Volume 45, Number 2 • May, 1977
The Effects ofDifferent Pasture and Rangeland Ecosystems on the Annual Dynamics ofInsects in Cattle Droppings
Richard W. Merritt and John R. Anderson A 2-yr study (1971-73) in the Sierra Nevada foothills of Cali fornia consisted of: 1) a quantitative analysis of the differences in diversity and abundance of the insect fauna colonizing and inhab iting diurnally and nocturnally excreted cattle droppings in four different pasture and rangeland ecosystems (natural woodland range, partially cleared woodland range, totally cleared woodland range, cultivated irrigated pasture); and 2) a study of the relation ship between the diversity and abundance of insect inhabitants per cowpat and the rate of pat degradation. The fauna consisted of three orders of insects containing 26 families and 102 species. There were 35 to 40 different kinds of Coleoptera, 50 of Diptera, and 12 of Hymenoptera, recorded from samples. Differences per pat in the mean number of species, number of individuals, and insect biomass among pastures, months, and years for the major taxa were analyzed and discussed. The pasture eco system and the season were most important in determining the diversity and abundance of insects colonizing droppings. Major differences among pastures in the number of individuals and spe cies per pat were mainly due to a combination of interacting loco and microclimatological factors associated with the environment of the different pastures. Most species of dung insects did not col onize pats dropped during the night. The most important insect species influencing biomass per pat was the scarab, Aphodius fimetarius (L.). The importance of con sidering species, individuals, and biomass in attempting to under stand changes in community structure and function was demon strated. (continued insitle blUk cooer)
THE AUTHORS: Richard W. Merritt is Assistant Professor, Department of Ento mology, Michigan State University, East Lansing; he was for merly Graduate Research Assistant, Department of Entomologi cal Sciences, University of California, Berkeley. John R. Anderson is Professor of Entomology, Department of Entomological Sciences, U.C. Berkeley. Richard W. Merritt and John R. Anderson
The Effects of Different Pasture and Rangeland Ecosystems on the Annual Dynamics of Insects in Cattle Droppings1
INTRODUCTION
CATTLE DROPPINGS constitute a special 1968, Blume 1970, 1972) ; 2) determin microhabitat, including both organisms ing succession of the fauna at or in pats, (biotic communities) and abiotic envi or on a seasonal basis (e.g., Laurence ronment, each influencing the proper 1954, Poorbaugh 1966, Rainio 1966, ties of the other (Hammer 1941, Mohr Papp 1971, Finne and Desiere 1971, 1943, Allee et al. 1948). Koskela 1972, Wingo et al. 1974) ; 3) Two important factors influencing biology and ecology of the horn fly (e.g., the dynamics of arthropod populations Bruce 1964, Morgan 1964, Morgan and inhabiting dung are: 1) environmental Thomas 1974) and face fly (Valiela (macro and micro) conditions in the 1969&, and annotated bibliographies of immediate area in which the pat is Smith et al. 1966, Smith and Linsdale dropped; and 2) the arthropods them 1967-71, Smith and Krancher 1974); selves, including their interspecific com and 4) ecological studies of other se petition, predator-prey interactions, lected species of Díptera or Coleóptera and various processes in their life his (e.g., Landin 1967, Houser and Wingo tories which may alter the physical or 1967, Foster 1970, Parker 1970, Hughes chemical nature of the dung (Hammer et al. 1972, Myrcha 1973, Macqueen and 1941, Mohr 1943, Snowball 1944, Lan- Beirne 1975). Valiela (1969a>) and Mer din 1961, Rainio 1966, Valiela 1974). ritt (1974) have provided a more ex Following the early original studies haustive bibliography on the biology by Hafez (1939) in Egypt, Snowball and natural history of dung arthropods. (1944) in Australia, Hammer (1941) The relative importance of various in Denmark, and Mohr (1943) in Illi Scarabaeidae in relation to the burial nois, on the taxonomy, biology, and ecol of cattle dung was analyzed by Linquist ogy of fauna associated with the drop (1933, 1935), Teichert (1959, 1961), pings of pastured cattle, there has been and Halffter and Matthews (1966); a renewed interest in this fauna in re however, it has been recognized only re cent years. However, much of the re cently as a result of the current research search has dealt with: 1) determining on pasture restoration in Australia the fauna inhabiting this medium in (Bornemissza 1960, Bornemissza and different geographical areas (e.g., San Williams 1970, Gillard 1967, Water- ders and Dobson 1966, Poorbaugh et al. house 1974, Hughes 1975). 1 Accepted for publication July 13,1976. [31] 32 Merritt and Anderson : Insects in Cattle Dropping The primary objectives of this study different pasture and rangeland ecd were: 1) to determine if there were systems; and 2) to determine and evaB quantitative differences in species di- uate the relationship between th versity and abundance of insects in- diversity and abundance of insect in habiting diurnally and nocturnally habitants per cowpat and the rate oj excreted cattle droppings in four pat degradation.
STUDY AREA General Description and Climate elevation of 100 to 600 m, is Méditer Research was conducted at the Uni- ranean, with cold, wet winters am versity of California Sierra Foothills dry, hot summers (Biswell 1956). Rain Range Field Station (SFRFS), Browns fall is usually restricted to the perio< Valley, California, approximately 97 from mid-October to mid-April, an< km north of Sacramento. It consists averages about 610 mm per annum of 2,347 hectares of brush- and oak- However, in 1971-72, a dry year, pre covered rolling hills and has been pri- cipitation was less than 500 mm (Fig marily used for research on beef cattle 2A). In contrast, 1972-73 was an ex production and management, and range tremely wet year in which rainfall tc improvement practices. tailed over 1000 mm (Fig. 2B). Froi The climate of the study area, at an May through September there may b
TABLE 1 PREDOMINANT VEGETATION OF THE SIERRA FOOTHILLS RANGE FIELD STATION
Pasture* Vegetation NW PC TC Trees: Blue oak (Quercus douglasii) X X Digger pine (Pinus sabiniana) X Shrubs: Buck brush (Ceanothus cuneatus) X Poison oak (Rhus diversiloba) X
Forbs: Filaree (Erodium spp.) X X Geranium (Geranium spp.) X Brodiaea (Brodiaea spp.) X Yellow star thistle (Centaurea solstitialis) X Legumes : Clovers (Trifolium spp., both native & introduced) X X X Bur clover (Medicago polymorpha) X X X Grasses : Bromus spp. X X X Wild oat (Avena barb ata) X X X Fescue (Festuca spp.) X X X Sown irrigated pasture species : Orchard grass (Dactylis glomerata) Perennial ryegrass (Lolium pererme) Ladino clover (Trifolium repens) Strawberry clover (Trifolium fragiferum)
• NW—natural woodland range; PC—partially cleared woodland range; TO—totally cleared woodta range ; I—cultivated irrigated pasture. HILGARDIA · Vol. 45, No. 2 · May, 1977 33
little or no precipitation. At this time are near freezing, and then becomes the indigenous annual rangeland forage rapid again in March. The forage ma is dry, and maximum air temperatures tures and dries in late April and May, are frequently above 40°C, with the after which only summer weed growth relative humidity sometimes as low as occurs until the fall rains. 10 to 15% (Biswelll956). Much of the diversity of grassland Vegetation is of the grass-woodland vegetation is related to differences in type, with an extremely diverse herba soils (Biswell 1956). The soil profile ceous flora. The predominant vegeta at SFRFS is variable in composition tion of each pasture is presented in and depth. According to Kay (1969), Table 1, and the principal vegetative the soils consist of a complex of the covers of the four pasture and range- Argonaut (clay loam) and Auburn land ecosystems are shown in habitat (gravelly loam) series. They are found photographs (Figs. 1A-1D). The her on both north and south slopes, and baceous vegetation on California are underlain by fractured and de rangeland consists mainly of annuals, composed metamorphosed igneous with the percentage of perennials rock (greenstone). varying with the region. In the SFRFS area, vegetation starts growing after Description of Pasture Ecosystems* rains begin in the fall (October, No Natural Woodland Range (NW).— vember). Growth subsides during the This type of rangeland ecosystem en winter (December, January, Febru compasses the largest area on the sta ary) because minimum temperatures tion, nearly 1,620 hectares. It has ap- ■For brevity, each of the four different experimental areas will be referred to as pastures throughout the text. 34 Merritt and Anderson : Insects in Cattle Droppings proximately 100 to 175 trees per mental feed (a mixture of cotton seed hectare and a few small creeks (Fig. meal and barley) from August 1A). The NW ecosystem has been dis through February. turbed less by range improvement Partially Cleared Woodland Range practices than the other three pasture (PC).—This 150-hectare area under ecosystems studied, and was not irri- went a range improvement practice in 1965 to improve herbaceous forage production. At that time, nearly all trees were chemically treated and killed with a 2,4,5-T—2,4-D amine mixture. A few trees were left for shade and aesthetic reasons. In 1970, a controlled burn was conducted on the entire area. Shortly after the burn, the area was reseeded to a mixture of annual clovers, orchard grass, and Harding grass (Table 1). From 1971- 73, follow-up poison oak control was conducted with a mixture of 2,4-D and S O N D J F MONTHS (1971 -72) 2,4,5-T. The rangeland was subdivided into four fields, each containing approxi mately 8 to 10 trees per hectare (Fig. IB). During each year, 25 to 30 cow- calf pairs were rotated among four pastures at 2-week intervals (4 to 5 hectares/head). They were given sup plemental feed from late October to mid-February. Totally Cleared Woodland Range (TC).—The 335-hectare study area was totally cleared of trees and brush through an extensive brush conver sion and range improvement program A S O N D J (Fig. 1C) similar to the one used on MONTHS (1972-73) the partially cleared range. Figs. 2A-2B. Average weekly maximum and The area was subdivided into 16 minimum air temperatures and total monthly precipitation at SFEFS during (A) 1971-72 pastures of 14 hectares each. There and (B) 1972-73. were four herds of 12 to 16 cattle, and each herd was rotated among four pas gated. The vegetation consists mainly tures every 2 weeks. Stocking rates of indigenous trees, shrubs, and herba ranged from 3 to 4 hectares per head. ceous plants (Table 1). The predomi Supplemental feed was provided from nant species of tree is blue oak mid-September .through February. (Quercus douglasU H. and A.). Irrigated Pasture (I).—The princi Twenty-five to 30 Hereford cattle pal study area was a 25-hectare pas were rotated twice between two pas ture near the lower end of a small tures during the year (6 to 8 hectares/ watershed (Fig. ID). The three most head). They were provided supple common soils, on slopes up to 30%, HILGAEDIA · Vol. 45, No. 2 · May, 1977 35 were Auburn, Sobrante, and Las Posas to 30 Hereford heifers (approximately (Hart and Borrelli 1970). The vegeta 1 hectare/head) were rotated among tion consisted of a planted mixture of the pastures at 2-week intervals. Cat clovers and grasses (Table 1). The pas tle grazed on irrigated pasture, with ture was totally cleared, and was sur out supplemental feed, from mid- face-irrigated by a gravity flow method. March through October. The pasture The 25-hectare pasture was subdi was free of cattle for the remaining vided into three like pastures, and 20 4 months.
