Ten insecticides were assayed for toxicity against an unselected and a resistant strain of Myzus persicae (Sulz.). Of the six topically applied insecticides parathion was the most effective, followed by diazoxon, diazinon, aldrin, dichlorvos and p, p′DDT in that order, while the resistance levels were, in descending order, parathion, dichlorvos, diazinon, diazoxon, p, p′DDT and aldrin. Of the four systemic insecticides, pirimicarb was most toxic, followed by dimethoate, phorate and demeton in that order, while resistance ratios were in descending order dimethoate, phorate, demeton and pirimicarb. The organophosphorus resistance spectrum for M. persicae indicated that more than one resistance mechanism is involved, and that resistance acts against diethoxy and dimethoxy compounds.

In eastern Africa between 1951 and 1955 and in south-western Morocco in 1960, orientations and densities of flying locusts in migrating swarms of Schistocerca gregaria Forsk. were recorded photographically, with supplementary visual observations. The densities ranged from 0·0006 to 1·23 locusts/m3 (mean spacing between nearest locusts 12 and 1 m, respectively) with a median value of 0·024 locusts/m3; in 50% of the samples mean spacing was 2–4 m, suggesting a preferred distance of that order. The orientations were affected by gregarious reactions to neighbouring fliers, and to locusts in a mass. In the swarms there was a preponderance of streaming groups in which locusts headed in the same general direction; in about half of these groups the angular deviation about the mean orientation was only ±20°. In comparatively dense swarms the orientations of the lower fliers in the interiors of swarms were diverse and random in relation to wind and to the swarm track. But at the leading, the trailing and the lateral edges they were predominantly into the swarm, as the result of observed changes of headings back towards the swarm in locusts flying out beyond the main mass. The orientations of locusts photographed at about 100 m and 200–400 m above the ground were found to be predominantly in the direction of the swarm track, i.e., with wind; it is suggested that they arose from compensatory optomotor responses to retinal velocities of substrate patterns, and are consistent with Kennedy's hypothesis of optomotor orientation to wind. Among lower-flying locusts such responses appeared to become important in diffuse formations and in strong winds. Thus flight on consistently into-wind courses was repeatedly seen in low-flying diffuse formations of sexually mature locusts migrating in light winds. In stronger winds the orientations of lower fliers in all types of swarms suggested responses to unacceptable retinal velocities, which interfered with the into-the-swarm orientations on the swarm edges; the continued cohesion of swarms may thus require a wind profile in which they are not evoked below a certain level. In persistent strong wind in excess of locusts' air speeds, flight activity was reduced, and swarms exhibited low into-wind flight by locusts in small numbers. It is suggested that the characteristic downwind tracks of discrete immature swarms are set primarily by the downwind orientations of their higherflying members. In sexually mature swarms the downwind displacements are probably performed mainly by the denser and the higher-rising swarms, while the into-wind flights of low diffuse formations would slow down movement, and could result in limited displacement up-wind.

Histological examination of the eyes of Glossina morsitans Westw. and G. austeni Newst. showed that visual acuity, as calculated from ommatidial size and interommatidial angle, varies in different zones and planes of the eye, being greatest in the forward-facing region. A study of optomotor responses to revolving black-and-white striped patterns indicated that the eyes could perceive both rapid and very slight movement: responses showed a unimodal distribution with frequency of ommatidial stimulation ranging from one flash/25 s to around 80 flashes/s, with an optimum response at 5 flashes/s. Movement perception was also enhanced by summation of ommatidia simultaneously stimulated, provided the stimulated ommatidia were not contiguous. Strong optomotor response was shown to the movement of black stripes so narrow as to cause merely a 7% reduction in the amount of light entering an ommatidium: from this it was inferred that the eye's contrast sensitivity is well developed. Visual acuity determinations from optomotor responses showed no species or sex differences, and the values corresponded closely with those obtained from anatomical measurements. Of the properties of selected figures examined for attractiveness to orienting flies, linearity of form and brightness contrast with background illumination were deduced to be the most important aspects.

