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.

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 status of the different cytological variants of Simuliumsanctipaulisensu stricto Vajime & Dunbar (sensu b8Post, 1986) found in Ghana and Côte d’Ivoire is cytotaxonomically evaluated in view of recent revisions of the S. sanctipauli subcomplex. Three geographical variants designated as ‘Pra’, ‘Comoé’ and ‘Sassandra’forms of S. sanctipauli are described. The ‘Pra’ form is genetically differentiated from the other two forms by a distinct sex-determining system. The ‘Comoé’ and ‘Sassandra’ forms are considered as the two ends of an interspecific stepped cline with the River Bandama basin as the zone of contact. The possibility that the ‘Comoé’ form populations breeding in southwestern Ghana could serve as reinvading S. sanctipauliinto the Onchocerciasis Control Programme (OCP) area in West Africa is discussed.

The effect of host availability at 6 h, 12 h and 24 h intervals on temporal variation in median host-biting frequency, oviposition and survival of the mosquito, Aedes aegypti (Linnaeus), was investigated under laboratory conditions. In each feeding interval, ten replicates containing five mosquitoes were assessed over 12 days. Median host-biting frequencies were 0.7 bites per female mosquito in the 24 h feeding interval, 0.54 bites per female in the 12 h feeding interval, and 0.47 bites per female in the 6 h feeding interval. Although the 24 h figure was comparable to previously documented levels, feeding increased by 1.5 and 2.7 fold in the 12 and 6 h feeding intervals over a 24 h period. Host biting and oviposition were observed to peak at dusk in the 6, 12 and 24 h feeding intervals, but substantial activity was also observed at dawn, noon and midnight. Daily feeding analysis showed that host biting decreased by approximately 50% in all feeding interval trials over the 12 day test period. Oviposition peaks coincided with biting decline, suggesting a three day gonotrophic cycle. Survival did not differ significantly between feeding intervals. The reported rate of 0.47 host bites per female mosquito per 6 h (≈ 1.9 per 24 h) is thus far the highest recorded for A. aegypti. The suggestion that A. aegyptiprobably feeds more regularly than once in a 24 h period in nature is consistent with the biting and oviposition results.

The effectiveness of varying weekly release rates of the parasitoid Eretmocerus eremicus Rose & Zolnerowich for control of Bemisia argentifolii Bellows & Perring on poinsettias was determined. Two variable release rate strategies for E. eremicus were evaluated: a low–high and a high–low release regimen. In the low–high treatment, one female parasitoid was released per plant per week for seven weeks, then the release rate was increased to five female parasitoids per plant per week for the remaining seven weeks of the trial. In the high–low treatment, five female parasitoids per plant per week were released for the first seven weeks, then the release rate was reduced to one female parasitoid per plant per week for the final seven weeks of the trial. Both release rates averaged three female parasitoids per plant per week. Life-tables were made for B. argentifoliiin the presence and absence of parasitoids. In the absence of E. eremicus, egg to adult survivorship for B. argentifolii was 65%. In low–high release greenhouses, average egg to adult survivorship for B. argentifoliiwas 6% and parasitism was 28%. In high–low greenhouses, average egg to adult survivorship for B. argentifolii was 5% and parasitism was 16%. Average net reproductive rates for B. argentifolii in the absence of parasitoids was 17 indicating a rapidly increasing population. Net reproductive rates were 1.46 and 1.24 for low–high and high–low release greenhouses, respectively, indicating substantially reduced B. argentifolii population growth. At week 14 of the trial, densities of live nymphs and pupae were lower in high–low greenhouses when compared to low–high greenhouses. Better whitefly control is achieved with inundative releases of E. eremicus when this natural enemy acts as a predator as opposed to a parasitoid.

The development period from birth to adult of alate and apterous virginoparae of the green peach aphid, Myzus persicae (Sulzer), reared on Brassica campestrisssp. chinensis, was measured at 13 constant and five natural temperature regimes. The day–degree model, the logistic equation, and the Wang model were used to describe the relationships between temperature and development rate at constant conditions. The constant temperature–development curves derived from the three models were used with a Weibull function describing the distribution of development times, to simulate the development of individuals of cohorts reared at natural temperature regimes. Comparison of the observed with simulated distributions of adult emergence indicates that all three models can simulate the development of M. persicaevery well when the temperature does not go below 4°C, the notional low temperature threshold of the day–degree model. When accumulation of temperatures below 4°C becomes substantial, only the logistic curve with a low temperature threshold of 0°C can offer accurate simulations; the other two models give falsely longer durations of development. Methods for accurately simulating the development of M. persicae in the field are suggested. The significance of modelling insect development at low temperatures by nonlinear models is discussed.

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.

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.

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.

Trichogramma spp. egg parasitoids are generally absent in eggs of Helicoverpa armigera (Hübner) collected from chickpea, Cicer arietinum. In this study, the plant characters responsible for the absence of egg parasitoids and the feasibility of increasing parasitism levels on chickpea by mass-releasing Trichogramma chilonis Ishii were investigated. The residence time of female T. chilonison chickpea leaves was affected by trichomes and the acidic trichome exudates secreted on all green parts of the plant. The parasitoids spent a longer time on chickpea leaves where the acidic trichome exudates had been washed off than on unwashed leaves, and longer on leaves of a glabrous chickpea mutant than on washed leaves. When placed on unwashed chickpea leaves, 6.8% of the parasitoids were trapped and killed by the exudates. In a filter paper bioassay, female T. chilonis were deterred by high concentrations of malic and oxalic acids, the major components of the trichome exudate. Acetone and hexane extracts from the surface of chickpea leaves did not elicit a response from the parasitoids in the bioassay. Similarly, the parasitoids did not respond to volatiles emitted by chickpea plants in a four-armed airflow olfactometer. No parasitized eggs were collected from a chickpea field in which T. chiloniswere released five times at a weekly interval at a rate of > 137,000 females ha–1. Sticky trap catches showed that no parasitoid population was sustained in the release field.

Development rates of the aphid, Brachycaudus rumexicolens (Patch), a recent arrival in Australia and a potential biological control agent against weeds in the family Polygonaceae, were measured over a range of constant temperatures. The theoretical lower limit for development is 6.4°C and the upper limit 32°C. Maximum fecundity per day was reached at 19°C. The rate of increase peaked at about 28°C giving a population doubling time of less than two days. These values were used with the current distribution to develop a CLIMEX model to predict the potential world distribution of the aphid. The model predicts that the aphid has suitable periods of population growth in autumn and spring, and that survival is unlikely over summer in most of south-western Australia where the aphid has the potential to contribute to the biological control of the polygonaceous weeds, Emex and Rumexspecies. The model predicts that years with cool summer temperatures and late summer rains in south west Australia, such as in 1990 when the aphid was first abundant, will be particularly suitable for aphid development. These conditions occurred twice between 1985 and 1995. To increase the effectiveness of the aphid as a biological control agent of weeds in other years, augmentation by provision of alternative hosts and/or the release of mass reared individuals during autumn is proposed.