A new diagnostic approach to fast-track and increase the accessibility of gastrointestinal nematode identification from faeces: FECPAKG2 egg nemabiome metabarcoding

Effective gastrointestinal nematode management in livestock industries is becoming increasingly difficult due to the rise of anthelmintic resistance and changes in the temporal and geographical distribution of major gastrointestinal nematodes. Underpinning the response to these challenges is the need for a fast-tracked diagnostic identification technique, making it easier for livestock producers to make informed gastrointestinal nematode management decisions. The traditional ‘gold-standard’ approach, larval culture followed by morphological differentiation, is laborious and potentially inaccurate. We developed a new diagnostic approach to identify gastrointestinal nematodes that integrates a remote-location digital faecal egg count platform, FECPAK^G2, with internal transcribed spacer 2 (ITS2) nemabiome metabarcoding. The technique involves a quick and simple protocol to harvest concentrated strongyle eggs from the FECPAK^G2 cassette utilising a repurposed pipette tip, followed by DNA isolation and Illumina next generation amplicon sequencing. The gastrointestinal nematode compositions and alpha diversity generated by our FECPAK^G2 egg nemabiome metabarcoding approach was not significantly different to traditional morphological larval differentiation and nemabiome metabarcoding of larval and faecal samples. We demonstrated that storing FECPAK^G2 harvested eggs in either DNA isolation lysis buffer or 80% ethanol (v/v) had no impact on gastrointestinal nematode identification outcomes for at least 60 days; enabling the transport of biological samples from their remote origins to a molecular diagnostic facility for nemabiome metabarcoding, in the absence of a cold chain. We discovered that sustained gastrointestinal nematode egg embryonation in the lysis buffer storage solution lead to higher yields of DNA compared with ethanol-stored gastrointestinal nematode eggs or faeces with gastrointestinal nematode eggs. Taking advantage of an already well-established platform such as FECPAK^G2, and providing the livestock producers that use it with the option to identify gastrointestinal nematodesin their samples and contribute to large-scale gastrointestinal nematode distribution and/or anthelmintic resistance surveys, is an important future direction for the FECPAK^G2 egg nemabiome metabarcoding approach.     

Eruption patterns of permanent front teeth as an indicator of performance in roe deer

In most species of vertebrates, teeth play a central role in the long-term performance of individuals. However, patterns of tooth development have been little investigated as an indicator of animal performance. We filled this gap using data collected during long-term capture-mark-recapture monitoring of 1152 roe deer fawns at Chizé, western France. This population fluctuated greatly in size during the 27 years of monitoring, offering a unique opportunity to assess how the eruption patterns of front teeth perform as indicator of animal performance. We used three indices of the eruption of permanent front teeth, the simplest being whether or not incisor I₂ has erupted, and the most complex being a 12-level factor distinguishing the different stages of tooth eruption. We also assessed the relevance of these indices as compared to fawn body mass, a widely used indicator of animal performance of deer populations. Dental indices and body mass were positively correlated (all r > 0.62). Similarly to body mass, all indices based on tooth eruption patterns responded to changes of population size and can be reliably used to assess the relationship between roe deer and their environment. We found a linear decrease in body mass with increasing population size (r² = 0.54) and a simultaneous delay in tooth development (r² = 0.48–0.55 from the least to the most accurate indicator). However, tooth development would be not further delayed in years with the highest densities (>15 adult roe deer/100 ha). A path analysis supported the population density effect on tooth eruption patterns being mainly determined by the effect of population size on body mass. Our study provides managers with simple indices (e.g., presence-absence of I₂) that provide a technically more easy way to standardize measurements of deer density-dependent responses over large geographical and temporal scales than would be possible with body mass.     

Serosurvey of roe deer, chamois and domestic sheep in the central Italian Alps

Roe deer (Capreolus capreolus), chamois (Rupicapra rupricapra rupicapra), and domestic sheep in the Orobie Alps, Italy, were serologically tested for antibodies to selected pathogens that may be transmitted across species. Antibodies against Brucella spp. and bovine herpesvirus 1 (roe deer and chamois only) were not detected in any species. In roe deer, antibodies were detected against Toxoplasma gondii (13%) and Neospora caninum (3%). Chamois tested positive for antibodies to T. gondii (5%), N. caninum (21%), bovine respiratory syncytial virus (BRSV) (41%), bovine parainfluenza type-3 virus (17%), pestiviruses (18%), and Mycoplasma conjunctivae (17%). In the sheep, particularly high antibody prevalence rates were found for T. gondii (78%), Chlamydophila spp. (20%), pestiviruses (90%), BRSV (82%), and M. conjunctivae (81%).     

