The effectiveness of inundative releases of the parasitoid Eretmocerus eremicus n. sp. Rose & Zolnerowich for control of Bemisia argentifolii Bellows & Perring on poinsettia in replicated experimental greenhouses was determined. We evaluated two release rates of E. eremicus: a low release rate (one female per plant per week, released in two greenhouses, in spring 1995) and a high release rate (three females per plant per week, released in two greenhouses, in spring 1994), each over a 14 week growing season. Each release trial had either one (1995) or two (1994) control greenhouses in which B. argentifolii developed on poinsettia in the absence of E. eremicus. Life-tables were constructed for B. argentifolii in the presence and absence of E. eremicus by using a photographic technique to follow cohorts of whiteflies on poinsettia leaves. Weekly population counts of whiteflies were also made. In the absence of E. eremicus, egg to adult survivorship of B. argentifolii on poinsettia was 75–81%. At the low release rate, egg to adult survivorship of B. argentifolii was 12% and parasitism was 34%. At the high release rate, egg to adult survivorship of B. argentifolii was 0.9% and parasitism was 10%. The average net reproductive rates (Ro) for populations of B. argentifolii in the absence of E. eremicus ranged from 20.5 to 26.1, indicating a rapidly increasing population density. Net reproductive rates for whitefly populations subject to parasitoid releases were 3.7 in the low release rate greenhouses, and 0.25 in the high release rate greenhouses, indicating substantially reduced B. argentifolii population growth. At week 14 of the trial, densities of immature whiteflies were lower in greenhouses at the low release rate when compared to the high release rate greenhouses. This was attributed to high levels of in-house reproduction by parasitoids at the low release rate.

Comparative bioassays of two chloronicotinyl insecticides, acetamiprid and imidacloprid, against the whitefly Bemisia tabaci (Gennadius), using foliar and systemic applications, were conducted under laboratory conditions and in field trials. Under controlled conditions, the ovicidal activity of foliar applications of acetamiprid on cotton seedlings was much higher than that of imidacloprid. According to LC50 and LC90 values, acetamiprid was 10- and 18-fold more potent than imidacloprid. Both compounds were effective when applied to soil against whitefly adults; however, the potency of imidacloprid was somewhat higher than that of acetamiprid 2, 7 and 14 days after application; resulting (with the concentration of 25 ml a.i./l) in adult mortality of 90, 93, and 96% and 76, 84, and 76% respectively. In an experimental cotton field, the efficacy of foliar applications of 60 g a.i./ha acetamiprid and 210 g a.i./ha imidacloprid was compared. Field residual activity of acetamiprid to whitefly adults lasted for approximately ten days, compared with three days for imidacloprid.

Site and time effects are important factors determining trap catches of tsetse flies. These factors may interact significantly and therefore confound interpretation of time series data used for population monitoring. We therefore investigated the magnitude and importance of site × time interactions in trap catches of Glossina pallidipes Austen and G. longipennis Corti using a 2200 trap-days (400 trap-months) data set. The interaction was found to be siginificant (p<0.05) in 46–100% of the combinations of different numbers of months and sites between 2 and 12. The mean percent variance due to the interaction ranged between 4% and 28% for G. pallidipes and 12% and 36% for G.longipennis. The interaction was usually less important than the effect of site alone but more important than the effect of time alone. These results suggest that tsetse researchers should examine critically the adequacy of existing approaches to population monitoring with traps and to testing new traps and odour baits.

