Investigations showed that there is a highly significant linear dependence of the percentage of bee (Apis mellifera L.) colonies detectably infested with Acarapis woodi (Rennie) on the number of colonies in England and Wales. A decline of infestation since 1947 corresponds to a decrease recorded in the number of colonies. The simplest explanation, based on current knowledge, is that the decrease has allowed the foraging activity of the remaining colonies to increase, so lessening the contact between old infested bees and young susceptible individuals sufficiently to hinder the spread and multiplication of mites within colonies.

Variations in density of adults of Anopheles merus Dön. in Jimbo Village on the Kenya Coast were found to be correlated both with rainfall and with salinity at their breeding sites. Densities started to increase at the beginning of the rains when several breeding sites were formed. This was followed by a decline in numbers resulting mainly from the decrease in salinity in the semi-permanent breeding sites. A second rise occurred after the end of the rains, corresponding with an increase in salinity in the semi-permanent breeding sites due to evaporation. Peak density coincided with salinities of 30–50% sea water in the breeding sites. Laboratory breeding experiments showed that the larvae were usually capable of completing development in 0–100% sea water, with optimum development at 0, 40 and 60% sea water. Failure to complete development in 100% sea water at certain periods of the year indicated that there could be some seasonal variation in salt tolerance. The larvae were also found to complete development in alkaline saline water collected from an inland location around Lake Jipe in Kenya. The LC50s of sea water for first and fourth-instar larvae after exposure for 2 h were 135·0 and 930·0%, respectively. First-instar larvae were less to lerant of sodium chloride than of sea water of equivalent strength. The LC50 of sodium chloride for first-instar larvae was only 102·5%, sea water equivalent. In tests against first-instar larvae of other soluble chemical salts normally present in sea water, the highest LC50 (122·0g/litre) was of sodium sulphate and the lowest (10·5g/litre) of potassium carbonate.

Aphid species found infesting sugar-beet in Tasmania were Aphis craccivora Koch, Aulacorthum solani (Kalt), Macrosiphum euphorbiae (Thos.) and Myzus persicae (Sulz.). The activity of infective alatae over plots of sugar-beet established by sowing at different densities and arrangements to produce 12 treatments was gauged by recording the numbers of plants which became affected with virus yellows symptoms. The incidence of yellows increased as plant density decreased and as plant arrangement altered from rectangular to more square patterns. A regression equation of the form: where a, b, c and d were constants and x and y the intra- and interrow spacings, respectively, accounted for 92% of the variation produced by the 12 treatments. These results indicate that the incidence of virus infection in row crops resulting from aphid flight activity may be manipulated through altering plant density and arrangement.

Zeteticontus utilis sp. n., an encyrtid parasite of larvae of Carpophilus hemipterus (L.) and Urophorus humeralis (F.) in pineapple fields in Kenya and of C. hemipterus larvae in decaying fruit in Israel, is described. The parasite has been released in an attempt to control C. hemipterus in pineapple fields in Hawaii and is to be released against the same pest in Ohio.

Resistance to carbaryl, lindane and methidathion was studied in field and laboratory strains of Dysdercus fasciatus Sign., D. nigrofasciatus Stål, D. superstitiosits (F.) and D. cardinalis Gerst. from Kenya. Four-day old fifth-instar female nymphs were found to be the most convenient for bioassay. The LC50s of carbaryl, lindane and methidathion for D. fasciatus were 372, 240, and 110 mg/litre, respectively, those for D. nigrofasciatus 337, 294, and 111 mg/litre, and that for carbaryl for D. cardinalis 147 mg/litre. The Meru and Ngwata strains of D. fasciatus had resistance factors of ×5·3 and ×6·1, respectively, to carbaryl. The field strains of all four species showed slight resistance (up to ×3·4) to lindane and methidathion. The poor control of Dysdercus spp. experienced in Eastern Province, Kenya, is probably due to the development of resistance to carbaryl. A laboratory and a field strain of each of D. fasciatus and D. nigrofasciatus were subjected to carbaryl selection pressure for six generations of doses equivalent to the LC50-LC70. The laboratory strain of D. fasciatus was also subjected to lindane selection for six generations. The laboratory and field strains of D. fasciatus developed resistance to carbaryl of ×3·7 and ×5·7, respectively, and cross-resistance to lindane of up to ×2·7. No significant increase in resistance was observed in D. nigrofasciatus after selection. The laboratory strain of D. fasciatus developed resistance to lindane of ×5·5 after selection and cross-resistance to carbaryl of ×4·3.