MATERIALS AND METHODS Measurement of Temperature, taken each collection date. In the irri Relative Humidity, and Moisture gated pasture, soil samples were taken Content 2 days after irrigation so the water had a chance to permeate the soil. The climate which is generally rec During the summer (1972), the mois ognized by meteorologists is called ture content of aging cattle droppings "macroclimate," and prevails about 1.5 was followed for a period of 1 month m or more above the ground. "Micro to determine how long it took a freshly climate" refers to the condition pre dropped pat to dry in different pas vailing in the actual dung pile, tures. Fresh pats of 85 to 90% mois whereas "lococlimate" refers to the con ture content were collected in buckets ditions prevailing in the environment and transported to pastures where 3 close to the dung (Landin 1961). Aver to 4 replicate experimental pats (i.e., age weekly macroclimatic maximum and pats dropped at a given time in the minimum air temperatures and total same pasture) of the same size and monthly precipitation, taken from consistency as natural cowpats were SFRFS weather station recordings, placed out in each pasture. Approxi have been graphed for the years 1971- mately three core samples (17 mm 73 (Figs. 2A-2B). Lococlimatic mea diam. x 25 mm length) were taken surements, which included daily maxi from pats on each sampling date to mum and minimum air temperatures establish the mean moisture loss. Pats and humidities in three pastures (irri gated, natural woodland, totally were sampled every 24 h for the first 7 cleared), were recorded by hygrother- days, twice the second week, and one mographs approximately 15 cm above or two times during the following 2 the ground during the second year of weeks. To prevent unnatural aeration the study. At certain times of the year, and desiccation of the pat, core holes more sensitive lococlimatic measure were filled with damp sand, and a ments of humidity were made using maximum of 12 core samples was an Atkins® thermistor psychrometer. taken from each replicate cowpat. Ground temperature was measured by thermographs, with the thermistor Insecticide Treatment of Cattle placed 2 to 3 cm under the surface During the 1972-73 pest fly season of the ground. (May-September), 2% Coral® and 3% Moisture contents of soil (0-5 cm) Ciodrin® dust formulations were made and fresh cattle droppings were de sporadically available in one dust bag termined gravimetrically, using an per pasture, but they had no effect on ovendry method, on triplicate samples the pat fauna studied (Merritt 1974). 36 M err it t and Anderson : Insects in Cattle Droppings
Sampling, Rearing, and The droppings were left field exposed Identification Methods for approximately 44-54 h, depending on whether they were diurnal or noc Sampling methods.—In this study turnal pats (see Expt. Design section). it was necessary to design a quantita The comparison of "early" and "late" tive method for determining the pop inhabitants was accomplished by ulation of surviving insects per drop marking pats to be exposed for 10 to ping. Visual counts and observations 14 days concurrently with those to be of insects attracted to droppings picked up in 44 to 54 h. No species (Hammer 1941, Mohr 1943, Poorbaugh inhabited or colonized 10- to 14-day- 1966, in part) provided little informa old pats which did not also occur in tion on degradation, since several pats exposed 44 to 54 h. Observations species of Díptera visit pats only to on insect emergence and develop feed. Initially, larval extraction and mental rates in field droppings were identification were attempted; how made throughout the study to substan ever, this procedure proved very time tiate laboratory data. consuming, and the extraction effi ciency was low (Valiela 19696, Mer- Rearing and identification methods. ritt 1974). Therefore, the rearing —After field exposure, the pats were method was used in this study for the collected using the methods described following reasons: It revealed the pop by Merritt and Poorbaugh (1975). Cli- ulation of surviving insects colonizing matological conditions in the labora (insects which pass their immature tory simulated those in the field. During stages in dung) and inhabiting (in the winter (mid-November through sects which visit dung only to feed) January), pats were held at 13°C cattle droppings after a fixed period (±5°) and 85% (±5%) relative humid of time. Also, it provided information ity. In summer (mid-June to mid-Sep on the relationship between the insect tember), pats were held at 27°C (±5°) inhabitants emerging per cowpat and and 45% (±10%) humidity. In the the resulting rate of pat degradation. spring and fall, values fell between Naturally dropped pats were field- those listed above. Also, pats were marked in all pastures except during kept moist during the winter by specific experiments in the irrigated spraying a fine mist of water on the pasture when no cattle were present surface about 2 or 3 times a week. for 4 months. At such times, buckets This prevented desiccation of winter- of freshly dropped dung had to be active species, such as Aphodius spp. transported to this pasture from other Droppings were held in the laboratory pastures. Except for the horn fly, for 2 months except those dropped in which lives on the host animal and ovi winter, which were held 3 months to posits in fresh droppings within the first collect slow-developing species. The ma 2 min after excretion, no insects were jority of species usually emerged within reared from naturally dropped pats one month. Rearing containers were that were not also reared from such ex emptied frequently (collection days perimental pats (Poorbaugh 1966, Mer- were usually twice a week). Insects rittl974). emerging from each pat were chloro In the field, pats of nearly uniform formed, placed in vials, labeled by col size, approximately 25 cm in diameter lection date, and stored. Information and 4 to 6 cm thick, were marked with on all insects was stored in a computer tongue depressors soon after they hit ized data management system (Merritt the ground. An attempt was made to 1974). A voucher collection has been mark pats in all areas of the pasture. deposited in the Department of Ento- HILGARDIA . Vol. 46, No. 2 · May, 1977 37 mological Sciences, University of Cali Therefore, the comparative analyses fornia, Berkeley. of species, individuals, and biomass A pooled estimate of the dry weight among the different pastures and per individual (mg/ind) was calcu months was largely confined to the lated for each species identified, and years 1972-73. is expressed as mg of insect biomass/ Nocturnal-Diurnal pats. — Since pat. For each taxon, a known number cows defecate about every 2 h (Peter of reared adult specimens (100 to 2000 son et al. 1956, Maclusky 1960), it was individuals) was oven-dried at 40°C equally important to study the fauna for 48 h, weighed, and reweighed. The of nocturnally dropped pats. These average fresh cowpat (10 pats sam pats were sampled 8 times during the pled) was 25 cm in diameter, 82% study to determine the difference in moisture, and weighed 1.70 kg. The faunal diversity, if any, between noc average dry pat weighed 0.320 kg. turnally and diurnally dropped pats. During the summer (July, August) Naturally dropped pats were marked of 1971, sweep net samples were peri between 2000 and 2300 h P.S.T. the odically collected from droppings in first night, field-exposed for approxi all four pastures. Also, insect flight mately 42 to 46 h, and returned to the traps (illustrated in Anderson and laboratory for emergence. Since at Hoy 1972) were placed in the irri times it was extremely difficult to find gated and totally cleared pastures on cattle at night in a partially cleared two separate occasions for a 2-day or natural woodland pasture, only 4 period. These experiments were con pats were collected per pasture, and it ducted to determine which adults of was not possible to collect pats from dung-inhabiting species or their para every pasture each sampling date. sites were present in specific pastures Nocturnal pats.—These pats were during the hot summer months. studied to determine what fauna were excluded from pats dropped and ex Experimental Design posed only during the night. Naturally The emergent faunas were collected dropped nocturnal pats were marked from three different types of pats: between 2100 and 2300 h P.S.T. the diurnal, nocturnal-diurnal, and noc first night, field exposed for 7 to 8 hr, turnal. and picked up between 0400 and 0500 Diurnal pats.—These were naturally h (before sunrise) and returned to the dropped and marked between 0800 and laboratory. The design did not con 1100 h P.S.T. the first day, field ex sider the "late inhabitants" which may posed for 48 to 53 h, then picked up have colonized droppings the second and returned to the laboratory. In night. For the reasons mentioned each of the four pastures, 4 to 8 pats above, only 6 nocturnal pats were col were collected each month from July lected each sampling date from one 1971 through May 1973. During the or two pastures. In addition, nocturnal first 8 months of the study, the fauna pats were sampled six times during emerging from all pats in each specific the study in those months of high in pasture were pooled; hence, no mea sect abundance. sure of variance was recorded between the numbers of individuals/pat or the Methods of Assessing the Degree species/pat. Beginning in March 1972, of Cowpat Degradation the insects emerging from each drop In each of the four pastures, 8 to ping were kept separate, and 8 pats 10 fresh, experimental pats (degrada were sampled from each pasture. tion pats) were set out and marked 38 Merritt and Anderson : Insects in Cattle Droppings about the same time as natural pats down of pat surface and solid matter. used for emergence studies. Fresh Percent degradation was not esti dung from cattle on the appropriate mated on the basis of fresh weight, pasture was collected in buckets and since 75 to 93% would have evapo immediately transported to a prede rated in a few weeks in most pastures termined site. A quantity of dung ap without any insect activity. Also, if a proximating the weight of a fresh pat remained solid and intact, even dropping (1.7 kg) was placed on the though it had lost most of its wet ground and formed into the shape of weight, it still prevented vegetation an average-sized cowpat (25 cm in from growing over the entire area diameter). From 4 to 6 of these re covered and resulted in a measurable formed pats were marked and left in loss of productive pasture acreage. the field. Their history was followed Instead, the percentage surface area until they decomposed to a point of a pat left intact was determined. where only a fine sawdust-like detritus Thus, a pat 25% broken down had remained on the soil surface, or until 75% solid matter remaining (Figs. they were 3 years old, whichever came 14A,B). When degradation reached first. These were referred to as un 100%, only a fine sawdust like detritus treated degradation pats. The remain remained and vegetation was able to ing pats (insecticide-treated degrada grow over the area. tion pats) were set out near each group of marked, natural pats to com Methods of Data Management pare the degradation time of pats and Analysis when all initial colonizing species A "nested" or "hierarchical" analy were excluded by the experimental ap sis of variance (Sokal and Kohlf 1969) plication of insecticides. Each insecti was used to test for significant differ cide pat was mixed thoroughly in a ences among the individuals, species, bucket with 10 ml of technical Lin- and insect biomass per pat with re dane® (1.65 lb./gallon), and then spect to the following interactions: placed in the field. Preliminary studies 1) cowpats and species; 2) months showed no insects emerged from pats and years; and 3) pastures and treated with insecticide (Merritt months. Field and laboratory observa 1974). There was little evidence to tions were involved with these main suggest that Lindane®, used in the parameters. The original ANOVA above concentration, was toxic to mi tables for this type analysis have been croorganisms (see Bollen 1961, Fran presented by Merritt (1974). Compari cis et al. 1975). sons among treatment means were The degree of pat degradation was made using the Duncan's (1955) Mul measured by visual observation. Black tiple Range Test. Interrelationships and white photographs were taken at among species, individuals, and loco- weekly, biweekly, and monthly inter and micro-climatological factors were vals to document and score the process evaluated by linear regression analy of pat degradation, thus eliminating sis. The G-test for goodness of fit any kind of analytically associated (Sokal and Rohlf 1969) was used to disturbance. test for significant differences between There are two types of degradation, samples involving qualitative attri biological and mechanical. The first butes. occurs when dung is recycled back Diversity indices are sometimes use into the soil by organisms, and the ful in that they permit summarization second refers to the physical break of large amounts of information about HILGAKDIA · Vol. 45, No. 2 · May, 1977 39 numbers and kinds of organisms and rii = the number of individuals (Wilhm 1968). The Shannon-Weaver in each S species, where (1949) index of dominance diversity i = 1,2 ,*. was used in the final analyses to graphically show the influence that Thus, for a given community, an in specific groups of dung insects had on crease in the total number of species the entire dung insect community. The and/or the numerical evenness with following equation was used: which the species are distributed will increase the diversity index, H(s). This index was chosen because: 1) it was the IT(*)=-S (PilogePi) one most concordant with the biological ¿=1 data; 2) it is dimensionless, permitting use of both numbers and biomass units where P» = Ui/N, in the equation (Wilhm 1968) ; and 3) it is least affected by sample size N = the total number of individuals, (Pieloul966).
