A prerequisite to studying the specific interactions involved in the persistent transmission of luteoviruses such as the potato leafroll virus (PLRV) is the characterization of both the virus and its vectors. A range of techniques was used to assess genetic differentiation among 27 clones belonging to the Myzus persicae complex (M. persicae (Sulzer), M. antirrhinii (Macchiati) and M. nicotianaeBlackman) and showing different efficiencies in transmitting PLRV isolates. All M. persicae/M. nicotianae clones belonged to one of two karyotypes, both 2n = 12, either normal or carrying an autosomal translocation (A1,3), and all M. antirrhinii clones had 13 or 14 chromosomes. Amplified esterase 4 genes were detected by PCR–REN assay in M. persicae/M. nicotianae taxa, with gene expression being modified by methylation. Similarly, amplified E4 genes were revealed in M. antirrhinii but they all showed unmethylated. Two allozyme and 11 microsatellite loci discriminated 10 different genotypic classes among the 27 clones. Analysis of genetic relatedness between these genotypic classes revealed that M. nicotianae clones were very closely related to M. persicaeclones, whereas the genetic differentiation between M. antirrhinii and M. persicae was greater. The implications of these results for the taxonomic status of these genotypes within the complex, and the transmission of PLRV, are discussed.

Realized heritability, h2, of resistance in European corn borer, Ostrinia nubilalis (Hübner), to Bacillus thuringiensisBerliner ssp. kurstaki endotoxins was examined in five resistant laboratory colonies. These colonies were reared on a meridic diet that incorporated a commercial formulation of B. thuringiensis, Dipel ES. Resistance in these colonies reached 42–67× by the seventh to twentieth selected generations and then plateaued. The realized heritability of resistance averaged 0.17–0.31 over all selected generations for the five colonies. In the three Iowa colonies, the highest realized heritability, 0.18–0.33, occurred during the second period of selection (seventh to thirteenth selected generations). In the two Kansas colonies, the highest realized heritability, 0.36 and 0.46, occurred during the first period of selection (first to sixth selected generations). In the absence of selection pressure, resistance in the southwest Kansas colony decreased from 62× to 42× after two generations, and remained at about that level for the next five generations.

The effect of vine phenological stage during larval feeding on the reproductive output of Lobesia botrana (Denis & Schiffermüller) adults was assessed. Larvae were reared under field conditions on vine inflorescences, unripe or ripe berries simulating the first, second and third insect generations respectively. The resulting adults showed significant differences in body weight, longevity and reproductive output as measured by oviposition period, total fecundity and reproductive efficiency (viable eggs/body weight) for females, and spermatophore number and volume of the first spermatophore for males. Viable egg number was positively correlated with female body weight for all treatments but male reproductive efficiency (spermatophores/body weight) was not. The reproductive output of females from larvae reared on a standard semisynthetic diet was comparable to that of females reared on ripe berries whereas males showed a higher reproductive output when reared on semisynthetic diet. These results clearly show that data obtained from insects reared on artificial diet cannot be extrapolated to ‘field-derived’ adults. The results suggest that the variation in L. botrana reproductive output due to the larval food source should be taken into account as a potential factor affecting insect population dynamics. It is suggested that different intervention thresholds, such as those based on pheromone catches, may be needed for each of the three moth generations, to compensate for the increased fecundity and potential to cause larger amounts of crop damage of later generations.

A survey was conducted on 84 pig and cattle farms in Denmark between August and October 1996 and 1997. The aim was to describe the activity and relative abundance of parasitoids (Hymenoptera: Pteromalidae and Ichneumonidae) that attack puparia of Musca domestica Linnaeus and Stomoxys calcitrans (Linnaeus). In total, seven pteromalid species were recovered: Spalangia cameroni Perkins, S. nigripes Curtis, S. subpunctata Förster, Muscidifurax raptorGirault & Sanders, Pachycrepoideus vindemiae (Rondani), Urolepis rufipes(Ashmead) and Nasonia vitripennis (Walker), an ichneumonid Phygadeuon fumatorGravenhorst, a diapriid Trichopria sp., and a staphylinid Aleocharasp. This is the first time that U. rufipes has been recorded in Europe. Spalangia cameroni and M. raptor were the most frequently recorded species in all regions of the country, and accounted for the main parasitism of Musca domesticaand Stomoxys calcitrans puparia. The overall rate of parasitism per farm was low: 12.9% of the total number of fly puparia collected. Direct ordination, used to assess the habitat distribution of the parasitoids, showed that Muscidifurax raptor mainly seeks fly puparia in outdoor manure heaps and especially in manure from pigs rather than from cattle, whereas Spalangia cameroni mainly seeks fly puparia indoors, irrespective of livestock.