The productivity of Glossina palpalis palpalis (R.-D.) reared in vitro via silicone rubber membranes on fresh guinea-pig blood equalled the productivity of flies fed in vivo on guinea-pigs. Over 50 days, the number of puparia per initial female was 3·0 in both cases. Puparial weights were greater than 31 mg throughout the four reproductive cycles. While fresh blood was an excellent diet for G. p. palpalis, freeze-dried guinea-pig blood was unsuitable; survival, reproduction and puparial weights were all low for flies fed on freeze-dried blood. The evidence lends support to the theory that there is no inherent nutritional deficiency caused by feeding on blood through a membrane.

Alcestis ingens sp. n. is described from a series of adults collected in stands of hybrid cacao between Ilhéus and Itabuna, Brazil.

The life-span and fecundity of females of Spodoptera littoralis (Boisd.) of strains that originated from Crete and Egypt were studied in relation to delays in mating. Virgin females and those that were not mated until eight days from emergence lived longest (means of 17 and 18 days, respectively). Earlier matings progressively reduced life-span; those mated at 0 or 1 day lived for averages of only 7·5 to 10·5 days. Preoviposition periods were extended when mating was delayed, from averages of 2 and 3 days, to averages of 9 and 10 days. Both the number of eggs laid and the percentage hatching were reduced by delays in mating beyond a critical period. In the Cretan stock this critical period was two days, but in the Egyptian stock it was less than a day. Cretan females mated early in life laid, on average, 726 eggs each and produced 541 caterpillars. When mating was delayed for four and six days, only 303 eggs were laid per female and only 93 caterpillars hatched. In the Egyptian stock females mated within one day of emergence laid 1208 eggs each and produced 948 caterpillars, compared with 499 eggs and 199 caterpillars for those not mated until six or eight days after emergence. Since a two-day delay in mating reduced the number of caterpillars to between one-fifth and one-tenth of those that resulted from early matings, it would appear that a smaller caterpillar population would result from control methods that reduced the availability of males, either by mass-trapping or blanket-spraying crops with pheromone.

The African rice gall midge, Orseolia oryzivora sp. n., is described and illustrated from adults of both sexes, larvae and pupae collected in West Africa. This species had previously been misidentified as O. oryzae (Wood-Mason), which is a major pest of rice in Asia, but the two species are morphologically distinct in the larval, pupal and adult stages. All available African material has been examined, and O. oryzivora is recorded from cultivated rice in Senegal, Upper Volta, Ivory Coast, Nigeria and the Sudan. Larvae and pupae collected from Paspalum in Upper Volta differ from typical O. oryzivora in some morphological characters and probably represent an undescribed species of Orseolia

Dimorphopterus cornutus novaeguineae subsp.n. is described from Papua New Guinea. Adults and immatures were collected from dying rice and a lawn of carpet grass (Axonopus compressus). Members of the genus Dimorphopterus and allied genera are known as chinch bugs and damage Gramineae in the tropics and subtropics. The differences between this subspecies and D. cornutus cornutus Slater are illustrated and described in detail.

The construction and functioning of a light-trap designed to catch only insects in flight at a height of greater than 5·5 m is described. The trap segregates the catch into hourly samples throughout the night.

