Arthropod Density Research Articles

A Sampling Device for Aquatic Arthropods Active at the Water Surface

A variety of methods has been used for estimating or indexing the densities of aquatic arthropods. The time-honored measure is the mean number of individuals collected in several samples taken with a net or dipper (Boyd 1930, Dixon and Brust 1972). This has the advantage of ease and rapidity but the variance is usually so great that this method is useful only for documenting gross differences in abundance. Some workers have made direct counts of animals trapped in enclosures (Bates 1941, Goodwin and Eyles 1942) or counted all of the animals in a pool by draining and sieving the contents (Christie 1954). These methods are much more reliable but tedious and disruptive. Mark and recapture (Pajunen and Jannson 1969) and removal (Pajunen 1972) methods have also been used but they tend to combine the difficulties of the other methods while adding questionable assumptions (Southwood 1966). The device described here was designed to estimate the relative densities of aquatic arthropods active at the water surface by allowing a count of individuals present or surfacing per unit time within a standard area of the surface. The technical problem was to delimit this area without disturbing the ani*mals.

The distribution and abundance of soil arthropods in the Northern Mojave desert

Arthropods were extracted from soil samples taken from around four perennial plant species in Rock Valley, Nevada, from January to December 1974. The pattern of distribution of the arthropods about the shrubs is described and a model has been constructed to estimate population densities and biomasses. Total arthropod densities ranged from 1600 per m2 in July to 12,400 per m2 in December. Total biomass was also lowest in July, 8·7 mg/m2, and reached 37·2 mg/m2 in May. The majority of animals collected belonged to the Acari, and of these the Cryptostigmata and the prostigmatid families, Nanorchestidae and Tydeidae, were most abundant. Seasonal variations in the distribution patterns are discussed.

The Impact of Zinc Smelter Emissions on Forest Litter Arthropods

Tullgren extractions were used to sample the litter arthropod fauna from mid-August through mid-October in three mixed-oak forest stands located about 1, 6 and 40 km from a zinc smelter in Pennsylvania. Mean arthropod density (n mn2) was estimated to be about 35000 at the 1-km site, about 72000 at 6 km, and about 161000 at the 40-km control site. Densities of all major taxonomic groups were lower near the smelter, with oribatid mites showing the greatest absolute decrease. Measurements of CO2 evolution were made on 02 litter samples and indicated that soil respiration rates were highest at the 40-km site and significantly less at both the 6-km and 1-km sites. Mean concentrations of about 26000 ppm Zn, 10000 ppm Fe, 2300 ppm Pb, 900 ppm Cd, 340 ppm Cu and 0.40% S were measured in the 02 litter layer at the 1-km site. Mean concentrations at 6 km were about 15000 ppm Zn, 6500 ppm Fe, 970 ppm Pb, 250 ppm Cd, 170 ppm Cu and 0.26% S. Mean concentrations from the control site (40 km) were 2800 ppm Fe, 650 ppm Zn, 260 ppm Pb, 50 ppm Cu, 9 ppm Cd and 0.13% S.

Faunal communities of the field stratum and their succession in reserved fields

The arthropod of the field stratum and small mammal fauna of 51 reserved fields were studied in Central Finland in 1974. In high summer the arthropod density was on the average 210 individuals/m2, of which Auchenorrhyncha formed 42 %, Hymenoptera 18 %, Coleoptera 14 %, and others 26 %. Arthropods were more abundant in fields that had been reserved after leys than in fields after open cultivations. The abundance of most arthropod taxa increased as the time in reservation increased. However, the abundance of most pests of any significance decreased with years. Sorex araneus L. and Microtus agrestis L. formed almost 90 % of the small mammal fauna of the fields. Their abundance was on the average much less than in the Scots pine seed orchards nearby. The leafhopper faunas were divided into three communities. One appeared in young (1st —3rd year) fields, and the other two in older (2nd—6th year) fields, one in dry and one in moist fields. The Apion fauna was divided into four communities. The dependence of the described arthropod communities on the vegetational communities of the fields was weak, although some relationships were observable.

Seasonal density, distribution and interactions of predatory and scavenger arthropods in accumulating poultry wastes in coastal and interior Southern California

Seasonal predatory and scavenger arthropod densities were studied at interior and coastal southern California poultry ranches. Though some seasonal population clumping occurred with some species, the distribution of predators and scavengers was fairly uniform within each ranch. Correlation analyses of key predators in theHisteridae, Staphylinidae, Hydrophylidae andDermaptera with the potential hosts,Musca domestica L.,Tinea fuscipunctellaHaworth, andFannia spp. suggested that predator activity was seasonally influenced. Possible periodic avoidance of a particular host's habitat was detected as significant negative correlations. The data tend to support the importance of different species of predators in different seasons and the need for natural enemy complexes rather than single species for biological control.

Effects of Insecticidal Placement on Non-Target Arthropods in the Peanut Ecosystem1

Abstract Three methods of applying insecticides to irrigated peanuts for soil insect suppression were compared to evaluate their impact on non-target arthropods. Insecticides were applied as basal directed sprays, broadcast sprays and granules. D-vac suction samples were utilized to compare population densities of non-target arthropods at regular intervals after insecticide application. All application methods showed immediate reductions in most non-target arthropod populations. Granular insecticide applications had the least detrimental impact on non-target arthropods and broadcast sprays the greatest.

