Fourteen populations of the western flower thrips Frankliniella occidentalis Pergande, originating from different hosts and countries in Asia, Europe, North America and New Zealand, were analysed for their competency and efficiency to transmit tomato spotted wilt virus (TSWV). All populations acquired and subsequently transmitted the virus, and were thus competent to transmit. They show marked differences in their efficiency, expressed as the percentage of transmitting adults. Efficiencies varied from 18% for a F. occidentalis population from the USA (US2) to 75% for a population from Israel (IS2). The differences between populations were not affected by the amount of virus ingested or by the host plant used. However, the tospovirus species studied and age at which the larvae acquired the virus affected the efficiency to transmit. First instar larvae of the NL3 population from The Netherlands were able to acquire tomato spotted wilt virus, whereas second instar larvae failed to do so. However, both instars of this population acquired impatiens necrotic spot virus (INSV), another tospovirus. This and tomato spotted wilt virus were both acquired by both larval stages of the populations IS2 and US2, although their ability to acquire virus decreased with their age. Hence, it is likely that, in general, both instar larvae of most F. occidentalis populations are competent to acquire both tospoviruses. These results show that large differences exist in the efficiency by which tomato spotted wilt is transmitted by the various F. occidentalis populations and that the ability to acquire tospovirus decreases with the age of the larvae

The factors of resistance to many insecticides were located and isolated in a homozygous condition from the diazinon-selected SKA strain of house-flies (Musca domestica L.) by inbreeding each of the five autosomes of the SKA strain into a susceptible multi-marker strain ac;ar;bwb;ocra SRS. The insecticides were: DDT, methoxychlor, tri-butyl tin, the methoxy and ethoxy analogues of parathion, chlorthion and malathion and their corresponding phosphates, diazinon and diazoxon.

The SKA flies' autosomes had the following factors of resistance:—autosome I—very slight resistance to ethyl-chlorthion; autosome II—gene a for low ali-esterase activity which conferred weak to moderate resistance against all organophosphates tested, and Deh (DDT-dehydrochlorinase) which gave great resistance to DDT, but none against methoxychlor; autosome III—Pen, which delayed knock-down by slowing down the entry of insecticides into the flies and had a negligible effect at death except against tri-butyl tin and methoxychlor, and a factor of resistance to Zectran unaffected by sesamex; autosome IV—Dld, the major factor of resistance to dieldrin; and autosome V—Ses, a sesamex-suppressed factor, which gave weak to moderate resistance against ethyl-malaoxon, diazoxon, diazinon, DDT and methoxychlor, but was ineffective against the other organophosphates tested.

TBTP (S,S,S tri-butyl phosphorotrithioate), an ali-esterase inhibitor, greatly synergised organophosphates only against insects with gene a. Pretreatment with sesamex, an inhibitor of microsomal activity, elicited two types of response: antagonism with most of the thioates, most pronounced in flies with gene a, and synergism with the phosphates, especially evident with flies with factor Ses. The possible reasons for differences in the response to organophosphates after pretreatment with TBTP or sesamex, and the nature of the resistance factors are discussed. High resistance in SKA flies against organophosphates arises through the interaction of resistance factors which singly give only weak to moderate resistance.

Whiteflies of the Bemisia tabaci (Gennadius) group are a major and increasing problem for agriculture throughout the world. In particular, the appearance and rapid spread of a highly virulent new form (silver-leaf whitefly, or B-biotype; Brown et ah, 1995), and recognition that the problem involves a complex of sibling species, host races and/or biotypes has stimulated intensive multidisciplinary research on this insect in recent years (Gerling & Mayer, 1996).

The intimate association between a blood meal and ovulation in all female mosquitos, with the exception of a few (de Buck, Roubaud) has been clearly recognised; but the peculiar manner in which the presence of blood in the stomach can influence the formation of eggs is not understood. Two explanations may be suggested: it may either act as a physico-chemical stimulus to the ovarian follicles, or certain constituents in the blood may furnish some nutrient material for the development of the eggs.

