Endectocide residues affect insect attraction to dung from treated cattle: implications for toxicity tests

A 3-year study was performed in southern Alberta, Canada to assess the effect of endectocide residues on the attractiveness of cattle dung to colonizing insects. In 2003 and 2004, insect captures were compared between pitfall traps baited with dung of untreated cattle and paired traps baited with dung of cattle that had been treated 7 days previously with topically applied doramectin, eprinomectin, ivermectin or moxidectin. Faecal residues associated with each compound affected insect captures in both spring and autumn of each year. Effects were detected (P < 0.05) for a total of 94 cases representing 27 insect taxa from 13 families in three orders (Coleoptera, Diptera, Hymenoptera). Two-fold differences in captures were common. Up to six-fold differences were observed. Eleven cases of attraction and 11 cases of repellency were associated with residues of doramectin. Eprinomectin tended to repel insects, with decreased captures for 19 of 29 cases of effect. Ivermectin showed a strong attractive effect, with increased captures for 17 of 25 cases. Moxidectin also showed a strong attractive effect, with increased captures for 17 of 18 cases. Comparisons between compounds suggested that results for doramectin best predicted results for eprinomectin and vice versa. In 2005, insect captures were compared between pitfall traps baited with dung of untreated cattle and traps baited with dung from cattle treated 3, 7 or 14 days previously with topically applied doramectin. Effects were detected in 14 cases plus one case of near significance (P= 0.053). Significant differences between control vs. days 3, 7 and/or 14 dung were detected in nine cases. Residues enhanced captures in seven of these cases. Day 14 dung affected captures in six of these cases. This study shows that endectocide residues can affect the number of insects attracted to colonize and oviposit in dung. Hence, the emergence of their offspring from field-colonized dung of untreated vs. endectocide-treated cattle should not be used as a measure of residue toxicity per se, but rather as a measure of 'insect activity'. Insect activity is a composite measure of residue toxicity, the number and species composition of insect colonists, and the mortality factors (e.g. predation, parasitism, competition) associated with the co-occurrence of these species in the dung pat.     

Determination of the toxicity of faeces of cattle treated with an ivermectin sustained-release bolus and preference trials using a dung fly, Neomyia cornicina

The toxicity of dung from cattle treated with an ivermectin sustained-release bolus was estimated in terms of ivermectin or ivermectin equivalents, using a laboratory bioassay with the dung fly Neomyia cornicina Fabricius (Diptera, Muscidae). The mortalities of flies measured 7 days after feeding for 24 h on dung containing known concentrations of ivermectin (between 0.125 and 1 g ivermectin per gram fresh dung) were compared with the mortalities of insects fed for 24 h on dung from cattle treated 21 days previously with an ivermectin sustained-release bolus. The toxicity of the bolus dung was equivalent to dung containing 0.66 g ivermectin per gram fresh dung. To determine whether insects could differentiate between control dung and dung from bolus-treated cattle, choice-chamber tests were carried out. There was no significant difference in the percentage of females that chose either dung type, suggesting that they were unable to distinguish the dung of bolus-treated cattle from control dung. Results are discussed in relation to the impact that bolus use can have on the insect fauna of cattle dung.     

Reductions of non-pest insects in dung of cattle treated with endectocides: a comparison of four products

Pour-on formulations of four endectocide products were compared to assess the effect of faecal residues on insects developing in naturally-colonized dung of treated cattle. In each of three independent experiments, suppression of insects was associated with application of doramectin, eprinomectin and ivermectin, but no effect was observed for moxidectin. When data were combined across experiments to increase sample sizes, suppression of insects was observed for each compound, with the least effect being observed for moxidectin. Based on the number of species affected and duration of suppression, doramectin > ivermectin > eprinomectin > moxidectin were ranked in descending order of adverse effect. A second set of three independent experiments was performed to assess the effect of endectocide treatment on dung degradation. Delayed degradation was observed for dung of cattle treated with doramectin, eprinomectin and moxidectin in the first experiment. No effect of treatment was detected in the second experiment. An effect of moxidectin was detected in the third experiment, but differences could not be detected with subsequent post-hoc tests. When data were combined across experiments to increase sample sizes, delayed degradation was detected only for eprinomectin. The apparent discrepancy between the low effect of moxidectin on insects versus its effect of dung degradation suggests the confounding action of other unidentified factors. Results of the current study indicate that use of moxidectin is least likely to affect the natural assemblage of insects associated with cattle dung.     