RESULTS AND DISCUSSION Faunal Composition and individuals emerging per pat (± stan Comparison dard deviation) in each month of the From 19 July 71 through 14 May 73, year and in each pasture, has been 798 undisturbed bovine droppings were given by Merritt (1974). collected from four different pasture The fauna consisted of three orders and rangeland ecosystems. A total of of insects ( Coleóptera, Diptera, Hymen 662,323 insects were collected. In 85% optera), 26 families, and 105 species. of the samples, each specimen was iden Thirty-five to 40 different kinds of tified as to species. A complete listing of Coleóptera, 50 of Diptera, and 12 of each taxon, with the mean number of Hymenoptera were found in samples
TABLE 2 FOOD HABITS OF DUNG-ASSOCIATED INSECTS BASED ON THE PERCENT SPECIES COMPOSITION OF EACH TAXON
Stage
Adult Immature Reported Taxon Dung Pred* Parb Other« Dung Pred Par Other prey Percent Coleóptera (40 )d 55 58 — 3 20 23 10 47e Primarily Diptera eggs, larvae, or pupae; occa• sionally Coleóptera lar• vae and adults
Diptera (50) 60 6 — 98 92 ?f 8 — — Primarily Diptera lar• vae and in one case Coleóptera adults
Hymenoptera (12) — — 100 — 100 — Diptera pupae
• Predators. b Parasitoids. « Either phytophagous (i.e., nectar), saprophagous (i.e. fungi, bacteria), or unknown. • The number of species representative for that particular taxon given. • Pood habits of immature Coleóptera (primarily Staphylinidae) are largely unknown. f Some species presumed to feed, but not certain. 40 Merritt and Anderson: Insects in Cattle Droppings taken at the SFRFS. The faunal analy pat for each pasture could be com sis considered only those species which pared with that of other pasture eco inhabited or colonized dung and ex systems. cluded those, such as the Calliphoridae As expected, on 90% of the sample (Díptera), which were attracted to dates, differences in the number of in dung for brief periods of time (min dividuals of the various species emerg utes) only to feed. Since organisms ing from cowpats were highly signifi such as spiders, mites (Machrochelidae, cant. The few samples with similar Acaridae), and soil arthropods were numbers of individuals of each species not completely sampled by the methods emerging per pat were collected used in this study, they were not eval largely in the winter months, when uated. colonization of droppings by a few species resulted in relatively low num Food Habits bers of individuals. Food habits among specific dung in Differences between months and sects were observed during this investi years.—The results of ANO VA showed gation and reviewed by Merritt (1976). seasonal variation with respect to spe A brief summary of these relationships cies colonization. Even though 1971-72 is presented in Table 2. Except for the was considered a relatively dry year, empid, Drapetis, no Díptera were re and 1972-73 an extremely wet year, corded predaceous on Coleóptera, differences between the 2 years for whereas over 50% of the Coleóptera, either individuals/pat or biomass/pat and all the Hymenoptera, were preda were not significant (Table 3). tors or parasitoids of Díptera. Most immature Díptera feed on dung, and Differences between pastures and nectar is the principal diet of adult months.—The results of ANOVA indi Díptera, in addition to the liquid from cated that the number of insects fluc the droppings (Merritt 1976). tuated in response to a monthly or There are limited data, other than seasonal cycle, and to different pasture Hammer's (1941) and Valiela's (1974) types. Insect biomass also fluctuated studies, regarding specific food habits seasonally; however, differences among and food webs of insect communities pastures in terms of biomass/pat were inhabiting bovine manure. It is par not significant (Table 3). ticularly true of the Aleocharinae and other staphylinid subfamilies (I. Diversity and Abundance: Moore, Univ. Calif. Eiverside, pers. Diurnal Pats comm.). This is largely due to the dif Species differences among pastures. ficulties involved in examining the —In Table 4, the species inhabiting or inter- and intra-specific interactions colonizing cattle droppings in the four inside the dung. different pasture and rangeland eco systems are arranged in major groups. Faunal Analysis In some instances the family has been Differences between pats and spe• retained as a distinct entity (e.g., cies.—On 86% of the sample dates Staphylinidae, Scarabaeidae) ; mothers, there were no significant differences several families have been combined between the total number of insects into one group (e.g., Nematocera, emerging from pats in each particular calypterate Díptera). It is probable pasture. This indicated that pastures, that the Aleocharinae (Staphylinidae) within themselves, were similar with in toto included five or more spe respect to different habitat sites, and cies; but due to problems involved therefore the mean number of insects/ with their specific identification they HILGARDIA . Vol. 45, No. 2 · May, 1977 41
TABLE 3 PROBABILITIES AND ASSOCIATED DEGREES OF FREEDOM FOR COMPARISONS BETWEEN MONTHS AND YEARS AND PASTURES AND MONTHS IN TERMS OF THE MEAN NUMBER OF INDIVIDUALS/PAT AND THE MEAN INSECT BIOMASS/PAT
Source df Significance* Between months 10 P < 0.01
P < 0.05
Between years N.S.b
N.S.
Between pastures P < 0.05
N.S.
Between months 22 P < 0.01
P < 0.01
•The number above horizontal line represents value for no. individuals/pat and number below horizontal line represents value for insect biomass/pat. The probability levels of 0.05 and 0.01 were used to denote significant and highly significant evidence, respectively. b N.S.—not significant at the 5% level.
TABLE 4 MAJOR GROUPINGS AND SPECIES COMPOSITION OF THE INSECT FAUNA INHABITING AND COLONIZING CATTLE DROPPINGS IN THE FOUR DIFFERENT PASTURE AND RANGELAND ECOSYSTEMS AT THE SIERRA FOOTHILLS RANGE FIELD STATION
Pasture*
I NW PC TO Taxonomic grouping (77%)b (93%) (83%) (72%)
COLEÓPTERA Hydrophilidae Cercyon haemorrhoidalis (L.) + + + Cercyon quisquüius (L.) + + + + Sphaeridium bipustulatum (Fab.) + + + + Sphaeridium lunatum (Fab.) + + + + Sphaeridium scarabaeoides (L·.) + + + Scarabaeidae Aphodius fime tarius ( L. ) + + + + Aphodius sp. nr. granarius (L.) + + + + Aphodius haemorrhoidalis (L.) + + + + Aphodius lividis (Oliv.) + + + + Aphodius pardalis (Lee.) + + + Aphodius vittatus Say + + + Staphylinidae Aleochara (2 + species) + + + + Aleochara bimaculata Gr. + + + + Aleochara bipustulata (L.) + + + -f Aleocharinae (5 + species) + + + + Apoloderus annectans (Lee.) + + + + Hyponygrus picipennis Lee. + + Leptacinus batychrus Gyll. + Leptacinus cephalicus Lee. JAthocharis ochracea (Gr.) + Oxytelus sp. + Table 4 continued »I—cultivated irrigated pasture; NW—natural woodland range; PC—partially cleared woodland range; TO—totally cleared woodland range. bThe total percent species composition of each pasture for all fauna inhabiting cattle droppings in the Sierra Nevada foothills of California. eThe plus ( + ) sign indicates the presence of a particular species in each pasture; the minus (-) sign* its absence. 42 Merritt and Anderson : Insects in Cattle Droppings
TABLE 4—CONTINUED
Pasture* I NW PO TO Taxonomic grouping (77%)* (93%) (83%) (72%) Philonthus cruentatus Gmelin +c + + + Phüonthus rectangulus Sharp + + + + Philonthus umbrinus (Gr.) — — + — Philonthus varians (Payk.) + - + + Platystethus americanus Erichson + + + + Quedius sp. - - + - Xantholinae - + - - Histeridae Peranus bimaculatus (L.) - + + + Saprinus sp. - + + - Rhizophagidae Monotoma picipes (Herbst.) - + + + DÍPTERA (Nematocera) Cecidomyiidae Colpodia sp. + + + - Xylopriona sp. nr. toxicodendri (Felt) + + + + Ceratopogonidae Forcipomyia brevipennis (Macquart) + + + + Forcipomyia sp. nr. texana (Long) - - + - Chironomidae Smittia byseinus (Schrank) Psychodidae Psychoda trinodulosa Tonnoir + + Psychoda pueilla (L.) + + Psychoda phalaenoides Tonnoir + Scatopsidae Regmoclemina sp. Sciaridae Lycoriella sp. S ciara sp. Tipulidae Típula acuta Doane
DÍPTERA (Calypterate) Anthomyiidae Calythea micropteryx (Thomson) Hylemya alcathoe (Walker) + + + Hylemya einer ella (Fallen) + + Scatophaga furcata (Say) + + + + Scatophaga stercoraria (L.) + + + + + + + + Muscidae Pseudophaonia orichalcoides (Huckett) + + Haematobia irritans (L.) + + + + Hydrotaea armipe» (Fallen) + + + + Hydrotaea tuberculata Rondani - + - - Morellia micans (Macquart) + + Musca autumnalie (DeGeer) + + + + Myospila meditabunda (Fab.) + + + + Orthellia caesarion (Meigen) + + + + »I—cultivated irrigated pasture; NW—natural woodland range; PC—partially cleared woodland range; TO—totally cleared woodland range. bThe total percent species composition of each pasture for all fauna inhabiting cattle droppings in the Sierra Nevada foothills of California. c The plus ( + ) sign indicates the presence of a particular species in each pasture; the minus (-) sign, its absence. HILGARDIA · Vol. 45, No. 2 · May, 1977 43
TABLE 4—CONTINUED
Pasture*
I NW PC TO Tazonomic grouping (77%)b (93%) (83%) (72%) Sarcophagidae Ravinia Iherminieri (R.-D.) +c + + + Ravinia plannifrons (Aldrich) - + + + Ravinia querula (Walker) + + + + DÍPTERA (Other Families) Sepsidae SatteUa sphondylii (Schrank) + + + + Sepsis sp. — + — + Sepsis biflexuosa Strobl. + + + + Sepsis brunnipes (M. and S.) + + + + Sepsis necocynipsea (M. and S.) + + + + Sepsis sp. nr. neocynipsea (M. and S.) + + + + Sepsispiceipes (M. and S.) + — - - Sepsis punctum (Fab.) + + + + Sphaeroceridae Oopromyza equina (Fallen) + + + + Copromyza marmorata (Becker) - + + + Ischiolepta pusilla (Fallen) — + + + Leptocera hirtula (Rondani) + + + + Leptocera sp. 1 - - + - Leptocera sp. 2 + + + + Leptocera sp. 3 + + + + Leptocera sp. 4 + — + — Olinea atra (Meigen) + + + + Stratiomyiidae Microchrysa flavicornis (Meigen) + + + - Sargus cuprarius (L.) + + + — Sargus decorus Say - + - - Empididae Drapetis sp. nr. septentrionalis Melander + + + + Drosophilidae Drosophila sp. - + + - HYMENOPTERA (Parasitic) Bethylidae 1 species Braconidae Aphaereta pallipes (Say) + + Àosbara fungicola (Ashmead) + + Idiasta sp. + Pentapleura triticaphis (Fitch) or + P. foveolata Viereck Phaenocarpa brachyptera Fischer Cynipidae Kleidotoma fossa (K.) + + Eucolia rufocincta ( K. ) + + Diapriidae Phaenopria sp. Figitidae Figites sp. Xyalophora sp. Ichneumonidae Phygadeuon sp.