Population density and phenotypic attributes influence the level of nematode parasitism in roe deer

The impact of parasites on population dynamics is well documented, but less is known on how host population density affects parasite spread. This relationship is difficult to assess because of confounding effects of social structure, population density, and environmental conditions that lead to biased among-population comparisons. Here, we analyzed the infestation by two groups of nematodes (gastro-intestinal (GI) strongyles and Trichuris) in the roe deer (Capreolus capreolus) population of Trois Fontaines (France) between 1997 and 2007. During this period, we experimentally manipulated population density through changes in removals. Using measures collected on 297 individuals, we quantified the impact of density on parasite spread after taking into account possible influences of date, age, sex, body mass, and weather conditions. The prevalence and abundance of eggs of both parasites in females were positively related to roe deer density, except Trichuris in adult females. We also found a negative relationship between parasitism and body mass, and strong age and sex-dependent patterns of parasitism. Prime-age adults were less often parasitized and had lower fecal egg counts than fawns or old individuals, and males were more heavily and more often infected than females. Trichuris parasites were not affected by weather, whereas GI strongyles were less present after dry and hot summers. In the range of observed densities, the observed effect of density likely involves a variation of the exposure rate, as opposed to variation in host susceptibility.     

Morphological variability in the mucosal attachment site of Trichuris muris revealed by X-ray microcomputed tomography

Parasitic infections can be challenging to study because two dimensional light and electron microscopy are often limited in visualising complex and inaccessible attachment sites. Exemplifying this, Trichuris spp. inhabit a tunnel of epithelial cells within the host caecum and colon. A significant global burden of this infection persists, partly because available anthelminthics lack efficacy, although the mechanisms underlying this remain unknown. Consequently, there is a need to pioneer new approaches to better characterize the parasite niche within the host and investigate how variation in its morphology and integrity may contribute to resistance to therapeutic intervention. To address these aims, we exploited three-dimensional X-ray micro-computed tomography (microCT) to image the mouse whipworm, Trichuris muris, in caeca of wild-type C57BL/6 and SCID mice ex vivo. Using osmium tetroxide staining to effectively enhance the contrast of worms, we found that a subset exhibited preferential positioning towards the bases of the intestinal crypts. Moreover, in one rare event, we demonstrated whipworm traversal of the lamina propria. This morphological variability contradicts widely accepted conclusions from conventional microscopy of the parasite niche, showing Trichuris in close contact with the host proliferative and immune compartments that may facilitate immunomodulation. Furthermore, by using a skeletonization-based approach we demonstrate considerable variation in tunnel length and integrity. The qualitative and quantitative observations provide a new morphological point of reference for future in vitro study of host-Trichuris interactions, and highlight the potential of microCT to characterise enigmatic host-parasite interactions more accurately.     

Faecal egg counts and nemabiome metabarcoding highlight the genomic complexity of equine cyathostomin communities and provide insight into their dynamics in a Scottish native pony herd

Understanding the composition of gastrointestinal nematode communities may help to mitigate or exploit parasite adaptations within their host. We have used nemabiome deep amplicon sequencing of internal transcribed spacer-2 (ITS-2) ribosomal DNA to describe the temporal and host species composition of gastrointestinal nematode communities following sampling of six Scottish ponies across 57 months. In the absence of parasite control, each horse showed seasonal trends of increases and decreases in faecal egg counts, consistent with the epidemiology of equine strongylid parasites, however, the composition of parasites within individuals changed over time. Sixteen presumptive strongylid species were identified in each of the horses, 13 of which were distributed in a complex clade together with small numbers of amplicon sequences which could not be classified beyond the Cyathostominae subfamily level. Egg shedding of seven trichostrongylid species, which had previously been identified in co-grazed Soay sheep, was identified during the early spring. Faecal egg counts and the percentage of amplicon sequences assigned to each gastrointestinal nematode species were combined to describe their relative abundance across both host and time. Significant differences in species diversity between horses and between months were observed, being greatest from March to May and least from October to December. The magnitude of the individual horse effect varied between months and, conversely, the magnitude of the seasonal effect varied between individual horses. The most abundant gastrointestinal nematode in each of the horses was Cylicostephanus longibursatus (46.6% overall), while the abundance of the other strongylid species varied between horses and relative to each other. Patent C. longibursatus infections over the winter months might represent a genetic adaptation towards longer adult worm survival, or a lower rate of developmental arrest in the autumn. This study provides insight into highly complex phylogenetic relationships between closely related cyathostomin species; and describes the dynamics of egg shedding and pasture contamination of co-infecting equine gastrointestinal nematode communities. The results could be applied to determine how climatic and management factors affect the equilibrium between hosts and their parasites, and to inform the development of sustainable gastrointestinal nematode control strategies for different host species.     