Life tables were developed to assess the significance of natural enemies on the dynamics of apple ermine moth, Yponomeuta malinellus Zeller, in southwestern Germany and to select parasitoid species for use in the biological control of this pest in Canada. During the study from 1993 to 1995 the abundance of Y. malinellus varied from 1.5 to 4.3 tents per 100 leaf clusters indicating that this was a non-outbreak population. From the life tables it was evident that the impact of egg predators accounted for 25–43% of the total generational mortality of Y. malinellus, more than any other known mortality factor. Percent parasitism varied from 18 to 30%, but the impact of parasitoids in relation to the total generational mortality of Y. malinellus from the life tables was remarkably constant at 11–14%. The loss of potential fecundity had an important influence on the generational mortality of Y. malinellus, but declined from 27% to 15% over the course of this study. This decline corresponded with a rise in the net rate of increase R0 from 1.35 in 1993 to 6.8 in 1995, despite the impact of insect predators and parasitoids on the generational mortality. Yponomeuta malinellus was attacked by five different obligate primary parasitoids, a single obligate hyperparasitoid, and three facultative hyperparasitoids. Of these, the oligophagous egg-larval parasitoid Ageniaspis fuscicollis Dalman (Encyrtidae) and the oligophagous larval-pupal and pupal parasitoid Herpestomus brunnicornis Gravenhorst (Ichneumonidae) were selected as potential biological control agents for Canada due to a minimal degree of interspecific competition.

Field surveys, manipulative field experiments and laboratory studies were employed to study the behaviour and development of a large coreid, Amorbus obscuricornis (Westwood), in response to changes in the architecture/foliar quality of Eucalyptus (Myrtaceae) hosts in Tasmania, Australia. Following tree decapitation and subsequent regrowth, A. obscuricornis nymphs were only associated with coppiced hosts. Eucalypts coppiced naturally by wild fire were found to carry significantly more nymphs than non-coppiced conspecific hosts. In contrast, adult A. obscuricornis were found on both coppiced and non-coppiced hosts. The foliar quality of coppiced hosts was superior to that of non-coppiced hosts; being softer, having a higher moisture content and a lower C/N ratio. Field collected fifth instar nymphs were heavier when collected from coppice vs. noncoppice; but in bagged shoot experiments second instar nymphs gained less weight on coppice than non-coppice. It is suggested that because coppice is softer the shoots may deteriorate (i.e. wilt) more quickly than non-coppice shoots. Through different exposure regimes, it was confirmed that first instar nymphs need only water to ecdyse, while feeding is initiated in the second instar. Differences in the nutritional requirements of first and second instar nymphs were reflected in their behaviour. First instar nymphs did not discriminate between conspecific hosts on the basis of whether they were coppiced or not, whereas second instar nymphs preferentially chose coppiced conspecific hosts. The findings of this work are discussed in the context of the plant vigour and resource regulation hypotheses.

Muscidifurax raptorellus Kogan & Legner is a gregarious pteromalid ectoparasitoid that attacks pupae and pharate adults from several families of the higher Diptera. Egg-to-adult development time, adult parasitoid size and emerging offspring ( = secondary) sex ratio of M. raptorellus were compared with clutch size in two hosts that differed greatly in mass, the small Musca domestica Linnaeus and the larger Calliphora vomitoria Linnaeus. The mean number of emerging parasitoids did not vary significantly with host species, although slightly higher clutch sizes were recorded in C. vomitoria. Irrespective of offspring sex, parasitoids completed development more rapidly in M. domestica than in C. vomitoria. In the small host, the development time and adult size of M. raptorellus were negatively correlated with clutch size. By contrast, female parasitoid size was unaffected by clutch size in the larger host, C. vomitoria. In both hosts, female parasitoids were significantly larger than male parasitoids. The secondary sex ratio (percentage males) of emerging parasitoids was significantly lower in C. vomitoria, and varied with clutch size in both hosts. In C. vomitoria, the greatest proportion of females emerged from hosts with the highest clutch sizes, whereas in M. domestica hosts with the highest clutch sizes produced the lowest proportion of female progeny. The results described here show that the development of M. raptorellus is profoundly affected by interspecific differences in host quality. Our results suggest that mating structure and host quality have potentially different effects on sex ratio decisions in M. raptorellus, and perhaps other gregarious parasitoids.