Lethal and sub‐lethal effects of faecal deltamethrin residues on dung‐feeding insects

Endectocides administered to livestock to facilitate pest and parasite control may be excreted in the faeces at concentrations that are toxic to coprophagous insects, including species of ecological importance. Although much research has focused on the effects of macrocyclic lactones, relatively less attention has been given to any similar impacts of the widely used pyrethroid insecticides. Here, the effects of faecal residues of the pyrethroid deltamethrin after application to Holstein–Friesian cattle in a proprietary pour‐on formulation are examined. Freshly dropped dung was collected 1, 3, 5 and 7 days after treatment and from an untreated control group. In laboratory bioasssays, female Lucilia sericata (Diptera: Calliphoridae) blow flies matured significantly smaller egg batches and had a lower percentage of eggs hatch after feeding on dung collected for up to 5 days after treatment, compared with flies feeding on dung from untreated cattle. In the field, artificial dung pats were constructed from the collected dung and left on pastureland for 7 days before being retrieved and searched for insects. Significantly more adult Diptera emerged from the faeces of untreated cattle than from the dung of treated cattle collected on days 1 and 3 after treatment. Adult Coleoptera were found in lower numbers in the dung of treated animals compared with control dung, suggesting a repellent effect. The results indicate that deltamethrin residues in cattle faeces have a range of lethal and sub‐lethal effects on dung‐feeding insects for up to a week after treatment, but that the precise duration and nature of toxicity varies depending on the sensitivity of the insect in question.     

Effects of avermectin residues in cattle dung on yellow dung fly Scathophaga stercoraria (Diptera: Scathophagidae) populations in grazed pastures

The effects of avermectin exposure on natural populations of the yellow dung fly, Scathophaga stercoraria Linnaeus, were investigated at the field scale on farms in south-west Scotland. Pastures forming the focus of the study were grazed with either untreated cattle or cattle receiving standard, manufacturer-recommended treatment regimes of an avermectin product. Flies were sampled between April and July in 2002 and 2003 using dung-baited pitfall traps. Abundance and wing asymmetry in S. stercoraria populations were examined in relation to a range of environmental and management variables (including avermectin exposure, pasture management intensity, weather and season). Data used for abundance analyses were collected in fields where treated cattle had been dosed with either doramectin or ivermectin, while the data for the asymmetry analyses were from a subset of fields where treated cattle had been dosed with doramectin only. While abundance of S. stercoraria varied significantly between years and with season, there was no difference in their abundance between fields grazed by avermectin-treated or untreated cattle. Asymmetry was significantly higher in fly populations in fields grazed by doramectin-treated cattle, suggesting that exposure to doramectin during development could have imposed some degree of environmental stress. While these results suggest that exposure to doramectin residues in dung on grazed pastures may have sublethal effects on the insects developing in that dung, there was no evident avermectin effect on the abundance of adult S. stercoraria occurring in the pastures.     

