To study the rate of invasion into brood cells, a group of varroa mites, Varroa jacobsoni Oudemans, was introduced into honeybee colonies, Apis mellifera Linnaeus. For each experiment one or two otherwise comparable colonies was treated, and the effect on the rate of invasion was assessed. The results showed that the rate of invasion increases with the number of available brood cells, and decreases with the size of the honeybee population. This is expected when the rate of invasion is limited because the bees have to carry the mites close to a brood cell for invasion to occur, and only alimited number of honeybees can come close enough to a brood cell simultaneously. In addition, the rate of invasion decreased when young brood was present. This counterintuitive result may arise because the mites prefer young honeybees, young honeybees are likely to stay in the brood nest area, and young honeybees in the brood nest are divided over areas with brood cells that are suitable for invasion and over areas with brood cells that are unsuitable for invasion by mites. Hence, an increase in the amount of young brood, which is not yet suitable for invasion by mites, may decrease the invasion rate. Differences in the period during which brood cells suitable for mite invasion were available to the mites, appeared not to affect the rate of invasion.

The coffee berry borer Hypothenemus hampei (Ferrari) has recently evolved high levels of resistance to endosulfan and other cyclodiene-type insecticides in New Caledonia. During population outbreaks this has contributed to levels of infestation of coffee berries reaching up to 90%. Using degenerate primers in the polymerase chain reaction (PCR) we have amplified a section of the cyclodiene resistance gene Rdl from H. hampei. This gene codes for a γ-aminobutyric acid (GABA) gated chloride ion channel. Here we report that resistant strains of H. hampei carry exactly the same single amino acid replacement (alanine to serine) as that found in resistant Drosophila melanogaster (Meigen) (Diptera: Drosophilidae). A molecular diagnostic based upon PCR-mediated amplification of specific alleles (PASA) is described. This technique is capable of detecting resistance or susceptibility in adults, larvae or eggs but not in susceptible females carrying resistant sperm. Its potential use in field monitoring is discussed.

Catches of moths in tower-mounted light traps in northern New South Wales were analysed in relation to local and synoptic weather. Catches were correlated with windspeed, relative humidity and possibly rainfall. No correlations were obtained with temperature or moon phase. Catches were more likely to occur when winds were from the east, and were associated with wind shifts. There was a significant association with the passage of depressions or troughs, but not cold fronts. The traps were considered to be poor indicators of migration associated with fronts, because these were accompanied by high winds in which trap efficiency was reduced. Stepwise multiple regressions using temperature, relative humidity, rainfall and windspeed accounted for only about 25% of the variance, much lower than in comparable studies with ground level light traps. These results are thought to indicate that the trap catches were reflecting long-distance migration, which was usually associated with disturbed weather. Back tracking with upper wind data was used to define probable sources of moths. In the spring and early summer, these sources were predominantly to the north and west of the traps, in semi-arid pastoral and subhumid cropping zones. In the late summer and autumn they were predominantly to the south and east, in the humid pastoral and forest zone. These results are discussed in relation to the migratory strategies of several important agricultural pest species.

Suppression tactics for the citrus stink bug pest, Biprorulus bibax Breddin, were developed and implemented during 1987–1992 in four lemon orchards in southern New South Wales, Australia. Tactics were based on introduction and conservation of natural enemies (principally egg parasitoids), physical or chemical treatment of overwintering populations and strategic low rate applications of a selective insecticide. Estimated adult populations of 10–35,000/1.5 ha and 70–90% fruit damage in untreated crops were reduced to <500/1.5 ha and <5%, respectively, following full implementation of the management programme. Integrated management of B. bibax removes the need for broad-spectrum insecticides to control this pest and lessens the risk of disruption to biological control of other citrus pests.

A method for the purification of elevated esterase B2 from the Sri Lankan Pel RR strain of Culex quinquefasciatus (Say) has been developed, using sequential column chromatography. The pure enzyme is stable, with no decrease in specific activity after several months, if stored in the presence of 25 mM dithiothreitol and 50% glycerol at –20°C. The enzyme has a pl of 5 and an estimated molecular weight for the monomeric enzyme of 63 kD from SDS-PAGE. In all Culex strains with elevated B2, another esterase (A2) is always co-elevated. The strains with these esterases are resistant to a broad range of organophosphorus insecticides. The previous purification and characterization of A2 from Pel RR indicated that the role of this enzyme was primarily to sequester rather than metabolize organophosphates. Purified B2, rapidly binds malaoxon, the activated form of malathion, but not malathion itself. The turnover rate of bound malaoxon is slow, suggesting that the role of this esterase in malathion resistance is also sequestration. The similar bimolecular rate constants for both A2 and B2 with malaoxon suggest both esterases are important in resistance, which may explain the almost complete linkage disequilibrium that the elevated forms of these two esterases are maintained in when under pesticide selection pressure.