*I—cultivated irrigated pasture; NW—natural woodland range; PC—partially cleared woodland range; TO—totally cleared woodland range. bThe total percent species composition of each pasture for all fauna inhabiting cattle droppings in the Sierra Nevada foothills of California. c The plus ( + ) sign indicates the presence of a particular species in each pasture ; the minus (—) sign, its absence. 44 Merritt and Anderson : Insects in Cattle Droppings were treated as one taxon. Also, for Of the 12 species of parasitic similar reasons, the three species of Hymenoptera, only five visited drop Psychodidae which colonized drop pings in the totally cleared pasture; pings were treated as one group in the but 10 were recorded from the irri analysis. gated and 11 from the natural wood For the majority of families there land pasture (Table 4). appeared to be little variation in the Considering the total species com number of species occurring in differ position of each pasture, the natural ent pastures. However, in a few woodland ecosystem contained the larg groups, there were marked differences est proportion (93% ) inhabiting or col (Table 4). Nearly all species of Nema- onizing cattle droppings, and the tocera (82 to 91%) occurred in the totally cleared pasture contained the natural woodland and irrigated pas lowest proportion (72%). There may tures, whereas only 55% of the species have been more species characteristic in this group colonized droppings in of the natural woodland ecosystem if the totally cleared pasture. The larg continued grazing pressure by domes est numbers of species of calypterate tic animals had not partially reduced Díptera occurred in the natural wood the ground cover. Although there was land and partially cleared pastures. an approximate 20% difference in Four species were recorded solely or species composition between the natu primarily from these areas; and two ral woodland and totally cleared pas species, Calythea micropteryx and Ba~ tures, only three groups were mainly vinia plannifrons, were reared from responsible for these differences: the droppings in all pastures except the Nematocera, calypterate Díptera, and irrigated one (Table 4). Haematohia parasitic Hymenoptera. The largest irritans, Scatophaga stercoraria, and number of species recorded from a Orthellia caesarion were most abundant single pat at any one time was 29 in in open fields, but emerged in large the irrigated pasture in June 1972. numbers from pats in both open and During the same month, the lowest shaded pastures, indicating their wide number of species in a pat was 10, in adaptability to different habitat sites. the totally cleared pasture. In the win Three species of Stratiomyiidae col ter, some pats were not colonized or onized droppings in the irrigated and/ inhabited by any species. or shaded pastures. During the summer Species differences between pas• in coastal California, Poorbaugh (1966) tures in different months.—In the Si observed that Sargus cuprarius erra Nevada foothills of California emerged only from sun-exposed pats, (Yuba County), differences among and S. decorus from shade-exposed seasons were shown by Merritt (1974). pats. In the current study, results were The present results were similar to similar for S. decorus. However, in those of Mohr (1943), who found three contrast, the largest number of S. faunal groups: a summer and a winter cuprarius emerged from pats in the complex, and some species characteris natural woodland setting, and few in tic of the spring and fall. dividuals emerged from pats in the Figure 3 shows the general seasonal totally cleared pasture (sun exposed). trend in all four pastures. There was This difference may have been due to an increase in the number of species the coastal climate in Poorbaugh's during the spring (February-April), study area, where cooler temperatures a slight decrease in species during the and higher humidities prevail during hottest month of the summer (July), the summer. an increase in the fall (October) ex- HILGARDIA · Vol. 45, No. 2 · May, 1977 45 responded with an increase in the s 20 number of coprophagous larvae of Cryptolucilia (Orthellia) caesarion. In B o our study area, the population fluctua a 20 tions of 0. caesarion in droppings did (Λ not appear to be associated with those of Sphaeridium. Seasonal chan ges in the species of Scarabaeidae were fairly regular in all pastures, with the greatest number of species occurring in the spring (Fig. 4B). The irrigated pasture always con tained the most species. Based on Lan JASONDJ FM MONTHS (1972-73) ding (1961) classification of different Fig. 3. Seasonal changes in the mean number habitats for the Aphodiini of Sweden, of insect species/pat (± standard deviation) in at least five species, four of which are the four different pasture ecosystems from also common to Sweden (Aphodius June 1972 through May 1973. The dotted line fimetarius, A. granarius, A. haemorrhoi- indicates that the pasture was free of cattle dalis, A. lividis), could be called "eury- during those months. topic," as they occurred in all four pasture and rangeland ecosystems. cept in the irrigated pasture, and a One species, A. pardalis, could be marked decrease in species in the late classified as "oligotopic," as it oc fall and winter (late November-Janu curred in all except the irrigated pas ary). To understand the changes in the ture (Table 4). total species diversity between differ ent pastures it was necessary to ex Four species of Staphylinidae amine changes in each major group (Platystethus americanus, Philonthus (Figs. 4A-4H). Adult Hydrophilidae cruentatus, Aleochara himaculata, Aleo- (five species) remained at almost a chara sp.) were common inhabitants constant density in the irrigated pas of droppings in all pastures during ture except during the winter months most of the year, whereas the other (Fig. 4A). This was not surprising, as species were sporadic in their appear most members of this family are ance (Fig. 4C). A few groups of aquatic (Borror and Delong 1971) and mainly predatory species, Philonthus adapt well to this type of environ spp., Aleochara spp., and the other ment. Three of the five species be Aleocharinae, inhabited pats during longed to the genus Sphaeridium the winter months when susceptible (Table 4). Poorbaugh (1966) found prey, such as certain nematoceran members of this genus to be important Díptera and Scatophaga spp. were predators of horn fly larvae only in abundant (Figs. 4D and 4B). sun-exposed pats during the drier Few studies (Laurence 1954, Poor months. In the Sierra Nevada foothills, baugh 1966) have been concerned with Sphaeridium spp. occurred in the open the nematoceran Díptera colonizing as well as in shaded pastures during cattle droppings. In the Sierra Nevada the summer months, but gradually de foothills, the Nematocera increased clined in early fall. Several authors during the fall in all pastures, gener (Hammer 1941, Poorbaugh 1966, Mac- ally remained abundant through the queen 1973) also observed this fall de winter months, then gradually de cline, and Hammer (1941) noted that clined in the spring (Fig. 4D). This the decrease in Sphaeridium spp. cor pattern contrasted with that of most 46 Merritt and Anderson : Insects in Cattle Droppings
CALYPTERATE DÍPTERA (16) HYDROPHILIDAE (5)
SCARABAEIDAE (6) SEPSIDAE (8)
"Ί 1 1 1 1 1 1- STAPHYLINIDAE (16) JJASONDJ F M A M
SPHAEROCERIDAE (9)
NW
PC
J J
PARASITIC HYMEN0PTERA(I2) NEMATOCERA (II)
ASONOJ FMAM MONTHS (1972-73) MONTHS (1972-73) Figs. 4A-4H. Seasonal changes in the number of species of each major group inhabiting cattle droppings in the four different pasture ecosystems from June 1972 through May 1973. The number in parentheses represents the number of species recorded. HILGAEDIA · Vol. 45, No. 2 · May, 1977 47 species of insects inhabiting drop Some species of sepsids occurred in pings. The natural evolution and bi both the fall and spring (e.g., Sepsis ology of these temperate insect groups neocympsea), whereas others occurred allows them to exploit a microhabitat primarily in the spring (e.g., Sepsis at a specific time period (late fall and biflexuosa) or in the fall (e.g., Sepsis winter) when it is nearly free from brunnipes). The seasonal trend in the competition for food and space, as Sphaeroceridae (Fig. 4G) was similar well as from predators and parasites. to that of the Sepsidae, except there Throughout most of the year, the nat were more species of sphaerocerids ural woodland pasture contained the present during the winter months. greatest number of species of nema- Two unidentified species of Leptocera, toceran Diptera. as well as Copromyza equina and Oli- The number of species of calypter- nia atra, emerged from droppings dur ate Diptera inhabiting droppings was ing December and January. Leptocera generally highest during the transi tion period between summer and fall (late September to mid-October), and in the spring (March, April) (Fig. 4E). During the winter months, two species of Diptera, Scatophaga sterco- rarm and S. furcata, colonized drop pings in all four pastures. The experi mental findings of Larsen and Thom- sen (1941) and Foster (1970), and dis tributional data by Hammer (1941), strongly indicated that Scatophaga spp. were adapted to cool climates. These species, as well as some of the previously mentioned nematoceran Diptera, may have had their origins in cool temperate zones and were able to exploit this niche more easily than groups with more southern, warmer, 5000 tropical origins. During the hot sum 4000 A mer of 1972, the only species of Musci- 3000 dae which colonized pats in the totally 2000 Λ cleared pasture were the horn fly, H. IOOCT tmfS ΙΛ s. 900 1 1, irritans, and the face fly, M. autumnalis. 1 I , \\ · * I1 cao 800 ' I · E VYV / \\l i 1 i Changes in the Sepsidae among dif 700 \ ■ 1 CO V / \1
TABLE5 THE PARTITIONED MEANS OF THE FIRST ORDER INTERACTION BETWEEN MONTHS AND PASTURES, USING DUNCAN'S MULTIPLE RANGE TEST (NUMBER OF INDIVIDUALS/PAT)a
Month Mar Apr Feb Oct Nov Sep Aug May Jun Jan Jul Dec
X 17,486b 5,671 5,251 3,582 3,385 2,745 2,735 2,529 2,108 1,410 1,365 350
Pasture I NW PC TO "x 1666« 1041 926 500
» Means underscored by the same line are not significantly different at the 5% level. b The mean no. of insects emerging/pat per month in all four pastures for both years of the study. c The mean no. of insects emerging/pat in each specific pasture for both years of the study. HILGARDIA · Vol. 45, No. 2 · May, 1977 49
A M MONTHS (1972-73) Fig. 6. Seasonal changes in the mean number of individuals/pat (± standard deviation) in the four different pasture ecosystems from June 1972 through May 1973. The dotted line indicates that the pasture was free of cattle during those months.