Ivermectin residues in cattle dung impair insect-mediated dung removal but not organic matter decomposition

1. Veterinary parasiticide residues in livestock dung have been repeatedly shown to negatively affect the abundance and diversity of dung-associated insects. While these losses are concerning from a conservation perspective, they can also translate to impairment of ecosystem functions in agricultural landscapes (e.g. nutrient cycling, primary productivity and greenhouse gas mitigation). 2. Most research focusing on decomposition-related ecosystem functioning has focused on dung beetles (Coleoptera: Scarabaeoidea) while other insects, particularly flies, have received comparatively less attention. 3. Using mesocosms, this study manipulated the insect groups colonising cow dung (beetles only, flies only, beetles and flies together, and an insect-free control). Half of the insects were exposed to 1 mg kg⁻¹ ivermectin in dung, while the other half were exposed to ivermectin-free dung. Dung decomposition (mass of organic matter lost) and dung removal (change in the dry mass of the dung pat attributed to both dung decomposition and burial) were measured. 4. Comparison of beetles and flies in ivermectin-free dung showed that beetles removed nearly twice as much dung as did flies. Comparison of dung removal across all treatments showed that ivermectin residues significantly reduced dung removal provided by beetles by 47% and dung removal provided by beetles and flies together by 32%. 5. Organic matter decomposition was not significantly affected by insect colonists or by the presence of ivermectin, indicating that organic matter decomposition can occur independently of insect activity and chemical perturbations.     

Larvicidal activity of endectocides against pest flies in the dung of treated cattle

Cattle were treated with topical formulations of endectocides to assess the larvicidal activity of faecal residues against horn fly, Haematobia irritans (L.), house fly, Musca domestica L., and stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae). In laboratory bioassays, doramectin, eprinomectin and ivermectin suppressed horn fly in dung of cattle treated at least 4 weeks previously and suppressed house fly and stable fly in dung of cattle treated 1-5 weeks previously. Moxidectin suppressed horn fly in dung from cattle treated no more than one week previously and did not suppress house fly and stable fly. Results combined for the three species across two experiments suggested that, ranked in descending order of larvicidal activity, doramectin > ivermectin approximately = eprinomectin > moxidectin.     

Adverse effects of ivermectin on the dung beetles, Caccobius jessoensis Harold, and rare species, Copris ochus Motschulsky and Copris acutidens Motschulsky (Coleoptera: Scarabaeidae), in Japan

Effects of the antiparasitic drug, ivermectin, on the dung beetles, Caccobius jessoensis Harold, 1867 and the rare species, Copris ochus Motschulsky, 1860 and Copris acutidens Motschulsky, 1860 were studied in laboratory and field experiments in Hokkaido, Japan. Ivermectin was detected in dung from 1 to 21 or 28 days following treatment, with a peak on the first day after treatment in two pour-on administrations (500 microg kg(-1)), although there were considerable differences between the two peaks. In C. jessoensis, brood balls constructed by the female were not reduced in the dung of treated cattle except for seven days after treatment in experiment 2. Also, there was no significant difference in the mean weight of brood balls between dung from treated and control cattle. However, the emergence rates were significantly reduced in dung 1-3 days after treatment. In the field study, brood balls constructed by C. jessoensis were more abundant in dung from treated cattle in experiment 1, but adult emergence was significantly reduced at one and seven days after treatments. Adult mortality of C. ochus Motschulsky at 90 days after the beginning of rearing was 11.1% in dung from control cattle with 22 brood balls constructed, whereas it was 84% in dung from treated cattle with no brood balls and/or ovipositioning. Also, in C. acutidens Motschulsky, adult mortality at 90 days after the beginning of rearing was 3.6% in dung from control cattle with 13 brood balls constructed, whereas it was 94.1% in dung from treated cattle with no brood balls or ovipositioning. The environmental risk in the use of ivermectin during breeding period of dung beetles in pasture is discussed.     

Effects of ivermectin and doramectin faecal residues on the invertebrate colonization of cattle dung

