In laboratory experiments, the responses to short photoperiod (10 h) of clones of Myzus persicae (Sulz.) established from random samples of summer populations in southern England were generally stable and characteristic for each clone, and were of four distinct categories: (i) holocyclic, with clones terminated under short photoperiod by production of male and female sexual forms, (ii) intermediate, with a mixed response involving alatae intermediate between gynoparae and virginoparae, (iii) androcyclic, with production of some males along with continued parthenogenesis, and (iv) truly anholocyclic, with no significant response to short photoperiod. All four types can occur within one population, but holocyclic and androcyclic forms are most common. There were clear differences in the proportions of these forms occurring simultaneously on adjacent crops of different host-plants, and in different years on the same crop in the same field. Males of androcyclic clones were able to transmit their partially anholocyclic character through the sexual phase.

Standard text-books on entomology (Imms, 1957; Ross, 1956) state that the insects of the order Thysanoptera feed by macerating leaf tissue with pointed stylets, and then suck the juices thus released by applying their mouth cone to the leaf surface.The drawings accompanying these statements indicate that the maxillary stylets and the single mandible are all simple acute needle-like structures. However, sections of the mouth cone including the stylets show that the mandible is a closed tubular structure, and that the maxillary stylets are grooved, i.e., C-shaped in section (Reyne,1927; Mickoleit, 1963). Moreover, Grasse (1951) states that although the maxillary stylets do not show the mutual adaptations found in the Hemiptera they do form a tube when fitted together, and Grinfel'd (1959) suggests that thrips may suck food through the tube formed by the stylets in addition to applying the mouth cone directly onto the food.

Sixty-one Culicoides spp. were collected in Kenya, Uganda and Tanzania between January 1966 and December 1967 using light-traps at 35 stations on a NW-SE transect from the Indian Ocean to central Uganda to evaluate the distribution of Culicoides spp. among ecological zones. Most species were confined to one or at least very few similar habitats. The largest number of species (30) occurred in the forest zone, probably because of the many suitable breeding sites, whereas only three species were recorded from the dry bushland zone. Forests also contained more exclusive Culicoides spp., whereas savanna species showed a wider distribution, suggesting that the forest species are less adaptable than others. The disease vectors C. grahamii Aust. and C. pallidipennis C, I. & M. were among the most abundant and widely distributed species.

The black citrus aphid, Toxaptera aurantii (Boy.), produces a distinct scraping sound by rhythmic movements of whole colonies. It is the only species of aphid known to produce audible sounds and the acoustical content of a preliminary recording of these sounds is reported in detail. During one recording the aphids stridulated 15 times in 21 seconds, giving an average period of 1–4 seconds between emissions and this rate remained virtually constant for at least an hour. Analysis of the recording established a clear peak frequency band at about 4–6 kHz with another around 800 Hz-1 kHz and possibly another in the ultra-sonic range above 18 kHz. Morphological adaptations of the abdominal cuticle and of the hind tibiae to form a stridulatory apparatus are illustrated and possible functions of stridulation as a defence mechanism or as a means of intraspecific communication are briefly discussed.

