Collections of mosquitoes of the Anopheles gambiae Giles complex were made from the geothermal springs and surrounding area in the Semliki Valley, Bwamba County, Uganda, which is the only known locality of A. bwambae White. Specimens were analysed in one of three ways: rDNA-PCR for unequivocal species identification, allozyme electrophoresis to determine superoxide dismutase (Sod) and octanol dehydrogenase (Odh) genotypes, or both methods. Ribosomal DNA-PCR identification revealed the presence of A. bwambae and A. gambiae. Allozyme electrophoresis of 181 individuals showed that A. bwambae possessed the Sod105and Sod100 alleles and was not monomorphic for Sod105as reported previously. In adults reared from collections made in the vicinity of the geothermal springs, the frequency of Sod105 was found to be 0.614. Anopheles gambiae was fixed for Sod100. The majority of individuals homozygous for the Sod100 allele could be identified to species using Odh. Odh95 was found to be common in A. bwambae (frequency = 0.988) while A. gambiae appeared to be fixed for Odh100. Since Odh100occurred at a frequency of 1.2% in A. bwambae (concomitant with Sodgenotypes of 105/105, 100/105 or 100/100), individuals homozygous for Sod100 and Odh100 could be either species. Among 25 A. bwambae specimens homozygous for Sod100, one (4%) was also homozygous for Odh100. At present, this subset of the A. bwambae population can only be correctly identified to species using rDNA-PCR analysis.

Recent experimental evidence has shown that learning occurs in the host selection behaviour of Helicoverpa armigera (Hübner), one of the world‘s most important agricultural pests. This paper discusses how the occurrence of learning changes our understanding of the host selection behaviour of this polyphagous moth. Host preferences determined from previous laboratory studies may be vastly different from preferences exhibited by moths in the field, where the abundance of particular hosts may be more likely to determine host preference. In support of this prediction, a number of field studies have shown that the ‘attractiveness’ of different hosts for H. armigera oviposition may depend on the relative abundance of these host species. Insect learning may play a fundamental role in the design and application of present and future integrated pest management strategies such as the use of host volatiles, trap crops and resistant crop varieties for monitoring and controlling this important pest species.

The effects of host and non-host plant odours on the foraging responses of the banana weevil, Cosmopolites sordidus (Germar), were investigated in the laboratory through arena and olfactometer bioassays. Contrary to previous reports that banana rhizome and pseudostem were the most attractive parts to the weevil, dead leaves were most preferred. Comparison of dead banana leaves with dead leaves of other plants showed that attractant odours were present in yam, cocoyam and dead grasses but absent in cocoa and soybean leaves. Complete leaf senescence while the leaf was attached to the mother plant proved necessary for the development of the dead-leaf-based odours but the involvement of microbial organisms could not be demonstrated. It is possible that dead-leaf-based attractants could be used in combination with microbials such as entomogenous fungi and nematodes in integrated management of C. sordidus.

Effects of five weed management regimes on abundance of weeds, insect pests, generalist predators and on pest damage and rice yield were investigated in upland rice in Côte d‘Ivoire over two years. In both years there was a highly significant negative correlation between weed biomass and grain yield across all treatments. Only two pest insect groups, Nephotettix spp. (Cicadellidae) and seed sucking Heteroptera, were consistently more abundant in unweeded plots and had a consistent significant positive correlation between abundance and weed biomass across all seven treatments. These polyphagous groups may have been more dependent on resources provided by weeds than the other pests studied. However, pest damage was not affected by presence or absence of weeds, suggesting that populations were below a damage threshold. Ants were the most abundant predators in the rice canopy and were most abundant in unweeded treatments. Abundance of both ants and spiders was significantly positively correlated with weed biomass across treatments. Abundance of reduviid bugs was positively correlated with weed biomass only in 1995. Any benefits due to presence of weeds in the crop were completely outweighed by loss of crop yield due to weed competition. However, if crop losses due to weeds were sufficiently reduced, it is possible that significant losses due to insect pests might emerge.

