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.

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.

Insect activity was significantly reduced in dung from cattle treated with a recommended topical dose (500 μg/kg) of the endectocide, ivermectin. Reductions affected an ecologically and taxonomically diverse group of insects including coprophagous flies, parasitic wasps, and both predacious and coprophagous beetles. Whereas some species appeared unaffected by faecal residues, the emergence of other species was reduced in dung voided ≤ 12 weeks post-application. The species most affected were the flies, Sepsis sp. and Coproica mitchelli (Malloch). eucoilid wasps. and the beetles, Cercyon quisquilius (Linnaeus) and C. pygmaeus (Illiger). Results were consistent within and between years. Similar reductions have been reported previously, but typically for a much shorter post-application period. The greater duration of effect observed in the current study is attributed to a more accurate bioassay, species-level identifications, and the use of sample sizes generally larger than those used in previous studies. Reduced insect activity was associated with slower dung pat degradation. When ivermectin was added directly to dung, at levels previously reported to occur in dung from treated cattle, the treated dung had not appreciably degraded after 340 days in the field. In contrast, untreated dung pats deposited at the same time and place had largely degraded after 80 days in the field. The effect of ivermectin use on pasture quality is probably ‘moot’ in southern Alberta because of the current pattern of use. Should this pattern change, however, results of the present study validate the need for future studies to assess the off-target effects of ivermectin use on pasture quality.

An often encountered problem associated with augmentative and inundative biological control programmes is the high cost of producing sufficient numbers of natural enemies necessary to suppress pest populations within the time constraints imposed by ephemeral agroecosystems. In many arrhenotokous parasitoids, overproduction of males in mass-rearing cultures inflates costs (per female) and thus limits the economic feasibility of these biological control programmes. Within the context of existing production technologies, experiments were conducted to determine if the sex ratio of Catolaccus grandis (Burks), an ectoparasitoid of the boll weevil Anthonomous grandis Boheman, varied as a function of boll weevil larval size. Results from natural and manipulative experiments demonstrate the following behavioural characteristics associated with C. grandis sex allocation behaviour: (i) female C. grandis offspring are produced on large size hosts and male offspring are produced on small hosts; (ii) whether a host is considered large or small depends upon the overall distribution of host sizes encountered by a female parasitoid; and (iii) female parasitoids exhibit a greater rate of increase in body size with host size than do male parasitoids. The observed patterns cannot be explained by sex-specific mortality of immature parasitoids developing on the different host size categories. In subsequent experiments, laboratory cultures of C. grandis exposed daily to successively larger sizes of A. grandis larvae produced successively greater female biased offspring sex ratios, cultures exposed daily to successively smaller sizes of host larvae produced successively greater male biased offspring sex ratios, and cultures exposed daily to equivalent host size distributions over time maintained a uniform offspring sex ratio. By increasing the average size of A. grandis larval hosts exposed to C. grandis by 2.5 mg per day in mass rearing cultures, the percentage of male progeny can be reduced from 33% to 23% over a period of four consecutive exposure days.

The effectiveness of inundative releases of the parasitoid Eretmocerus eremicus n. sp. Rose & Zolnerowich for control of Bemisia argentifolii Bellows & Perring on poinsettia in replicated experimental greenhouses was determined. We evaluated two release rates of E. eremicus: a low release rate (one female per plant per week, released in two greenhouses, in spring 1995) and a high release rate (three females per plant per week, released in two greenhouses, in spring 1994), each over a 14 week growing season. Each release trial had either one (1995) or two (1994) control greenhouses in which B. argentifolii developed on poinsettia in the absence of E. eremicus. Life-tables were constructed for B. argentifolii in the presence and absence of E. eremicus by using a photographic technique to follow cohorts of whiteflies on poinsettia leaves. Weekly population counts of whiteflies were also made. In the absence of E. eremicus, egg to adult survivorship of B. argentifolii on poinsettia was 75–81%. At the low release rate, egg to adult survivorship of B. argentifolii was 12% and parasitism was 34%. At the high release rate, egg to adult survivorship of B. argentifolii was 0.9% and parasitism was 10%. The average net reproductive rates (Ro) for populations of B. argentifolii in the absence of E. eremicus ranged from 20.5 to 26.1, indicating a rapidly increasing population density. Net reproductive rates for whitefly populations subject to parasitoid releases were 3.7 in the low release rate greenhouses, and 0.25 in the high release rate greenhouses, indicating substantially reduced B. argentifolii population growth. At week 14 of the trial, densities of immature whiteflies were lower in greenhouses at the low release rate when compared to the high release rate greenhouses. This was attributed to high levels of in-house reproduction by parasitoids at the low release rate.

Site and time effects are important factors determining trap catches of tsetse flies. These factors may interact significantly and therefore confound interpretation of time series data used for population monitoring. We therefore investigated the magnitude and importance of site × time interactions in trap catches of Glossina pallidipes Austen and G. longipennis Corti using a 2200 trap-days (400 trap-months) data set. The interaction was found to be siginificant (p<0.05) in 46–100% of the combinations of different numbers of months and sites between 2 and 12. The mean percent variance due to the interaction ranged between 4% and 28% for G. pallidipes and 12% and 36% for G.longipennis. The interaction was usually less important than the effect of site alone but more important than the effect of time alone. These results suggest that tsetse researchers should examine critically the adequacy of existing approaches to population monitoring with traps and to testing new traps and odour baits.

