is determined by the distance to which the temperature zone suitable for oviposition extends from the skin. This is regulated mainly by skin temperature, skin topography, the depth of the air blanket trapped within the fleece, and atmospheric temperature. Usually the eggs are laid within 1/4 in. of the skin. The factors which influence the lateral distribution are the presence of suitable fibres and temperatures for oviposition. Eggs are not laid on the bare areas of the body because fibres are absent. There are, however, few bare areas on the sheep. The bases of certain hairs on the face, legs, and axilla and inguinal regions are too large in diameter for oviposition but mingled with them are many fibres which are suitable. As there are no areas on the sheep which are entirely covered with hairs of unsuitable diameter for oviposition, fibre diameter has little influence on the lateral distribution of the eggs of D. ovis. When sheep are exposed to low atmospheric temperatures, the skin temperature of the extremities falls below that at which D. ovis can oviposit. Skin temperature is the main factor which determines the lateral distribution of the eggs of D. ovis on the sheep.

The behaviour pattern of Damalinia ovis (L.) is adapted to the physical features of the environment in which the louse lives. In stage 1, the louse was attracted to temperatures between 35 and 40C and this temperature zone was necessary for oviposition to proceed satisfactorily. Optimum temperature conditions were between 37 and 39C. In stage 2, the louse orientated itself so that its head was directed towards the warm end of a temperature gradient or towards the saturated end of a humidity gradient, but when these gradients were antagonistic the orientation to temperature dominated. At the commencement of stage 3, the louse reversed its orientation to both temperature and humidity gradients but again the attraction to temperature was dominant. Before egg laying commenced, a fibre of suitable diameter had to be caught by a gonopod and held next to the abdomen. The resulting tactile stimulus was critical and its absence inhibited oviposition. Other factors which influenced oviposition were the depressant effect of high humidities, the orientation to light, and the attraction to other ovipositing lice and eggs.

The behaviour patterns of Damalinia ovis (L.), Linognathus stenopsis (Burm.), and Haematopinus eurysternus (Nitz.) were found to be similar and readily divisible into three stages. In the first stage the louse sought the warm end of a temperature gradient. There it entered upon the second stage in which it remained stationary for a variable period with its head pointed towards the warm end. In D. ovis there was marked abdominal movement. The third stage lasted only 3 or 4 min and culminated in the deposition of the egg. In this stage the louse suddenly turned about and attached the egg to the fibre, sometimes backing into the warmer end first. This resulted in eggs being aligned similarly with the end of attachment nearest to the warm end of the temperature gradient. It is suggested that the behaviour patterns of these lice are adapted to common physical characteristics of the environments in which they live, notably the presence of a temperature gradient.