Determination of the effective dose rate for monepantel (AAD 1566) against adult gastro-intestinal nematodes in sheep

Monepantel (AAD 1566) is the first compound from the recently discovered amino-acetonitrile derivative (AAD) class of anthelmintics to be developed for use in sheep. Three dose determination studies were conducted in Australia and Europe to identify the therapeutic dose of monepantel, when formulated for the oral treatment of sheep, to control adult gastro-intestinal nematodes. In each study, sheep infected with various nematode species were treated with either 1.25, 2.5 or 5.0 mg monepantel/kg bodyweight. Following euthanasia and worm counting, their worm burdens were compared with those from untreated control groups. At a dose rate of 1.25 mg/kg, monepantel showed efficacy above 91.9% against all major nematode species, with the exception of Chabertia ovina and Oesophagostomum venulosum. Efficacy against these two species was 93.6% and 94.0%, respectively, at a dose of 2.5 mg/kg. At this dose, efficacy was above 99.2% against nine other nematode species including Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus spp. and Nematodirus spp. It was concluded that 2.5 mg/kg would be a suitable dose rate for a commercial product.     

Unexpected population genetic structure of European roe deer in Poland: an invasion of the mtDNA genome from Siberian roe deer

Introgressive hybridization is a widespread evolutionary phenomenon which may lead to increased allelic variation at selective neutral loci and to transfer of fitness‐related traits to introgressed lineages. We inferred the population genetic structure of the European roe deer (Capreolus capreolus) in Poland from mitochondrial (CR and cyt b) and sex‐linked markers (ZFX, SRY, DBY4 and DBY8). Analyses of CR mtDNA sequences from 452 individuals indicated widespread introgression of Siberian roe deer (C. pygargus) mtDNA in the European roe deer genome, 2000 km from the current distribution range of C. pygargus. Introgressed individuals constituted 16.6% of the deer studied. Nearly 75% of them possessed haplotypes belonging to the group which arose 23 kyr ago and have not been detected within the natural range of Siberian roe deer, indicating that majority of present introgression has ancient origin. Unlike the mtDNA results, sex‐specific markers did not show signs of introgression. Species distribution modelling analyses suggested that C. pygargus could have extended its range as far west as Central Europe after last glacial maximum. The main hybridization event was probably associated with range expansion of the most abundant European roe deer lineage from western refugia and took place in Central Europe after the Younger Dryas (10.8–10.0 ka BP). Initially, introgressed mtDNA variants could have spread out on the wave of expansion through the mechanism of gene surfing, reaching high frequencies in European roe deer populations and leading to observed asymmetrical gene flow. Human‐mediated introductions of C. pygargus had minimal effect on the extent of mtDNA introgression.     

Use of winter habitat by roe deer at a northern latitude where Eurasian lynx are present

Winter climate at northern latitudes is a challenge to small-bodied ungulates, and they modify behaviour to save energy and to increase the likelihood of survival. Also, the ongoing expansion of large carnivores in several European countries can lead to the recovery of (potentially energetically costly) anti-predator behaviours. In an area recently recolonized by Eurasian lynx Lynx lynx , we snow-tracked radio-collared roe deer Capreolus capreolus in order to investigate their bedding and feeding behaviour during winter, and assess how environmental factors affect their habitat use. We also tested the prediction that roe deer use more open sites than locally available in areas with a stalking predator such as the lynx. Our results showed that both bed sites and foraging sites had more cover, compared with random sites. Most of the variation in canopy cover and in the distance and foraging sites between bed sites and foraging sites was explained by prevailing weather. As the winter progressed, the presumed depletion of fat reserves promoted the use of more canopy cover at foraging sites by night, less by day and a decrease in the distance between beds, foraging sites and human activities. Males used artificial feeding sites less often and bedded further from humans than females. The data fit the hypothesis of tighter energy budgets for family groups (females with fawns) or that males are more cautious towards humans. There was no support for the hypothesis that roe deer used more open habitat than locally available in order to reduce their vulnerability to lynx predation. Owing to severe winter conditions and the danger of starvation, roe deer seem to be forced to accept a high risk when predators are present, not changing their main pattern of habitat use from comparative areas where predators are absent.     

