The life cycle of Strobilomyia anthracina (Czerny) which exploits Norway spruce seed cones was investigated in 1992 and 1993 in the Alps at c. 1800 m at Torgnon (Valle d'Aosta, Italy) and Lac de Tseuzier (Valais, Switzerland) by sampling cones at fortnightly intervals. Oviposition occurred primarily singly in the basal third of cones at the beginning of June when cone scales were open for pollination. Infestation rates were higher when cone crops were poor. Most larvae left the cones in August to pupate in the litter beneath trees, usually at a depth of 1–4 cm. Prolonged diapause of pupae coincided with failed or poor cone crops. Parasitism was investigated at these two and 27 additional sites in the Swiss, French and Italian Alps. Among several hundred host eggs only one was parasitized by Trichogramma sp. (Trichogrammatidae). Among the larval-pupal endoparasitoids, the figitid Sarothrus areolatus Hartig was more common than an ichneumonid, Atractodes sp., but parasitism by both was commonly below 10%. Parasitism by an ichneumonid larval ectoparasitoid, Scambus sp., also rarely exceeded 10%. Puparia of S. anthracina that were buried in the litter to detect pupal parasitoids revealed the gregarious pteromalid Tritneptis sp. near lophyrorum (Rushka). This is the first record of a pupal parasitoid of Strobilomyia species. Information on the biology of the three larval parasitoids is presented. The potential for biological control of North American Strobilomyia neanthracina Michelsen and S. appalachensis Michelsen by importation of natural enemies of S. anthracina appears limited.

Four new species of Encarsia, E. lanceolatasp. n., E. paracitrellasp. n., E. pseudocitrellasp. n. and E. unicitrellasp. n. are described and illustrated. All four parasitoid species were reared from the Bemisia tabaci-complex and/or other whitefly hosts in the Neotropical region. Encarsia paracitrella, E. pseudocitrella and E. unicitrella are extremely closely related, to each other and to E. citrella (Howard). A diagnosis is therefore given for the E. citrella-complex, with a key to the four currently included species. For E. citrella (Howard) a lectotype is designated, the male is described and illustrated for the first time, and the female is redescribed and illustrated. A key and a modification to an existing key are provided to facilitate the identification of the five species treated.

Apterous aphids need to move from ageing to younger leaves in order to survive UK winters. This behaviour was studied at low temperatures in field and laboratory trials using Myzus persicae (Sulzer) clones representing all five recognized categories of esterase-based insecticide resistance found in UK populations. Both studies showed that the tendency of aphids to move from deteriorating leaves was inversely related to their insecticide resistance level. This maladaptive behaviour associated with greater insecticide resistance could lead to increased risks of aphids becoming separated from plants after leaf fall, and subsequent death from starvation when adverse cold and wet conditions prevent return. Revertant clones, that had spontaneously lost extreme resistance to insecticides by ceasing to express their amplified esterase genes, tended to show similar behaviour to aphids that had retained their high resistance phenotypes. This implies that rates of movement were not related directly to esterase production.

Four possible biochemical mechanisms of organophosphate resistance were examined in populations of Rhyzopertha dominica (Fabricius) collected from eight locations in the states of Minas Gerais and São Paulo in Brazil and from seven locations in northeast Kansas, United States. Results from insecticide bioassays with synergists (triphenyl phosphate, diethylmaleate, and piperonyl butoxide) suggested that metabolic detoxification mechanisms might be involved in organophosphate resistance in some of the populations of R. dominica. However, overall low synergism, non-synergism or even antagonism presented by these synergists in all 15 resistant populations suggested that carboxylesterases, cytochrome P450 monooxygenases and glutathione S-transferases were not likely to play a major role conferring organophosphate resistance in R. dominica. This hypothesis was strongly supported by our biochemical studies showing no significant difference in these enzyme activities, as well as cytochrome b5, P420, and P450 levels between the susceptible and resistant populations. In contrast, all resistant populations of R. dominica showed higher acetylcholinesterase activity than the susceptible population both in the presence and absence of malaoxon. Furthermore, acetylcholinesterase from the resistant populations was less sensitive to inhibition by malaoxon than that from the susceptible. These results suggested that quantitative and qualitative changes in acetylcholinesterase might contribute to organophosphate resistance in these populations of R. dominica.