The distribution of ants in a 2·25-ha cocoa plantation at the University of Ghana Agricultural Research Station, Kade, was recorded in December 1970. The 44 species of ants found could be grouped as dominant, co-dominant, sub-dominant and nondominant. Oecophylla longinoda (Latr.) and Macromischoides aculeatus (Mayr) were mutually exclusive as were six Crematogaster spp.; the latter were also exclusive of O. longinoda and M. aculeatus. Camponotus acvapimensis Mayr became dominant under insolated conditions, and Platythyrea frontalis Emery for reasons unknown. The distribution of these ant species in cocoa plantations resembles a three-dimensional mosaic which is preserved by their aggressiveness and by competition for food and nesting sites. It is suggested that this mosaic is due to vegetative succession.

Melicharia obtusanguloides sp.n. (Flatidae) infesting tea in southern India is desscribed and compared with M. obtusangula Distant and Idume plicata Melichar whose male genitalia are illustrated. The male type of M. obtusangula is designated as lectotype. Brief notes are given on the habits of Ketumala thea Ghauri (Flatidae) and Ricania fenestrata (F.) (Ricaniidae), and the male genitalia of the latter species are figured.

Dentichasmias busseolae Heinr., an important pupal parasite of Pyralid graminaceous stem-borers in East Africa, is widely distributed in the Ethiopian Region but is more abundant in areas with an equatorial humid climate. In the laboratory adults mated immediately after emergence and started oviposition the same day. The female oviposits only in a borer pupa without a cocoon in a stem, and oviposition is stimulated by the presence of the frass of Chilo partellus (Swinh.) larvae. D. busseolae does not attack Busseola fusca (Fuller), Sesamia calamistis Hmps. or Eldana saccharina Wlk. in the field but these were accepted for oviposition when exposed in C. partellus pupation tunnels or with frass of C. partellus larvae, and were suitable for development. D. busseolae could complete its development in one- to eight-day-old C. partellus pupae when the pupal period of C. partellus was 10·5 days. The life-cycle was completed in 15–19 days at a mean temperature of 25°C, but could not be completed at a constant temperature of 30°C; temperatures fluctuating between 22°C and 30°C were not detrimental. At Namulonge (Uganda) percentage parasitism showed a positive correlation with rainfall, with a lag of about a month.

The Varley & Gradwell method of population analysis is applied to data on populations of Saccharosydne saccharivora (Westw.), comprising 51 generations from 21 fields, obtained in Jamaica in 1961–62. Populations were estimated at five points in each generation, namely, maximum potential natality, and numbers of eggs laid, instar 1, peak instars 3–5, and of normal reproducing adults. Taking maximum potential natality as the first point in each life budget, graphical analysis showed that the key factor was mortality between instar 1 and reproducing adults or between peak instars 3–5 and reproducing adults. Reduced fecundity, due to submaximal leaf nitrogen, was density independent or possibly inversely density dependent; one egg parasite, Tetrastichus sp., was inversely density dependent while another, Anagrus flaveolus Waterh., and an undetermined egg mortality factor were density independent; parasitism of nymphs and presumably adults also by Stenocranophilus quadratus Pierce was density dependent, and was Considered to be the only regulating factor. The key factor was density independent, and it is concluded that, of the separate mortality factors contained within it, dispersal of adults is the most important. This itself depends on crop characters which could be altered by selective breeding or agricultural practice.

Larval populations of the Anopheles gambiae Giles complex (species A and B) were sampled in Kenya, and from the frequencies of the age distribution of the immature stages time-specific life-tables were constructed. Daily survival rates and instar mortalities showed that there was high mortality amongst fourth-instar larvae, due at least in part to infections of larval nematodes, Coelomomyces and epibionts. Antiserum to the A. gambiae complex was prepared in rabbits so that the precipitin test could be employed to detect the presence of A. gambiae in gut smears taken from possible predators. By this serological technique various spiders, Diptera, Coleoptera and amphibia were identified as predators. These may be very important in regulating populations of A. gambiae even in small collections of water.

The choriothete in Glossina austeni Newst. and G. morsitans Westw. was studied from serial sections of females, from dissected material and whole mounts of eggs and larvae. The choriothete cells are secretory and, while an embryo or first-instar larva is attached to it, are not stretched. The external muscles dilate the uterus or support the uterus and embryo. There is no sign of major folding or muscular tension during dechorionation of the egg. It is concluded, in contrast to recent work, that the choriothete is an organ for the support of developing embryos. Hatching of the first-instar larvae is probably achieved by means of a labral egg tooth.