Abstract: The effects of avermectin [ivermectin (IVM) and doramectin (DRM)] faecal residues on dung colonization and degradation by invertebrates were evaluated during late spring in the east of La Pampa province, Argentina. The study was conducted after collection of faecal material from animals (10 steers per group) allocated to the following groups: untreated control group (CG) and groups treated subcutaneously (200 μg/kg) with either DRM (DG) or a long‐acting formulation of IVM (IG). Fifty pats (550 g each) per group were collected, prepared and deposited on the field on days 3, 7, 16 and 29 post‐treatment (pt). Eight pats per group were recovered after 7, 14, 21, 42, 100 and 180 days post‐deposition (pd) on the field. The weight, percentage of dry matter, number of arthropods and nematodes from faeces were determined. The faecal concentrations of IVM and DRM were measured by high performance liquid chromatography (HPLC) throughout the trial period to correlate the pattern of drug degradation in dung with pd time. The total number of arthropods in dungs from CG was higher (P < 0.05) than those counted between days 3 and 29 pt in IG and DG. A decrease in the number of Coleoptera larvae (P < 0.05) between days 21 and 42 days pd was observed in both treated groups. Diptera larvae counts in CG pats were significantly higher (P < 0.05) than those obtained in treated groups in the 7‐ and 14‐day‐old pats. A lower number (P < 0.05) of Collembola, compared with pats from CG, was recovered from IG and DG pats deposited at days 3 and 7 pt and exposed from day 42. The counts of Acari in pats from treated animals were lower (P < 0.05) than those observed in CG pats at 3, 8 and 16 days pt. There were no differences neither in adult Scarabaeidae recovered nor in the proportions of dung buried and destroyed by great dung beetles. Dung specific nematodes were reduced (P < 0.05) in IG and DG pats from 3 and 7 days pt compared with those of CG pats. The comparative results shown here demonstrate that the negative effects of both IVM and DRM on dung colonization are similar. The pattern of drug degradation in the environment was very slow. High residual concentrations of both active parent compounds were recovered in dungs exposed in the field for up to 180 days pd. Concentrations as high as 13 ng/g (IVM) and 101 ng/g (DRM) were measured in faeces obtained from pats deposited on day 27 pt and exposed to the environment during 180 days. The results show a decrease in invertebrate colonization of dung recovered from IVM‐ and DRM‐treated cattle, which is in agreement with the large drug residual concentrations measured in faeces.     

Influence of carrion smell and rebaiting time on the efficiency of pitfall traps to dung beetle sampling

Dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) are very useful insects, as they improve the chemo-physical properties of soil, clean pastures from dung pads, and help control symbovine flies associated with bovine cattle. Their importance makes it fundamental to sample and survey them adequately. The objectives of the present study were to determine the influence of decaying insects trapped in pitfalls on the attractiveness of Moura pig Sus scrofa L. (Suidae) and collared peccary Tayassu tajacu (L.) (Tayassuidae) dung used as baits to lure dung beetles, and to establish how long these baits remain attractive to dung beetles when used in these traps. Some dung beetle species seemed to be able to discriminate against foul smell from decaying insects within the first 24 h, hence decreasing trap efficiency. This was more evident in peccary dung-baited traps, which proved to be the least attractive bait. Attractiveness lasted only 24 h for peccary dung, after which it became unattractive, whereas the pig dung bait was highly attractive for 48 h, after which its attractiveness diminished but was not completely lost.     

Efficacy of the ivomec SR bolus for control of horn flies (Diptera: Muscidae) on cattle in South Texas

The concentration of ivermectin in the serum of Hereford heifers treated with a single Ivomec SR bolus reached a maximum of 8.8 +/- 0.9 ppb at 2 wk post-treatment. The single bolus treatment resulted in <10% mortality of adult horn flies feeding on the blood of the treated animals over the 21-wk trial. Bioassays of the manure from treated cattle showed complete inhibition of development of immature horn flies through week 19 post-treatment. When the trial was repeated using two Ivomec SR boluses/heifer, the concentration of ivermectin in the serum of the treated cattle reached a maximum level of 31.2 +/- 3.9 ppb at week 13 post-treatment. During the first 17 wk of treatment, the use of two boluses/heifer resulted in 96.2 and 81.2% mortality of adult male and female horn flies feeding on the blood of treated animals, respectively. From these studies, we conclude that a single Ivomec SR bolus used as an anthelmintic treatment can be expected to provide significant control of immature horn flies developing in the manure, but not of adults feeding on the treated cattle.     