Between 1961 and 1967 intensive and extensive field studies on the sugar-cane pest Saccharosydne saccharivora (Westw.) were carried out in Jamaica (with supplementary observations from British Honduras). Egg populations were scored for size, and egg mortality and nymph-adult parasitism were estimated directly. In epidemic, but not endemic, populations, successive generations of the pest were segregated and their development was synchronised over areas of up to 80 miles2 despite its 6½—7-week life-cycle and potential for continuous breeding. Segregation was due to the sterilising action of the parasite Stenocranophilus quadrat us Pierce (Halictophagidae); in the drier months this spread so rapidly through the nymph and adult population that oviposition ceased until the first adults of the next generation reached maturity. In the wet season this effect was complemented by the entomogenous fungus Metarrhizium anisopliae. Synchronisation was ensured by the dispersal of parasitised adult Saccharosydne saccharivora before oviposition. In ratoon cane there were six or seven generations between successive annual harvests; egg populations were highest in generations 1–3 (up to 1·0×106/chain-row (≡2O·2-m row-length)), and declined in old cane irrespective of season. In plant cane, egg populations did not show a decline with age and sometimes increased. In epidemic areas a factor associated with older cane sometimes caused over 90% egg mortality; elsewhere Tetrastichus sp. (Eulophidae) was the leading cause of egg mortality (ca 30%). Data from extensive surveys showed that the early stages of outbreaks were invariably associated with plant cane; heavy infestations rarely occurred on cane subjected to adverse growing conditions; and populations were smaller on the variety B42231 than on B4362 and B41227. Outbreak periods since the 18th century have been associated with periods of prosperity within the sugar industry, when presumably more attention was paid to improving production. Rainfall, in that it improves cane growth, is beneficial to S. saccharivora, whereas drought is detrimental; published records of outbreaks in dry periods are due to the preference of migrating adults for young cane which is most prevalent in the dry season. It is concluded that the essential prerequisite for an outbreak is plant cane growing under favourable climatic and agricultural conditions; present conditions, namely the long harvest period, high standards of cultivation, irrigation and fertiliser practice, and favourable cane varieties together offer the minimum chance for a natural end to outbreaks.

In both experimental and naturally developed colonies, Aphis fabae Scop., and Acyrthosiphon pisum (Harris) were concentrated on the upper parts of broad bean plants. A. pisum resembled Myzus persicae (Sulz.) rather than Aphis fabae by normally infesting leaves, not stems. Colonies of M. persicae were dispersed over the whole plant. In laboratory experiments, apterous adult aphids were observed walking on bean plants, and their activity was recorded in terms of their actions at each node. Moving aphids of both species tended to maintain their direction at a node although the structure of the plant does not appear to favour this. Aphids of both species changed their direction of movement more often after going onto the leaf at a node than when they stayed on the stem. M. persicae adults went upwards as often as they went down, but those of Acyrthosiphon pisum walked up more often than down and were more likely to turn round if they were moving downwards. These differences in the behaviour of active individuals would tend to produce the differences between the observed spatial distributions of the two species, although other factors, including leaf age and reproductive rates are probably more important in determining the form of aphid colonies.

Male bushflies (Musca vetustissima Wlk.) are attracted to and feed on proteincontaining substances, although under laboratory conditions they ingested smaller quantities of blood and dung than did the females. Laboratory experiments showed that they are able to obtain water from fresh dung and blood, but no physiological requirement for the protein was found. Feeding on protein did not increase the life span or the total numbers of matings; it did not improve the mating success of males that had previously been multiple-mated; and it did not enhance sexual activity, contrary to the situation found in Lucilia cuprina (Wied.). It is concluded that protein feeding in male bushflies is casual, possibly a behaviour pattern that ensures their presence near females.

The effects of residual sprays of methoxy-DDT wettable powder at 2 g/m2 on the mortality and behaviour of Anopheles gambiae Giles, Mansonia uniformis (Theo.) and Culex pipiens fatigans Wied. females were investigated in four verandah-trap huts, one of which was used as control. The overall mortality of no species ever exceeded 29%, and no consistent deterrent effect on entry was demonstrated. The proportions of mosquitoes in the exit traps were, for A. gambiae 80–90% in treated huts and 29–70% in the control, for M. uniformis 90–100% in treated and control huts, and for C. p. fatigans 26–84% in treated huts and 38–66% in the control. There were more unfed mosquitoes of all three species in the treated huts than in the control, for A. gambiae 35–64% and 10–53%, respectively, for M. uniformis 38–84% and 35–64%, respectively, and for C. p. fatigans 22–58% and 21–43%, respectively. Bioassays with wild-caught A. gambiae exposed to the treated surfaces for one hour, showed that the deposits remained highly toxic for 16 weeks on grass, six weeks on iron and two weeks, or less, on mud.

A distinct black species of Cicadulina from sugar-cane in East Africa is described as new, and notes on the distribution of other Cicadulina spp. are given.

Ketumala thea sp. n. is described from tea and the shade trees Erythrina lithosperma and Glirididia sepium in South India. Descriptions are also given of K. singapurana sp. n. and K. nigropunctata (Distant) comb. n.