Radar observations have consistently shown that high-altitude migratory flight in insects generally occurs after mass take-off at dusk or after take-off over a more extended period during the day (in association with the growth of atmospheric convection). In this paper, we focus on a less-studied third category of emigration – the ‘dawn take-off’ – as recorded by insect-monitoring radars during the summer months in southern England. In particular, we describe occasions when dawn emigrants formed notable layer concentrations centred at altitudes ranging from ca. 240 m to 700 m above ground, very probably due to the insects responding to local temperature maxima in the atmosphere, such as the tops of inversions. After persisting for several hours through the early morning, the layers eventually merged into the insect activity building up later in the morning (from 06.00–08.00 h onwards) in conjunction with the development of daytime convection. The species forming the dawn layers have not been positively identified, but their masses lay predominantly in the 16–32 mg range, and they evidently formed a fauna quite distinct from that in flight during the previous night. The displacement and common orientation (mutual alignment) characteristics of the migrants are described.

A wind-tunnel bioassay system, developed previously for the evaluation of long-range host-location stimuli, was used to investigate the responses of Anopheles arabiensis Patton to floral odours. Mosquitoes were found to respond by flight and landing to Achillea millefolium inflorescences and also to the odour of A. millefolium in the absence of visual stimuli. An air-entrainment technique was used to extract floral odours for biological and chemical testing. Both sexes of Anopheles arabiensis were found to respond to the floral odour extract. The major component of the floral odour was tentatively identified as a cyclic or bicyclic monoterpene.

Omnivory is common among arthropods, but little is known about how availability of plant resources and prey affects interactions between species operating at the third and fourth trophic level. We used laboratory and field cage experiments to investigate how the provision of flowers affects an omnivorous lacewing, Micromus tasmaniae (Hemerobiidae) and its parasitoid Anacharis zealandica (Figitidae). The adult lacewing is a true omnivore that feeds on both floral resources and aphids, whereas the parasitoid is a life-history omnivore, feeding on lacewing larvae in the larval stage and floral nectar as an adult. We showed that the effect of floral resources (buckwheat) on lacewing oviposition depends on prey (aphid) density, having a positive effect only at low prey density and that buckwheat substantially increases the longevity of the adult parasitoid. In field cages, we tested how provision of flowering buckwheat affects the dynamics of a four trophic level system, comprising parasitoids, lacewings, pea aphids and alfalfa. We found that provision of buckwheat decreased the density of lacewings in the first phase of the experiment when the density of aphids was high. This effect was probably caused by increased rate of parasitism by the parasitoid, which benefits from the presence of buckwheat. Towards the end of the experiment when the aphid populations had declined to low levels, the effect of buckwheat on lacewing density became positive, probably because lacewings were starving in the no-buckwheat treatment. Although presence of buckwheat flowers did not affect aphid populations in the field cages, these findings highlight the need to consider multitrophic interactions when proposing provision of floral resources as a technique for sustainable pest management.

Responsiveness to stimuli eliciting probing was measured in individual, suspended males of Glossina morsitans Westw. The standard stimulus was a warmed foam rubber ball offered from below; a positive response was recorded if the fly exsheathed its haustellum and probed the foam. During four days without food, probing responsiveness increased linearly from zero in mature flies, but with an initial step-up in tenerals. Each day's increase was steeper than the overall rate, and apparently modulated in the V-shaped pattern typical of other responses in tsetse flies. Starvation is thus seen to induce changes in feeding thresholds which parallel those induced in flight behaviour.

A granulosis virus was tested on a field scale at Manjimup and Pemberton in Western Australia for control of its host, the potato moth Phthorimaea operculella (Zell.). The virus was produced on laboratory-reared larvae, and applied as a suspension of pulverised larvae (6 275 in 111 gal/ha) to second-crop (December-planted) potatoes. There were untreated and insecticide-treated (DDT, dieldrin, methyl-demeton) fields for comparison. The effectiveness of the treatments was assessed on numbers of larval mines and tuber damage. Virus infection rates of 100% were achieved, with a residual effect of 12 weeks. Variation in larval body weight indicated that initial dosages and those due to recycled virus were excessive, but were optimum after two months. Virus applications were as effective in preventing damage as insecticide treatments. Virus spread to untreated crops some miles distant was attributed to movements of personnel, farm materials or birds.