Biological and chemical assays of pyrethroids in cattle dung

Bioassays were developed in Zimbabwe to measure pyrethroid in cattle dung. These and chemical assays then estimated concentrations in dung from treated oxen and elucidated risks to dung fauna. Laboratory bioassays with adult beetles (Histeridae and Scarabaeinae, including Copris, Digitonthophagus, Onitis and Sisyphus spp.) and muscoid larvae (Musca lusoria Wiedemann) indicated that the LC50 of pyrethroids, as ppm in the wet weight, averaged 0.04 for deltamethrin pour-on, 0.25 for deltamethrin dip, 0.22 for alphacypermthrin pour-on, 0.10 for cyfluthrin pour-on, 0.23 for cypermethrin dip and 0.63 for flumethrin dip. Field bioassays involved artificial dung pats of 800 g, deployed in woodland and inspected after 24 h to record insects dead and alive. Beetles were most abundant in the wet season. Muscoid larvae were less seasonal. The LC50 of insecticides in the field confirmed laboratory indications. Adult Diptera (muscoids and Sgifidae) were not repelled or killed until the deltamethrin concentration reached 10 ppm. Pat dispersal by dung fauna and termites (Microtermes spp.) was halved by deltamethrin at 0.1-1 ppm. Scavenging of dead beetles by ants was greatest with small beetles (< 15 mm long) uncontaminated with insecticide. Dips and pour-ons of deltamethrin on cattle gave residues of about 0.01-0.1 ppm in dung produced in the fortnight after application. About 1.6% of the deltamethrin applied was transferred to dung. Deltamethrin and alphacypermethrin in dung showed no detectable degradation in 64 days. Contamination levels threaten populations of slow-breeding beetles.     

Effects of ingested ivermectin on body mass

Abstract. Adults of Neomyia cornicina (F.) given continuous access to cow dung containing ivermectin at concentrations of 0.5.0.25 and 0.125 μg g^-1, the range found in the dung of injected cattle (Sommer et al. , 1992), were monitored every 12 h for changes in mass and excretory rates over a period of 3–5 days. Compared with the control insects, adult females that had ingested ivermectin showed disrupted patterns of daily mass change, an increase in dawn mass, and greatly reduced rates of excretion. Flies fed continuously with dung containing ivermectin at 0.25 μg g^-1 and 0.125 μg g^-1 in a regime identical to the above showed significantly increased abdominal mass compared with the controls. The observations are discussed in relation to other known effects of ivermectin on insect physiology.     

Modelled impact of insecticide-contaminated dung on the abundance and distribution of dung fauna

Deterministic models assessed the effects that contaminated dung from insecticide-treated cattle had on populations of three hypothetical species of dung fauna that dispersed randomly and could double their numbers every 1-28 weeks at low density. Insecticide was allowed to kill 2-98 % of adults and prevent 16-100% of breeding in pats produced immediately after cattle treatment, with toxicity declining to < 1% in pats produced 2-23 days later. Treatment intervals were 10-40 days. The modelled impact of insecticide was affected little by approximately four-fold variations in: length and density dependence of the attractive life span of pats, frequency of pat occupation by immature adults, distribution of pat toxicity during treatment interval, and changes in dispersal rates due to age and population density. Of greater importance were variations in: pat toxicity, treatment interval, frequency of pat occupation by breeding adults, density dependence of recruitment and death, natural adversity and mortality in dormancy, general rate of dispersal, and the size and shape of the area with treated cattle. Overall, it seemed that wide variations in the impact of contamination will occur in the field, but in many situations the risk to dung fauna can be substantial, especially for slow breeding beetles, and muscoids contacting insecticide on cattle. Risk extends outside the treated areas, for a distance equal to several daily displacements of the insects. Untreated refuges for species survival should be compact blocks at least 25 daily displacements wide.     