Sublethal concentrations of azadirachtin incorporated into artificial diet and offered to third-instar larvae of Spodoptera littoralis (Boisduval) prolonged larval instars and reduced food intake. These effects were observed after the treated larvae had been transferred to plain diet; the reduced food intake was therefore a secondary antifeedant effect. Azadirachtin did not influence digestion efficiency but diminished the ability of the larvae to convert both ingested and digested nutrients into growth, particularly immediately after treatment. This effect declined with time once the treatment with azadirachtin had ceased. Growth was more severely reduced than food intake, and the reduction in growth also occurred during periods when food intake was not affected, possibly due to post-ingestive effects.

Studies were made of the behaviour of Glossina pallidipes Austen and G. morsitans morsitans Westwood during the hot season (September–November) in Zimbabwe, and attributes of samples of tsetse from refuges, odour-baited traps, targets and mobile baits were compared. Various arrangements of electric nets were used to study tsetse as they entered or left artificial refuges. The peak time of entry into a refuge varied between 0800 h and 1400 h and coincided with the time when the air temperature reached 32°C; the response was stronger if 32°C occurred earlier in the day. The peak time of exit varied between 1500 h and 1700 h, being significantly later on hotter days, but did not show a clear temperature threshold. Micro-meteorological measurements showed that refuges were significantly cooler than the surrounding riverine woodland during the day but warmer at night. There was no significant difference between the air temperatures in leafless mopane woodland and semi-evergreen riverine woodland during the day but at night the riverine woodland was significantly cooler. Combining the micro-meteorological data with the estimated local movements of tsetse suggested that during the hot season, tsetse experienced temperatures 2°C cooler than the daily mean in a Stevenson screen located in mopane woodland. Compared with the catches of tsetse from traps, refuges had higher proportions of G. m. morsitans, males, young flies and females in the later stages of reproduction, and it is suggested that during the hot season, samples from refuges were less biased than traps with respect to species and sex composition, age and reproductive status. During the hot season, tsetse populations declined by c. 90% and although air temperatures exceeded lethal levels (c. 40°C), the refuge-entering responses meant that adult flies probably experienced a maximum of only c. 35°C. It is suggested that the decline in numbers is not due to direct mortality effects of temperature on adults but may be due, in part, to a doubling in the rates of reproductive abnormality during the hot season and an increase in adult mortality related to a temperature-dependent decrease in pupal period.

The effect of artificial and natural sources of adult food on the survival and reproduction of the tropical fruit fly, Anastrephaserpentina (Wiedemann) was studied. Caged adult flies were exposed during their whole lifespan to water and one of the following diets: sucrose, intact fruit, open fruit, bird faeces, sucrose plus intact fruit, sucrose plus open fruit, sucrose plus yeast hydrolysate, and sucrose plus bird faeces. All flies exposed to intact fruit or bird faeces died within the first five days of adult life without laying eggs. Females exposed to open fruit exhibited the greatest mean longevity (56.7 days). The highest net fecundity rate was recorded from individuals exposed to sucrose plus yeast hydrolysate (164 eggs per female), followed by those exposed to bird faeces plus sucrose and open fruit (38 and 26 eggs per female, respectively). Some individuals were able to lay viable eggs late in life (>105 days of age). Only populations in which adult flies had access to either sucrose plus yeast hydrolysate, open fruit, or sucrose plus bird faeces exhibited positive intrinsic rates of increase (r). Flies offered a combination of dry sucrose plus open fruit exhibited greatly reduced net fecundity levels when compared with those individuals exposed to open fruit. Even more significantly, populations of flies offered the combination of open fruit plus sucrose exhibited negative rates of increase while those exposed to open fruit alone, grew. We postulate that this reduction in egg production can be explained by a ‘junk food syndrome’.