A survey was made to assess the biotype status of populations of the whitefly Bemisia tabaci (Gennadius) in Spain. The study involved observation of the squash silverleaf reaction, analysis of esterase patterns and application of a RAPD-PCR technique. The results obtained by the three methods were fully consistent and showed that the Spanish populations of B. tabaci were composed of two genetic types. One corresponded to populations of the B biotype, found in Tenerife (Canary Islands), Barcelona, Madrid, Malaga and Almeria. The other, showing a unique RAPD and esterase pattern, was found in Majorca (Balearic Islands), Seville, Valencia, Murcia and Almeria, as well as in the Algarve Region of Portugal. RAPD patterns of other populations from the rest of the world used for comparison showed that populations from Arizona (USA), Israel, France, Denmark, Italy, Netherlands and Japan have similar RAPD patterns typical of the B biotype. By contrast, populations from the Iberian Peninsula, Turkey, India, Pakistan and Arizona (A biotype), showed different and unique patterns.

The taxonomic status of Phylacteophaga Froggatt is re-evaluated using the independent techniques of allozyme electrophoresis and detailed morphological comparison. Analysis of 45 scorable loci showed highly significant fixed differences (46–51%) among two currently recognized subspecies, P. eucalypti eucalypti Froggatt P. e. froggatti Riek, and a previously unrecognized taxon from Tasmania, demonstrating that they are different species. In addition to colour, significant variation is revealed among P. e. occidens Benson, P. rubida Riek and the three electrophoretically defined species, in body size, structure of the antennae, the shape of the crest, dorsal spines and saw teeth of the ovipositor, and in male genitalia. Based on these results there is substantial justification in recognizing P. occidens and P. rubida as separate species, distinct from P. eucalypti, P. froggatti, and P. amygdalinisp. n. Further, comparison of the holotype of P. e. tasmanica Riek shows it to be conspecific with the lectotype of P. eucalypti (designated here) so that the former species is considered a junior synonym. The distribution of P. eucalypti and P. froggatti is extended to include Tasmania, and a key is presented to distinguish the males and females of all five species. The biology and host plant relations of the species concerned are discussed, along with their pest status and potential to spread to other regions of the world where eucalypts are grown.

The oviposition aggregation pheromone of six species or forms of the Simulium damnosum Theobald complex (Diptera: Simuliidae) from different sites in West Africa, was investigated by gas chromatographic analysis of hexane extracts of the ovaries from wild-caught flies, bloodfed and maintained until gravid in the laboratory. The two compounds previously shown to be released from fresh eggs and associated with mediation of oviposition aggregation were found in S. leonense Boakye, Post & Mosha (Sierra Leone), S. yahense Vajime & Dunbar (Ghana), S. sanctipauli Vajime & Dunbar (Ghana), S. sqnamosum; Enderlein (Cameroon), S. sirbanum Vajime & Dunbar (Ghana) and the Bioko form (island of Bioko, Equatorial Guinea). Coupled gas chromatography–mass spectrometry of the S. leonense, S. sanctipauli and the Bioko form extracts showed the two compounds to be identical in all three. Volatile emissions from freshly laid eggs of S. sanctipauli were similar to those previously described from S. leonense, and identical in chemical composition to gravid ovaries. No new compounds were detected in any ovary extracts or volatile emissions examined, demonstrating that the composition of the aggregation pheromone is similar throughout the S. damnosum species complex. Analysis of S. leonense adults of different age groups and physiological states showed that the compounds are detectable only in gravid ovaries at 2 or more days following the bloodmeal, suggesting that production of the pheromone occurs during egg development. Demonstration of an oviposition aggregation pheromone common throughout the species complex raises the possibility of developing an odour-baited trapping system for blackflies, which could be employed across the large area of Africa where they are the vectors of onchocerciasis.