Genetic variation within triatomine bugs was investigated by amplification of a 400 bp portion of the mitochondrial 16S ribosomal RNA gene by polymerase chain reaction (PCR), using evolutionarily conserved primers, from a selection of species representative of the genera Rhodnius, Triatoma and Panstrongylus. Amplification products were subsequently screened for sequence variation using single strand conformational polymorphism analysis (SSCP) and also subjected to direct sequencing. Single strand conformational polymorphism analysis could detect variation within and between genera; intraspecific variation was also detected and SSCP profiles appear to be useful for identification purposes at the inter- and intraspecific levels. A 290 bp multiple alignment of 15 sequences obtained from nine species was generated, phylogenetic inference subsequently used three methods; a distance estimate, maximum parsimony and maximum likelihood. This 16S region exhibited considerable variation which ranged from intergeneric to intraspecific levels. Phylogenies from these three methods of inference were in broad agreement. Triatoma and Panstrongylus were more closely related to each other than either was to Rhodnius, in keeping with the current taxonomic appraisal.

Highly resistant and extremely resistant clones (R2 and R3) of Myzus persicae (Sulzer) exhibited a significantly lower mortality and developed a deleterious dark stomach deposit less frequently on sugarbeet than a susceptible (S) clone. After allowing equal populations of four resistant clones to develop together on sugarbeet for four weeks, approximately half of the aphids recovered were from the moderately resistant (R1) clone, suggesting that this clone had a significantly greater reproductive rate than the others. There was no significant difference in the propensity of any clone to produce alates on sugarbeet, although none of the clones produced very many. It is suggested that, even in the absence of insecticides on sugarbeet, resistant clones may become dominant due to their higher fecundity (R1 clones) and lower mortality (R2 and R3 clones) than susceptible clones.

To investigate the population density and dispersal of the sheep blowfly Lucilia sericata (Meigen) mark-release-recapture trials were carried out in lowland pastures in south west England. In three trials, 2142, 1351 and 451 fluorescent dust marked flies were released of which 4%, 14% and 10% were recaptured using a grid of sticky, odour-baited targets, placed between 8 m and 1000 m from the release point. There was no significant effect of wind direction on dispersal pattern and no apparent directional movement of the flies from the release point. Using the method described by Hawkes (1972) the mean distance travelled by all the flies on the first day of each of the three trials was calculated to be 108 m, 128 m and 137 m respectively. Using the method described by Fletcher (1974) the mean distances travelled were calculated to be 135 m (±42), 118 m (±27) and 183 m (± 61) on the first day of each of the three trials, respectively. The median distances travelled by the flies on the first day of each of the three trials were calculated to be 109 m, 130 m and 150 m, respectively. A Lincoln Index was used to estimate the population density of wild female L. sericata. The number of female flies was estimated to be zero in June, approximately one per hectare in July and six per hectare in August in 1994.

Flight and surface activity of the African black beetle, Heteronychus arator (Fabricius), detected by pitfall, light and window traps, was seasonally reversed. High surface activity relative to flight occurred in spring when beetles were mature, while relatively higher levels of flight occurred in autumn when they were immature. Pitfall trap captures were male-dominated in spring and female-dominated in autumn, and were a poor estimator of adult density. Light trap captures were consistently female-dominated. Although autumn flight was dispersive and inferred to have some role in population regulation, it was largely localized within the usual pasture habitat of the species. Some beetles flew into irrigated potato crops in autumn, but not specifically, as beetle abundance was consistently less than in surrounding dry pasture. High surface activity indicates spring is a strategic time for surface-applied control measures to prevent increase of H. arator in the next generation, a less disruptive alternative to conventional soil-incorporated insecticide directed at the new generation's larvae in summer. Such an approach would be best aimed early in the upsurge of activity, as most of the season's cohort of eggs was laid by the time surface activity peaked in mid-spring.

