PCR-based techniques to investigate predator-prey trophic interactions are starting to be used more widely, but factors affecting DNA decay in predator guts are still poorly understood. Here, we investigated the effects of time since feeding, temperature and amplicon size on the detectability of prey DNA in the gut content of two closely related predator species. Cereal aphids, Sitobion avenae, were fed to the carabid beetles Pterostichus melanarius and Nebria brevicollis. Beetles were allowed to digest their meal at 12°C, 16°C and 20°C, and batches of beetles were subsequently frozen at time periods from 0–72 h after feeding. Aphid DNA was detected within beetles' gut contents using primers amplifying fragments of 85, 231, 317 and 383 bp. Prey DNA detection rates were significantly higher in N. brevicollis than in P. melanarius, indicating fundamental dissimilarities in prey digestion capacities. High temperatures (20°C) and large amplicons (383 bp) significantly decreased detection rates. The shortest amplicon gave the highest prey DNA detection success, whereas no differences were observed between the 231 bp and the 317 bp fragment. Our results indicate that factors such as ambient temperature, predator taxon and amplicon size should all be considered when interpreting data derived from PCR-based prey detection. Correction for such factors should make calculation of predation rates in the field more accurate and could help us to estimate when predation events occur in the field.

Projects undertaken on the biological control of insect pests in Bermuda since the first introduction of Bufo marinus in 1875 and including those still in progress are discussed. Work on 15 pests or groups of pests has been undertaken involving the introduction of over one hundred species of beneficial organisms.

Icerya purchasi Mask. is considered to be under excellent control as a result of the introduction of the Coccinellid, Rodolia cardinalis (Muls.), and the fly, Cryptochetum iceryae (Will.). Pseudaulacaspis pentagona (Targ.), a serious pest of oleanders, was brought under control about 1922 by the introduction of Aphytis diaspidis (How.). However, in recent years heavy infestations have periodically developed. In addition to A. diaspidis, the Aphelinids, Aspidiotiphagus citrinus (Craw) and A. lounsburyi (Berl. & Paoli), the Coccinellids, Lindorus lophanthae (Blaisd.) and Chilocorus cacti (L.), and the Nitidulid, Cybocephalus sp., now attack it.

Comstockiella sabalis (Comst.) at one time causing severe injury to the endemic palm, Sabal bermudiana, was brought under control by the introduction of Physcus sp. Bracon gelechiae Ashm. has been established on the potato tuber moth, Gnorimoschema operculella (Zell.), but satisfactory control has not resulted.

Two cedar scales, Carulaspis minima (Targ.) and Lepidosaphes newsteadi (Sulc), have decimated the stands of Juniperus bermudiana despite an extensive programme of biological control. C. minima, which proved to be the more serious, is attacked by the Aphelinids, Prospaltella sp., Aspidiotiphagus lounsburyi, A. citrinus, probably introduced with the scale, and the Coccinellids, Lindorus lophanthae and Microweisia suturalis (Schwarz), which were liberated in large numbers. The predacious mite, Hemisarcoptes malus (Shimer), and the fungus, Myiophagus ucrainica, were established on Lepidosaphes newsteadi which for unknown causes became very scarce.

Damage by Calpodes ethlius (Cram.), a pest of ornamental cannas, is less serious since the introduction of Ooencyrtus sp. and Trichogramma sp.

Several parasites were liberated to control various species of mealybugs. Pseudococcus adonidum (L.), serious on a number of ornamentals, is under satisfactory control as the result of the establishment of the Encyrtids, Tetracnemus peregrinus Comp. and Anagyrus fusciventris (Gir.). Planococcus citri (Risso) is now attacked by the introduced Encyrtids, Leptomastidea abnormis (Gir.) and Pauridia peregrina Timb., as well as by Leptomastix dactylopii How., which was present at the start of the investigation. Acerophagus pallidus Timb. has been recovered from the mealybug, Phenacoccus gossypii Tns. & Ckll.

The Encyrtid, Microterys kotinskyi (Full.), and the Coccinellids, Azya luteipes Muls. and Cryptolaemus montrouzieri Muls., have been effectively established on the soft scale, Pulvinaria psidii Mask. Tree lizards, Anolis spp., which feed readily on Azya and Cryptolaemus, are considered undesirable and accordingly the passerine bird, Pitangus sulphuratus, has recently been liberated in an attempt to reduce their numbers.