Reciprocal crosses between strains of Aedes aegypti (Linnaeus) from different geographical areas have revealed an unexpectedly complex pattern of holandrically inherited male biased sex ratios in F2. The variation has been interpreted in terms of a web of X–Y interactions in Fl, in which the Y chromosome may or may not show meiotic drive against the X chromosome with which it is paired. The pattern of inheritance is not in agreement with a single form of Y chromosome, driving with different degrees of intensity against Xs of different sensitivity, but indicates different forms of driving Y chromosome. A rule has emerged that if Fl males from any cross give rise to a male distorted sex ratio in their progeny (F2), the males from the reciprocal cross give rise to a normal sex ratio. All eleven newly colonized strains from Ghana showed Y meiotic drive against the Xs of five strains, one of American and four of Australian origin, although one of the eleven showed a greater degree of drive than the other ten against the same sensitive strains. The variation observed is discussed in relation to previous studies on meiotic drive by the MD haplotype, and to the possible exploitation of sex ratio distortion in controlling this potentially dangerous insect.

Coprophagous beetles (endocoprid and paracoprid Scarabaeidae, Hydrophilidae, and Staphylinidae) were extracted from 698 sheep droppings from a pasture in southwest Germany. To quantify the pairwise niche overlap of these species, pairwise discriminant function analysis was used to calculate the overlap of the discriminant distributions in a four-dimensional niche space. Niche separation was studied considering the following four factors: season (month) and macrohabitat when and where the dropping was deposited, dropping size, and water content of the dropping. Multiple discriminant function analysis was used to describe the distribution of species in a space defined by four discriminant functions. The first discriminant function was mostly influenced by the factor ‘season’. The importance of different factors for niche separation in different functional groupings of dung beetles is compared with results from the literature. Advantages and disadvantages of pairwise and multiple discriminant function analysis, and univariate evaluation methods are compared. The following problems and restrictions of discriminant function analyses are emphasized: (i) the usage of non-numerical variables; (ii) the calculation of niche breadths; (iii) failures, when bimodally distributed variables are considered; and (iv) the ecological interpretation of statistical significances.

The blood feeding patterns of Anopheles freeborni Aitken and Culex tarsalis Coquillett were studied, and the effects of host availability on these patterns were assessed in four different habitats within a northern California rice agroecosystem. Resting mosquitoes were collected from June to September of 1991 and 1992. The source of mosquito blood meals was identified with the modified precipitin test. Anopheles freeborni exhibited a ‘specialized’ (fixed) blood feeding pattern, predominantly (99% of the time) feeding on mammalian hosts; leporids and bovids were the major hosts, while equines, suids, and other mammals were minor hosts. Culex tarsalis exhibited a more ‘generalized’ (catholic) blood feeding pattern, taking blood meals from both birds and mammals at a ratio of 3:1 with Passeriformes being the most fed upon host group. Human blood indices were under 3% for both mosquito species, and multiple blood meals were estimated at less than 2%. The host feeding patterns for both mosquito species differed among the four (riparian, rice, pasture and mixed) habitats. The host feeding pattern for C. tarsalis reflected the distribution of both mammalian and avian hosts available. On the contrary, the host feeding patterns for A. freeborni reflected the distribution of mammalian but not the available avian hosts. Overall, host availability may be an important determinant of population size of some mosquito taxa (e.g. A. freeborni) than others (e.g. C. tarsalis) in rice culture agroecosystems.

When Myzus persicae (Sulzer) feeds on healthy sugarbeet it develops a white precipitate inside its stomach which causes the stomach to enlarge. Infection of sugarbeet plants with beet yellows virus (BYV), but not beet mild yellowing virus (BMYV) results in further increases in stomach size. The influence of the white precipitate on the transmission of BYV and BMYV was investigated by rearing M. persicae on sugarbeet Beta vulgaris, Tetragonia expansa and Capsella bursa-pastoris, which are hosts for both BYV and BMYV, BYV and BMYV respectively, but the latter two hosts do not stimulate the formation of white precipitate in the aphid's stomach. Aphids reared on BYV-infected T. expansa were significantly better vectors of BYV than those reared on BYV-infected sugarbeet, but aphids reared on BMYV-infected C. bursa-pastoris did not transmit BMYV more efficiently than those reared on BMYV-infected sugarbeet. The consequences of these results for the spread of beet yellowing viruses are discussed.