tures in different months.—In all pas the total number of individuals/pat tures, the largest number of individ among the four pastures, the specific uals/pat occurred in the spring ; how groups or individual species influenc ever, in the totally cleared pasture the ing these numerical differences, and peak was considerably lower than in the factors associated with a particu the other pastures for the same time lar pasture, were examined. period (Fig. 6). This difference was Even though all five species of hy- almost entirely due to the smaller drophilids were present during most number of psychodids which inhabited of the year in the irrigated pasture, this pasture. In the irrigated pasture the largest numbers of individuals/pat there was a constant rise in the num occurred in the wooded pastures (NW, bers of psychodids colonizing pats be PC) during the spring (Fig. 7A). Gen ginning in August and continuing erally, the totally cleared pasture con through November. In the other pas tained fewer individuals/pat of all hy- tures (NW, PC, TC), insect abundance drophilid species, except in late August increased during the fall (October), 1972 when Cercyon quisquüius in then gradually decreased with the on creased in numbers. During the sum set of colder temperatures. mer the largest number of individuals Influence of specific groups or spe• of Sphaeridium occurred in the irri cies on différences.—Within the over gated pasture, whereas this group was all picture of the major differences in nearly absent in the totally cleared HYDROPHILIOAE i «ΡΡθΓ O Carcvow spp(2) I
S 0 N 0 J F MONTHS (1972-73) MONTHS (1972-73) Figs. 7A-7G. Seasonal changes in the mean number of individuals/pat of each major group inhabiting cattle droppings in the four different pasture ecosystems from June 1972 through May 1973. Fig. 7A includes 3 Sphaeridiim and 2 Cercyon spp. HILGAEDIA · Vol. 45, No. 2 · May, 1977 51 pasture during the same time period. cattle droppings was Aphodius fime- It is unlikely that the greater abun tarius. This species was generally more dance of Sphaeridium in the irrigated abundant in the drier pastures (NW, pasture was due to increased prey PC, TC) and accounted largely for availability, as no correlation was the peaks during late spring, fall and found between the number of suscep mid-winter (Fig. 7B). Another apho- tible prey (mainly calypterate mus- dine, A. vittatus, also contributed to coid Díptera) and the number of the spring abundance, whereas A. Sphaeridium spp. for the 3-month pe haemorrhoidalis appeared to replace A. riod (June through August). There fimetarius during the summer months, was, however, a positive correlation particularly in the irrigated and par in July (r = 0.665) and in August (r = tially cleared pastures during 1972. The 0.644) between the relative humidities low numbers of A. fimetarius adults in the different pastures and the num present in the irrigated and partially ber of Sphaeridium which inhabited cleared pastures during May 1973 are droppings. Because the air tempera difficult to explain. In May 1972 the tures were higher in the drier pastures number of individuals/pat in these during the summer (Fig. 8A), differ two pastures, as well as the other pas ences in soil temperature and moisture tures, was extremely high (200 to 500 among pastures were investigated. In per pat). Possible explanations are July and August 1972, the mean that large numbers of A. fimetarius monthly soil temperature in the adults had not yet emerged from older totally cleared pasture was 12 to droppings in these two pastures, or 17°C higher than in the irrigated or that the adults had not colonized the natural woodland pastures (Fig. 8C). droppings by the time they were picked Also, there was approximately a 12 up. The latter could have been due to to 15% difference in soil moisture be adverse lococlimatic conditions in the tween the irrigated and drier pas two pastures (I, PC) at the time of pat tures. Moisture measurements in the deposition or shortly after. This may irrigated pasture were taken at field have affected the dispersal of the spe moisture capacity. On a relative basis, cies or the microclimate of the dung, there was probably a 100% difference preventing higher rates of inhabita at times, as the TC pasture was "air tion. Comparatively low numbers of dry" and the I pasture was flooded. other aphodines were also found in Since the larvae of Sphaeridium pu these two pastures during May 1973. pate in the soil beneath or beside the Earlier workers (Mohr 1943, Landin dung (Mohr 1943, McDaniel et al. 1961, 1968) showed that temperature 1971), the high soil temperature and and light greatly affected the dispersal low soil moisture during the summer activities of A. fimetarius, as well as may have affected their survival in those of other species. The low num the totally cleared pasture. In addi bers of aphodines did not appear to be tion, the more rapid desiccation of a result of competitive interaction pats which were dropped in the totally with other species, as no species were cleared pasture during the summer recorded from the irrigated and par may also have inhibited development tially cleared pasture that were not of the larvae inside the pat (Fig. 8D). recorded from other pastures. Also, The numbers of individuals per total species abundance among pas species of Scarabaeidae varied con tures fluctuated only slightly. siderably among pastures. The most Seasonal changes in the numbers of abundant species which occurred in Staphylinidae in different pastures are 52 Merritt and Anderson: Insects in Cattle Droppings shown in Fig. 7C. The most noticeable ids in the irrigated pasture as opposed difference was the low density of to the drier pastures, was primarily staphylinids which occurred in the ir due to the greater abundance of the rigated pasture throughout the year, Aleocharinae in these drier areas (Fig. except in the month of June. In the 7C). From August through October drier pastures (NW, PC, TC) there 1972, two to five individuals/pat belong were abundance peaks in spring, sum ing to this group were recorded from mer, and fall. The low numbers during the irrigated pastures, whereas over the spring in the irrigated pasture 100 individuals/pat were recorded paralleled the absence of nearly all from the drier pastures. This appeared staphylinid predators and parasites to be a habitat preference by the Aleo from the droppings, such as Philon- charinae, as low numbers of this group thus spp., Aleochara spp., and Platy- were generally present in the irrigated stethus americanus. From December pasture throughout the year. 1972 through March 1973 cattle were The Nematocera were responsible kept off the irrigated pasture, and ex for marked changes in the abundance perimental colonization pats were of insects inhabiting cattle droppings. placed out once a month. Since natural This was largely due to three species pats were not continually dropped in of Psychodidae: Psychoda phalae- the irrigated pasture over a 4-month noides, P. trinodulosa, and P. pusilla. period, there were possibly fewer num The latter two species occurred in bers of suitable prey available to col nearly all samples. In the spring, up to onize the pats, and therefore fewer 8000 individuals/pat were common in predators were able to survive in the certain pastures. As shown in Fig. 9, droppings. For example, during Feb the psychodids dominated the irrigated ruary and March the mean number of and dry pastures 3 to 6 months of the Scatophaga stercoraria (Díptera: An- year, when 50 to 94% of all individuals thomyiidae) per dropping in the irri which emerged from droppings be gated pasture (when cattle were ab longed to this family. In the absence sent) was less than 50 individuals per of the psychodids, there would have experimental pat. In the drier pas been a marked drop in faunal abun tures, the mean number was greater dance during the fall in the irrigated than 100 individuals per natural pat pasture in contrast to the drier pas (Merritt 1974). It is not known tures (NW, PC, TC) where there was whether the greater abundance of 8. an increase in all other species. In the stercoraria in drier pastures was due shaded pastures (NW, PC) the psy to the presence of cattle in these areas chodids were extremely abundant dur or to a more preferred habitat. How ing the spring and accounted for the ever, the mean number of individuals/ high peaks from February through pat increased to 108 in the irrigated April 1973. During the summer (Au pasture when cattle were returned in gust through Sepember) there was a April. Also, the number of staphylinid significant positive correlation be parasites and predators started to in tween the number of psychodids crease in the months following. Kos- emerging per pat and the relative hu kela (1972) studied dung-inhabiting midity in different pastures. This in Staphylinidae in Finland and also dicates that the large number of psy found that the carnivore species were chodids in the irrigated pasture may very dependent on the number of suit have been associated with the high able prey in the droppings. During the humidity in this pasture, especially fall, the smaller number of staphylin during the warmer months (Fig. 8B). HILGAEDIA · Vol. 45, No. 2 · May, 1977 53
TC PASTURE NW PASTURE I PASTURE i 30
2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 ΙΘ MONTHS (1972) DAYS AFTER DEPOSITION
K 20|
3 20i
JULY AUG SEP OCT MONTHS (1972)
ASONDJ FMAMJ MONTHS (1972-73)
u H î 20
MONTHS (1972) PigB. 8Δ-8Ε. Lococlimatic and macroclimatic measurements taken at the SFEFS during 1971-73.
A marked difference occurred in the inhabiting droppings. Their foraging number of individuals/pat of calyp- behavior in the dung resulted in the terate Díptera which inhabited the physical disruption of the intact pat, totally cleared pasture during April reducing potential oviposition by flies 1973 (Fig. 7D). This abundance peak and developmental sites for the larger during the spring was primarily due dipteran larvae. This phenomenon was to three species which colonized drop also observed by Hammer (1941). High pings in large numbers: Scatophaga emergence peaks in the irrigated pas stercorana, Hylemya cinerella, and Or- ture during August and September thellia caesarion. The latter two species were due to greater numbers of horn were particularly abundant in the flies and face flies colonizing droppings. drier, more open pastures (PC, TC). The most abundant species of sepsid The decline of calypterate Díptera in all pastures was Sepsis neocynipsea, (particularly the horn fly and face fly) which accounted for the major popula during May coincided with an increase tion fluctuations within this family in the numbers of A. fimetarius adults (Fig. 7E). In the irrigated pasture this 54 Merritt and Anderson: Insects in Cattle Droppings species had two major emergence peaks, gated pasture during the spring and one in the early spring (February early summer (Fig. 7G). Smaller num through March) and one in late sum bers of individuals emerged from pats mer (late August through September). in the natural woodland pasture, and However, in the drier pastures (NW, no individuals were recorded from PC, TC), the emergence peaks occurred droppings in the partially and totally in late spring (April through May) and cleared pastures during the entire in late summer or fall, depending on summer. Since prey availability in the the pasture. The additional abundance different pastures did not appear to be peak of S. neocynipsea in the totally a consideration (Merritt 1974), cer cleared pasture during October may tain loco-environmental factors were have been due to the warmer tempera examined to determine which of these tures prevalent in open, sun-exposed may possibly have influenced the de areas, which would have allowed mat crease in Hymenoptera in the drier ing and oviposition activities to con pastures (PC, TC). Figure 8E shows tinue. The cooler fall temperatures in the mean relative humidity differences the more humid and shaded pastures among pastures over months. The larg (I, NW, PC) may have restricted the est differences (nearly 20%) occurred above activities and prevented pat col in the hot summer months (July, Au onization in these areas. Another spe gust) between the irrigated and to cies of sepsid, Saltella sphondylii, oc tally cleared pastures. Differences curred in all four pastures during the were not as pronounced between the spring, but was almost entirely re other pastures for the same time pe stricted to the irrigated pasture dur riod. Only a few face flies were col ing the hot summer months. A positive lected from flight traps during the correlation was found during July (r summer in the totally cleared pasture, = 0.522) and August (r = 0.675) be but large numbers of Díptera and two tween the relative humidities in the species of Hymenoptera were collected different pastures and the numbers of individuals of S. sphondylii emerging 7000i per pat. This indicated that low hu 5000 midities in the drier pastures during 30001 the summer (Fig. 8B) may have been I 0001 a factor in restricting this species to 750 the cooler, more humid irrigated 500 pasture. 250 0 The greatest difference in the num ■l· ■l· «II4 · ber of Sphaeroceridae colonizing drop u_ 7000 r ■ Psychodidae 0 ' i pings occurred between the irrigated O, 5000 □ All other species UJ PC and drier pastures during the spring 95 3000 (Fig. 7F). The high abundance peaks 1 100? in the drier pastures, especially the 750 wooded areas, were due to one species, 500 Olinea atra. This species preferred the 250 wooded pastures, where up to 1000 in 0 S 0 N D J iF M dividuals emerged per pat. In contrast, MONTHl·^S (1972-73 ) less than 200 individuals per pat were Fig. 9. Comparative seasonal changes in the recorded from the open pastures. mean number of individuals/pat of the Psycho didae and all other species in a wet (I—irri The largest numbers of parasitic gated) and a dry (PC—partially cleared) Hymenoptera occurred in the irri pasture. HILGAEDIA . Vol. 45, No. 2 · May, 1977 55 in the irrigated pasture. Sweep net per pat and the mean relative humid samples netted parasitic Hymenoptera ity in three different pastures (I, NW, visiting pats in the irrigated and natu TC) revealed a positive correlation ral woodland pasture, but none were during the summer months of July (r netted in the partially and totally = 0.556) and August (r = 0.441) 1972. cleared pastures. The results of a re In addition to lococlimatological gression analysis between the number factors, microclimatological measure of parasitic Hymenoptera emerging ments were also recorded. Figure 8D
TABLEO THE PARTITIONED MEANS BETWEEN MONTHS, USING DUNCAN'S MULTIPLE RANGE TEST (INSECT BIOMASS/PAT)»
Month May Nov Feb Apr Mar Jan Jun Oct Aug Dec Jul Sep Ï ll,861b 5,255 4,199 3,979 8,300 2,880 2,565 2,157 2,035 1,855 1.474 1,310
* Means underscored by the same line are not significantly different at the 5% level. * The mean insect biomass/pat per month in all four pastures for both years of the study.