Several species of parasites and predators were liberated against the soft scales, Saissetia oleae (Bern.), S. coffeae (Wlk.) and Coccus hesperidum L. Aphycus stanleyi (Comp.) is well established on Saissetia spp.

Although the Braconid, Opius humilis Silv., was established on the Mediterranean fruit-fly, Ceratitis capitata (Wied.), for a number of years it has now disappeared.

Parasites and predators introduced against Nipaecoccus nipae (Mask.), the onion thrips, Thrips tabaci Lind., and the red spider mite, Oligonychus ununguis (Jacobi), did not become established.

Projects at present in progress to control tree lizards, Anolis spp., and snails cannot yet be evaluated.

In the discussion a number of factors which may have contributed to the failure of establishment of some beneficial organisms are mentioned.

On Mahé in the Seychelles, Anoplolepis longipes (Jerd.) is a pest, mainly because of the nuisance it causes to man and domestic animals but also because it increases the numbers of sap-feeding insects and the occurrence of sooty mould on plants. The most important sap insect associated with sooty mould on citrus and cinnamon was Ceroplastes rubens Mask., the numbers of which sometimes increased a hundredfold in the presence of A. longipes, and up to 90% of leaves were infected with sooty mould. The rapid population expansion of the ant on Mahé prior to 1973 has since slowed down, and infestations in some areas have diminished, possibly because of a decreasing source of protein. Movement of ant-infested material has initiated secondary infestations, which are difficult to eradicate once established. The ant is not considered a threat to conservation as differences between the fauna in infested and uninfested areas tend to be quantitative rather than qualitative. Attempts to eradicate the ant on Mahé would be costly and inappropriate. The use of toxic baits and sprays is recommended only where ants become a domestic nuisance, threaten productivity or reach Other islands in the Seychelles group.

The genotypes of chromosomally-identified individuals from natural populations of the known species of the group of Anopheles gambiae Giles were scored for the enzyme protein structural loci coding for adenylate kinase (Adk), α-naphthyl acetate esterase (Est-1, Est-2, Est-3), glutamic-oxaloacetic transaminase (Got), α-glycerophosphate dehydrogenase (αGpd), hexokinase (Hk), isocitric dehydrogenase (Idh), lactic dehydrogenase (Ldh), ‘leucine’ aminopeptidase (Lap-2), malic enzyme (Me), octanol dehydrogenase (Odh), phosphoglucomutase (Pgm-1, Pgm-2), 6-phosphogluconic dehydrogenase (6-Pgd), phosphohexose isomerase (Phi) and superoxide dismutase (Sod), following starch gel electrophoresis. In the material examined, Est-1, Est-2, Est-3, Got, ldh, Lap-2, Odh, Pgm-1, Pgm-2 and Sod were segregating for two or more alleles; unique alleles at the Est-1, Got and Sod loci produced species-specific phenotypes in A. melas (Theo.), species C and species D, respectively. The further sampling of A. merus Dön, populations supported the presence of a unique SOD phenotype by which this species can also be identified. Of the other enzyme systems examined, no activity following electrophoresis was detected for aldolase and fructose-1,6-diphosphatase, and the resolution of acid and alkaline phosphatase, glyceraldehyde-3-phosphate dehydrogenase, glucose-6-phosphate dehydrogenase, malic dehydrogenase and xanthine dehydrogenase was too poor under the particular electrophoretic conditions for genetic analyses of the enzyme phenotypes.

Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is an invasive citrus pest in southern California, which secretes honeydew and has the potential to spread a lethal bacterial disease, huanglongbing, of citrus. In urban citrus, Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae), also an invasive pest, tends honeydew-producing hemipterans. We used field data to determine whether the mutualistic relationship between L. humile and six established species of honeydew producers may hinder or favor the establishment of D. citri and its biological control with Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) in citrus via competition or mutualism for ants, respectively. In the field, L. humile and D. citri are engaged in a mutualistic relationship. Ants harvest solid honeydew secreted by psyllid nymphs and tended more than 55% of observed D. citri colonies. Linepithema humile displayed a preference hierarchy when tending honeydew producers infesting citrus. It responded equally or less intensively to D. citri than to other honeydew-producing species. Consequently, the mutualism between L. humile and D. citri was affected by the presence of other honeydew-producing species, and the percentage of D. citri colonies tended by L. humile. The number of ants per D. citri colony also decreased as the number of other honeydew producers increased. Diaphorina citri density was also affected by the presence of other honeydew producers. Both colony size and the number of D. citri nymphs counted per tree decreased as the number of other honeydew producers increased. Our results indicate that competition between honeydew producers for the mutualist ant L. humile may hinder the establishment of D. citri by possibly facilitating increased biological control.

