In a Gambian village, the peak collections of females of the complex of Anopheles gambiae Giles occurred three months after the onset of the heaviest rains; 32% of these were A. melas Theobald, and 54% of blood-meals were identified as originating from man. Counts of A. gambiae s.l. in rooms containing permethrin-treated bed nets were compared with those in rooms containing placebo-treated nets. The numbers in the permethrin-treated nets were far lower than in placebo-treated nets. A higher rate of exophily was noted in rooms containing permethrin-treated nets. The numbers of unfed A. gambiae s.l. found inside the rooms with placebo-treated nets were significantly higher than those with permethrin-treated nets. However, the proportion fed and the mortality in the exit traps were not significantly affected by permethrin treatment. Three-minute bioassays conducted on four different fabric types impregnated at the same concentration showed that the toxicity varied between the fabrics. Handwashing severely reduced the toxicity and approximately halved the permethrin content. Bed nets are frequently washed in Gambian villages, and this could be a problem in the application of permethrin impregnation of bed nets for vector control. Methods are discussed to overcome this problem at the village level.

Trioza erytreae (Del Guercio), the vector of the serious citrus greening disease, was found to be highly attracted to yellow surfaces, particularly fluorescent yellow-green (about 530 nm). The phototactic response was used to develop a monitoring trap using 3M Saturn Yellow self-adhesive tape adhering to a glass or Perspex sheet. Transparent PVC foils smeared with a thin layer of clear polybutene were clipped in position over the Saturn Yellow surface and acted as the sticky catchment surface. A spectroradiometric comparison of new and weathered traps indicated only a 10% decrease in reflectance after one year. The traps were a sensitive indicator of psylla abundance. Valencia orchards in the Transvaal, South Africa, supported higher population levels than did navel orchards. A mass-trapping experiment was also done, and involved a cordon of yellow sticky polyethylene strips (Gundle Flexipipe smeared with polybutene) placed around an orchard. This perimeter barrier was combined with aldicarb-treated trap trees within the orchard in an attempt to reduce further the already low psylla numbers. Inside the experimental area there was no statistically significant drop in psylla numbers compared with the control trees outside. These poor economic results making use of the flight response of T. erytreae suggest that carefully integrated biological and chemical suppression of the psylla vector is at present the most practical entomological method for containing greening disease on mature trees.

The survival of Oryzaephilus surinamensis (L.) and Sitophilus granarius (L.) adults at the surface and centre of two 40-tonne bins of wheat, each aerated at about 10 m3/h per tonne was studied in separate experiments over three successive years. In one bin, fan operation was controlled manually, but in the other an automatic differential thermostat was used. This switched on the fan when the centre of the bin was 2°C warmer than the ambient. O. surinamensis always survived better than S. granarius in the same bin and position. Both species survived better at the surface of each bin than at the centre, and both died quicker at the centre of the bin with aeration controlled with a differential thermostat, where the grain temperature was usually less than 4°C, than in the bin with aeration regulated manually, which was mainly above 6°C. However, there was no difference between bins in the survival of either species at the surface. S. granarius always died out in both positions in both bins, but O. surinamensis always survived at the surface of both bins, and in one year it survived at the centre of the bin with aeration controlled manually.

Migration and colonization of the coconut palm by Eriophyes guerreronis (Keifer) was studied in St Lucia in the West Indies. Mites were not found in unfertilized flowers but were present within a few weeks of fertilization. Nuts remained vulnerable to colonization for a number of months, and mites were present on nuts for up to 13 months. Protection of nuts for the first few months after fertilization is of most importance. On the tree, much migration could be due to mites walking in large numbers across nut surfaces, and they could move from one inflorescence to another if the two were in contact. Increased nut damage appeared to encourage mite migration.