Effects of ingestion of dung containing ivermectin on aspects of behaviour in the fly Neomyia cornicina

Abstract. Adults of the dung fly Neomyia cornicina (Fabricius) were fed continuously on either dung containing no ivermectin (control dung) or dung containing 0.125 μg g^-1or 0.25 μ g^-1ivermectin (wet weight).Comparisons were made between the behaviour of flies during the first 24 h of dung feeding and that observed after 96 h of feeding.Subsequent experiments investigated the effects of ivermectin ingestion on three measures of locomotory ability: escape time, time to re-right, and capture time.
Analysis of behavioural data showed a significant reduction in the activity of ivermectin-fed flies compared to that of the controls.After 96 h of feeding on dung containing ivermectin, there was a significant increase in the duration of time spent standing and a reduction in duration and frequency of walking and grooming behaviours compared to controls.
Seventy-two hours after the onset of dung feeding, flies fed dung containing ivermectin took significantly longer to escape from a glass tube and to re-right themselves after overturning than flies fed control dung.The time taken to capture flies that had fed on dung containing ivermectin at 0.25 μg g^-1was significantly shorter than that required to catch control flies when flies from the different treatment groups were presented blind and randomly.     

The Ivomec SR Bolus for control of Boophilus annulatus (Acari: Ixodidae) on cattle in South Texas.

When Hereford heifers infested with Boophilus annulatus (Say) were treated with a single Ivomec SR Bolus, the concentration of ivermectin in the serum of the treated cattle reached a maximum of 8.8 +/- 0.9 ppb at 2 wk posttreatment. The single bolus treatment resulted in 84.4% control of standard engorging B. annulatus females on treated cattle over the 20-wk trial. Although fewer engorged ticks were collected from the sentinel heifers exposed in the treated pasture than those in the control pasture at weeks 4, 10, and 16 posttreatment, none of the differences was statistically significant. Each exposure of sentinel cattle found free-living ticks in both the treated and control pastures, indicating the infestation was not eliminated by the treatment. When the trial was repeated using two Ivomec SR Boluses/heifer, the concentration of ivermectin in the serum of the treated cattle reached a maximum level of 31.2 +/- 3.9 ppb at week 13 posttreatment. The use of two boluses/heifer resulted in 99.6% control of standard engorging B. annulatus females over the 20-wk trial. No ticks were found on sentinels placed in the treated pasture after week 9 posttreatment, an indication that the treatment had eliminated the free-living population in the treated pasture. From these studies, we conclude that a single Ivomec SR Bolus is incapable of sufficient control of B. annulatus to meet the rigid requirements of the Cattle Fever Tick Eradication Program in South Texas. Although two boluses per animal did eliminate the ticks from treated heifers and the pasture they were in, the treatment would not be sufficiently efficacious for mature cattle (>400 kg) for it to be useful in the program.     

The volatile organic compounds of introduced and native dung and carrion and their role in dung beetle foraging behaviour

1. The decomposition of biological material produces a plethora of volatile organic compounds (VOCs), which are implicated in the foraging behaviour of coprophagous and necrophagous insects. Dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) have an acute olfactory system used to locate food resources. Accordingly, identification of food resource VOCs potentially used in food location is integral to understanding dung beetle foraging ecology. 2. In this study, volatile emissions from dung and carrion of native and introduced animals in New Zealand were analysed using solid‐phase microextraction (SPME) and gas chromatography‐mass spectrometry (GC‐MS). Volatile profiles were compared via principal component analyses (PCAs) and cluster solutions based on attractiveness using canonical discriminant analysis (CDA). 3. A total of 115 compounds were detected from 21 food types. Statistical analyses showed that dung and carrion volatile profiles clustered according to attractiveness to the dung beetle Saphobius edwardsi, and that different dung types formed distinct clusters and grouped separately from carrion. 4. This study suggests that volatile profiles emitted by food resources used by dung beetles are complex, producing distinct odours, which potentially mediate foraging decisions.     