To investigate the population density and dispersal of the sheep blowfly Lucilia sericata (Meigen) mark-release-recapture trials were carried out in lowland pastures in south west England. In three trials, 2142, 1351 and 451 fluorescent dust marked flies were released of which 4%, 14% and 10% were recaptured using a grid of sticky, odour-baited targets, placed between 8 m and 1000 m from the release point. There was no significant effect of wind direction on dispersal pattern and no apparent directional movement of the flies from the release point. Using the method described by Hawkes (1972) the mean distance travelled by all the flies on the first day of each of the three trials was calculated to be 108 m, 128 m and 137 m respectively. Using the method described by Fletcher (1974) the mean distances travelled were calculated to be 135 m (±42), 118 m (±27) and 183 m (± 61) on the first day of each of the three trials, respectively. The median distances travelled by the flies on the first day of each of the three trials were calculated to be 109 m, 130 m and 150 m, respectively. A Lincoln Index was used to estimate the population density of wild female L. sericata. The number of female flies was estimated to be zero in June, approximately one per hectare in July and six per hectare in August in 1994.

The influence of the host plant of the cassava mealybug, Phenacoccus manihoti Matile Ferrero on the encyrtid parasitoid Apoanagyrus lopezi De Santis was studied in the laboratory. Four different host plants were used: two cultivars of cassava, Manihot esculenta (Euphorbiaceae), cv. Incoza and cv. MM79; Faux caoutchouc, a hybrid of M. esculenta × M glaziovii; and talinum Talinum triangularae (Portulacaceae), a common weed in cassava fields. Plants were selected for different levels of antibiotic resistance to P. manihoti. Mealybug mortality due to host feeding by the adult parasitoid and the percentage of mealybugs parasitized were significantly lower when mealybugs were reared on the Manihot cultivars and hybrid than when reared on talinum. However, the encapsulation rate was significantly lower in P. manihoti reared on talinum. The highest percentage parasitism and the lowest rate of emergence were recorded on cv. Incoza, the most resistant Manihot cultivar. The sex ratio did not vary significantly with the host plant used. The total developmental time and size of male and female progeny of A. lopezi differed significantly between P. manihoti reared on different host plants. Among Manihot plants, parasitoid size was positively correlated with development time and negatively with plant resistance. Results suggest that the parasitoid, A. lopezi, might perform better if cassava cultivars were selected for their strong antixenosis but low antibiotic characteristics.

The pear thrips Taeniothrips inconsequens (Uzel) was sampled for four years in a small sugar maple Acer saccharum plantation in Centre County, Pennsylvania, USA. The life cycle of T. inconsequens was univoltine with the main period of emergence and flight from late March to mid May. Adults, eggs, and first and second instar larvae were associated with sugar maple budburst and early leaf development from late April to late May. Larval drop occurred from mid to late May. Mature second instar larvae, propupae, pupae and adults spent from June to March in the ground; development from larva to adult occurred between September and November. From March to May most (usually >90%) thrips adults and larvae sampled were T. inconsequens. No T. inconsequens males were found. In soil samples taken in spring, summer and autumn T. inconsequens were found to a depth of 50 cm but over 87% were in the top 20 cm. Almost no T. inconsequens were found in the litter layer. Large variations in T. inconsequens adult emergence and larval drop were recorded. The most important contributing factors in fluctuations of T. inconsequens populations were the length of sugar maple budburst, the degree of synchrony between thrips emergence and sugar maple budburst, and the occurence of sugar maple flowering.

The performance of the egg parasitoid Uscana lariophaga Steffan was studied when reared on eggs of the bruchid storage pest, Callosobruchus maculatus (Fabricius) developing in seeds of cowpea, chickpea and pigeonpea. The beetle laid more and larger eggs on pigeonpea than on cowpea and chickpea, indicating that there was not a trade-off between number and size of the eggs. The bruchid larvae reared on pigeonpea exhibited a longer development time and a higher mortality than those reared on cowpea and chickpea. The resulting males weighed less than those reared on cowpea and chickpea. The trichogrammatid U. lariophaga parasitized more eggs when C. maculatus was reared on chickpea than when reared on the other hosts. Parasitoid larvae developed slowest and had the highest mortality in eggs of C. maculatus reared on pigeonpea compared to those reared on cowpea and chickpea; the sex ratio (% of females) of the resulting adults was also higher. The high mortality and long development time of C. maculatus reared on pigeonpea indicated that this legume was less favourable to C. maculatus than chickpea or cowpea. This was probably also true for the parasitoid since the mortality was higher and development longer in eggs of C. maculatus reared on pigeonpea compared to those reared on cowpea and chickpea. Therefore, when host eggs were larger and of lower nutritional quality, the proportion of female egg parasitoids was greater.