The biology of overwintering populations of adults of Culex pipiens L. was studied between October 1977 and April 1980 in southern England. Data obtained from population studies showed that there was a rapid build-up at the beginning of hibernation in August, reaching a peak in late October-early November each year and gradually decreasing from December. Extensive movement both in and out and within the hibernation site occurred, with many individuals changing their locations or hibernacula during the course of hibernation. Studies on induced feeding showed that in the early months of hibernation (August-October) exposure to constant light for a minimum period of 12 days was required before the females would take a blood-meal. This period decreased during the course of hibernation. Observations on the physiological condition of hibernating females revealed that up to 90% of the population were inseminated. A few parous females entered hibernation shelters at the onset of winter but did not survive the winter. Furthermore, females used up about 80% of their fat food reserves during hibernation, while there was little or no change in the quantity of glycogen present. From an assessment of the impact of mortality factors on a population of known size, it was observed that exodus from the hibernation shelters accounted for about 30% reduction in the population size while depletion of food reserves and predation by spiders accounted for approximately 15 and 20% mortality, respectively.

Acclimation had a beneficial effect on Scottish clones of Aulacorthum solani (Kaltenbach) as seen in enhanced reproduction and development at 5°C, compared with non-acclimated clones at this temperature. In contrast, not all Myzus persicae (Sulzer) clones tested benefited. When reared at 5°C for a second generation, both species had slower nymphal development and M. persicae also had less efficient adult reproduction (a longer pre-reproductive period and reduced fecundity) compared with the first generation. Both species demonstrated a high capacity for recovery from low temperatures, A. solani being the better of the two. In general however, the ability of clones to survive, reproduce and develop at low temperatures or upon transfer to high temperatures, was variable and was not related to annual cycle, origin or organophosphorus resistance. These differing responses support previous results and are suggested as being an efficient means of ensuring variability in aphid populations surviving after winter.

Laboratory bioassays with gravid females of Lucilia cuprina (Wiedemann) were used to isolate the source(s) of olfactory attractants emanating from larvae-infested media. Adults were not attracted by odours from axenic (micro-organism-free) larvae, but volatiles from xenic larvae were highly attractive. The attractants proved to be kairomones not pheromones, as odours from other species of calliphorids and a sarcophagid species were also attractive. Axenic, proteinaceous media produced a low level of attractive volatiles, which was increased by the activities of axenic larvae growing on the media. A greater degree of attraction occurred to odours from xenic media, and this too was much increased by the actions of growing larvae. The order of attractiveness of such volatiles is therefore: xenic with larvae >> xenic without larvae > axenic with larvae > axenic without larvae. It is concluded that larvae-infested media owe their great attractiveness to the volatiles produced by the action of micro-organisms, not to specific larval volatiles. Larval activity accentuates the output of attractive volatiles from both xenic and axenic proteinaceous media, possibly due to the effects of digestive enzymes, pH changes, mechanical mixing, warming or aeration or a combination of some or all of these factors.

Spodoptera exempta (Walker), in common with several noctuid moths, exhibits a density-dependent phase polyphenism. The abdominal glyceride contents of both sexes at emergence were 2·5 to 6·1 times greater in the gregaria than in the solitaria phase moths. Abdominal and thoracic total protein levels, haemolymph total protein, glyceride and carbohydrate, and the relative quantities of tri-, di- and monoglycerides were comparable in the two forms. Weight-related fecundity was strongly influenced by larval phase. Females from solitaria larvae produced approximately half the numbers of eggs laid by those reared in crowded conditions, but this difference was only evident in moths allowed distilled water. Moths having access to sucrose laid comparable numbers of eggs, irrespective of phase. There were no differences in the levels of metabolic reserves in the eggs. Differences in glyceride content, preoviposition period, fecundity and lifespan were apparent between laboratory strains. The implications of these differences for migratory flight and reproduction in the field are discussed.

Radioactive (32P) and genetic (recessive eye-colour mutation) markers were used to estimate egg to pupal survival of Musca vetustissima Walker. Both marking techniques provided similar survival estimates under laboratory and field conditions in Australia. Egg to pupal survival rarely exceeded 10% in samples at intervals during spring and summer. Abiotic (dung quality and weather) and biotic (other dung fauna) mortality agents were both important in limiting the breeding success of M. vetustissima, being jointly responsible for a seasonal mean mortality of 93·8%.

Sporadic previous reports of chironomid larvae feeding on roots of horticultural plants are reviewed and related to the growing recognition that a particular parthenogenetic species can damage severely indoor horticultural crops, particularly lettuce and young tomatoes. The taxonomy of the pest, Bryophaenocladius furcatus (Kieffer), is assessed, new synonymy proposed and a neotype and lectotype designated. The species is redescribed from the larva, pupa and adult female.