The morphology and ultrastructure of aphid mummies formed by diapausing and non-diapausing larvae of Aphidius rhopalosiphi De Stefani Perez, are described. Two types of silk thread were present in both types of cocoons: well-structured rounded threads, and flat threads which form a gum coating. Differences in thecocoon weight were observed depending on parasitoid development. A morphometric characterization of the two groups of mummies is given.

Two new species of Eulophidae, which are potential biological control agents of economically important pests, are described from China. Aprostocetus prolixussp. n. (Tetrastichinae) is an egg-parasitoid of Apriona germarii (Hope) (Coleoptera: Cerambycidae), and Hyssopus grossorissp. n. (Eulophinae) is a larval parasitoid of Paranthrene tabaniformis (Rottenburg) (Lepidoptera: Sesiidae). The species Elachertus pallidus Askew is transferred to Hyssopus, comb. n.

The host preference and acceptance behaviour of populations of Aphidius ervi Haliday and A. microlophii Pennacchio & Tremblay from southern Italy was investigated. In no host-choice conditions, A. ervi females showed significantly higher attack and oviposition rates on the natural host Acyrthosiphon pisum (Harris) than on the non-host aphid Microlophium carnosum (Buckton)(Homoptera: Aphididae). In contrast, A. microlophii, which specifically parasitizes M. carnosum in the field, attacked both aphid species. However, dissections showed that oviposition of A. microlophii occurred only in a few of the attacked Acyrthosiphon pisum and was significantly less frequent than in M. carnosum. These results were confirmed in experimental host-choice conditions, suggesting that Aphidius microlophii oviposition is possibly regulated by a host haemolymphatic kairomone. Hybrids obtained by crossing A. ervi females with A. microlophii males attacked and oviposited in both aphid species, suggesting that these behavioural events have a strong genetic basis. The oviposition into host or non-host aphids did not elicit an immune defence reaction. The presence of the host's food-plant had no evident close-range effects on parasitoid attack and oviposition in non-host aphids. Aphidius microlophii reared on the non-host aphid Acyrthosiphon pisum produced a significant higher number of mummies after a few generations, suggesting a possible role of larval and early adult conditioning in the host selection process. These results, together with those from previous studies, suggest that Aphidius ervi is best considered as a complex of differentiated populations, characterized by a varying degree of genetic divergence.

A key is provided for the recognition of the hymenopterous parasitoids of the African white rice borer, Maliarpha separatella Ragonot, a pest of rice in Africa and Madagascar. Five species are described as new: Braconidae: Chelonus maudae Huddleston, Rhacanotus carinafus Polaszek; Ichneumonidae: Prisfomerus bullis Fitton, Prisfomerus caris Fitton, Venturia jordanae Fitton. The following synonyms are proposed: Goniozus indicus Muesebeck, G. natalensis Gordh and G. procerae Risbec are synonymized with Goniozus indicus Ashmead. Phanerotorna major Brues is synonymized with Phanerotoma saussurei Kohl. Lectotypes are designated for Goniozus procerae Risbec, Rhaconotus scirpophagae Wilkinson and Garouella ovicida Risbec. The known distributions, biologies and alternative hosts of each parasitoid are provided, and their use as biological control agents or components of integrated pest management programmes are discussed.

Reactions of the lemon leaf-cutting ant, Atta sexdens rubropilosa Forel, to natural sources of allelochemicals has been investigated at the University of Southampton. A linear hypothesis model in a randomized block design of a factorial experiment was utilized to assess the responses of the ants to the treatment combinations. When workers were offered flowers and leaves of the specified plant species simultaneously with mesocarp and endocarp of orange, they exhibited a consistent preference for the flowers. Flower fragments comprised 93.64% of the experimental material brought to the nest, leaves 6.20%, orange mesocarp 0.04% and orange endocarp 0.12%. Deterrent effects were noticed in leaves of Scilla spp. (Liliaceae) and the ants were chemically stimulated to explore, cut and transport the highly attractive flowers of Mahonia aquifolium (Berberidaceae).