Regression analyses of a long series of light-trap catches at Narrabri, Australia, were used to describe the seasonal dynamics of Helicoverpa armigera (Hübner). The size of the second generation was significantly related to the size of the first generation, to winter rainfall, which had a positive effect, and to spring rainfall which had a negative effect. These variables accounted for up to 96% of the variation in size of the second generation from year to year. Rainfall and crop hosts were also important for the size of the third generation. The area and tonnage of many potential host crops were significantly correlated with winter rain. When winter rain was omitted from the analysis, the sizes of both the second and third generations could be expressed as a function of the size of the previous generation and of the areas planted to lucerne, sorghum and maize. Lucerne and maize always had positive coefficients and sorghum a negative one. We extended our analysis to catches of H. punctigera (Wallengren), which declines in abundance after the second generation. Winter rain had a positive effect on the sizes of the second and third generations, and rain in spring or early summer had a negative effect. Only the area grown to lucerne had a positive effect on abundance. Forecasts of pest levels from a few months to a few weeks in advance are discussed, along with the improved understanding of the seasonal dynamics of both species and the significance of crops in the management of insecticide resistance for H. armigera.

The responses of Glossina fuscipes fuscipes Newstead and other Diptera to carbon dioxide were studied in linear and dense forests along the shores of Lake Victoria, Kenya. Flies were caught in biconical traps and were intercepted with electric nets while in flight near traps. Carbon dioxide dispensed at a high rate (5 l min–1) in linear forest failed to increase the numbers of tsetse attracted to or caught in traps. In contrast, catches of non-biting Muscidae, Stomoxyinae and Tabanidae were improved by up to 11 times. Inside dense forest, carbon dioxide released at half this rate increased both the numbers of female tsetse attracted to a trap and the catches in a trap by about 2–3 times. Catches of male tsetse were, however, not affected. Striking improvements for other Diptera were also realized (up to 102 times). Under a variety of conditions, unbaited biconical traps attracted many Diptera to the vicinity of a trap, but caught few flies due to low capture efficiencies (typically less than 10%). In contrast, efficiency estimates for G. f. fuscipes were good, varying from 37 to 82% in different habitats and seasons. These results are discussed in relation to the search for practical odour attractants for riverine tsetse.

Life table studies of Mussidia nigrivenella Ragonot, a pest of maize in Benin, showed that host plant species had a significant effect on larval survival and developmental time. The maximum percentage of larvae surviving was recorded on jackbean, Canavalia ensiformis (36%) and lowest on maize (18%). Mean developmental time for larvae was longest on maize (19.8 days) and shortest on jackbean (17.2 days). The number of eggs laid was highest for females from larvae fed on jackbean (x– = 176), followed by velvetbean, Mucuna pruriens(x– = 143), and lowest for females where larvae had fed on maize (x–= 127). Longevity of ovipositing females was higher on jackbean (5.4 days) than of those from any other host plants. According to the growth index and life table statistics, jackbean was the most suitable host plant, followed by velvetbean, and maize, the least suitable. Thus, jackbeans should be recommended for use in mass rearing programmes of M.nigrivenella, e.g. as a host for parasitoids in future biological control programmes. Because of the high suitability of jack- and velvetbeans for M.nigrivenella, planting of these increasingly important cover crops should be timed in such a manner that the emergence of female moths from mature pods does not coincide with maize plants in a suitable developmental stage for oviposition and development of young M. nigrivenella larvae.

This paper reports on the performance of an atmospheric numerical model called BLAYER which has been adapted to forecast the movement of migrant brown planthopper Nilaparvata lugens (Stål) and white-backed planthopper Sogatella furcifera (Horvarth) populations from China to Korea. Comparison of model forecasts with trapping data for the 1987 and 1988 migration seasons indicated: (i) that the model is capable of successfully simulating the movement of planthoppers to Korea; (ii) that the model has sufficient detail to simulate insect movement into different regions of Korea; (iii) the source region for early season migrants is most likely to be south-eastern China (i.e. south of 25°N and east of 115°E); (iv) later season migrants may not necessarily always originate from an expanded northward region (south of 30°N); (v) the flight level of migrants may vary from about 500 to 2000 m altitude from one migration episode to another; and (vi) flight times ranging between 24 and 45 h are required to explain the migratory influxes. The results reported here have led to BLAYER forecasts of planthopper migration being produced on an operational basis within Korea.