shows the percent moisture loss of solation, higher air temperatures, and droppings in the I, NW, and TC pas higher evaporation) in these dry pas tures over time. After 2 weeks, only tures may be a factor in restricting the 6% moisture was left in pats in the colonization of certain species of para TC pasture. In contrast, after 50 days, sitic Hymenoptera to more humid 65% moisture was left in pats in the areas during the hot summer months. I pasture and 30% in pats in the NW If humidity was not the primary pasture. Many insects, especially para causal factor, it appears very likely sitic Hymenoptera, require a longer that it was at least associated with developmental time in the dropping, other related factors, such as the rapid and this rapid drying would certainly dehydration of the pat, high soil tem limit the numbers of insects, as well as peratures, and/or low soil moisture species, inhabiting pats in the TC area. content. As shown earlier, the influ The study was repeated again in the ence of the microclimate of the insect early fall (late September through Oc on species colonization in cattle drop tober) when cooler temperatures pre pings is not unique to the Hymenop vailed. Pats dropped in the totally tera, but also occurs among the sep- cleared pasture during the fall con sids, hydrophilids, and psychodids. tained 40% moisture after 30 days, in Biomass differences among months comparison to the 6% moisture found and years.—Distinct and important after 14 days in midsummer. This differences were present between the showed the influence of high tempera number of individuals/pat and bio- ture and low humidity on the loss of mass/pat. The Duncan multiple range moisture from the dung. test (1955), which was applied to the These results indicate that low hu ranked mean values in Table 6, showed midities (as influenced by greater in- there was considerable overlap in 56 Merritt and Anderson : Insects in Cattle Droppings terms of biomass/pat during most peared to be a trimodal curve with months of the year. However, mean respect to biomass, the largest peak biomass values for the months of May occurring in late spring with smaller and November were significantly peaks in the late fall and winter. In greater than for all other months, and the fall, Aphodius fimetarius (Scara- accounted for the biomass peaks in baeidae) contributed significantly to emergent insects in the fall and spring insect biomass, and in the late winter, (Fig. 5B). In both years there ap pats were colonized by Scatophaga
MONTHS (1972-73) Fig. 10. Seasonal changes in the mean insect biomass/pat (mg/pat) in the four different pas ture ecosystems from June 1972 through May 1973. The seasonal changes in the mean number of individuals/pat in the four pasture ecosystems has been superimposed on the biomass values (unshaded). spp., A. fimetarius, and some nemato- totaled over 1000 mm, and below cerous Díptera. The peak in late freezing temperatures were common spring was again due to the invasion in December. These freezing tempera of cattle droppings by newly emerged tures accounted for the large drop in adults of A. fimetarius, one dropping fauna in December 1972, as few, if containing 1000 beetles on occasion. any, insects colonized the droppings The monthly differences in biomass then. During the spring, the monthly between years (Fig. 5B) were largely abundance curves were in greater due to climatic conditions. The same synchronization with each other. faunal groups which contributed sig Biomass differences between months nificantly to insect biomass in the drop in different pastures.—In the irrigated pings during 1971-72, colonized drop pastures during the fall and spring, pings 1 month earlier in the second and in the wooded pastures (NW, PC) year. The extremely warm climatic con during the spring, the large differ ditions during the fall (1971) appar ences between numbers and biomass ently delayed the appearance of A. were due to three species of psycho- fimetarius, which did not colonize dids. Although present in large num droppings until November and Decem ber, they represented very little bio ber of that year. In contrast to 1971 mass (Fig. 10). In the natural wood when precipitation was less than 500 land and the partially and totally mm, the rainfall for the year 1972-73 cleared pastures, the psychodids were HILGABDIA . Vol. 45, No. 2 · May, 1977 57 not as prevalent in the fall, and spe to 79% of the total number of indi cies with a greater biomass, such as A. viduals (depending on the pasture) fimetarius, inhabited the droppings. which emerged from droppings during This was especially evident in the lyr. totally cleared pasture during 1972- 73 when the mean number of indi Nocturnal-Diurnal Pats and viduals/pat was never greater than Nocturnal Pats 1500, yet high biomass values oc Most species of dung insects did not curred. colonize pats dropped during the night Only those species which contrib (Merritt 1974). The following species uted significantly to the major were considered to have a definite noc changes in biomass in the four pas turnal activity period, based on the ture ecosystems have been discussed. mean number of individuals which col In both a wet (I) and a dry (NW) pas onized a dropping (20 to 440 individ ture, the biomass peaks in the fall and uals/pat) : Haematohia irritans, O. cae- late spring were largely due to one sarion, Psychoda spp., Rivinia querida, species, Aphodius fimetarius (Fig. 11). Sepsis neocynipseay Hylemya cinerella, In the midwinter and spring, two and a hymenopteran parasite, Aphae- other species, Scatophaga stercoraria reta pallipes. There were other spe and 8. furcata, contributed signifi cies of Díptera and some Coleóptera cantly to insect biomass in both pas which visited droppings at night; tures. However, A. fimetarius repre however, they occurred sporadically sented 50 to 98% of the biomass per in small numbers (one to three indi dropping during 5 months of the year. viduals/pat), and therefore are not Together, A. fimetarius and Scatophaga considered here. The horn fly, H. irri• spp. represented 51% and 70% of the tans, was the most abundant species total annual insect biomass/pat in the colonizing cattle droppings during the irrigated and natural woodland pas night. tures, respectively. In contrast, three The number of species which colon species of psychodids represented 65 ized diurnal droppings was signifi
■ A. fimetorius cantly greater than the number which □ All other species colonized nocturnal-diurnal droppings. Ê53 Scotophoqq spp. This result was expected, as the over all succession of insect species in cat tle droppings is related to the age of the pat (Mohr 1943). Since there was little nocturnal activity among dung- inhabiting species, pats dropped dur ing the night would remain relatively uncolonized until the following day. By that time, the dung had aged to a point where certain species would be excluded from colonization due to their successional position. However, ASONDJFM except for a few species of Nemato- MONTHS (1972-73) cera and two species of Hymenoptera, Fig. 11. Comparative seasonal changes in the most species were collected from both mean insect biomass (mg/pat) of Aphodius diurnal and nocturnal-diurnal pats at fimetarms, Scatophaga spp., and all other spe cies in a wet (I—irrigated) and a dry (NW— one time during the study. This indi natural woodland) pasture during 1972-73. cated that differences may not have 58 Merritt and Anderson : Insects in Cattle Droppings been solely due to the age of the dung, tures. In the wooded pastures, espe but that the rate at which the micro- cially the natural woodland, insolation and loco-environmental factors de was reduced by vegetational cover. creased the susceptibility of the drop This resulted in cooler air tempera ping to colonization might also be tures, lower evaporation of moisture involved. from the soil and cowpats, and slightly Even though significantly fewer spe higher humidities. In the irrigated pas cies emerged from nocturnal-diurnal ture, watering resulted in higher soil droppings, there was no significant moisture and greater transpiration difference in the mean number of in and cover from perennial grasses and dividuals emerging between diurnal clovers. This also resulted in lower and nocturnal-diurnal pats. Keduced temperatures and higher humidities interspecific competition or less pred during the warmer months. The effect ator-prey interaction inside the dung of wind and precipitation on insects could have accounted for the increase inhabiting cattle droppings was not in the numbers of insects emerging monitored closely. The wind velocity from nocturnal-diurnal droppings. in the totally cleared pasture aver Field observations revealed that few aged 4 to 5 km/h greater than in the species colonized or inhabited pats at natural woodland pasture, and this night, and that 98% of these were may have contributed to the lower coprophagous. We suggest that re humidity in the former. Also, it may duced interspecific competition was have been a factor in restricting the more important than reduced preda numbers of smaller Díptera, such as tor-prey interaction ; however, further the psychodids, from colonizing drop experimental evidence is needed to pings in the totally cleared pasture. confirm this hypothesis. Precipitation appeared to have the greatest influence on species coloniza Discussion of Diversity and tion when it was raining at the time Abundance Analyses the pats were dropped. This prohib Major differences in the number of ited many species, especially the Díp individuals/pat, as well as in the num tera, from colonizing the dung. Díp ber of species/pat, between pastures tera also appeared to be excluded from were due mainly to a combination of cowpats during cloudy, overcast days, interacting loco- and microclimatologi- or during unsettled weather condi cal factors associated with the envi tions. The frequent changes in climatic ronment of the different pastures. conditions and their effects on the These differences were most evident numbers and species of insects colon during the summer months when high izing droppings, provided a source of temperatures prevailed (Figs. 8A-8E). variability which was difficult to Because of the absence of shade or evaluate. cover in the totally cleared pasture, The variability of cattle dung (for there was greater insolation and age composition and moisture content) higher air temperatures, resulting in has been shown to have some effect on higher soil temperatures and a higher species colonization and development evaporative loss of soil and pat mois (Bay et al. 1969, Hughes and Walker ture. These conditions, and the lack 1970, Greenham 1972a). In the present of transpiration from the dry herba study, the greatest differences in pat ceous plant cover during the sum moisture occurred between the irri mer, led to a much lower humidity gated and rangeland pastures during near the ground than in other pas the late spring and summer. Pats HILGAEDIA · Vol. 45, No. 2 · May, 1977 59 dropped in the irrigated pasture con NUMBERS tained 86 to 93% moisture, whereas BIOMASS those dropped in the drier pastures contained 79 to 85% moisture. This was primarily due to the higher water content of the soil and vegetation (perennial grasses and clovers) in the irrigated pasture. Cattle on rangeland were usually provided supplemental feed (cotton seed meal and barley) during this period. Preliminary experi ments on the variability of cattle dung (Anderson and Merritt, unpublished data) indicated that moisture content had a greater effect on species coloniza tion than did forage composition. The mean dominance diversity 0 1 1 1 1 1 1 1 1 ι 1 1 i— changes in numbers of individuals/pat JJASONDJFMAM and insect biomass/pat in the four dif MONTHS (1972-73) ferent pasture systems during 1972- J. 73 are shown in Fig. 12. During the Fig. 12. Graph of diversity index ^ nx/n log summer, the diversity values for both nj/n when basic data were numbers of individ uals/pat ( ), and biomass units in numbers and biomass were relatively mg/pat ( ) in four different high, and only minor