About 130 species of parasitoids and predators are reported, most of them for the first time, to be associated directly or indirectly with the cassava pest Phenacoccus manihoti Matile-Ferrero and its parasitoid, Epidinocarsis lopezi (De Santis), newly introduced into Africa as a biological control agent. About 20 species are common. The species are grouped in 11 guilds, which include the indigenous hyperparasitoids, which originally attacked parasitoids of other mealybugs, the predators with which E. lopezi competes for the same food source and their antagonists.

The three-dimensional pattern of dispersion of five species of grain-infesting beetles was analysed in a 12-in.-cube bulk of wheat, kept in darkness at 25°C. and 14 per cent, moisture content, and built up of four layers, each of 16 three-in.-cube bags of Terylene net; the net retained the grain but allowed passage of insects. One hundred adults were placed in the centre of the upper surface of the topmost layer and after two weeks the entire bulk was broken down and the number of insects in each bag was determined. Five replicates were used for each species. More recoveries of Sitophilus granarius (L.), Tribolium castaneum (Hbst.), Rhyzopertha dominica (F.) and Cryptolestes ferrugineus (Steph.) were made from the top quarter of the bulk than from any of the lower layers. The vertical dispersion of Oryzaephilus surinamensis (L.) was homogeneous. Lateral dispersion was homogeneous with T. castaneum, R. dominica and C. ferrugineus, but with S. granarius and O. surinamensis relatively more recoveries were made from the corner units of the bulk than from elsewhere. The dispersion pattern assumed by a species in a uniform bulk is affected by locomotory activity, boundary response and intragroup stimulation. Thigmotaxis was demonstrated in S. granarius, persisting at relatively high densities; thus, following dispersal, individuals collect along habitat boundaries and then move up them as a result of intragroup stimulation. The positive response to boundaries shown by individuals of T. castaneum in isolation breaks down in crowded conditions, producing movement back into the bulk of grain and thus homogeneous lateral dispersion. O. surinamensis shows a positive response to habitat boundaries but no movement up them. Dispersal is slow in R. dominica, but the ultimate pattern of vertical dispersion is homogeneous. C. ferrugineus shows a tendency to form clumps, even in conditions free from marked physical gradients. The data are discussed in relation to ecology of the species, low-density populations, aggregation behaviour and a dynamic concept of population dispersion.

Characteristic temporal patterns of attack by Sirex noctilio F. in Tasmania were obtained when Pinus radiata trees were either felled, completely lopped or high trimmed and girdled. Felling resulted in immediate attack whereas lopped and girdled trees were not attacked until some 9–12 days later. Felled trees were susceptible to attack for about 14 days, but lopped and girdled trees were attacked for longer periods. In some instances girdled trees remained susceptible for more than one season. Oviposition by caged S. noctilio females on healthy trees was followed by attack from wild females about 9 days later. It is shown that the timing and duration of attack by S. noctilio are correlated with the degree of stress undergone by the host tree.

1-Octen-3-ol is a kairomone for many haematophagous insects including mosquitoes. Numerous studies have examined the effects of racemic 1-octen-3-ol; however, few studies have investigated the role of individual enantiomers in relation to mosquito attraction. In the present study, we investigated the behavioural and electrophysiological responses of two mosquito species, Aedes aegypti and Culex quinquefasciatus, to individual enantiomers and mixtures of 1-octen-3-ol, employing a laboratory Y-tube olfactometer and single sensillum recordings. The olfactory receptor neurons of both Ae. aegypti and Cx. quinquefasciatus had a significantly higher response to the (R)-1-octen-3-ol enantiomer compared to the (S)-1-octen-3-ol enantiomer at 10−9 g μl−1 to 10−6 g μl−1. Behaviourally, Ae. aegypti was more responsive to the (R)-1-octen-3-ol enantiomer, showing an increase in flight activity and relative attraction compared to Cx. quinquefasciatus. The (R)-1-octen-3-ol enantiomer caused an increase in activation for Cx. quinquefasciatus. However, the most notable effect was from an (R:S)-1-octen-3-ol mixture (84:16) that caused significantly more mosquitoes to sustain their flight and reach the capture chambers (demonstrated by a reduced non-sustained flight activity), suggesting that it may have a behaviourally excitatory effect. For Cx. quinquefasciatus, a reduced relative attraction response was also observed for all treatments containing the (R)-1-octen-3-ol enantiomer, either on its own or as part of a mixture, but not with the (S)-1-octen-3-ol enantiomer. This is the first time enantiomeric selectivity has been shown for Ae. aegypti using electrophysiology in vivo. The implications of these results for exploitation in mosquito traps are discussed.