The species composition and population dynamics of mosquito adults trapped at 76 sites in southern Israel are described. Almost 200 000 specimens representing 23 species were collected. Five species, Aedes detritus (Haliday), Culiseta subochrea (Edwards), Culex antennatus (Becker), Cx. martinii Medschid and Cx. poicilipes (Theobald), are new records for this area, with Cx. poicilipes being recorded for the first time outside Africa. Six types of distribution patterns were discerned. The most abundant species was Cx. pipiens L. (79·7% of the total catch) followed by Ae. caspius (Pallas) (10%), Anopheles sergentii (Theobald) (2·1%), An. tenebrosus Dönitz (1·8%) and Cx. perexiguus Theobald (1·3%). All other species found each made up less than 1%. The spatial and temporal patterns of mosquito species in southern Israel are discussed.

The characteristics of the high and low density forms of noctuid moths, including Spodoptera exempta (Walker), exhibiting a density-dependent phase polyphenism have frequently been discussed in relation to migration. However, the only previous (unpublished) demonstration of an effect of larval phase on adult flight performance, using a tethered-flight technique, was invalidated by the recent discovery that the principal determinant of flight potential in S. exempta is genetic. When the incidence of prolonged flight was measured in moths derived from genetically-matched (full-sib) samples, there was a clear increase in long flights by females derived from the high-density gregaria phase larvae compared with those from solitaria phase larvae. The reasons for the apparent absence of a similar effect in males is not clear, but it is possible that the tethered-flight technique provides a less reliable index of flight capacity in this sex. The characteristics and significance of phase polyphenism in migratory noctuids are discussed. It is suggested that, in S. exempta and possibly some other comparable species, the high-density phase is adapted to accelerate re-dispersal after populations become concentrated, in order to escape the detrimental consequences of high larval densities.

Examples of Chrysomphalus aonidum (L.) from which the scale covers had been removed, were about six times as sensitive to malathion as intact insects (LC50s of 0·09% and 0·55%, respectively). These results indicate that the scale cover probably absorbed part of the insecticide. Immature stages of the external parasitoid Aphytis holoxanthus DeBach on C. aonidum were not affected by 0·13% malathion applied to the host. However, adults of the parasitoid, which were extremely susceptible, were exposed before or during emergence to lethal levels of the insecticide present in the host scale cover. The findings are discussed in the light of the adverse effects of malathion-bait sprays applied against Ceratitis capitata (Wiedemann) on beneficial insects, and failures of biological control of scale pests on citrus in Israel.

Field studies in Zimbabwe of the orientation of males of Glossina morsitans morsitans Westwood to decoy ‘females’ (9 × 3-mm rectangles of 2-mm thick brushed nylon, baited with sex pheromone, 15,19,23-trimethyl-heptatriacontane, and placed on a vertical, 1-m2 black cloth screen) demonstrated that (1) no olfactory response to air-borne pheromone was involved in the orientation of males to decoys, (2) the presence of decoys on a stationary screen did not increase the numbers of males landing on the screen, but they directed landings onto the decoys or the adjacent screen surface, (3) males did not differentiate between black or brown decoys, (4) males were more attracted to vertically oriented decoys on the screen surface than to decoys held away from the surface, and (5) males were more attracted to decoys at the centre of the screen than to decoys near the top or bottom edges. Points 1, 2 and 4 also applied in the case of G. pallidipes Austen using decoys dosed with its pheromone (13,23-dimethylpentatriacontane), but this species preferred black to brown decoys and showed less overt sexual activity than G. m. morsitans. Males of G. m. morsitans each removed 1–2μg of pheromone by contact with a decoy, leading to a gradual loss of the decoy's stimulatory power.

The biology of the predacious cricket Metioche vittaticollis (Stål) collected from rice in the Philippines was studied in the laboratory and greenhouse. The cricket preyed on the eggs of a range of insect pests of rice including Chilo suppressalis (Walker), Cnaphalocrocis medinalis (Guenée), Hydrellia philippina Ferino, Mythimna separata (Walker) and to a lesser extent on the eggs of Leptocorisa oratorius (F.). There was no predation on the eggs of Scirpophaga incertulas (Walker).