Although Culiseta morsitans (Theobald) is a common Holarctic mosquito very little is known about its biology so many aspects of its life-history were studied, mainly in southern England, from 1964–1987. More limited observations were made in the south on the coastal Culiseta litorea (Shute). Both species laid an average of 109 eggs as an egg raft deposited on wet mud and leaf litter. At high humidities C. morsitans eggs can remain unhatched and viable for many months. Populations of both species overwinter as fourth instar larvae, pupation occurs in April and adults start emerging in early May. The adult season lasts until September or October. Both species feed principally on birds. Serological tests, however, on blood-engorged females show that a few feed on humans, although none has been caught in human bait collections. Light-traps are not very effective in sampling adults, although a few were caught in them, as they were in non-attractant suction traps. The relative sizes of adult populations of both species were monitored in most years from 1964–1980 on Brownsea Island, Poole Harbour, England, and showed a marked decline in the proportions of C. litorea, but there was a resurgence of this species after eight years, when the population again crashed.

The intergenic spacer region of the rRNA cistron was used as a molecular fingerprinting probe to study clonal diversity in Schizaphis graminum (Rondani). A high degree of clonal diversity was found in overwintering populations on wheat from Kansas, Texas and Oklahoma. Out of 184 individuals tested, 132 unique maternal lineages wereidentified. Overall, clonal diversity of overwintering populations was no less than in spring and summer populations. However, in some fields there were more instances where individuals of the same genotype were identified. By partitioning the total population diversity into various sampling components (fields, counties and states), 93.1% of the total diversity was found among individual S. graminum within fields. Overwintering of many genetically distinct clones as parthenogenetic morphs is one mechanism by which clonal diversity is maintained in populations of S. graminum. The incidence of clonal diversity further substantiates the importance of the S. graminum holocycle for generating genetic heterogeneity in the USA.

A technique for initiating artificial strikes on sheep using eggs or larvae of Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae) under controlled conditions is described. A liver based implant provides protein for initial larval development. The technique has been found to produce viable strikes more reliably than other currently-used methods for the purpose of screening insecticides in controlled experiments.

The effects of nine pesticides commonly used in citrus orchards were tested on adults, larvae and pupae of the parasitoid Eretmocerus debachi Rose & Rosen in the laboratory. All pesticides caused immediate mortality to adult parasitoid females and significant losses in efficiency, if applied to larvae of E. debachi in its host Parabemisia myricae (Kuwana). Only the fungicide captan and the insecticide Mercathion (malathion) were slightly harmful and harmless to the parasitoid larva. Gramoxone (paraquat), Dursban 4 (chlopyrifos-ethyl), Mercathion and Supracide (methidathion) were harmful to E. debachi pupae, while five other pesticides were only moderately harmful or harmless.

Field studies in Zimbabwe elucidated the responses of Glossina morsitans morsitans Westwood and G. pallidipes Austen to natural and artificial trunks of trees baited with odours of acetone, 1-octen-3-ol and phenols. The numbers of tsetse electrocuted in flight near the base of the trunk increased 2–12 times when the trunk was shortened from 7.2 m to 0.9 m and its diameter was increased from 25 cm to 5 m, when the base was coloured blue or black to contrast with the upper trunk, or when the upper trunk was separated from the base by a gap of 2.7 m. A swarm flying near short trunks was more compact than near tall trunks. Electrocuting grids to catch alighting tsetse indicated that only about 20% of the attracted tsetse alighted on the base of the trunk, whether this was blue or blue/black. Since there is presently no apparent means of cost-effectively avoiding the inhibitory effects of tall trunks, the use of odour-baited trees as baits for tsetse control seems uneconomical.

Following the discovery of Lydella jaliscosp. n. (from Jalisco, Mexico), a parasite of the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Pyralidae), the limits of the genus Lydella Robineau-Desvoidy have been widened to include Diatraeophaga Townsend syn. n., Metoposisyrops Townsend syn. n., and Metagonistylum Townsend syn. n. All species regarded as belonging to Lydella are listed, with L. minense (Townsend) comb. n., L. oryzae (Townsend) comb. n., L. scirpophagae (Chao & Shi) comb. n., L. sesamiae (Mesnil) comb. n., and L. striatalis (Townsend) comb. n.

We determined how frequently multiple mating occurs in a field population of Anopheles freeborni Aitken. We used enzyme electrophoresis to analyse field collected females and their offspring, and determined the parity rates of females mating in swarms. The genotypes of progeny in one of the 36 families examined showed conclusive evidence of two sires. 4·3% (n═93) of females mating in swarms were parous, as opposed to 33·9% of host seeking females (n═103). We conclude that multiple mating in A. freeborni occurs at low frequency in the field, and may be ascribed to incomplete transfer of sperm or male accessory gland substance, rather than to routine renewal of receptivity by females.