Biological characteristics of the poinsettia strain of Bemisia tabaci Gennadius were investigated on poinsettia by laboratory experiments at five temperatures (range: 16°C–28°C). In addition, the effect of rearing B. tabaci on the two plant species, Nicotiana tabacum (tobacco) (Solanaceae) and Euphorbia pulcherrima (Euphorbiaceae) (poinsettia) was investigated. The temperature-dependencies were established for the developmental time for eggs and egg-to-adult phase, juvenile mortality, adult female life-span, pre-oviposition period, age-specific fecundity, and sex-ratio. The lower temperature thresholds for egg-development, development from egg to adult and for ovipositional adults were estimated as well as the lower temperature threshold for oviposition. The thresholds were 12°C, 14°C, 8°C and 14°C, respectively. Egg-development required 126 day-degrees and the entire development into adults 327 day-degrees. Mortality was highest at 16°C, being 19.3% in the egg-stage and 95% from egg to adult. The pre-oviposition period and the adult life-span were 40 and 360 day-degrees. The age-specific fecundity of B. tabaci was described by a temperature-dependent model. The maximum daily fecundity rate was attained after 60 and 125 day-degrees for B. tabaci reared on tobacco and poinsettia, respectively. The fecundity was highest for B. tabaci reared on poinsettia. The sex-ratio was in favour of females at and above 19°C and increased with temperature. Estimates of the net reproductive rate, the intrinsic rate of increase, the finite rate of increase, the mean generation time and the doubling time were obtained. A positive linear relationship was found between rm and temperature, the values ranging from 0.0012 at 16°C to 0.1263 at 28°C.

Electrophoresis was used to characterize the esterases in Lucilia cuprina (Wiedemann). Of the 16 esterase bands visualized, only one was associated with resistance to organophosphorus insecticides. In laboratory reference strains, the esterase E3 was consistently found in both susceptible and heterozygously resistant flies, but was absent from homozygously resistant flies. It was postulated that resistant flies possessed a non-staining form of E3, designated E3null. Genetic analyses mapped the locus for E3null to a position in the same region as the gene for organophosphorus resistance. No recombinants between the genes for resistance and E3null were detected. In field populations of L. cuprina from several areas in Australia, a close association was found between the frequency of E (0·97) and the proportion of flies resistant to organophosphorus insecticide (0·967). This association suggests that E3null represents the product of a major resistance gene in terms of the ‘mutant ali-esterase’ theory. E3 as found in susceptible blowflies, represents the ‘original’ ali-esterase, the gene for which mutated to one coding for E3null. This mutant enzyme can hydrolyse organophosphates more efficiently than E3 but has lost the ability to hydrolyse 1- and 2-naphthyl acetate (the substrates used to visualize the esterases after electrophoresis).

The taxonomy of the Oriental species of Helopeltis is revised and a review of the economic literature is given. An identification key is provided for the 14 recognized species, one of which, H. sulawesi, is described as new. A diagnosis and brief description is given for each species, as well as illustrations of useful taxonomic characters, information on distributions and host records, and a discussion of any known or suspected misidentifications. Lectotype designations are made for 13 nominal species and the following new synonymies are established: H. bradyi Waterhouse = H. ceylonensis De Silva, syn. n and H. romundei Waterhouse, syn. n;H. cinchonae Mann = H. brevicornis Poppius, syn. n.;H. clavifer (Walker) = H. australiae Kirkaldy, syn. n and H. niger Walker, syn. n;H. cuneata Distant = H. elegans Poppius, syn. n;H. fasciaticollis Poppius = H. pallidus Poppius, syn. n and H. pallidiceps Poppius, syn. n;H. theivora Waterhouse = H. oryx Distant, syn. n The somewhat obscure synonymy of H. theobromae Miller under H. theivora is confirmed. Two subgenera are recognized and diagnosed: Afropeltissubgen. n (type species Eucerocoris westwoodi White), including all African species of the genus, and Helopeltis sensu stricto, containing the Oriental and Australasian species.