After preliminary collections with suction traps at heights of 30 and 135 cm had shown that most mosquitoes were caught in the lower trap, suction trap catches were made for three years from about April to November in a wooded area in southern England. Flight periodicities of females of Aedes cantans (Mg.) and Ae. geniculatus (Ol.) and of both sexes of Anopheles plumbeus Steph. and Culex pipiens L. were determined by traps incorporating automatic segregating devices. In all species maximum flight activity was between 19.00–20.00 h GMT. The biting cycles of the first three species were similar to their general flight patterns. Mean hourly densities of all four species were calculated from the suction trap catches. Collections were made with traps placed at five different heights (23–223 cm) in 1968 and at eight heights (23–550 cm) in 1969 and 1970. In most species there was a well defined and rapid decline in aerial density of both sexes with increasing height, but more unfed females and males of Culex pipiens L. and females of Culiseta morsitans (Theo.) were caught in the highest trap. From about mid-August onwards, when adults of Culex pipiens were searching for hibernation sites, both males and females with fat reserves were commonest in the lowest trap. The slopes of the regression lines of log. density on log. height were calculated separately for Ae. cantans and C. pipiens, and for all adults combined for five less common species. In all catches, except those of C. pipiens, unfed females predominated.

The arrival of mosquitoes at human bait under natural conditions could be divided into three behavioural phases, the exploratory, the penetration and feeding periods. The duration of these periods was recorded in Mansonia richiardii (Fie), Anopheles plumbeus Steph., Aedes punctor (Kby.), Ae. detritus (Hal.), Ae. cinereus Mg. and Ae. cantans (Mg.). Adults of M. richiardii took the longest (about 4 min) and those of Ae. cinereus the shortest (about 2 min) time to obtain a blood-meal. Penetration by the mosquitoes' mouthparts was felt in about 17% of the feeds, and irritation was caused by about 18% of the mosquitoes during feeding. The natural host preferences of these, and 11 other species, were determined by precipitin tests on blood engorged mosquitoes. Adults of Culex pipiens L., C. torrentium Mart, Culiseta morsitans (Theo.) and C. litorea (Shute) were essentially avian feeders; three adults of the latter two species had also fed on unidentified reptiles. Most adults of the other species had fed mainly on mammals. There were few multiple feeds. Although the ability of a mosquito to take a blood-meal quickly from a host was recognised as important, other phenomena such as uninterrupted feeding, simultaneous feeding by large numbers of mosquitoes and host desensitisation to bites were also considered important in contributing to the success or failure of a mosquito in obtaining a blood-meal.

Laboratory experiments showed that the mated status of male sheep blowflies (Lucilia sericata (Mg.)) can be reliably detected a week after mating, but subsequently the test is less accurate. Injection of 4–36 Ϝg tepa/male fly induced approximately 95% sterility. Tepa-injected flies mated freely, and the treatment did not interfere with the mated status test subsequently performed. The test has potential value in sterile male release studies.

When virgins of both sexes of the sheep blow-fly Lucilia sericata (Mg.) are placed together in cages, the cumulative mating frequency curve has a regular form: the shape of this curve is believed to be largely a consequence of the progressive decrease in the density of flies available for mating. A model based on this hypothesis is successfully tested against experimentally obtained data. A mating rate coefficient is proposed.

The spectral sensitivity of gravid female Aedes aegypti (L.) was investigated in the laboratory using their responses to oviposition sites illuminated by light of defined intensity and spectral composition. An inverse relationship between the illumination of an oviposition site and its selection for egg-deposition enabled the sensitivity of the mosquitoes to narrow wavelength bands to be assessed. This species showed low sensitivity to long (red) wavelengths; a peak of maximum spectral sensitivity near 550 mμ (yellow-green) with a range of significant sensitivity about this maximum between 450 (violet) and 630 mμ (orange); and positive sensitivity at 366 mμ (ultraviolet) which, from the different order of effectiveness in deterring oviposition, may represent a second, independently functioning, light receptor system. This pattern of sensitivity is sufficient to explain all published observations on the responses of mosquitoes, in physiological conditions other than gravidity, to coloured stimuli. It may, therefore, represent the spectral sensitivity of mosquitoes in general.