In recent decades, aphids identified as Cinara cupressi (Buckton) have seriously damaged commercial and ornamental plantings and native stands of Cupressus, Juniperus, Widdringtonia and other Cupressaceae in Africa, Italy, Jordan, Yemen, Mauritius and Colombia. Aphids currently identified as Cinara cupressiappear to belong to a species complex. This work was undertaken to identify the pest, its likely area of origin and any specific natural enemies, to facilitate a biological control programme. The biogeography of the species complex was studied using morphometric analysis of specimens from all the major regions where they have been collected, and analysis of host-plant ranges, parasitoid records and host association information. The cause of tree damage is shown to be an unnamed species, here described as C. (Cupressobium) cupressivora Watson & Voegtlin sp. n., which probably originated on Cupressus sempervirens in a region from eastern Greece to just south of the Caspian Sea. The remainder of the complex, Cinara cupressisensu lato, apparently consists of three morphologically similar species (C. sabinae(Gillette & Palmer) and C. cupressi (Buckton), probably originating in North America, and an unidentified species). There is insufficient data available to separate these taxa, or to determine the status of C. canadensis Hottes & Bradley, so C. sabinae and C. canadensis are left in synonymy under C. cupressi (Buckton). Lachniella tujae del Guercio and L. juniperi signata del Guercio, thought to be part of the C. cupressi complex, were found to be junior synonyms of C. tujafilina (del Guercio); these new synonymies are proposed and lectotypes of L. tujae and L. juniperi signataare designated.

In Zimbabwe, odour-baited targets impregnated with deltamethrin were deployed at 4 km-2 in a 9 km-wide band as an invasion barrier against dense populations of Glossina morsitans morsitans Westwood and G. pallidipes Austen. Tsetse populations across the barrier were monitored by a line of traps. Invasion pressure was estimated by the catches from two additional traps about 6 km into the invasion source. After 14 months all traps more than 7 km from the invasion source recorded zero catches for 12 consecutive months, indicating that the barrier was effective in preventing re-invasion, and that the 9 km-wide barrier gave a good margin of safety.

A total of 4420 male Glossina morsitans morsitans Westwood were captured on man fly-rounds in Katete District, Eastern Province, Zambia between February 1991 and December 1993. Of these flies, 1680 were captured before June 1992, during which period 989 flies were also captured on odour-baited electric screens operated in the same area. Non-teneral flies were analysed for fat, haematin and residual dry weight and their wing-vein length was measured. There were well marked annual cycles in wing length, fat and residual dry weight. Flies were biggest at the end of the rainy season, and smallest at the end of the hot dry season. Fat levels were lowest before the onset of the rains and highest in the cool season. Residual dry weight was a function of haematin content and the degree of wing-fray; these factors were used to correct the residual dry weight to zero haematin. Corrected residual dry weight and wing-vein lengths were most highly correlated with relative humidity in the month prior to capture (r > 0.8 and 0.6 respectively). Correlations with saturation deficit were weaker; temperature accounted for <20% of the variance. Fly-round flies had a consistently higher residual dry weight than those from the electric screen, but their fat levels were lower. The distributions of log haematin levels differed little between the two sampling methods and were adequately described by a model where capture and feeding rates increased exponentially after each meal. The increase in the feeding rate after each meal differed little with season and was closely similar to that estimated for female G. pallidipesAusten in Zimbabwe.

The gypsy moth, Lymantria dispar Linnaeus, is one of the most serious insect pests of palaearctic and nearctic hardwood forests. We used amplified fragment length polymorphism (AFLP) to detect genetic diversity within and among gypsy moth populations. Five AFLP primer combinations were used on 98 L. dispar samples from different parts of Europe, Asia and North America, detecting a total of 481 polymorphic and 58 monomorphic fragments. Genetic similarities based on these data were calculated and cluster analysis was performed to graphically display groupings between isolates. Lymantria dispar individuals from close geographical areas of Europe were mostly grouped together in cluster analysis resulting in the formation of subgroups corresponding to the origin of the samples. Supporting this observation, clustering of individuals from 22 neighbouring populations in southern Germany agreed well with the region they originated from. Thus, AFLP analysis revealed the existence of a certain degree of genetic variability between European gypsy moth populations that could be explained by the accumulation of polymorphisms resulting from both historical population bottlenecks and the adaptation to different environmental conditions. The results of this study therefore demonstrate that AFLP analysis is a sensitive technique for distinguishing genotypes from different geographic origins as well as from neighbouring local populations and provides sufficient molecular markers for future characterization of the gypsy moth genome.