Seasonal variation of activity patterns in roe deer in a temperate forested area

We investigated the activity patterns of a European roe deer (Capreolus capreolus) population living in a forested Apennine area in central Italy, in order to shed light on the environmental and biological factors that were expected to account for the observed activity patterns on daily and yearly bases. Daily and seasonal activity patterns of 31 radio-collared roe deer were assessed through sessions of radio tracking for a total period of 18 consecutive months. Roe deer showed bimodal activity patterns throughout the year, with the two highest peaks of activity recorded at dawn and dusk. Activity patterns of males and females differed during the territorial period (from early spring to late summer), whereas they did not during the nonterritorial period. Most likely, behavioral thermoregulation can be held responsible for variation of daily activity patterns in different seasons. In winter, for instance, activity during the dawn period was significantly higher than in other seasons and daylight activity was significantly higher than at night. Nocturnal activity was highest in summer and lowest in winter. During the hunting season, moreover, roe deer showed lower activity levels than during the rest of the year. The prediction that roe deer would show lower activity levels during full moon nights, when the predation risk was assumed to be higher, was not confirmed by our data. Activity rhythms in roe deer were thus subjected to both endogenous and environmental factors, the latter working as exogenous synchronization cues. Accordingly, in changing environmental and ecological conditions, a circadian cycle of activity could be seen as the result of complex interactions among daily behavioral rhythm, digestive physiology, and external modifying factors.     

Deep amplicon sequencing as a powerful new tool to screen for sequence polymorphisms associated with anthelmintic resistance in parasitic nematode populations

Parasitic gastrointestinal nematodes contribute to significant human morbidity and cause billions of dollars per year in lost agricultural production. Control is dependent on the use of anthelmintic drugs which, in the case of livestock parasites, is severely compromised by the widespread development of drug resistance. There are now concerns regarding the emergence of anthelmintic resistance in parasitic nematodes of humans in response to the selection pressure resulting from mass drug administration programs. Consequently, there is an urgent need for sensitive, scalable and accurate diagnostic tools to detect the emergence of anthelmintic resistance. Detecting and measuring the frequency of resistance-associated mutations in parasite populations has the potential to provide sensitive and quantitative assessment of resistance emergence from an early stage. Here, we describe the development and validation of deep amplicon sequencing as a powerful new approach to detect and quantify the frequency of single nucleotide polymorphisms associated with benzimidazole resistance. We have used parasite communities in sheep to undertake a proof-of-concept study of this approach. Sheep provide an excellent host system, as there are multiple co-infecting trichostrongylid nematode species, each likely with a varying prevalence of benzimidazole resistance. We demonstrate that the approach provides an accurate measure of resistance allele frequencies, and can reliably detect resistance alleles down to a frequency of 0.1%, making it particularly valuable for screening mutations in the early stages of resistance. We illustrate the power of the technique by screening UK sheep flocks for benzimidazole resistance-associated single nucleotide polymorphisms at three different codons of the β-tubulin gene in seven different parasite species from 164 populations (95 from ewes and 69 from lambs) in a single MiSeq sequencing run. This approach provides a powerful new tool to screen for the emergence of anthelmintic resistance mutations in parasitic nematode populations of both animals and humans.     