Fresh evidence is described which supports the theory that moths of the Noctuid Spodoptera exempta (Wlk.) (the adult stage of the African armyworm) are migratory. The evidence comes from four main sources: a study of fluctuations in numbers of moths caught in a network of light-traps operated in East Africa; the fertilisation rates in samples of females as shown by dissection; the sex ratios in samples of moths caught in light-traps; and a study of the behaviour of moths in the field during the period immediately following emergence. In certain of these features S. exempta is compared and contrasted with the related S. triturata (Wlk.), in which the evidence points against extensive migration.

It is concluded that migration occurs in S. exempta, probably on an extensive scale, and that it therefore has an important bearing on the occurrence and distribution of outbreaks of the larvae.

A method for the routine quantitative estimation of mealybug populations on cacao trees is described and the results obtained from 24 successive monthly samples are tabulated.

The quantitative results obtained are of such variability that only gross differences in population density are shown as statistically significant.

From a series of analyses based on the survey data the following conclusions have been reached with regard to P. njalensis, the most important mealybug vector of swollen shoot virus :—

(a) The species is almost invariably attended in the field by Crematogasterine ants, the most important ant species building protective carton tents over the mealybug colonies.

(b) Crematogaster density is closely correlated with mealybug density and the ants construct their carton tents in relation to the numbers of mealybugs to be protected. Some of the arboreal Crematogasterine groups investigated are shown to be consistently associated with higher mealybug populations, and to have a more advanced tent building habit, than others.

(c) Tree to tree variation in mealybug density is shown to be largely dependent on the identity of the dominant ant group.

(d) No direct correlation is apparent between mealybug density and incidence of swollen shoot though populations in areas devastated by virus are usually smaller than in areas in which virus is actively spreading.

(e) The factors of importance in the natural control of P. njalensis populations have been discussed in some detail. It is clear that the species is maintained by ant protection at a density level considerably above that prevailing amongst closely related pseudococcid species which are not ant attended to the same extent. At this level of “ protected steady density ” balance is maintained partly by losses during crop harvesting, and partly by swollen shoot rendering the host plants unsuitable as feeding stations. It is concluded, however, that natural enemies must, in the last analysis, be responsible for maintaining balance.

(f) Since the protected density of P. njalensis is a direct result of ant associations it follows that factors tending to control the attendant ant species will have a delayed effect on mealybug density. In this respect it is believed that Oecophylla, which is strongly negatively correlated with Crematogaster spp., is of importance. Any attempts that may in the future be made to control the mealybugs by killing the ants will have to be designed as specific against the Crematogasterini and non-lethal to Oecophylla and the other large predatory ants common on cacao.

Aspidiotus destructor is a well-known pest of several tropical crops, mainly coconuts and bananas, and is present in most tropical countries. In Fiji it was a serious menace to the copra industry, and attempts to control it by biological means were made in 1920, when parasites were introduced from Tahiti ; in 1927, when other parasites were introduced from Java ; and in 1928, when predators were imported from Trinidad. The introductions made in 1920 and 1927 proved of no economic value, but the predators from Trinidad completely suppressed the pest in 1928 and 1929, and have controlled it most satisfactorily ever since.

Recent studies on the ecology of two cereal aphid species, Sitobion avenae (F.) and Metopolophium dirhodum (Wlk.), are reviewed. The most important factors affecting their abundance were used to construct decision trees to assess the risk of outbreaks of these species in the summer in England. These factors for S. avenae were crop sowing date, the size of the autumn migration, the severity of the winter, the size of the spring migration and the incidence of natural enemies in spring and early summer. For M. dirhodum, only the last two factors were considered as it does not occur on cereals until the spring in England. These decision trees were successfully tested using field data from 1983, when no outbreaks of either species occurred due to the effects of natural enemies.