A comparison of the mosquito fauna in a forest near Zika forest, Uganda, in July-August 1971, showed that Mansonia (Coquillettidia) fuscopennata (Theo.), Culex (C.) annulioris Theo. and M. (Mansonioides) africana (Theo.) made up 84% of the catch taken at 24-h human baits in a horizontal transect, whereas M. (C.) metallica (Theo.) made up 90% of those taken at rest. Precipitin tests showed that 98% of M. metallica and most individuals of the other Coquillettidia spp. had taken avian blood, but that two out of seven individuals of M. fuscopennata had taken primate blood. In olfactometer studies M. metallica did not respond to the human hand or a chicken. It is concluded that none of the Coquillettidia spp. caught resting, except M. fuscopennata, has any preference for man.

Observations on Aphis craccivora Koch at Serere, Uganda, in 1964–68 showed that dry season carry-over of aphids could occur on the common weeds Euphorbia hirta and E. prostrata; at other times aphids were seen on Gliricidia sepium, Cassia tora, Centrosema pubescens and Macroptilium atropurpureum, the last two being increasingly used as pasture legumes. In pot tests, attempts to transfer the virus through G. sepium, Cassia tora, Stylosanthes guianensis and Centrosema pubescens were unsuccessful. Volunteer groundnuts growing in open situations were an important source of virus and vector. Field studies on menazon-sprayed and unsprayed plants closely or widely spaced showed that aphid numbers increased rapidly on the groundnut crop 31–45 days from emergence but declined rapidly as the plants matured. Superficially the plants appeared to be free of aphids but large populations were often found on hypanthia, flowers and gynophores. Coccinellids, especially Cheilomenes sulphurea (Ol), were important predators. Aphid numbers were far higher on groundnuts with low plant densities, possibly because the number of favoured feeding sites is increased, but the number of plants infested was not significantly different at high and low densities. Yellow panels had little effect on aphid numbers. Spraying with menazon (294 g active ingredient/ha, 5 times) prevented breeding by incoming alates.

Examination of the cephalic lobes of larvae of Psila rosae (F.) by means of light and scanning electron microscopes revealed the presence of 24 sensilla, ten campaniform, eight basiconic, four ampullaceous and two styloconic. By comparison with the known functions of similar sensilla in other insects, it is suggested that the ampullaceous and basiconic sensilla respond to plant emanations in soil, air and water, respectively, and that styloconic sensilla determine the palatability of the root hairs; the role of the campaniform sensilla is obscure.

The effect on the size of sample of 32 taxa of Macrolepidoptera, and on the index of diversity α, of various modifications of the light in Rothamsted and Muguga light-traps was investigated in experiments at Muguga, Kenya, in 1968. The sample of moths from the standard Muguga mercury-vapour trap was fifty times as big as that from the standard Rothamsted Tungsten trap. Using a mixed mercury-vapour and tungsten lamp in a Muguga trap halved the sample, as also would obscuring 60% of the light from a standard mercury-vapour lamp. Overall size of sample, direction of illumination and source of illumination all affected the proportion of different taxa in the sample, but the diversity index differed little in any of the combinations of traps, lamps and sites. Analysis of the pattern of sample distribution over the site showed that moths of all sizes were migrating downwind and height of flight was found to be positively correlated with size. Interaction between traps and sites, combined with the differing heights of flight of the different taxa, complicated the definition of specific sample size; a three-dimensional representational model attempts to define the spatial population parameters required to define the specific sample.

Epidemiological studies of Rhodesian sleeping sickness and its vector Glossina morsitans Westw. were made near Motsowi in the western floodplains of the Okovango Swamps, Botswana, during 1967–68. The low apparent densities of the fly (12–27 in three fly rounds compared with 124 in a fourth located in a more densely forested area to the east) and low recapture rates (1·3–3·9%) indicated the Motsowi area to be a feeding ground. Peak densities in January and troughs in October reflected seasonal movements of the fly to and from their dry-season retreats to the east. Most bloodmeals (61%) were on warthog, but 5·5% were on reedbuck in which the Trypanosoma brucei infection rate was 33%. In the Motsowi area the total trypanosome infection rate in G. morsitans was 5·7%,, with T. brucei 0·6%, but the rate varied between localities elsewhere in the Okovango. Man's movements into the fly areas to the east offer the main pathway for transmission of T. brucei, perhaps aided by seasonal movements of reedbuck closer to the settlements. The incidence of human trypanosomiasis is therefore unlikely to be reduced by insecticide campaigns in the farming areas, but livestock will benefit from a reduction in cattle trypanosomiasis.

