Life-history parameters of different biotypes of the whitefly Bemisia tabaci (Gennadius) species complex were reviewed. This included the B-biotype of B. tabaci, identified as B. argentifolii (Bellows & Perring). Comparisons were made among different biotypes on cotton, among host plants for biotype B and among the whitefly species B. tabaci and Trialeurodes vaporariorum (Westwood), the greenhouse whitefly. The biotype identification of different populations of B. tabaci was summarized in a table. Biotypes discussed were A, B, Indian and biotypes of the Old World group. Temperature dependent relationships were estimated for egg development rate, development rate from egg to adult, immature mortality, adult longevity, sex-ratio, pre-oviposition period and fecundity. The fitted curves will be used as input for a simulation model of the population dynamics of B. tabaci in a greenhouse when parasitoids are released. The model makes it possible to evaluate the integrated effect of different life-history parameters and behavioural parameters of parasitoids on whitefly population levels in a greenhouse.

This review identifies key ways in which manipulations of the crop environment based on detailed understanding of tritrophic interactions can contribute to improvements in the control of insect pests. Such approaches are likely to be of particular benefit against those pests, notably certain species of Lepidoptera and aphid, which are difficult to control with insecticides because of insecticide resistance or suppression of natural enemies. Particular attention is given to the compatibility (or otherwise) of partial plant resistance and biological control, citing examples which support contrasting tritrophic theories. Other areas considered and supported with examples include the use or effects of allelochemicals, refugia, intercropping, crop backgrounds, fertilization regimes, parasitoid conditioning (by host plants) and transgenic crops. Examples of manipulations involving use of selective insecticides which show compatibility with biological methods are also included owing to their possible suitability in integrated crop management programmes.

Chilocorus nigrita (Fabricius) is a well-known predator of scale insects. It has been widely used for biological control and has spread naturally beyond its previous native range over the last three decades or so. Three other Oriental species closely resembling C. nigrita can now be separated. Chilocorus melas Weise is redescribed and a lectotype designated. Chilocorus gressitti Miyatake is a junior synonym of C. melas. Chilocorus subindicus from the southern parts of the Indian subcontinent and C. gracilior from eastern Indonesia are described as new.

A diverse range of novel molecular (DNA) markers are now available for entomological investigations. Both DNA and protein markers have revolutionized the biological sciences and have enhanced many fields of study, especially ecology. Relative to DNA markers, allozymes are cheap, often much quicker to isolate and develop, even from minute insects (aphids, thrips, parasitic wasps, etc.), and subsequently easy to use. They display single or multi-locus banding patterns of a generally easily interpretable Mendelian nature, and the statistics for their analysis are well established. DNA markers are also suitable for use with small amounts of insect material and can be used with stored, dry or old samples. They have an expanding range of applications, many involving intra- and interspecific discriminations. Like allozymes, they can be single or multilocus, whilst methods for their statistical analysis have recently been published. However, they can be considerably more expensive than allozymes, require more complex preparatory protocols, expensive equipment, may involve lengthy development procedures (e.g. isolating cloned oligonucleotides to develop primers to detect microsatellite regions) and some have complex multi-locus banding patterns which may be of a non-Mendelian nature (e.g. RAPDs, randomly amplified polymorphic DNA), and are in some cases, not easily repeatable. In this review, we hope to inform the general reader about the methodology and scope of the main molecular markers commonly in use, along with brief details of some other techniques which show great promise for entomological studies. Thereafter, we discuss their applications including suitability for particular studies, the methods used to load and run samples, subsequent band detection, band scoring and interpretation, the reliability of particular techniques, the issues of safety involved, cost effectiveness and the statistical analyses utilized.

Control of yellow stem borer, Scirpophaga incertulas (Walker), in rice was attempted by mating disruption using the natural ratio of pheromone components, a 1:3 blend of (Z)-9- and (Z)-11-hexadecenal, in replicated trials at three locations in Andhra Pradesh, India, during the 1994 and 1995 dry seasons. The pheromone was formulated in SelibateR and applied by hand at a rate of 40 g a.i./ha. In Medchal and Nellore, pheromone-mediated communication was reduced by at least 94% for the first 50 and 64 days after application respectively, as measured by pheromone trap catch suppression. Compared with adjacent farmers' practice plots, subsequent dead heart and white head damage were reduced by 74 and 63% and 83 and 40% in Medchal and Nellore, respectively. In Medchal, average rice yields were increased compared to the farmers' practice plots, 4108 and 3835 kg/ha respectively, but in Nellore, they were the same as those obtained in the farmers' practice plots, 6400 and 6733 kg/ha respectively. In Warangal, the level of communication disruption over the first 70 nights after pheromone application was less than obtained in either Medchal or Nellore and averaged between 50 and 87%. The maximum dead heart and white head damage recorded in the pheromone-treated plots in Warangal were 2.8 and 15.7% respectively compared to 7.0 and 20.9% respectively in the farmers' practice plots. Differences in S. incertulas larval damage estimates obtained from the pheromone-treated and farmers' practice plots in Warangal were reflected in grain yields, 4036 and 3715 kg'ha respectively. Surveys of insecticide use indicated that 92% of smallholders in Medchal applied insecticide at least once per season while in Warangal over 60% applied insecticide on two or more occasions. The data show that season-long control of S. incertulas comparable to that obtained with conventional insecticides can be achieved by mating disruption in smallholder rice fields in India.