Nineteen sites throughout Ghana were selected as representative of the three major zones of natural vegetation. At these sites, samples of ticks were collected from groups of approximately five each of cattle, sheep and goats. Ticks were identified by light microscopy. In order of abundance, tick species found on livestock were: Amblyomma variegatum (Fabricius), Boophilus decoloratus (Koch), Rhipicephalus senegalensis Koch, Boophilus annulatus (Say), Hyalomma marginatum rufipesKoch, a Rhipicephalus species in the sanguineus group of uncertain identity close to both R. turanicus Pomerantsev and R. sulcatus Neumann, Boophilus geigyi Aeschlimann & Morel, Hyalomma truncatum Koch, Rhipicephalus evertsi evertsi Neumann and Rhipicephalus lunulatus Neumann. Amblyomma variegatum was found on every sample of the sheep, goats and cattle examined and was equally abundant in all vegetation zones. Boophilus species were found mainly on cattle, with some on sheep and were widely distributed by vegetation zone. Hyalomma species were found predominantly on cattle and widely distributed by vegetation zone. Rhipicephalus e. evertsi and R. senegalensis were found on sheep and cattle in all vegetation zones. The tick fauna of Ghana is similar to those of other West African countries and this shows that control strategies developed in neighbouring countries can be applied to Ghana. The significance of this tick fauna is discussed in relation to potential for pathogen transmission.

Cotesia flavipes Cameron, a gregarious larval endoparasitoid native to the Indo-Australian region, was imported from Pakistan and released in Kenya in 1993 for management of the exotic stemborer, Chilo partellus (Swinhoe). Recent reports confirmed the successful establishment of the parasitoid in three locations in Kenya and in northern Tanzania. Functional response studies on this parasitoid and an indigenous congener, Cotesia sesamiae (Cameron), indicated that C. flavipes had a higher searching ability and attacked more larvae when Chilo partellus was the host. When a native stemborer, Sesamia calamistis Hampson, was the host, there was no significant difference between numbers attacked by both parasitoids. Numerical response studies showed that Cotesia flavipes produced more total progeny and female progeny per female parasitoid on Chilo partellus than did Cotesia sesamiae. No significant difference in progeny production was detected between the two parasitoids on S. calamistis. Functional and numerical responses tested in the laboratory gave the same ranking of the two parasitoids on the two hosts as in the field. This study suggests that Cotesia flavipes is a more efficient parasitoid and it is anticipated that it will contribute to the control of both exotic and native stemborers in Kenya.

Bioassays in Zimbabwe with wild-caught Glossina pallidipes Austen and G. morsitans morsitans Westwood showed that formulations of deltamethrin (Decatix, SpotOn and an experimental variant of SpotOn), alphacypermethrin (Renegade) and cyfluthrin (Cylence) applied to oxen at the manufacturers' recommended doses gave knockdowns above 50% for 5–24 days in hot months and 24–55 days at cooler seasons. Within these periods, the average knockdowns were 77–86% with deltamethrin, 74% with alphacypermethrin and 59% with cyfluthrin. None of the insecticides affected the numbers of tsetse attracted to oxen from a distance, the proportion of tsetse that engorged, and the alighting responses on cloth screens. In the hot season most tsetse engorged on the belly. At other times the front legs were preferred, especially in the wet season and for a few months after. Chemical assays indicated that insecticide persisted at greatest concentration on the backs of oxen and least on the legs. Modelling the experimental data suggested that 4–21 annual applications of insecticide in areas >1000 km2 would give good control at least 10 km from the invasion source if the treated cattle contributed at least 50% of tsetse diet. No treatment regime under any diet conditions would give good control near an invasion front. Insecticide at concentrations up to 0.15 ppm occurred in dung from treated oxen for up 12 days post-treatment. Dead beetles occurred in and near fresh dung.