Apoptosis is not the cause of seasonal testicular involution in roe deer

Apoptosis is involved in the regulation of spermatogenesis. The involution of testes in seasonal breeders might be expected to involve enhanced apoptotic cell elimination. We have compared seasonally changing testicular apoptosis in roe deer with that in non-seasonally breeding cattle. Apoptotic cells were detected as TUNEL-positive cells by both flow-cytometric analysis and in situ localisation of fragmented DNA in tissue sections. Apoptosis-induced DNA fragments were also assessed by enzyme-linked immunosorbent assay (ELISA) in homogenised testicular parenchyma. As expected, the testis mass and the percentage of haploid cells in roe deer showed a seasonal pattern with a significant maximum during the rut (August), whereas no annual variation of these parameters was found in bulls. All three methods for determining apoptosis showed similar findings. Roe deer exhibited significant seasonal fluctuation of total apoptotic activity (ELISA, apoptotic cells per tubule cross section) with a maximum during the breeding season. However, the seasonal differences in the number of apoptotic cells corresponded to the variable total numbers of spermatogonia and spermatocytes per tubule cross section. Thus, the percentages of TUNEL-positive cells related to the combined number of both germ cell types showed no seasonal variance, as confirmed by percentages of apoptotic cells analysed flow-cytometrically. The maximum level of apoptosis during the rut in roe deer was similar to the values obtained during the invariably high spermatogenic activity in cattle. These results suggest that, in roe deer, apoptosis is not the cause of the seasonal involution of testes. This study was partially supported by grant Bl 319/6-1 from the Deutsche Forschungsgemeinschaft.     

Effects of population density and female body mass on litter size in European roe deer at a continental scale

Roe deer (Capreolus capreolus) has a wide distributional range in Europe and inhabits a broad range of habitats and environmental conditions. Thus, populations of roe deer show substantial variation in demographic parameters. We aimed to determine whether body mass and population density—which influence the reproductive potential of roe deer at a local scale—affect their reproductive potential at a biogeographical scale as well. We reviewed the literature (covering years 1948–2015) on in utero litter size in roe deer from 59 locations in 14 countries in Europe. Across study sites, mean litter size varied from 1.0 to 2.4 embryo or corpora lutea per female, and population density ranged from 4.5 to 73.5 individuals/km². Mean body mass varied from 11.2 to 20.8 kg in subadult females and from 12.1 to 22.4 kg in adult females. Between 46° and 56° N, body mass of females did not show a significant trend of increase, whereas between 56° and 63° N, it increased with latitude (Bergmann’s rule). We used linear mixed-effects models (LMMs) to analyse the influence of body mass and population density (analysed separately) on litter size. Females with larger body mass produced larger litters, and this pattern was pronounced at both higher and lower latitudes. Higher population densities negatively affected litter size in a sample of all females. This macroecological analysis showed that factors influencing the reproductive potential of roe deer females at local scales produce similar effects at the biogeographical scale.     

Interaction of vesicular arbuscular mycorrhiza with root knot nematodes in tomato

Summary The interaction between the VA mycorrhizal fungus,Glomus fasciculatus and the root-knot nematodes,Meloidogyne incognita andM. javanica, and their effects on the growth and phosphorus nutrition of tomato was studied in a red sandy loam soil of pH 6.0. Inoculation of tomato roots with root-knot nematodes enhanced infection and spore production byG. fasciculatus. Inoculation of tomato plants withG. fasciculatus significantly reduced the number and size of the root-knot galls produced byM. incognita andM. javanica. Inoculation withG. fasciculatus although improved plant growth and its total phosphorus content compared to the uninoculated plants, the difference were not statistically significant.     

Variations in adult body mass in roe deer: the effects of population density at birth and of habitat quality

Body mass is a key determinant of fitness components in many organisms, and adult mass varies considerably among individuals within populations. These variations have several causes, involve temporal and spatial factors, and are not yet well understood. We use long-term data from 20 roe deer cohorts (1977-96) in a 2600 ha study area (Chizé, western France) with two habitats contrasting in quality (rich oak forest in the North versus poor beech forest in the South) to analyse the effects of both cohort and habitat quality on adult mass (i.e. median body mass between 4 and 10 years of age) of roe deer (Capreolus capreolus). Cohort strongly influenced the adult body mass of roe deer in both sexes: males born in 1994 were 5.2 kg heavier when aged between 4 and 10 years old than males born in 1986, while females born in 1995 were 4.7 kg heavier between 4 and 10 years old than females born in 1982. For a given cohort, adult males were, on average, 0.9 kg heavier in the rich oak forest than in the poor beech forest. A similar trend occurred for adult females (0.5 kg heavier in the oak forest). The effects of cohort and habitat were additive and accounted for ca. 40% of the variation observed in the adult mass of roe deer at Chizé (males: 41.2%; females: 40.2%). Population density during the spring of the birth accounted for about 35% of cohort variation, whereas rainfall in May-June had no effect. Such delayed effects of density at birth on adult body mass probably affect population dynamics, and might constitute a mechanism by which delayed density-dependence occurs in ungulate populations.     