A method for identifying the members of the endemic genus Wiseana Viette from New Zealand is described. Seven species have been described in the genus: W. cervinata (Walker), W. copularis (Meyrick), W. fuliginea (Butler), W. jocosa (Meyrick), W. mimica (Philpott), W. signata (Walker) and W. umbraculata (Guenée). No morphological characters have been identified to distinguish between the larvae of each species and adult females exhibit high levels of intra and interspecific morphological variation making identification difficult or impossible. Adult males can be distinguished by a combination of scale, antennal and genital characters, but this requires considerable taxonomic experience. Molecular markers were generated via amplification of the cytochrome oxidase subunit I and II (COI and II) of the mitochondrial DNA by the polymerase chain reaction (PCR). Amplified DNA was digested with restriction enzymes to give characteristic fragment patterns. Fourteen restriction enzymes were surveyed and a combination of four of these distinguish all Wiseana taxa except W. fuliginea and W. mimica.

The mealybug Phenacoccus herreni Cox & Williams causes considerable damage to cassava Manihot esculenta Crantz. Field surveys conducted between 1988 and 1994 indicated the mealybug was present in 57 municipalities in six States in north-eastern Brazil, in some places reaching high levels of infestation. Several native natural enemy species were found associated with the pest in Brazil. Exotic encyrtid parasitoids were imported and released in fields in the States of Bahia and Pernambuco. Apoanagyrus diversicornis (Howard) was introduced from Colombia, and Acerophagus coccois Smith, and Aenasius vexans (Kerrich) were introduced from Venezuela. By the end of 1996, a total of 35,930 parasitoids had been released. In Bahia, Apoanagyrus diversicornis was recovered 130, 234, 304 and 550 km from its release site after 6, 14, 21 and 33 months, respectively. Acerophagus coccois was recovered at 180 km from its release site nine months after release. Aenasius vexans, however, did not disperse at all despite being consistently recovered at its release site. In Pernambuco, 9010 parasitoids were released from October, 1995 onwards. Acerophagus coccois and Aenasius vexans were recovered up to 40 km from the release sites after three and five months of their initial releases, respectively. The establishment and dispersal of these parasitoids are discussed.

Calyptrate fly populations were monitored with sticky traps at the following sites in Hampshire, UK during August to November 1998: a landfill and composting site (Paulsgrove), a site adjacent to this landfill (Port Solent), a site with no landfill nearby (Gosport), and a composting site with no landfill nearby. Overall, house flies Musca domestica(Linnaeus) and lesser house flies Fannia spp. were not important constituents of the dipteran catch, while bluebottles (Calliphora spp.) and greenbottles (Lucilia spp.) comprised approximately 12% of the total. Very large fly populations were found at the two composting sites, and it seems likely that these provide ideal breeding grounds for a range of fly species since they offer an abundance of warm decaying organic matter. Large fly populations were also evident at the landfill site. The suitability of household waste for the development of calyptrate Diptera was confirmed in a controlled trial: a mean of 0.43 adults emerged per kilo of one-week-old waste. Since many hundreds of tonnes of waste are delivered to the landfill daily, it is clear that the landfill is likely to substantially increase the local population of calyptrate flies. However, the data suggest that there was little movement of Diptera from the landfill to Port Solent situated approximately 500 m away. The most important calyptrate flies at this site were the cluster flies Pollenia rudis (Fabricius) and P. amentaria (Scopoli); the landfill site is unlikely to provide a suitable breeding site for these flies, as the larvae develop as parasites of earthworms. Significantly more flies emerged from one-week-old than from two-week-old household waste. A comparison of different barriers to the emergence of adult house flies from waste demonstrated that sacking provided an effective barrier to fly emergence, but that soil did not differ significantly from control treatments. If managed appropriately, it seems that the use of sacking over landfill waste could substantially reduce associated fly populations.