Apterous adult Myzus persicae (Sulz.) of a glasshouse strain differed greatly in their ability to colonise sugar-beet according to the plant on which they and their forebears were cultured. Those from Chinese cabbage (Brassica pekinensis) settled least readily on beet, whilst aphids from broad beans (Vicia faba) produced larger populations than those cultured on sugar-beet. When reared wholly on groundsel (Senecio vulgaris) young adults differed in their ability to colonise Chinese cabbage, sugar-beet and broad bean according to their parents' culture host species, and these differences were detected in a second generation reared wholly on groundsel. The responses of clones isolated from cultures maintained continuously on Chinese cabbage and broad bean were similar, showing that the effect was caused by the aphids' host-plant experience, and was not due to fixed, heritable characters of the sub-cultures. Some, but not all clones of M. persicae collected from the field showed enhanced colonising ability after culture on broad bean as compared with Chinese cabbage. This was apparent on sugar-beet and lettuce (Lactuca sativa). These effects of former hosts on the ability of M. persicae to colonise plants may be important both in work on resistance to aphids and in the epidemiology of aphid-borne diseases.

A new species of Tachinidae of the genus Metacemyia (tribe Acemyini) is described and figured, and keys are given to the Acemyines of the Ethiopian Region. The new species is recorded as a parasite of the wingless Eumastacid grasshopper Manowia sp. nr. alca Bolívar in Malawi. Taxonomic notes are included on the other Acemyini known from the Ethiopian Region.

The diploid chromosome number of G. austeni Newst. from the Langford colony is 2n = 14 ± 2, + XX/XY. Chromosomes have been karyotyped and include a pair of large submetacentrics (L1), a pair of shorter metacentrics (L2) and a group of small telocentries (S). The X and Y elements constitute a heteromorphic pair. The S chromosomes together with the Y element display allocyclic behaviour during nuclear division. Pre-meiotic RNA synthesis has been followed by autoradiography, and differential staining of DNA with quinacrine dihydrochloride by fluorescence microscopy.

In Britain adults of the clouded drab moth, Orthosia incerta (Hfn.), appear in the spring and are especially common during April and early May. The larvae feed on various trees and shrubs from May to June or early July, and in orchards may cause damge to the flowers or developing fruitlets. There are six larval instars. These are described, and illustrations are given of the immature stages and adults.

The distribution of the larvae and pupae of Culicoides melleus (Coq.) in a natural beach habitat in an inlet on the Florida coast was studied in relation to tidal level and time of day. Larvae and pupae were confined to the intertidal zone and these distributions were unaffected by time of day or tidal level. Distributions of younger larval instars were displaced towards the inferred area of oviposition at higher elevations on the beach. Pupae were associated with the zone at and somewhat below high tide level. Differences in the vertical distribution of larvae between 0 and 2 in. deep between dark (pre-dawn)/low tide, morning/low tide and afternoon/low tide conditions were probably associated with larval response to light and heat.

In laboratory experiments with a temperature gradient, second- to fourth-instar larvae preferred the 18–25°C range, but the fourth instars were the least discriminating. Laboratory experiments with a simulated beach showed that pupae flooded on an incoming tide remained in their burrows and immediately buried themselves more deeply when waves were generated in the water; they were able to return to the surface if buried, and survived drowning for four days. Inundated areas were avoided as pupation sites. The orientation of pupae at the sand surface and their formation in burrows was related to negative phototactic responses of the pupating larvae.

As part of a research project directed at the genetic control of Teleogryllus commodus (Wlk.) in Australia, hybridisation studies have been carried out between T. commodus and the sibling species T. oceanicus (Le Guillou). A cytological examination of a hybrid strain (male progeny of T. commodus × T. oceanicus backcrossed to T. oceanicus) was made in the F4 generation when meiotic stability had been reached. The karyotype was very similar to that of T. oceanicus, suggesting that only those combinations in which the chromosomes were structurally homologous to T. oceanicus survived. But the stridulation pattern of the hybrid males, intermediate between that of the two parental species, and a consistent sex ratio of 2:1 in favour of the males, indicate profound genetic differences from T. oceanicus. These effects are attributed to introgression, with chromosomal material from T. commodus being incorporated in the T. oceanicus genome as an outcome of the initial hybridisation of the two species.