The flight performance of Simulium ornatum Mg. s.l. was measured under laboratory conditions using a simple flight mill. Males and unmated females were flown and the duration, distance and average speed of flight were recorded for adults fed on water only, sucrose, blood & water, or blood & sucrose. On 91% of all test occasions sucrose-fed insects flew but 25% of those on water only did not fly. Feeding flies on 10% sucrose solution markedly improved both willingness to fly and flight performance, and under these conditions maximum duration, distance and average speed recorded were 4.9 h, 4·2 km and 2·84 km/h, respectively. The ratio of average to maximum speed was 0·631 for females and 0·610 for males, with absolute maximum speeds of 3·19 and 2·99 km/h, respectively. Duration and distance flown were well-correlated, speed being the least variable aspect of flight performance measured. The distributions of flight duration and distance flown were skewed such that few insects made long flights. Mean flight performance at different ages was measured; unmated females appeared to retain a high level of willingness to fly throughout the age-range tested (up to 33 days). The longest recorded flight (5·3 h) was made by a female during an overnight experiment. The implications for long-range flight movements by simuliids are discussed.

Three benzyl-l,3-benzodioxoles and three benzylphenols were tested for their ability to sterilise Glossina morsitans morsitans Westw. following topical application in acetone. Two of the former compounds, 5-ethoxy-6- (4-methoxyphenylmethyl)-l,3-benzodioxole and 5-ethoxy-6-[l-(4-meth-oxyphenyl)ethyl]-l,3-benzodioxole, caused total sterility in females at a dose of 10 μg per fly, and remained effective even after one year's storage at 4°C. Dose-fecundity data indicate a reduction to 50% fecundity (ED50) was achieved with 2·5 μg of the former or 0·5 μg of the latter per fly. An ED90 of 8·5 μg and 2·5 μg, respectively, is indicated. The latter compound reduced the survival of treated females and males and surviving males were incapable of inseminating even though copulation appeared normal. The effects on female survival and fecundity, of feeding the compounds at 0·25 and 1·0% in blood, were variable, owing to their low solubility and variations in the size of blood-meals. The highest doses of the former compound led to ovarian atrophy in females, which can be described as an effect on fecundity. Lower doses induced sterility through egg death and atrophy after ovulation. The latter compound acted more rapidly than the former, preventing ovulation of the first mature oocyte in a higher proportion of flies. The activity of these compounds, which were derived by modification of plant materials, and are non-mutagenic, renders them likely candidates for evaluation as contact insecticides for Glossina in the field.

In the presence of the odour of carbon dioxide and acetone, an electrified net adjacent to a stationary cylindrical black model in the Zambezi Valley, Zimbabwe, in the hot dry season caught more adults of Glossina morsitans morsitans Westw. and G. pallidipes Aust. than in the absence of odour. In the absence of odour, a moving model attracted more G. m. morsitans males than did a stationary model. Between 20 and 50% of males of G. m. morsitans but only 0 to 12% of males of G. pallidipes near a model were caught by electrified decoys (surrogate females) on the model. Hidden observers recorded the numbers of flies copulating with decoys baited with pheromone or pheromone plus bisazir (P, P-bis(1-aziridinyl)-N-methylphosphinothioic amide) on a stationary model with odour between 16.00 and 19.00 h daily. Males of G. m. morsitans contacted the decoys with much greater frequency than did males of G. pallidipes although the latter species was the more abundant. The numbers of copulatory attempts by G. m. morsitans males during each 10 min suggested that changes were a function of the total numbers of flies attracted to the model. At all times of the day, the average duration of copulation was 37–40 s. However, approximately 50% of responses were of 10 s duration or less and fewer than 10% endured for longer than 3 min. The presence of bisazir on the decoys did not influence the response duration or the total numbers of flies responding. A comparison with laboratory data suggested that further refinement of technique will allow pheromone-baited decoys to be used in the autosterilisation of G. m. morsitans males with bisazir in the field.