The biology and pest status of Hylobius abietis Linnaeus in Europe are critically reviewed. New data are presented and the relationships between the weevil and its host plants considered. In Europe, H. abietis is the major pest of establishment forestry causing millions of ECUs of damage annually and perpetuating the addition of insecticide residues to sensitive habitats. Predator and parasitoid complexes in Britain and Europe are compared and contrasted. The lack of knowledge of the processes involved in adult dispersal and longevity are highlighted as major areas of concern. The biology and behaviour of the adult and larval stages are reviewed and new data presented. The feeding preferences of the adult weevils are considered and the possibility of using deterrents as a pest management strategy discussed. The development of risk assessment and forecasting tools aimed at more effective deployment of pest-management options are discussed. Risk criteria have their origins in important ecological relationships which require new understanding, but the prospects for determining high-risk forest sites are promising. The options for biological control are evaluated, in particular the use of mycopesticides and increased larval predation. It is concluded that much more research into the biology and ecology of H. abietis is required before a successful Integrated Pest Management (IPM) programme can be initiated.

Fifty-five species of exotic dung beetles have been introduced into Australia and in many areas, several species are now established and often abundant. Controversy exists in the dung beetle literature concerning the use of ivermectin as an anthelmintic treatment for livestock and its subsequent lethal and sub-lethal effects on adult dung beetles. A study was conducted in the field exposing replicate dung pats containing residues of ivermectin excreted 0–15 days post-injection. At the time of the study, the introduced species of dung beetle Onthophagus taurus (Schreber) was present in high numbers (>1000 beetles per pat). After 24 h exposure, dung pats collected from cattle treated 7 and 10 days earlier with ivermectin were dispersed significantly less than untreated dung. A similar pattern was evident in the numbers of dung beetles present in each pat. This study is discussed in the context of anthelmintic usage in cattle and their potential ecotoxic effects against dung beetles.

A cytotaxonomic study was carried out on 13 species of Encarsia Förster, known to parasitize aleyrodids and diaspidids. The chromosomes varied greatly both in number and morphology, with E. protransvena Viggiani having the lowest chromosome number (2n = 6) and E. asterobemisiae Viggiani & Mazzone the highest (2n = 20). The most common chromosome number was 2n = 10. C-banding, G-banding and silver staining for nucleolar organizer regions (NOR) provided the possibility of distinguishing between karyotypes with the same chromosome number and morphology and to identify all the pairs of homologues in a diploid set for advanced cytogenetic studies. The karyotype of Coccophagus lycimnia (Walker) was also examined. The chromosome data suggested that in Encarsia, karyotype differentiation has mainly occurred through a series of centric fusions, although other rearrangements may also have been significant. The importance of karyological data in systematic studies and in the identification of biotypes and cryptic species of economic interest is outlined.

Pretreatment of first instar larvae of 28 resistant strains of Lucilia cuprina(Wiedemann) with the inhibitor of microsomal oxidases, piperonyl butoxide, resulted in a biphasic response to the phosphorothioate insecticide diazinon. Analysis of the data revealed a complex response in which both synergist-dependent and independent effects occurred. The responses varied markedly from strain to strain. A laboratory susceptible strain and field strains with resistance factors of less than 20-fold exhibited, in the presence of piperonyl butoxide, an increased LC50 with respect to diazinon whereas those strains with > 20-fold resistance were synergized by the compound. We conclude tentatively that microsomal mixed-function oxidases play a contributory role in the development of resistance and that the variation in synergist effect from strain to strain may be attributed, at least in part, to the two-fold effect of these enzymes on phosphorothioate insecticides such as diazinon.

Bioassay data for a reference strain of Nasonovia ribisnigri (Mosely), exhibiting similar responses to proven susceptible strains of Myzus persicae (Sulzer) and Aphis gossypii Glover, were used to assess insecticide resistance in two suspected resistant strains and nine field strains of N. ribisnigri originating from lettuce in the UK. Results showed widespread but varied levels of resistance to pirimicarb, lower and also varied resistance to pyrethroids and organophosphates, and no significant differences in response to imidacloprid. In some strains, resistance was associated with an intensely-staining esterase band disclosed by polyacrylamide gel electrophoresis (PAGE). However, no direct relationship between esterases and resistance has yet been established. There was no biochemical evidence of an altered acetylcholinesterase contributing to pirimicarb resistance in these strains.