Rhopalosiphum maidis (Fitch) collected on barley in the northern hemisphere usually has a ten-chromosome karyotype, whereas samples from maize, sorghum and Johnson grass (Sorghum halepense) from all parts of the world commonly have 2n = 8. Samples with other karyotypes (2n = 9, 2n = 11 and 2n = 8 heterozygous for an interchange between the X chromosomes) occur less frequently on these and other species of Gramineae. Multivariate morphometric analysis, principally by the method of canonical variates, indicated that the ten-chromosome form may be regarded as a single clone of R. maidis recognizable by its karyotype and host-plant relationships, although not completely separable by morphology alone from all other clones of this permanently parthenogenetic species complex.

Females of the Pakistan strain of Apanteles flavipes (Cam.) (which originates from Japan and is maintained on larvae of Chilo partellus (Swinh.) reared on maize) were readily attracted to maize stems but not to sugar-cane stems in the laboratory. Ovipositor probing occurred in the presence of unwashed host larvae, particularly of C. partellus and/or frass from host larvae fed on maize. Ovipositor probing did not occur in the presence of dried frass, dried frass that had been remoistened with water or frass from C. partellus fed on a diet of gram (Cicer arietinum) flour. The Pakistan strain of A. flavipes is morphologically identical to a strain of A. flavipes imported from India into Florida and established on Diatraea saccharalis (F.) fed on a soyabean flour-wheat germ diet. Reciprocal crosses between the two strains (Pakistan and USA) and between the F1, adults produced both male and female progeny. Nevertheless, behavioural differences between the strains were found in laboratory tests in that the USA strain responded more strongly to larvae of Acigona steniellus (Hmps.) fed on sugar-cane, was more attracted to sugar-cane stalks than to maize stalks and was not encapsulated by D. saccharalis larvae, whereas at least one-fifth of the Pakistan strain larvae were encapsulated. The existence of different strains of Apanteles flavipes adapted to different graminaceous crops suggests that parasite plant preference as well as host preference and suitability must be considered during attempts to introduce exotic parasites. It is recommended that A. flavipes strains adapted to sugar-cane be introduced into Pakistan for establishment on stem-borers of sugar“-cane.

The distribution and species composition of lepidopterous maize borers was studied in six locations in southern Nigeria during the second planting season (August-November) of 1985 and 1986. Sesamia calamistis Hampson (Noctuidae) and Eldana saccharina Walker (Pyralidae) were the stem borers most abundantly found in the locations sampled. S. calamistis was the dominant species up to eight weeks after planting in all locations. E. saccharina was the most abundant species from nine weeks after planting onwards, except at Umuahia where S. calamistis always comprised over 50% of the borer population. Mussidia nigrivenella Ragonot (Pyralidae) was found attacking maize ears in all locations, while Busseola fusca Fuller (Noctuidae) was found only at Idah and Alabata, and even there constituted only a small proportion of the population. Other borer species found were Coniesta (= Acigona) ignefusalis (Hampson) (Pyralidae) and Cryptophlebia species (Olethreutidae).

Variation in canopy arthropod abundances and community structure were evaluated in an old-growth (500-year-old) forest at the Wind River Canopy Crane Research Facility in southwestern Washington, USA. Arthropods were sampled at three canopy levels and two seasons in each of four tree species (Pseudotsuga menziesii, Tsuga heterophylla, Abies grandis, and Thuja plicata). The four tree species had distinguishable arthropod species compositions and community organization. Thuja plicata (Cupressaceae) had a particularly distinctive canopy fauna dominated by several mite taxa which did not occur on the other tree species (all Pinaceae). Pseudotsuga menziesii hosted a relatively diverse arthropod fauna with greatest richness of taxa and functional groups. Distinct arthropod assemblages were not observed among canopy levels and sampling dates, but these factors significantly influenced abundances of 63% of the arthropod taxa, either individually or interactively with other factors. These data indicate that forests managed for fewer tree species eliminate important components of arthropod diversity in Pacific Northwest forests and that sampling for biodiversity assessment also should represent season and canopy level.