Distribution of trichostrongylid nematodes in the abomasum of sheep

The distributions of Haemonchus contortus, Ostertagia circumcincta and Trichostrongylus axei during their development in lambs were studied by freezing and sectioning the abomasum and then recovering the worms from the contents and mucosa of each section. In previously worm-free lambs, the distribution of fourth stage H. contortus was very regular, the frequency of larvae being highest in the anterior fundic area and then decreasing in each section towards the pylorus. The distributions of the early larval stages of O. circumcincta and T. axei were variable but tended to be biomodal, with one peak of larvae in the fundic area and a second in the pyloric area. It is suggested that the difference in distribution between H. contortus and the other two species may be due to a difference in the rate of response of exsheathed third stage larvae to stimuli in the abomasum. In the later stages of development, H. contortus and O. circumcincta tended to migrate towards the pyloric area. In previously infected lambs, the distribution of inhibited early-fourth stage H. contortus was similar to that of normally developing fourth stage larvae in previously worm-free lambs and appeared to be unaffected by the host response which caused an altered distribution and rejection of late-fourth stage and adult worms. The rate of rejection of adult O. circumcincta differed between the fundic and pyloric areas of the abomasum, which suggests that the host response in these two areas may be different.     

Faecal avoidance and the risk of infection by nematodes in a natural population of reindeer

We tested whether Svalbard reindeer (Rangifer tarandus platyrhynchus) minimise the risk of gastro- intestinal nematode infection by avoiding patches with a high density of faeces. This experiment was performed in preferred summer foraging habitat. The possibility that reindeer assess infection risk on the basis of faecal contamination levels across plant communities was determined by measuring the distribution of faeces in seven plant communities, and nematode developmental success in two plant communities with contrasting soil moisture content. We explored whether variation within individual reindeer in the levels of infection by gastro-intestinal nematodes was related to their diet. Reindeer avoided pastures where faecal contamination was increased, and thereby potentially reduced the risk of becoming infected by Trichostrongyle nematodes. Dung density was inversely related to soil moisture content, with high densities of faeces in dry plant communities and low densities in wet communities. However, nematode developmental success was positively related to soil moisture content, and was highest in the wetter sites. Thus, by avoiding dry areas with high dropping densities, reindeer would tend to feed in wetter areas where nematodes thrive. Therefore, dung density may be an unreliable predictor of the risk of infection. The absence of a strong relationship between an individual’s infection level and its diet might be due to the unpredictability of pasture infection level. Received: 8 July 1999 / Accepted: 20 January 2000     

Ecology in the service of biological control: the case of entomopathogenic nematodes

 Biological control manipulations of natural enemies to reduce pest populations represent large-scale ecological experiments that have both benefited from and contributed to various areas of modern ecology. Unfortunately, economic expediency and the need for rapid implementation often require that biological control programs be based more on trial and error than on sound ecological theory and testing. This approach has led to some remarkable successes but it has also produced dismal failures. This point is particularly well illustrated in the historical development and use of entomopathogenic nematodes for the biological control of insect pests. Intense effort has focused on developing these natural enemies as alternatives to chemical insecticides, in part because laboratory assays indicated that these nematodes possess a broad host range. This illusory attribute launched hundreds of field releases, many of which failed due to ecological barriers to infection that are not apparent from laboratory exposures, where conditions are optimal and host-parasite contact assured. For example, the entomopathogenic nematode Steinernema carpocapsae is a poor choice to control scarab larvae because this nematode uses an ambusher foraging strategy near the soil surface whereas the equally sedentary scarab remains within the soil profile, shows a weak host recognition response to scarabs, has difficulty overcoming the scarab immune response, and has low reproduction in this host. Conversely, two other nematodes, Heterorhabditis bacteriophora and S. glaseri, are highly adapted to parasitize scarabs: they use a cruising foraging strategy, respond strongly to scarabs, easily overcome the immune response, and reproduce well in these hosts. Increased understanding of the ecology of entomopathogenic nematodes has enabled better matches between parasites and hosts, and more accurate predictions of field performance. These results underline the importance of a strong partnership between basic and applied ecology in the area of biological control. Received: 15 July 1996 / Accepted: 5 November 1996