The within-field spatial distribution of some common farmland arthropods from the Carabidae, Araneae and Collembola was assessed using two-dimensional grids of pitfall traps distributed across whole winter wheat fields. In the first year, the extent to which arthropod capture was influenced by location within the field and sampling intensity was examined using a nested grid design (1.5 m, 7.5 m and 30 m spacings). In the second year, distributions within two different-sized winter wheat fields were compared. Spatial pattern and association between arthropods and weed cover were analysed using SADIE and trend surfaces were used to visualize distributions. Many of these arthropod groups exhibited aggregated distributions within the fields in clusters larger than 30 m across, demonstrating that the numbers captured will vary depending on the location of sampling within a field. Amara species, Bembidion lampros Herbst, Carabidae and Lycosidae were predominantly found within 60 m of the field edge. Nebria brevicollis Fabricius and Pterostichus madidus Illiger were found within the field in patches of one and two hectares, respectively. Linyphiidae were relatively homogeneously distributed across the fields. There was some evidence of clustering by Collembola. The spermophagous Carabidae and Lycosidae were positively associated with the degree of weed cover. SADIE analytical techniques were useful for identifying the importance and location of patches with greater and less than average numbers, although a minimum of 36 sample points is recommended.

Termites were sampled using randomized soil pits in 64 cropping plots, each 25 x 25 m, forming an experimental agrisilvicultural system in both a 6- and an 18-year-old Terminalia ivorensis plantation, in which canopy cover, crop, cropping system and land preparation were the principal treatment variables. The treatments were established in April 1995 and sampling was carried out in November 1995, February 1996 and July 1996. A total of 82 termite species were found, of which 67 were soil-feeders. Overall termite abundance and the abundance of soil-feeders increased between November 1995 and July 1996, reaching a mean of nearly 6000 m-2. Pooling termite data from these sampling dates, in the old plantation, the high canopy cover treatment (192 stems ha-1) had a greater abundance of termites, compared with the low canopy cover treatment (64 stems ha-1) and this effect was independent of crop type (plantain or cocoyam), cropping system (single stands or mixed crops) and land preparation (mulch retained or burned, plantain only). The young tree plantation (same tree densities as in the old plantation) showed no significant difference in termite abundance between high and low canopy (levels of tree foliage) densities, though the high canopy sheltered a greater number of termites. Analysis of covariance showed that crop yield (both plantain and cocoyam) was not directly linked to the abundance of all termite populations, but that the cocoyam yield was positively correlated with the abundance of soil-feeding termites (the majority in the assemblage) in the young plantation. This may be due to the beneficial conditioning of soil resulting from the foraging and construction activities of soil-feeders.

Growing interest in biodiversity and conservation has increased the demand for accurate and consistent identification of arthropods. Unfortunately, professional taxonomists are already overburdened and underfunded and their numbers are not increasing with significant speed to meet the demand. In an effort to bridge the gap between professional taxonomists and non-specialists by making the results of taxonomic research more accessible, we present a partially automated pattern recognition system utilizing artificial neural networks (ANNs). Various artificial neural networks were trained to identify spider species using only digital images of female genitalia, from which key shape information had been extracted by wavelet transform. Three different sized networks were evaluated based on their ability to discriminate a test set of six species to either the genus or the species level. The species represented three genera of the wolf spiders (Araneae: Lycosidae). The largest network achieved the highest accuracy, identifying specimens to the correct genus 100% of the time and to the correct species an average of 81% of the time. In addition, the networks were most accurate when identifying specimens in a hierarchical system, first to genus and then to species. This test system was surprisingly accurate considering the small size of our training set.