Visual counting was found to be the most accurate method of estimating cereal aphid numbers in field studies in England. Vacuum sampling decreased in efficiency as aphid density increased, but could be a useful alternative to visual counts at very low aphid densities when the latter became too time-consuming. Cutting tillers for later washing in the laboratory was less efficient than visual counting as aphids, especially Metopolophium dirhodum (Wlk.), fell off the plants during sampling, but this method was useful in determining the proportion of different morphs of Sitobion avenae (F.) present at very high densities.

Two mark-release-recapture experiments with Anopheles culicifacies Giles were carried out immediately before and one month after a round of malathion spraying of houses (at 2 g/m2) in a village in north-western Sri Lanka. In the first experiment the measurement of bidirectional movement of females collected in two halves of the village showed that movement was somewhat affected by wind direction; the percentage of migrants moving partially upwind was greater (11·4) than that in the reverse direction (6·4). The best estimates of daily survival were 0·79 before spraying and 0·44 after spraying; population sizes were about 44 500 and 1300, respectively. The proportion of females resting in the collection huts rose after spraying. The results are discussed with reference to the evolution of insecticide resistance in populations under insecticidal pressure and those populations not selected by spraying.

A method for screening resistance of cowpea (Vigna unguiculata) to the legume pod-borer Maruca testulalis (Geyer) was developed. Several damage parameters were measured, including damage to stem, flowers, pods and seeds. Some of these parameters were assessed in more than one way. A decision was made at the end of the study as to which parameters were most appropriate for a field screening methodology. A plant resistance index, Ipr, was generated to aid in this decision. Based on this, it was concluded that flower, pod, and seed damage measurements provided the most important assessment of resistance to the borer. The larval population in the flowers showed marked differences in infestation levels between cultivars and is suggested as a means of comparing results in the future. Based on the methodology described, TVu 946 was the most resistant cowpea cultivar in every category of assessment. Five other cultivars were also selected for further evaluation as probable resistance donors: Kamboinse Local, TVu 1, VITA-5, TVx 3890–010F and VICAM-1/SP. The rationale behind the development of a field-screening methodology and some of its shortfalls are discussed.

Alatae of Myzus persicae (Sulz.) were made to fly and then released directly onto untreated or chemically treated surfaces where settling behaviour was studied. Most aphids probed host-leaf surfaces even in the presence of vapour of (E)-β-farnesene, the main component of aphid alarm pheromone, or when related behaviour-controlling chemicals were painted on the leaf. Flown aphids attempted to probe most surfaces on which they landed, including glass and green paper. However, they did not probe white filter papers. Sublethal deposits of deltamethrin did not prevent initial probing on plant surfaces but caused uncoordinated leg movements which resulted in aphids falling from the plants.

Surveys of parasites of Sylepta derogata (F.) on cotton at Ibadan, Nigeria, in 1979–80 showed that there were three larval parasites: Apanteles syleptae Ferrière, A. sagax Wlkn. and Charops sp. An average of 17·7% parasitism was recorded, and A. syleptae accounted for 98·6% of this. There were three pupal parasites: the chalcidid Brachymeria feae Masi, the ichneumonid Xanthopimpla sp. and the tachinid Cadurcia auratocauda (Curr.). Together, they caused an average of 31·7% parasitism. Xanthopimpla was the most abundant, while B. feae was of secondary importance.

In the Gambia, bed nets are often used for protection from mosquitoes although some of the nets are often in poor condition. In a village where the most abundant man-biting mosquito was Anopheles gambiae Giles s.s., nets in different condition were compared by assessing the success of mosquitoes in feeding. All the nets tested reduced mosquito feeding, and this reduction correlated with the number and size of holes in the nets. The experiments were conducted in purpose-built huts with verandah traps to sample the mosquito population leaving the hut. Although the majority of males and fed females of A. gambiae remained in the huts each morning, unfed females usually left the huts the same night, probably in search of alternative food sources.