In a rural area of southeastern Tanzania, studies were undertaken on the dispersal and survival of Anopheles funestus Giles and A. gambiae Giles s.l. during the rainy season. Blood fed, resting mosquitoes were collected indoors, marked with fluorescent powder and released on the same day from two different sites in the study area. For two weeks indoor resting mosquitoes were collected from 11 houses in the release area. Additional collections were made with a light trap from a sentinel house in the centre of the study area. Anopheles funestus was more abundant than A. gambiae s.l. Of 4262 A. funestus and 645 A. gambiae s.l. released, 4.3% and 7.4%, respectively, were recaptured. Dispersal of mosquitoes was not random: one of three areas was favoured significantly more than the other areas, as shown by the recapture and movement rates of marked mosquitoes. Based on the regression of the recapture rate, estimated daily survival rates of A. funestus and A. gambiae s.l. were 0.63 and 0.78, respectively. These were significantly different. The differences in dispersal and survival rates between the two species are discussed in view of local topography and species-specific characteristics.

In the absence of insecticide there may be intense selection against alleles conferring insecticide resistance, so that these alleles will decline in frequency. On the other hand, selection will act to favour alleles at modifier loci which cause resistance alleles to become coadapted and increase in fitness even in the absence of insecticide. The relative effectiveness of these two processes is of practical importance and theoretical interest. The fate of polymorphism for malathion resistance was studied in the saw-toothed grain beetle, Oryzaephilus surinamensis (Linnaeus). Five to six lines of each of four strains (8401, 8401sel, 8518B and L1040), each polymorphic for resistance phenotypes, were maintained in insecticide-free culture for up to nine generations, over which period the response of individuals to a discriminating dose of 65 mg m-2 malathion was determined. There was significant reversion to susceptibility in the related strains 8401, 8401se1 and 8518B. Assuming resistance to be primarily controlled by a single major locus, resistant homozygote and heterozygote fitnesses in the absence of insecticide were estimated to be 0.92, 0.83 and 0.68, respectively. The initial frequency of the resistant allele was inversely related to the time since last exposure to insecticide, and also to the fitness of the resistant allele. This could be explained by the selection of modifier alleles that reduce the fitness cost of resistance in the absence of insecticide. In strain L1040 the proportion of resistant individuals actually increased over time (after the second generation) in the absence of insecticide. The fitness of the susceptible allele in this case was 0.83. In all strains there was significant variation among lines in relative fitness and initial resistance allele frequency. Analysis of knockdown proportions revealed highly significant variation between generations that is not easily interpreted in genetic terms but is better explained by limitations of the knockdown bioassay.

Vertical polythene exclusion barriers combined with trapping out using pitfall traps have been used to create enclosures within which arthropod numbers can be manipulated. This technique has been primarily used to investigate the impact of ground-dwelling polyphagous arthropods on cereal pests. Arthropod numbers in a total of 42 enclosed areas were compared to adjacent unenclosed areas over three years in Hampshire, UK. A range of arthropod monitoring techniques was used, including pitfall traps, fenced pitfall traps and D-vac suction samples. The enclosures were effective in reducing most species of Carabidae, Linyphiidae and Lycosidae encountered and numbers in pitfall traps were reduced by an average of 74%, 62% and 77% respectively. Similar reductions in densities of these taxa were found. Staphylinidae were less effected with an average reduction of only 32% in pitfall traps, although Philonthus species were reduced by 82%. Results were compared to previous studies.