Populations of rice leaffolders and their natural enemies were studied in eight crops of irrigated rice in Laguna Province, the Philippines. The rice leaffolder complex consisted of three species: Cnaphalocrocis medinalis (Guenée), Marasmia patnalis Bradley and M. exigua Butler. Leaffolder population dynamics were characterized by an egg peak at maximum tillering and a broad larval peak around booting stage. Peak densities ranged from 0.2 to 2.0 larvae per hill. Most larvae originated from immigrant moths and there was no substantial second generation. The seasonal percentage egg parasitism by Trichogramma sp. ranged from 0 to 27%, and percentage larval parasitism from 14 to 56%. The braconid Macrocentrus philippinensis Ashmead was the most commonly reared larval parasitoid. Forty natural enemy taxa that may attack rice leaffolders were identified from suction and sweepnet samples: 24 predator taxa and 16 parasitoid taxa. The estimated survival rates from leaffolder egg to larval stages and between larval stages showed large variation between rice crops, but were not clearly correlated with observed levels of parasitism, natural enemy abundance, or natural enemy to leaffolder ratios. It is suggested that the generally low densities of rice leaffolders in Philippine transplanted rice are caused by their ovipositional preference for crops at the maximum tillering stage, allowing for only one generation, and by high immature mortality caused by the abundant and diverse complex of natural enemies.

The factors that set broad-scale limits on the species ranges of ticks have not been clearly defined, despite their potential importance for the study and control of ticks. A database of 33,989 published collection records for African ticks is used to test the hypothesis that the outer limits to tick species ranges are determined by the distributions of their hosts. Distribution maps for many of the more economically important tick species are given. Direct comparisons of the known ranges of ticks and their hosts show that the hypothesis of a host-determined species range is supported for only one tick species, Amblyomma rhinocerotis (de Geer), which has been constrained by the near-eradication of its rhinoceros hosts. At least 97 other species are not host-limited; the quality of available host-use and distribution information is insufficient to draw strong conclusions about the (approximately) 132 remaining species. In general, the boundaries to tick species ranges are more likely to be set by factors such as vegetation and climate.

The times for knockdown of resistant and susceptible strains of both Anopheles stephensi Liston (DUB234 and BEECH) and A. gambiae Giles (RSP and KWA), on exposure to a permethrin impregnated net were determined to evaluate the effect of age on susceptibility to permethrin. The mean knockdown times of pyrethroid resistant strains of A. stephensi and A. gambiae were significantly shorter if they were 10 days old (either fed or unfed), as compared with those of newly emerged mosquitoes. Based on KT50 values, the resistance ratios between resistant and susceptible A. stephensi were 3.5 and 2.2 for the newly emerged and 10-day-old mosquitoes, respectively. After 1 h exposure to paper impregnated with 0.25%permethrin, mortality of newly emerged individuals of the susceptible and resistant strains of A. stephensi was significantly less than when they were 10 days old. Irritability by permethrin was less with the resistant strain of A. stephensi. In the other strains irritability declined significantly with age. Pre-exposure of susceptible mosquitoes of BEECH and IRAQ strains of A. stephensi for a short time to permethrin did not increase tolerance when the mosquitoes were re-exposed 24 h later. Because of the age effect and the possibility of an effect of pre-exposure under some circumstances, confirmatory tests on newly emerged F1 individuals reared from wild collected mosquitoes are recommended in monitoring for resistance in wild populations.

Existing attempts to estimate the survival rate of tsetse flies from ovarian age distributions generally assume that the population is stationary. The fact that the survival rate cannot be dissociated from the growth rate by these methods poses a problem. Under the assumption of a stable age distribution, we propose a maximum likelihood method to estimate the ‘apparent survival rate’ for three categories of females: nulliparous (β0), young parous (β1) and old parous flies (β2). The rate depends both on ‘real survival rates’ a0, a1 and a2, and a growth rate λ: β0 = a0/λ, β1 = a1/λ, and β2= a2/λ. We used a matrix model, which can be parameterized if the pupal survival rate and the pupal period are known. Replacing a0, a1 and a2 by β0,λ, β1λ, and β2λin the projection matrix, the problem amounts to calculating its dominant eigen-value λ, and hence a0, a1 and a2. The application to a field population of Glossina palpalis gambiensis Vanderplank in Burkina Faso showed there was a marked difference in survival rate according to age category. The average survival rate increased with age with decreasing variability. The results suggested that sampling (by trapping) may have had an effect on the dynamics of this tsetse population by ageing it artificially. This method may be a useful tool for monitoring tsetse control.