Area-wide impact of macrocyclic lactone parasiticides in cattle dung

Following the treatment of cattle with veterinary parasiticides and insecticides, residues are excreted into the dung in concentrations that may be toxic to functionally important dung-colonizing insects. In the dung, these residues cause a range of well-studied lethal and sub-lethal effects, the magnitudes of which vary with the compound used, mode of administration and concentration, and the insect species in question. Particular concern has been associated with the use of macrocyclic lactones in this context. Loss of insect colonizers may delay pat decomposition, but field studies report contrasting results that reflect confounding factors such as weather conditions, pat moisture content, pat location, time of year and dung insect species phenologies. The question of fundamental concern is whether the impacts seen in experimental or laboratory studies are likely to have a functional impact on insect populations, community interactions and the economically important process of dung decomposition. Recent studies which have attempted to address these wider, landscape-level impacts in temperate ecosystems are reviewed here. These show that the extent to which chemical residues may have any sustained ecological impact will depend on both a range of farm management factors, such as the temporal and spatial patterns of chemical use, the number of animals treated and the choice of active ingredient, and a range of insect-related factors, such as abundance, population dynamics and dispersal rates. However, they also demonstrate that considerable uncertainty remains about the likely extent of such effects and that current data are insufficient to support firm conclusions regarding sustained pasture-level effects. More large-scale, longterm field experiments are required, particularly in relation to insect dispersal and functional interactions within the dung insect community.     

Disintegration of Dung Pats from Cattle Treated with the Ivermectin Anthelmintic Bolus,or the Biocontrol Agent Duddingtonia flagrans

An experiment was performed during the grazing seasons of 1998, 1999 and 2000 to study the influence of the antiparasitic drug ivermectin and the nematophagous fungus Duddingtonia flagrans on cattle dung disintegration. The faeces originated from groups of animals that were part of a separate grazing experiment where different control strategies for nematode parasite infections were investigated. Each group consisted of 10 first-season grazing cattle that were either untreated, treated with the ivermectin sustained-release bolus, or fed chlamydospores of D. flagrans. Faeces were collected monthly on 4 occasions and out of pooled faeces from each group, 4 artificial 1 kg dung pats were prepared and deposited on nylon mesh on an enclosed pasture and protected from birds. The position of the new set of pats was repeated throughout the 3 years of the study. Each year, the dung pats were weighed 4, 6, 8 and 10 weeks after deposition and immediately afterwards replaced to their initial positions.

Results showed that there was no difference in faecal pat disintegration between groups. However, the time-lag between deposition and complete disintegration of the faeces varied significantly between deposition occasions. Dung pats disappeared within 2 weeks (visual observation) when subjected to heavy rainfall early after deposition, whereas an extended dry period coincided with faeces still remaining 12 months after deposition.

     

Effects of herd management and the use of ivermectin on dung arthropod communities in grasslands

Agroecosystems represent a large geographical footprint in most terrestrial landscapes, and management decisions within these systems affect their function in species conservation. We evaluated the effects that rangeland management systems (based on stocking density, rotation frequency, and the number of avermectin applications) have on conserving the dung arthropod community in the Northern Great Plains of North America. Comprehensive bioinventories of arthropods were collected from 16 rangelands using core samples of dung pats. Ivermectin was quantified in pats from each ranch using enzyme-linked immunosorbant assay (ELISA). Arthropods in dung were abundant (116,244 specimens) and diverse in eastern South Dakota (172 morphospecies). Rangelands managed with more regenerative practices (frequent rotation at high stocking densities and lack of ivermectin applications) had greater species richness, diversity, predator species abundance, and dung beetle abundance than more conventionally managed rangelands. Ivermectin quantity in cattle pats was negatively correlated with dung beetle abundance and diversity. This work shows that herd management (specifically high-intensity, frequent rotational grazing and eliminating prophylactic ivermectin use) that aims to mimic intensive grazing of large migrating herds of ruminants can foster dung arthropod community structure, a key trait correlated with nutrient cycling, pest suppression, and productivity of cattle-grazed rangelands.