differences oc pasture ecosystems during 1972-73. curred between them, indicating rela tive uniformity in the proportionment which accounted for the increase in of individuals and biomass among spe number and biomass community diver cies in all four pastures. During the sity in February in the drier pastures fall (October, November) there were (NW, PC, TC). Yet, in the irrigated marked differences between biomass pasture, there was a sharp decline in and numbers diversity estimates in all community diversity in the numbers but the irrigated pasture. These differ of individuals/pat. This was due to the ences were due to colonization in all mass colonization of pats during Feb pastures by large numbers of A. ftrne- ruary and March by the Psychodidae. tarius, which reduced community bio They did not colonize droppings in the mass diversity. In the irrigated pas wooded pastures until March, as evi ture, community diversity in numbers denced by the sharp decline in these was also low, due mainly to the high two pastures (NW, PC) during that density of psychodids colonizing drop month (Fig. 12). Since the Psycho pings in October and November. Dur didae colonized very few droppings in ing the winter, community diversity the totally cleared pasture, diversity was generally low in numbers and bio in numbers did not decline sharply in mass, as fewer species and individuals the early spring. Community diversity colonized the droppings. However, in in numbers increased in all pastures January, large numbers of A. fime- during late spring and was attribu tarius inhabited droppings in the irri table to the greater number of species gated and totally cleared pastures, colonizing droppings, and to the more lowering the biomass diversity esti even distribution of individuals among mates. A greater number of species species. The large numbers of psycho colonized droppings during the spring, dids colonizing droppings in the 60 Merritt and Anderson : Insects in Cattle Droppings spring had little effect on the commu north central California, which led to nity biomass diversity in all pastures. the rapid desiccation and hardening The decline in biomass values in May, of the cowpats, particularly during the especially in the natural woodland and warmer months. These conditions totally cleared pastures, was due to the would inhibit bacterial and fungal de late spring emergence and subsequent composition. invasion of pats by A. fimetarius The effects of insects on pat degra• adults. dation.—The majority of insect spe cies which colonized or inhabited drop Pat Degradation pings had a synergistic effect on the The rate of pat degradation, as af process of pat degradation. This usu fected by insects and four different pas ally resulted from their many tunnels ture management systems, was moni promoting (enhancing) and acceler tored over a 3-yr period (1971-73). ating aeration and desiccation of the Several other groups of animals were solid, intact pat, and allowing vegeta also associated with the droppings. In tion to grow through the dropping. frequently, skunks had turned pats over This process eventually contributed to and dug through them, apparently its physical breakdown and disappear searching for insects. Also, earthworms ance. The extent to which different were occasionally found beneath pats species contributed to pat degradation during winter, but contributed little depended on numerous factors, such to pat degradation. One species of bird, as the number, size, and develop the western meadowlark (Sturnella ne- mental stage of the insect colonizing glecta), contributed significantly to droppings, as well as on the behavior pat degradation during the winter of a particular species inside the drop months (November to February) (An ping. Since many species colonized derson and Merritt, 1977). Large droppings concurrently, it was often flocks of this species aggregated in difficult to determine the effects of any open pastures, and individual birds one species on pat degradation, espe pecked cattle droppings apart in cially if the effects were minimal. search of seeds and insects. These ac The smaller Díptera (Nematocera, tivities accelerated disruption of the Sepsidae, most Sphaeroceridae), al intact pat and hastened revegetation. though often more abundant, contrib Cattle occasionally trampled their own uted less to pat degradation than did droppings, sometimes disrupting the the larger Díptera (Anthomyiidae, pat completely. Such an occurrence Muscidae, Sarcophagidae). Large was related to the number of cattle numbers of psychodids and sphaero- present, pasture size, and pat degrada cerids colonized droppings in the fall ; tion rate in the particular pasture. however, the additional time required Trampling occurred mainly in the ir for pat degradation during this sea rigated pasture, where 35 to 40 head son indicated they had little effect on of cattle were sometimes confined to the degradation process (Figs. 13A- an 8- to 16-hectare pasture for short 13C). Also, the insecticide-treated deg periods of time. The slower degrada radation pats placed out during the tion rates of the cattle droppings fall that excluded insects degraded treated with insecticide to exclude in approximately as fast as naturally sects indicated that micro-organisms dropped pats. During early spring did not play an important role in the (mid-February), numerous pats were process of pat degradation. This was abundantly colonized by the large- probably attributable to the climate of bodied larvae of two anthomyiid spe- HILGAEDIA · Vol. 45, No. 2 · May, 1977 61 cies, Scatophaga stecoraria and S. fur- TOTALLY CLEARED PASTURE (TC) cata (100 to 300 individuals/pat). c (12/358/281) These larvae contributed to pat degra 40 "90* dation by aerating and desiccating the 36 dung through their foraging and feed (8/362/1035) 32 100% ing activities, which allowed sprouting 90% vegetation in the spring to grow 28 - through the dropping. Other species 24 "äwi (16/661/794) "«% of Díptera which appeared to have a 20 synergistic effect on pat degradation 100% (14/578/5064) 16 during times of high abundance were 100% Orthellia caesarion, Ravinia spp., and I 2- 'ffoK ed* "β%Η "¿bV Hylemya cinerella. In contrast, Papp Θ "Í9% "40% [9%Γ "iö% (1971) noted that in Hungary the 4 Sepsidae, Sphaeroceridae, and certain [ "9%^ "20% Muscidae played the most important FEB-APR MAY JUN-SEP 0CT-JAN MONTHS OF PAT DEPOSITION ß Figs. 13A-13C. Minimum pat degradation IRRIGATED PASTURE (I) rates in the (A) irrigated, (B) wooded, and (C) totally cleared pastures. The numbers in (18/614/642) parentheses represent the mean no. species/ 9h ΚΧΛϋ (8/M0I/665) pat, mean no. of individuals/pat, mean insect biomass/pat, respectively. lOOHJ
(18/3259/692) role in promoting the desiccation and 6h ,00Ή (Ι9/Ι242/2559) breakdown of the dung. Among the Coleóptera, the role of the Staphylinidae in pat degradation was the most difficult to determine, be cause many species were not confined to cow dung and inhabited droppings for only short periods of time. Most species contributed to the aeration of the dropping through their constant WOODED PASTURES (NW.PC) D prey-searching behavior in and be- neath the dung. The Hydrophilidae
(15/524/308) (mainly Sphaeridium spp.) appeared 33 100% to have a greater effect on pat degra 30 - dation than did the Staphylinidae. (8/277/646) 27 - Adults of Sphaeridium were active 100% 24 burrowers in cowpats, and contributed "90% to the aeration and desiccation of the 21 ~ (21/1770/821) "β9% dropping by producing tunnels which 18 100% (18/619/2890) originated at the surface of the dung (Fig. 14E), a phenomenon observed 15 - 100% by other investigators (Mohr 1943, 12 - To% "«49% Saunders and Dobson 1966). These 9 - tunnels also aided staphilinids and
6 - "30% 99% "9%" "20% parasitic Hymenoptera in locating 3 prey in the droppings, and opened the 7o% "¿JWfc n ' dung pats to invasion by saprophytic 62 Merritt and Anderson : Insects in Cattle Droppings fungi and other microorganisms (Mc- There was a nonsignificant inverse Daniel et al. 1971, Gary and Wingo relationship between the time required 1971). Under Sierra Nevada foothill for a pat to break down and the in conditions, the burrowing activity of sect biomass/pat (Figs. 13A-13C). Sphaeridium spp. was greatest during This was due to the variability asso the late spring and early summer. Con ciated with the season of the year and siderable numbers of Cercyon (two the pasture in which the pat was species) colonized the droppings; but, dropped. due to their small size (2 to 3 mm), it The effects of different pasture man• was difficult to determine their exact agement systems and seasonality on role in degradation, although they ap pat degradation.—The season of the peared to aid in the internal aeration year and the type of pasture in which of the dropping. the pat was dropped had a greater The greatest physical changes in the effect than insects in determining the dropping were caused by colonization rate of pat degradation. Pats dropped by the scarab, Aphodius fimetarius. in the irrigated pasture had the fastest Other aphodines inhabited dung dur degradation rate, sometimes requiring ing different times of the year, but not only 5 months for complete breakdown all species passed their life stages in (Fig. 13A). Perennial grasses grew the droppings. Larvae of A. fimetarius continually from spring through fall, occurred in droppings in both winter but there was little or no growth dur and spring. During the time of larval ing the winter. Due to this lush vege growth, they produced, by ingestion tation and the lococlimatic factors and excretion, a frass-like material which existed in the irrigated pasture, which was easily separated from the cattle excreted pats with a high mois hardened pat covering. A substantial ture content which remained moist for amount of this material from such 2 to 3 months in the field. This promoted pats could easily be blown and scat further insect development and tunnel tered by the wind during the remain ling, and enabled newly sprouting vege der of the year, or be worked into the tation to grow through the pat more soil by the fall-winter rains, leaving easily and at a faster rate than in other only the pat crust to be further de pastures. After one month, pats dropped graded. Also, the loose frass-like ma in the irrigated pasture during the terial allowed vegetation to grow spring had vegetation growing through through the dropping, thus aiding pat them and 25% of the surface area de breakdown. graded (Fig. 14A). After 6 months, The most important effect on pat pats had decomposed to the point that a degradation by A. fimetarius occurred fine sawdust-like detritus remained on during May. At this time, large num the soil surface, and vegetation com bers of adults emerged from older pletely covered the area of the drop droppings and reinvaded freshly ping. dropped pats (200 to 600 individuals/ Since pat degradation rates were pat). Their foraging behavior in the quite similar for the natural woodland dung resulted in the physical disrup and partially cleared pastures, the tion of the intact pat (Figs. 14C,D), data were combined for these two and led to a faster rate of pat degra pastures (Fig. 13B). Compared to the dation in all pastures. A more detailed irrigated pasture, pat degradation analysis of pat degradation activities was slow in the wooded pastures. A of A. fimetarius will be treated else pat dropped during the summer in the where (Merritt and Anderson, in wooded pastures took 30 to 33 months prep.). for complete degradation. Twelve HILGABDIA · Vol. 45, No. 2 · May, 1977 63