Bemisia tabaci (Gennadius) is a pest of global importance which resists many conventional insecticides. Novel strategies for control are required and these may incorporate compounds whose lethal and sublethal effects have gone unremarked. Although most commonly employed as an insecticide synergist, piperonyl butoxide alone was lethal to predominantly second instar nymphs of the cotton whitefly, B. tabaci at LC50s of between 60 and 600 ppm, depending on the strain. Formulated and technical material were similarly toxic and far more so than detergents. Some strains exhibited slight tolerance (c. 3–10 fold) but there was no correlation of this with the presence of known resistance mechanisms or enzyme banding patterns. Residues of piperonyl butoxide alone were toxic to adult B. tabaci at c. 2000 ppm which was similar to the toxicity of paraffin oil. Piperonyl butoxide also increased developmental times among B. tabaci nymphs at doses as low as 10 ppm and exerted a transient effect on oviposition. There was strong evidence that it did not reduce the feeding activity of insects surviving treatment. Such effects offer scope for incorporating this compound into resistance management programmes, especially in conjunction with natural enemies (e.g, parasitoids active specifically against immature hosts).

The efficiency of miniature CDC light-traps in catching West African malaria vectors was evaluated during two rainy seasons in a village near Ouagadougou, Burkina Faso. Traps were employed both indoors and outdoors using human baits protected by an insecticide-free mosquito-net and different sources of light. Indoors, light from incandescent bulbs increased the catch of Anopheles gambiae s.l. (mainly A. arabiensis Patton and the Mopti chromosomal form of A. gambiae s.s. Giles) and A. funestus Giles c. 2.5 times as compared to traps whose light bulb was removed. Conversely, the difference was not significant when a UV ‘Blacklight-blue’ fluorescent tube was compared to the incandescent bulb. Protecting the bait with a mosquito-net increased the catch c. 3 times for A. gambiae s.l. and c. 3.5 times for A. funestus. A prototype model of double bednet gave intermediate yields. Outdoors, the addition of incandescent bulbs to unlighted traps did not significantly increase the number of vectors caught, but the addition of the mosquito-net to the unprotected human bait did so by c. 1.5–4 times. Thus, the CDC light-trap hung close to a human sleeping under a bednet and fitted with an incandescent bulb, was considered the most practical and efficient in terms of numbers of vectors caught, consequently its indoor efficiency was compared to human landing catches on single collectors and estimated to be 1.08 times and density-independent. Outdoor light-trap catches were either not significantly correlated to biting collections (as for A. gambiae s.l.), or density-dependent in their efficiency (as for A. funestus); thus, they were not considered a reliable means for estimating malaria vector outdoor biting densities in this area. No difference was found in the parous rate of A. gambiae s.l. samples obtained with CDC light-traps and human landing collections.

Four polymorphic enzymes (PEP, PGI, PGM and IDH) were separated from adult individuals of five aphid parasitoid species of the genus Aphidius Nees (A. ervi Haliday, A. microlophii Pennacchio & Tremblay, A. eadyi Starý, Gonzalez & Hall, A. picipes Nees and A. urticae Haliday) using horizontal cellulose acetate plate electrophoresis. These markers were used to investigate the genetic relationships, including reproductive isolation and host adaptation/specificity, in laboratory and field populations. Samples were collected from the pea aphid, Acyrthosiphon pisum (Harris) and/or the nettle aphid, Microlophium carnosum (Buckton) in the UK and Bulgaria between 1991 and 1994. Whilst all loci discriminated between some species, PGM discriminated all five species, one species (A. eadyi) bearing two unique alleles (PGMa and PGMc). Aphidius microlophii (from nettle aphid) and A. ervi (from pea aphid), which are difficult to separate morphologically, possessed unique PGM alleles – PGMb and PGMe, respectively. Both parasitoids occur sympatrically, and whilst hybrids heterozygous for PGM were produced in the laboratory (PGMb,e), such genotypes were not observed in the field populations sampled. Hence, the species appear to be reproductively isolated. Most parasitoid populations studied showed mean heterozygote deficiencies per locus (homozygote excess) compared with Hardy-Weinberg expectations. In particular, A. eadyi bearing PGMa alleles were always homozygous whilst additionally, many were homozygous for another allele, PGIb. This is evidence for the existence of one or more morphologically-indistinguishable ‘cryptic’ species occurring sympatrically within European field populations. A dendrogram of relatedness was produced following calculation of Nei's genetic identity coefficient, I from the parasitoid population allele frequency data. All species showed very high similarity between populations at the intraspecific level (>0.9), but fewer interspecific similarities (0.23–0.63). These values compare well with previously published values for Aphidius populations and for other insects.