Investigation of 16 Scottish clones of Myzus persicae (Sulzer) and four of Aulacorthum solani (Kaltenbach) indicated that anholo-and androcyclic clones were predominant. A high incidence of organophosphorus resistance was found in androcyclic clones of M. persicae, but there was no indication of such resistance in A. solani. At 5°C as compared to 20°C, reproduction was decreased and development of nymphs was slower in both species. In addition, the pre-reproductive period and nymphal development time of A. solani were longer than those of M. persicae. Clonal differences in M. persicae at 5°C could not be related to origin, annual cycle or level of organophosphorus resistance, however A. solani clones from the west of Scotland may have been less affected by this temperature than those from the east. The lower limit of reproduction and development in both species was near 2°C. Neither adult survival nor fecundity of clones at this temperature were related to annual cycle, origin or organophosphorus resistance, but anholocyclic M. persicae nymphs survived longer at 2°C than holo- or androcyclic nymphs. A. solani adults survived significantly longer than those of M. persicae. M. persicae survived sub-zero temperatures better than A. solani. In neither species could percentage survival be related to stage of development, gut contents, presence or absence of wings, annual cycle, origin or organophosphorus resistance. Acclimation did, however, increase percentage survival.

Bibionid flies were sampled in grassland in Northern Ireland from 4 April to 13 June 1985 using water and sticky traps with a range of characteristics. Nearly 70 000 bibionids were taken, of which 89·5% were males. Bibio johannis (L.) accounted for 96% of the catch, the rest comprising Dilophus febrilis (L.) (3%) and D. femoratus Meigen (1%). Trapping was carried out adjacent to a hedgerow and in the centre of the field. Differences in the abundance of the flies at these two locations occurred for all three species. Yellow was the best colour for maximizing catches. Greater numbers of B. johannis (63%) were taken in water than sticky traps, but over 76% of Dilophus spp. were caught on the latter. Increasing the diameter of water traps tended to enlarge the catch (principally B. johannis), but catch per unit area was relatively constant. The height of sticky traps above the ground affected the catch of all three species, indicating different flight levels.

The effect on aphid population development of creating natural enemy refuges by spraying only alternate strips of winter wheat with the aphid-specific insecticide pirimicarb at 140 g a.i./ha was compared with those in an unsprayed and a completely sprayed block in south-eastern England. The numbers of Sitobion avenae (F.), Metopolophium dirhodum (Walker) and Rhopalosiphum padi (L.) increased rapidly in the unsprayed block and in the unsprayed strips to reach similar peak densities in early August. Natural enemy activity was similar in these two areas, indicating negligible movement of predators and parasitoids from the sprayed strips to the unsprayed strips. Instead, aphids re-colonized the sprayed strips more quickly than the sprayed block, and the peak density in the former was similar to those in the unsprayed areas.

Changes in adult populations of Haematobia thirouxi potans (Bezzi) were studied in Hluhluwe Game Reserve, Natal, South Africa, between October 1981 and May 1983. While there were no unequivocal seasonal changes in fly abundance, population increases were recorded late spring–early summer and mid–late autumn. Of the two measures of fly abundance, namely the number of flies that emerged from dung pads almost free of other fauna and counts of flies from culled buffalo (Syncerus caffer), the former was correlated with the proportion of nulliparous females in the population (r = 0·82). While the average female completed a minimum of 2·7 ovarian cycles, up to 78% of females during winter were in the 4th or subsequent cycle. The size of flies collected from buffalo and from dung pads showed an overall reduction during the study period and was an important factor in both survival and fecundity. Differences in the preference of flies for buffalo over an Afrikander-Shorthorn cross heifer, were manifested in the sex ratio and proportions of nulliparous females and fed flies.

The efficiencies of people sampling cabbage plants in the field for total numbers of Myzus persicae (Sulzer) were found to differ. Significantly more aphids were counted on leaves taken to the laboratory than on leaves examined by inexperienced people in the field, but field counts by an experienced person did not differ significantly from the laboratory sample. The implications of differences between people and the possibility of correcting for them in surveys are discussed.