Figs. 14A-E. Degradation pats at various stages of breakdown. (A) Untreated degradation pat. Pasture: (I). Date placed out: II-9-72. Date photo taken: III-21-72. Time elapsed: 1 month. Percent degradation: 25%. Crust of pat breaking apart due to newly sprouted vegetation growing through. Pat also breaking down around edges. (B) Untreated degradation pat. Pasture: (I) Date placed out: 11-19-72. Date photo taken: V-21-72. Time elapsed: 3 months. Percent degrada tion: 75%. Only 25% of the pat surface area remained with vegetation growing through the drop ping. Visual evidence of fine sawdust-like detritus which can be blown away or worked into the soil. (C) Untreated degradation pat. Pasture: (TC). Date placed out: V-23-72. Date photo taken: VII-7-72. Time elapsed: 45 days. Percent degradation: 20%. The disruption of the intact pat caused by A. fimetarms adults. (D) Insecticide-treated degredation pat. Pasture: (TC). Date placed out: V-23-72. Date photo taken: VII-7-72. Time elapsed: 45 days. Percent degradation: 1-2%. Insecticide excluded insects from invading dropping. Compare with untreated degradation pat dropped on same date (Fig. 14C). (E) A 4-day-old pat dropped in the irrigated pasture during May 1973 showing holes through the pat surface made by adults of Sphaeridmm spp. and A. fimetarius. 64 Merritt and Anderson : Insects in Cattle Droppings months after an experimental pat was weather followed the deposition of the dropped, 90% of it still remained in dung, particularly in the summer and tact. The 10% loss was largely due to fall. Vegetation was not able to grow the mechanical shrinkage around the through the pat the following spring, edges of the dropping as moisture thus impeding any mechanical break evaporated. After 20 months, the pat down of the dropping. After on-site was 30% degraded, due partly to the study of pat degradation rates over cracking of the hardened crust as a time, and examination of photographs result of intermittent freezing and of the droppings, it was apparent that thawing during the winter. This al once the intact pat was broken apart, lowed rain to penetrate the cracks and the process of degradation occurred at permitted some new growth of vegeta a faster rate. Such nondegraded cow- tion through the dropping and around pats existed in the totally cleared pas the edges. Also, small fragments which ture and prevented the growth of new had broken off the dropping (after forage during two, and in some cases the weathering effect of rain, wind, three growing seasons. The time re freezing, and thawing) were blown quired for formation of the pat crust away or worked into the soil. After and subsequent desiccation and hard 2.5 yr, approximately 10% of the pat ening of the dropping, was largely in remained intact, and vegetation had fluenced by the lococlimatic conditions almost grown completely over the in the particular pasture. area. Pats dropped during the spring Pats dropped in the totally cleared (February to May) had the fastest pasture took the longest time to break degradation time in all four pastures down, sometimes 3 to 4 yr if they were (Figs. 13A-13C). This was due pri dropped during the summer (Fig. marily to the herbaceous vegetation 13C). The process of pat degradation which achieved its maximum growth in the totally cleared pastures was during the spring, usually concurrent similar to that in the wooded pastures. with continued seasonal rainfall. Due The slower pat degradation rates in to the favorable lococlimatic condi these pastures were due primarily to tions in all pastures, pats remained the seasonal growth cycle of the pre relatively moist for 3 to 6 weeks with dominately annual vegetation, and the out formation of a hard crust. Also, microclimate of the pat. The annual the greatest insect biomass per pat grasses are limited to one peak grow occurred in the spring (Figs. 13A- ing season during the spring. Pats 13C), and this contributed to the aera dropped in these pastures during other tion, desiccation, and, in the case of times of the year did not have the A. fimetarius, the partial breakdown of synergistic effect of sprouting vegeta the dropping. This combination of fac tion to break apart the droppings. tors allowed vegetation to grow Also, the dry consistency of the drop through the droppings and disrupt the pings in the drier pastures during the intact pat at a faster rate than at any summer and fall favored rapid crust other time during the year. formation. Unless the degradation Pats dropped during the summer process was initiated by insects such took the longest time to break down as A. fimetarius in the late spring in all four pastures. In the drier pas (Fig. 14C), a hard crust formed on tures, the dead annual vegetation, the pat within a few days, followed rapid desiccation of the droppings, by the desiccation and hardening of and the smaller numbers of individ the solid, intact dropping (Fig. 14D). uals colonizing pats resulted in slower This condition occurred when dry degradation rates. HILGAEDIA · Vol. 45, No. 2 · May, 1977 65 Since the times required for pats to havior, as did the larger numbers break down during the fall or winter found in cowpats in late spring. were similar in each pasture, the data Precipitation appeared to acceler were combined for these two seasons ate the rate of pat degradation if it (Figs. 13A-13C). Pat degradation was immediately followed pat deposition. relatively slow during this time of Formation of a hard crust before pre year, requiring 2 to 3 yr for complete cipitation decreased the eroding effect breakdown in the drier pastures. A of rain. These findings were similar to fall emergence peak of insects, con those of Weeda (1967) and MacDi- sisting mainly of the Nematocera, oc curred in all pastures; yet they con armid and Watkin (1972) in New Zea tributed little to pat degradation. land. In a sprinkler-irrigated pasture From October through December, at the SFRFS pats disappeared com feeding and ovipositing adults of A. pletely by 8 weeks. This was primarily fimetarius inhabited droppings for sev due to the intermittent sprinkling and eral days, which accounted for the subsequent penetration of water on high biomass values in specific pas freshly dropped pats, which often pre tures. However, they did not disrupt vented the formation of a hard pat the dropping by their feeding be- crust.
CONCLUSIONS The interacting factors which influ mainly to a combination of interacting ence both the diversity and abundance loco- and microclimatological factors of insect species colonizing dung, and associated with the environment of the rate of pat degradation, are sum different pastures. It appeared that marized in Fig. 15. Economic consid the number of species and individuals erations are important criteria de were highest in areas where environ termining the type of pasture ecosys mental factors were less limiting. In tem on which cattle are grazed. Con ter- and intraspecific competition for sistent with man's tendency to alter food and space were less important existing wildland ecosystems for ag than the loco- and microclimatological ricultural purposes, much of the factors in determining the diversity wooded Sierra Nevada foothills and and abundance of insects colonizing coastal mountain foothills in Califor dung, except during late spring when nia has been completely or partially numerous adults of A. fimetarius in cleared of trees and brush (Cornelius vaded and disrupted the droppings. 1966). This has been done to increase The insect species which contributed forage production and grazing acre most to pat degradation (A. fimetarius age for beef cattle and to improve and Scatophaga spp.) also produced handling of range animals. This study the greatest changes in the total insect revealed that the type of pasture eco biomass/pat, indicating that insect system and the season in which a cow- biomass was more important than the pat was dropped were most important number of species/pat or the number in determining the diversity and of individuals/pat in influencing the abundance of insects colonizing drop rate of pat degradation. However, to pings and the rate of pat degradation. understand changes in community Major differences between pastures in structure and function, it was impor the number of individuals/pat, as well tant to consider species and individu as the number of species/pat were due als as well as biomass. 66 Merritt and Anderson : Insects in Cattle Droppings ECOLOGICAL RELATIONSHIPS
ECONOMIC CONSIDERATIONS 1$)
SPECIES DIVERSITY AND ABUNDANCE OF INSECTS TYPE OF. TIME OF PAT PASTURE* DEPOSITION LOCATION OF DROPPING WITHIN PEST FLY PASTURE POPULATIONS VERTEBRATE ACTIVITY RATE OF PAT DEGRADATION CLIMATIC — _ FACTORS TEMPERATURE FORAGE HUMIDITY MOISTURE CONTENT PRODUCTION RAIN, etc. OF DROPPING — Fig. 15. Ecological relationships of cattle droppings in the pasture ecosystem.
To date, one component overlooked dung (Bornemissza 1970). Our study in the systems approach to manage showed that the establishment of ment of U.S. rangelands and in the totally cleared, dry grassland pastures ecosystem concept of natural resource in California resulted in a general re management (e.g., Lewis 1969, Van duction of the indigenous dung insect Dyne 1966), has been the role of dung- fauna, with a consequent slower rate inhabiting insects. In Australia, soil of cowpat breakdown during 8-10 nutrients and acres of productive pas months of the year, and a loss of pro ture are lost each year because of ductive pasture acreage. This loss was dried-out, nonrecycled cattle drop also cumulative, because nondegraded pings (Bornemissza 1960, Waterhouse 1974). Bornemissza (1960) noted that cowpats in totally cleared pastures cattle dung from five cows would de also smothered new vegetation for crease the effective area of pasture by three or four growing seasons. Some one acre over a period of a year. Scien of the adverse ecological effects asso tists there have undertaken a major ciated with the clearing of wooded research program to evaluate the in foothills in California are reminiscent troduction of exotic beetles as a means of the existing situation in Australia. of accelerating cowpat degradation A primary difference in these two sit (Ferrar 1973, Hughes 1975). This has uations is that in California, man is improved the efficiency of nutrient re creating in part, the same unfavorable cycling, while concurrently reducing situation which the Australians are at populations of pest flies breeding in tempting to correct. HILGARDIA · Vol.45, No. 2 · May, 1977 67
ACKNOWLEDGMENTS Our sincere thanks go to K. W. F. Shon, C. Bennett, R. King, J. Chen, Cummins, W. E. Cooper, and S. P. and P. Kwan. Hubbell for their helpful comments We are grateful to the following and suggestions in the preparation of specialists for their taxonomic deter this manuscript. Our thanks to E. I. minations: J. T. Doyen, L. E. Caltagi- Schlinger, C. A. Raguse, J. T. Doyen, rone, B. Wharton, E. Rogers, (Univer and M. L. Pressick who provided sity of California, Berkeley) ; F. An ideas, advice, and assistance during drews (California Department of Ag the research period. riculture, Sacramento) ; W. Miller We wish to extend thanks to the fol (Danville, California) ; B. Keh (State lowing persons for their assistance and/ Department of Public Health, Berke or advice on various aspects of the ley) ; I. Moore (University of Califor study: H. V. and B. Daly, P. S. Mes nia, Riverside) ; L. W. Quate (Poway, senger, E. S. Sylvester, C. S. Koehler, California) ; K. C. Kim (Pennsylvania E. C. Loomis, W. W. Allen, and S. State University, University Park) ; Gaede. H. C. Huckett (Riverhead, New We would like to acknowledge the York) ; R. E. Woodruff (Florida De following individuals at the Sierra partment of Agriculture, Gainesville) ; Foothills Range Field Station for their and A. Smetana (Entomological Re cooperation and field assistance during search Branch, Ottawa, Ontario). the study: P. Rowell (Station Superin tendent), D. Springsteen, T. Clark, R. This research was supported, in Delmas, E. Coffin, D. Hill, and other part, by a predoctoral traineeship associated staff. from the National Institutes of Health, We thank P. Rauch and D. Tuggle No. AI00218, and the University of for assistance in developing the data California Agricultural Experiment management system for the project, Station. Additional support came from and the following individuals who a Grant-in-Aid of Research from the helped with data processing in various Society of the Sigma Xi and a Chan ways: L. Young, D. Yeirs, V. Lewis, cellor's Patent Fund grant.
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