The predominantly Afrotropical fruit fly genus Ceratitis contains many species of agricultural importance. Consequently, quarantine of Ceratitis species is a major concern for governmental regulatory agencies. Although diagnostic keys exist for identification of all described Ceratitis species, these tools are based on adult characters. Flies intercepted at ports of entry are usually immatures, and Ceratitis species cannot be diagnosed based on larval morphology. To facilitate identification of Ceratitis pests at ports of entry, this study explores the utility of DNA-based diagnostic tools for a select group of Ceratitis species and related tephritids, some of which infest agriculturally important crops in Africa. The application of the polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) method to analyse three mitochondrial genes (12S ribosomal RNA, 16S ribosomal RNA, and NADH-dehydrogenase subunit 6) is sufficient to diagnose 25 species and two species clusters. PCR analysis of the internal transcribed spacer region 1 (ITS-1) is able to distinguish three of the five species left unresolved by mitochondrial DNA analysis.

Epitrix species (Coleoptera: Chrysomelidae) feed mostly on plants from the family Solanaceae and some of them are major pests of potato crops. All Epitrix species are morphologically highly similar, which makes them difficult to identify and limits their study and management. Identification of species is mostly based on the observation of the genitalia and requires a high level of expertise. Here, we propose a tool to reliably identify all developmental stages of the most economically important Epitrix species feeding on potato in Europe and North America (Epitrix cucumeris, Epitrix similaris, Epitrix tuberis, Epitrix subcrinita and Epitrix hirtipennis). We first sequenced two DNA markers (mitochondrial cytochrome c oxidase I (COI) and nuclear internal transcribed spacer 2 (ITS2)) to test their effectiveness in differentiating among six Epitrix species (126 specimens). Morphospecies of Epitrix were well-differentiated by both DNA barcodes and no mitochondrial introgression was detected. Then, we developed an RFLP-based diagnostic method and showed that unambiguous species discrimination can be achieved by using the sole restriction enzyme TaqI on COI polymerase chain reaction products. The tool proposed here should improve our knowledge about Epitrix species biology, distribution and host range, three capacities that are particularly important in the detection and management of these pest species. Specifically, this tool should help prevent the introduction of E. tuberis and E. subcrinita in Europe and limit the spread of the recently introduced E. cucumeris and E. similaris, with minimal disruption to Solanaceae trade.

With an increasing incidence of cutaneous leishmaniasis in Sri Lanka, particularly in northern provinces, insecticide-mediated vector control is under consideration. Optimizing such a strategy requires the characterization of sand fly populations in target areas with regard to species composition and extant resistance, among other parameters. Sand flies were collected by human bait and cattle-baited net traps on Delft Island, used as an illegal transit location by many refugees returning to the north of Sri Lanka from southern India where leishmaniasis is endemic. For species identification, genomic DNA was extracted and a fragment of the ribosomal 18S gene amplified. The sequence from all flies analysed matched that of Phlebotomus argentipes Annandale & Brunetti, the primary vector in India and the most likely vector in Sri Lanka. Independent morphological analysis also identified P. argentipes. To establish the current susceptibility status of vector species, data were obtained at the biochemical level, from which potential cross-resistance to alternative insecticides can be predicted. The Delft Island collection was assayed for the activities of four enzyme systems involved in insecticide resistance (acetylcholinesterase, non-specific carboxylesterases, glutathione-S-transferases and cytochrome p450 monooxygenases), establishing baselines against which subsequent collections can be evaluated. There was preliminary evidence for elevated esterases and altered acetylcholinesterase in this population, the first report of these resistance mechanisms in sand flies to our knowledge, which probably arose from the malathion-based spraying regimes of the Anti-Malarial Campaign.

For the first 150 years following their introduction, eucalypts planted in the California landscape were free of both insect pests and diseases. In the last 15 years, numerous herbivorous insect species have been introduced accidentally into the State and have caused significant damage to the trees. Several of these species, e.g. Phoracantha semipunctata (Fabricius), Phoracantha recurva Newman (Coleoptera: Cerambycidae) and Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae), have also been introduced into other parts of the world where eucalypts are grown, whereas others, e.g. Glycaspsis brimblecombei Moore (Hemiptera: Spondyliaspidae) and Eucalyptolyma maideni Froggatt (Hemiptera: Spondyliaspidae), are currently restricted to California and Australia. Research programmes have provided management solutions to individual pest problems, but as more pest species are introduced, these solutions must be integrated across broad geographic, horticultural, and economic scales, in a systems approach.