Genetic variation in the southern green stink bug Nezara viridula (Linnaeus) from 11 geographically separated sampling locations (Slovenia, France, Greece, Italy, Madeira, Japan, Guadeloupe, Galapagos, California, Brazil and Botswana) was studied by sequencing 16S and 28S rDNA, cytochrome b and cytochrome c oxidase subunit I gene fragments and random amplified polymorphic DNA (RAPD) analysis. Sequencing revealed 11 distinct haplotypes clustering into lineages A, B and C. Lineage C was characteristic for a single analysed specimen from Botswana. Lineage B was detected in Japan, and it probably arose in Asia. Haplotypes of European and American specimens belonged to lineage A; specimens from France, Slovenia, Madeira and Brazil shared highly similar haplotypes (>99%) from subgroup A1, while all the specimens from Greece, California, Galapagos and Guadeloupe shared a haplotype from subgroup A2. RAPD data were more variable but consistent with mtDNA sequences, revealing the same clustering. They separated the Botswanian specimen from Japanese specimens and from a group of more closely related specimens from Europe and America. Sequence and RAPD results both support the African origin of N. viridula, followed by dispersal to Asia (lineage B) and, more recently, by expansion to Europe and America (lineage A). RAPD analysis revealed two highly supported subgroups in Japan, congruent with mtDNA lineages A2 and B, suggesting multiple colonization of Japan. Invariant sequences at the 28S rDNA combined with other results do not support the hypothesis that cryptic (sibling) species exist within the populations investigated in this study.

In this method the toxicant is absorbed with blood serum onto a loose roll of chromatography paper; first-instar larvae of Lucilia cuprina (Wied.) are inserted into the air spaces of the roll and allowed to feed. Mortality of the larvae is assessed 24 h later. Typical results using diazinon, dichlofenthian and chlorfenvinphos against susceptible and resistant strains of L. cuprina showed larvae to have resistance factors 6–8 times higher than those for adults determined by established techniques.

Larvicide tests were conducted on five species of mosquitoes, each of which had one or more DDT-resistant strains. The high potencies of DDT and, to a large degree, of DDD were completely lost by resistance. Other compounds were affected in different degrees according to the resistance mechanisms present, as indicated by resistance spectra and the effects of synergists. DDT-resistant strains of Culex pipiens fatigans Wied., Anopheles quadrimaculatus Say and A. stephensi List, showed highly specific resistance to DDT, probably dependent on a dehydrochlorination mechanism. DDT-resistance in Aedes aegypti (L.) and A. gambiae was also high, but there was definite evidence of cross-resistance to biodegradable DDT-analogues (about ×4 and ×10, respectively). This low-level, but definite, cross-resistance extended to a number of other compounds, notably pyrethroids, insect development inhibitors, amines, etc. The presence of synergistic action by piperonyl butoxide suggested that this depended on a microsomal oxidation system.

Isotopically labelled (14C) DDT and malathion were used to study pick-up and penetration of these insecticides by larvae of normal and resistant Ae. aegypti. Both the actual and the percentage penetration of DDT were greater in the resistant than in the normal strain. Whatever the reason for this, it disposes of the possibility of reduced pick-up and penetration as a factor in DDT-resistance. With malathion, the percentage penetration was always higher in the susceptible strain than in the resistant one, though in some cases the actual amount was less.