The synthetic juvenile hormone analogue (S)-hydroprene can control populations of the oriental cockroach Blatta orientalis Linnaeus. Eradication of B. orientalis infestations, however, can take in excess of two years. In an attempt to reduce the time (S)-hydroprene takes to eliminate a population of oriental cockroaches, we explored the possibility of using the oothecal endoparasitoid Aprostocetus hagenowii Ratzeburg in combination with (S)-hydroprene. For such a strategy to be successful, it is important that the parasitoid remains substantially unaffected by (S)-hydroprene. When A. hagenowii was exposed to B. orientalis oothecae in the presence of (S)-hydroprene, female parasitoids showed no reduction in their capacity to attack hosts and their fecundity was not compromised. (S)-hydroprene, at dose rates of 18 mg/m2 and 100 mg/m2, induced deformity in approximately 12% and 33% respectively of parasitoids that emerged. No reduction in reproductive viability was seen in morphologically normal F1 parasitoids. Deformed F1 parasitoids, exposed to the higher (S)-hydroprene dose, showed a 71% reduction in the number of oothecae attacked and a 50% reduction in the number of offspring produced. These results indicate that A. hagenowii could be used in combination with (S)-hydroprene in an integrated pest management programme against B. orientalis.

African cassava mosaic virus (ACMV), vectored by the whitefly, Bermisia tabaci (Gennadius), is considered the most damaging pathogen of any African crop. Information about vector movement is important for understanding the epidemiology of this disease and the experiments reported here were designed to examine B.tabaci flight activity both in and around a cassava crop in relation to time of day, crop growth stage, wind direction and speed, and to the resulting pattern of infected plants within the field at harvest. At wind speeds of <0.4 ms−1 adult B. tabaci approached the yellow traps by flying upwind. At greater wind speeds, significantly fewer B. tabaci adults approached the traps from downwind, thus reversing the directionally of the catch. When the direction of the prevailing south-west wind reversed, so did the directionality of the catch. Bemisia tabaci adults were flight active throughout the day and the greatest percentage were caught above the canopy between 06.00–08.00 h, when wind speeds were lowest. Trap height and position significantly affected catch with the greatest numbers caught on the lowest traps. More than three times as many B. tabaci adults were caught on traps situated downwind from the field compared to those upwind. Suggesting that the field was acting as a source of whiteflies. In both years, Africa cassava mosaic disease (ACMD) incidence was highest and lowest, respectively, on the edges and in the middle of the trials, with the highest incidence occuring on the edges facing the prevailing wind direction. These results are discussed in relation to the epidemiology of ACMD and to potential cultural control methods such as the use of ACMD-resistant guard rows to protect a mainly susceptible crop.

Tethered flight studies, carried out in southern Uganda with the leafhoppers Cicadulina storeyi China and C. mbila Naudé, showed that depending on species, the factors of age, gender, gravid status and rearing on virus infected maize had significant effects on flight, whereas host plant species and mated status appeared unimportant. Distributions of wing length (WL), body length (BL) and the parameters WL/BL and WL-BL were mostly uni-modal, but in two cases very weakly bi-modal. Regressions of log-transformed flight duration against these morphometric parameters were all non-significant, except for very weak (r2 = 0.01–0.04) relations with wing length. There was no conclusive evidence for the existence of separate short- and long-duration flight morphs among the leafhoppers. It is proposed that differences between our results and those of an earlier study of Zimbabwean Cicadulina populations, particularly in respect of the effects of gravid status on flight, and the existence of distinct flight morphs, are explicable in terms of the different seasonal and environmental constraints experienced by Ugandan and Zimbabwean populations. These favour long-range migratory flight at certain times of the year in Zimbabwe, but not in Uganda.