The influence of the host plant of the cassava mealybug, Phenacoccus manihoti Matile Ferrero on the encyrtid parasitoid Apoanagyrus lopezi De Santis was studied in the laboratory. Four different host plants were used: two cultivars of cassava, Manihot esculenta (Euphorbiaceae), cv. Incoza and cv. MM79; Faux caoutchouc, a hybrid of M. esculenta × M glaziovii; and talinum Talinum triangularae (Portulacaceae), a common weed in cassava fields. Plants were selected for different levels of antibiotic resistance to P. manihoti. Mealybug mortality due to host feeding by the adult parasitoid and the percentage of mealybugs parasitized were significantly lower when mealybugs were reared on the Manihot cultivars and hybrid than when reared on talinum. However, the encapsulation rate was significantly lower in P. manihoti reared on talinum. The highest percentage parasitism and the lowest rate of emergence were recorded on cv. Incoza, the most resistant Manihot cultivar. The sex ratio did not vary significantly with the host plant used. The total developmental time and size of male and female progeny of A. lopezi differed significantly between P. manihoti reared on different host plants. Among Manihot plants, parasitoid size was positively correlated with development time and negatively with plant resistance. Results suggest that the parasitoid, A. lopezi, might perform better if cassava cultivars were selected for their strong antixenosis but low antibiotic characteristics.

The effect of temperature on the rate of consumption of the lipid reserves in Ixodes ricinus Linnaeus was characterized in constant temperature experiments. There was a consistent linear relationship between temperature and lipid consumption in nymphs and adult females and males between 5 and 37°C. Nymphs and adults were able to withstand extended periods of exposure to temperatures within the range of 2–37°C, although at 2°C there was evidence of thermal stress. The variance about the median rate of lipid consumption was found to increase with increasing rate of lipid consumption. Predictions of longevity were made using the rates of lipid consumption for the three stages studied, which ranged from 16 weeks to more than two years depending on temperature and stage. The predictions were consistent with reported survival times for I. ricinus and followed patterns reported for other ixodid ticks.

Surveys of egg pods of agriculturally important grasshoppers were carried out in northern Benin between 1992 and 1995. Searches were made of oviposition sites under shrubs of the perennial legume Piliostigma thonningi along field margins. In 1993 and 1995, surveys were extended to include sorghum, Sorghum bicolor, and the perennial thatch grass Vetiveria nigritana. The four principal grasshopper species found at these oviposition sites were Hieroglyphus daganensis Krauss, Cataloipus fuscocoeruleipes Sjöstedt, Kraussaria angulifera (Krauss) and Tylotropidius gracilipes Brancsik comprising 86% of 4545 identified egg pods while 651 egg pods could not be identified to species level. Predation by meloid beetles (Epicauta, Mylabris and Psalydolytta spp.) varied between 0 and 50% for the four dominant grasshopper species. From 1993 and 1994 data, nymphal eclosion from egg pods damaged by meloids was significantly lower than emergence from undamaged egg pods. The hymenopterous parasitoids Scelio africanus Risbec and S. mauriticanus Risbec were reared from the four dominant grasshopper species and parasitism levels of 0.0–3.3% were recorded from these hosts. There were significant differences in nymphal emergences between parasitized and unparasitized egg pods of H. daganensis.

Trajectory analysis was used to determine the direction and extent of windborne migrations of insects trapped in autumn and winter in south-east and east Asia for 12 years between 1968 and 1987. Nearly 2600 trajectories were drawn upwind at 10 m and 1.5 km from 15 catching sites and within the time (⋜60 h), wind speed (⋝5 km h-1) and temperature (⋝10°C) thresholds used, only 5% of the trajectories failed to locate a possible source and over 90% were completed in 40 h or less. The delphacids Nilaparvata lugens Stål and Sogatella furcifera (Horváth) dominated the trap catches (96%) with Cicadellidae (2.3%) and Diptera (0.5%) as the next most numerous. Very few Lepidoptera were reported (<0.3%). Nearly 80% of the trajectories were constructed in the prevailing Winter Monsoon and Trade winds, resulting in a southward displacement of insects towards putative overwintering areas as reported in previous studies. Tropical cyclones in autumn, produced trajectories which differed in both direction and extent from those in the prevailing winds, supporting the suggestion that the contraction of the distribution areas of rice pests at this time of year is the product of a series of movements in different directions. The results suggest that migrations continue throughout the year in the tropics and sub-tropics and indicate that this may be one way the capacity for long distance migration is maintained in some rice pest populations.