A scattergram method was developed for explaining the variability in the levels of fat, residual blood-meals and residual dry weights (RDW) of field samples of Glossina. The pattern of changes in mean RDW and fat levels was shown to be similar for five species of Glossina (G. morsitans morsitans Westw., G. swynnertoni Aust., G. fuscipes fuscipes Newst., G. palpoiis palpalis (R.-D.) and G. tachinoides Westw.) but different for the two sexes. On the basis of previous laboratory and field work, a simple descriptive model is developed that suggests priority pathways during the life of the adult fly for the products of successive blood-meals. Initially, for tenerals of both sexes, the priority is to increase thoracic musculature (RDW) without excessive production of fat. Subsequently, male flies devote each blood-meal exclusively to the production of fat, an energy store used mainly for flight activity. Females show a gradual increase in both fat and RDW levels, which probably corresponds with the development of the larva in utero. Wing-fray measurements support this interpretation. During each pregnancy cycle, females accumulate a reserve of fat over and above that necessary for the production of each larva. This is apparently required at the end of each cycle when res piratory losses exceed the energy supply from blood-meals taken. Mean thaematin levels of the four larger species studied (G. morsirans, G. swynnertoni, G. fuscipes and G. palpails) also showed a consistent pattern of change during each pregnancy cycle. Females apparently feed once at the beginning of each cycle, once at a stage of pregnancy when the larva in utero is approaching the moult from the second to the third instar and finally during the middle of the third larval instar, when the meal may be quite small and repeated.

A survey of the populations of eggs and larvae of Heliothis armigera (Hb.) was made on the Cotton Research Station, Namulonge, in Buganda Province, Uganda, over the four-year period, 1954–57 inclusive, on cotton, maize, groundnuts, beans and, in one year, sunflower. The populations encountered were low in comparison with some other cotton areas in Africa. The oviposition rate on each crop closely followed the flowering cycle, and there was no indication of the population from one crop influencing that on a subsequent crop, even when their flowering cycles overlapped. Under the normal crop sequence there is a sufficient gap between the attractive phases of successive crops to cause dispersal, possibly to wild host-plants, of the moths emerging from pupae bred in the preceding crop.

The variation in population from year to year on a given crop was no greater than that between different localities in any one season. Maize and sunflower did not prove successful when tested as trap crops grown adjacent to cotton.

Earias spp. and Argyroploce leucotreta Meyr. were less abundant than Heliothis and together constituted only 27 per cent, of the total population of Lepidopterous larvae on cotton.

A method is described for breeding H. armigera, in the laboratory, in which the mean duration of the various stages was: egg, 4 days; larva, 24·8 days; pupa, 22·9 days; preoviposition period, 3·1 days; and oviposition period, 10·4 days. The mean number of eggs laid per female was 751·6, of which 71·4 per cent, hatched. Larval diets consisting of differing species and parts of food-plants caused significant differences in larval and pupal periods, the former being least (21·8 days) on maize silks and greatest (33·6 days) on sunflower corolla and receptacle, and the latter least (19·7 days) after larval feeding on three-week-old maize cobs and greatest (26 days) after seven-week-old cotton bolls. Pupae developing from larvae collected from the field did not exhibit any diapause or resting stage.

Two egg parasites and 15 larval parasites (three of which were probably secondary) were bred from material of H. armigera collected in the field, but the degree of parasitism remained low throughout the year. A nuclear polyhedral virus disease of the larvae was also recorded.

It is concluded that under the climatic conditions encountered, H. armigera is active throughout the year because wild or cultivated food-plants are always available and no resting stage of the insect is induced; this continuous activity is accompanied by biologically controlling factors that maintain populations stable at a relatively low level.

Newly emerged females of Euoniticellus intermedius (Reiche) have no differentiated oocytes in their single ovariole. The eggs mature sequentially during the maturation period, and at 27°C the first egg is laid 4–8 days after emergence. The rate of oviposition increases with temperature between 18 and 32°C. The threshold for oviposition is 19·6°C, and one egg is produced for every four day-degrees above this threshold. Most females can be sorted into the nulliparous or one of three parous categories, covering the period from emergence to the time when between 75 and 127 eggs have been deposited, on the basis of the quantity of yellow body in the ovariole. The hardness of the cuticle, the degree of oocyte development, and the presence or absence of fat-body in the abdomen can be used to subdivide the nulliparous category into three parts and to recognise old or ‘spent’ beetles. The degree of wear on the tibial teeth gives an age estimate that is independent of nutritionally induced delays and with which the ovarian age can be compared. Actual age cannot be estimated in field-caught-beetles, however, since many factors besides temperature alter the rate of brood production.