The damson–hop aphid, Phorodon humuli (Schrank), is a serious pest of hops in England. It is holocyclic (with obligatory sexual phase) and host alternating. From suction trap data, P. humuli aerial densities are known to be greatest in the main hop growing regions of Herefordshire and Kent (mid-west and south-east England, respectively), some 260 km apart. The aphid is now resistant to several insecticides. This is in part conferred by elevated carboxylesterase activity, ranging from low in susceptible to high in very resistant strains. Enzyme markers, including carboxylesterases (EST-4 to -7), separated electrophoretically from individual insects, have been used to examine the degree of genetic heterogeneity among P. humuli sub-populations on both its hosts – Prunus spp. (primary overwintering host) and hops, Humulus lupulus (secondary summer host). The esterase data revealed heterogeneity among subpopulations collected from wild, unsprayed hosts in regions less than 30 km in area, with a higher mean frequency of elevated esterase variants in the commercial hop growing regions of Herefordshire and Kent, compared with samples from a non-commercial region around Rothamsted. Esterase distributions remained similar over consecutive years. Similarly, allele and genotype frequencies for another enzyme (6-phosphogluconate dehydrogenase, 6-PGD) were also heterogeneous among subpopulations sampled at less than 30 km apart (especially from Prunus) in each of the three regions surveyed, whilst allele and genotype frequencies sometimes remained stable over a number of summers. In addition, 6-PGD genotype frequencies were mostly congruent with Hardy-Weinberg expectations, even for parthenogenetically-reproducing aphids colonizing hops. These data suggest that the 6-PGD alleles tested are selectively neutral; that gene flow (=migration) is restricted between aphid populations, even within a single region (≤ 30 km) and, that the autumn migration from hops to Prunus is probably of shorter range (perhaps less than 20 km) compared with the spring migration from Prunus to hops.

Despite the large number of collection rocords available, there has recently been some debate concerning how host-specific ticks are. A quantitative data set is presented for the host preferences of African ticks. The results are based on 43,615 individual collection records from published sources covering most countries in mainland Africa. Out of 223 ticks species, 112 have been collected 20 times or more; 14 of these are generalists and at least 39 are potential specialists. Further collections are needed for greater clarity in many cases. It is important that people working on problems that relate to tick-host interactions are aware of the context in which these occur, lest they make false a prior hypotheses about the importance of hosts or parasites in the system.

Canopy knockdown of arthropods using mist-blowing was carried out in Brumas, Sabah (north-east Borneo), in plantations of exotic (non-indigenous) tree species (Acacia mangium, Eucalyptus deglupta, Gmelina arborea, Paraserianthes [=Albizia] falcataria, and Pinus caribaea), plus secondary natural forest and dense understorey within E. deglupta stands. Each habitat had three 1 m2 samples taken four times in one year. The average arthropod species richness within the stands of the exotic tree species ranged from 27 in E. deglupta, to 68 in natural, secondary forest. The total number of individuals caught ranged from 137 in G. arborea to 1628 in secondary forest. The dense and plant-species rich understorey within E. deglupta stands yielded both higher numbers of species and individuals than the eucalypt trees themselves, indicating the importance of allowing the development of a luxuriant understorey for the enhancement of conservation and biodiversity. Though arthropod biodiversity is reduced by the conversion of tropical forests to plantations, abundance and richness are still substantial in the latter habitats.

The facultative ectoparasite, Lucilia sericata (Meigen) has been described as a pioneer colonizer of carrion. This behaviour is believed to enable it to escape the intense interspecific competition which can occur between dipterous larvae within carrion. Such escape is necessary as this fly species has been thought to have reduced competitive ability, resulting from its evolutionary progression towards parasitism. In the work reported here, the attraction of L. sericata to carrion bait at different stages of decomposition (fresh to 28 days old) was investigated in the field. Trials were run over three years, with carrion bait presented in the presence and absence of sodium sulphide. Decomposition had a significant effect on the numbers of L. sericata caught; more decomposed bait caught greater numbers of L. sericata than fresh bait. However, this effect was not apparent if sodium sulphide was added to the carrion. With sodium sulphide added, there was no significant difference in the attraction of female L. sericata, regardless of bait age. There was no general relationship between carrion bait age and the number of female L. sericata caught in different stages of ovarian development. The present data, therefore, suggest that L. sericata does not act exclusively as a pioneer species. Furthermore, this work suggests that, if used with sodium sulphide, the stage of carrion bait decomposition does not significantly modify carrion bait attractiveness.

The well-established carboxylesterase-based resistance to insecticides in Myzus persicae Sulzer has recently been accentuated by the appearance of aphids with a modified acetylcholinesterase (MACE) insensitive to pirimicarb and the novel aphicide, triazamate. This target site resistance mechanism was found in M. persicae from crops in the UK for the first time in 1996, together with especially large proportions of aphids with R2 and R3 levels of carboxylesterases, a combination that was associated with serious insecticide failures. This paper describes the incidence of both mechanisms and discusses the implications for future recommendations for aphid control in the UK.