Litterbag Studies of Microarthropod Populations in Three South Carolina Old Fields

Microarthropod population diversity, distribution, and species composition were studied in three South Carolina old fields with the use of fiberglass—mesh litterbags. Mean total arthropod densities were highest in a 1st—year successional field (abandoned cornfield), lowest in a 12—year broomsedge field, and intermediate in a 12—year lespedeza field. Densities differed significantly with season, field, and litter type within field. Litter moisture content also differed significantly with these factors and changes in moisture were correlated with changes in density or microarthropods. Both species diversity and species composition differed significantly between fields, but litter type had no significant effect. Conclusions were (1) the litter fauna is a transient subset of a larger and possibly more diverse soil fauna, present in the litter only during favorable moisture regimes; (2) species diversity and composition of the litter fauna are determined primarily by the successional stage of the field and are affected little by the introduction of allochthonous litter in the small amounts contained in the decimeter—square litterbags used in this study.

Soil Acari and Collembola Populations Affected by Logging and Slash Burning in a Coastal British Columbia Coniferous Forest 1

Acari and Collembola in soil from 3 differently treated adjacent areas—forest, clear–cut, and slash-burned—were sampled monthly for 1 year in the 2nd year after logging and slash burning. Samples were separated into 5 levels: litter, and four 225.8-cm2 (35 in.3) soil layers, each 2.54 cm (1 in.) deeper than the preceding one. Organisms were extracted for 10 days in modified Tullgren funnels, preserved in ethanol at 4°C, and identified using published keys. Densities of organisms were transformed using log10 X + 1, and subjected to an analysis of variance. No seasonal fluctuations were found in any of the 3 areas. There was no correlation of density with soil moisture, p H , or temperature. Vegetation in the logged area differed considerably from that in the burned area. Density of Acari, Collembola, and other arthropods was reduced by logging and further by slash burning. The population levels and diversity in both logged and burned areas were relatively high, indicating that neither treatment induced total mortality, and/or there was rapid reinvasion of treated areas. For the Cryptostigmata, the population reduction posttreatment became less with depth. Density of Astigmata, Prostigmata, Mesostigmata, and Collembola in the family Isotomidae in the litter and the first 2 levels of soil was progressively reduced by logging and slash burning, but in the 3rd and 4th soil levels, density was increased, indicating that migration to deeper levels or adaptation to conditions further below the surface had occurred.

The Effects of Two Acute Stresses on the Arthropod Component of an Experimental Grassland Ecosystem.

The effects of two acute stresses, mowing and burning, on the arthropod component of an experimental grassland ecosystem were investigated. Oats (Avena sativa L.) were planted in two comparable and adjacent 1-acre areas. Midway in the growing season (July), one area was mowed and the other areas was both mowed and burned. Density and biomass were used to measure the effects of both stresses on the total arthropod community, while species diversity and equitability were used to analyze the species composition and apportionment of the Coleoptera. Effects of mowing on arthropod density and biomass appeared to be relatively brief (2 weeks) as compared with those of burning (3 months). This difference was attributed to a shift from live primary producer energy to detritus in the mowed area, as compared to the almost complete destruction of the energy source in the burned area. Coleoptera species/area diversity was significantly lower (P < 0.01) in the burned area. This was attributed to a greater energy supply and a larger number of ecological niches in the unburned grid. Margalef's species diversity, D = (S-1)/1nN, for the total Coleoptera community was significantly reduced (P < 0.05) in response to the fire. When analyzed by trophic levels on a long-term basis, herbivorous Coleoptera species diversity was significantly reduced (P < 0.01), whereas that of the carnivorous Coleoptera was not measurably affected. Herbivorous Coleoptera equitability values, in response to mowing, exhibited a brief increase before returning to the premow level. In response to burning, however, herbivorous Coleoptera equitability values remained higher than those in the unburned area, indicating a longterm limitation of resources. Carnivore equitability values did not exhibit a long-term increase in response to the fire stress. Coleoptera responses to fire revealed that biomass, species/area diversity, and primary consumer species diversity and equitability were the most sensitive indicators for evaluating the effects of an acute environmental stress such as fire. Coleoptera responses appeared to be representative of the total arthropod community.

Energy and Nutrient Dynamics of Spider and Orthopteran Populations in a Grassland Ecosystem

Population dynamics, energy budgets, and nutrient concentrations were used to develop a compartment model for evaluating energy flow and nutrient fluxes in the spider and orthopteran components of an eastern Tennessee grassland ecosystem. The arthropod community consisted of; herbivores–Melanoplus sanguinipes (Acrididae), Conocephalus fasciatus (Tettigoniidae), and several of the Homoptera—Hemiptera; omnivore–Pteronemobius fasciatus (Gryllidae); and predators–Lycosa spp. (Lycosidae). Weekly estimates of arthropod density and biomass and monthly estimates of vegetation biomass were made during the 1965—69 growing season. Supporting studies included: (1) determination of caloric equivalents; (2) measurements of arthropod metabolism; (3) determination of whole—body concentrations of Na, Ca, and K; (4) estimation of biological turnover rates of these nutrients with radioactive analogues; and (5) field studies of arthropod feeding habits and food consumption. Total net primary production of the grassland ecosystem was 1,274 kcal/m2; 89% of this total was by grass species (Festuca arundinacea and Andropogon virginicus) and 11% by green forbs. Herbivores and omnivores consumed 9.6% (122.9 kcal/m2) of net primary production. Annual net secondary production by the insect community was 32.05 kcal/m2. Total net tertiary production by spiders was 2.26 kcal/m2. Total annual energy flow (= total assimilation) through the community was 75.6 kcal/m2. Herbivores accounted for 79.8% of this total, omnivores 12.2%, and predators 8.1%. Whole—body concentrations of sodium increased with higher trophic position in the food chain: vegetation (0.43 mg/g ash free dry wt = AFDW), prey (1.18 mg/g AFDW), and predators (1.94 mg/g AFDW). Calcium concentrations decreased from vegetation (5.82 mg/g AFDW) to prey (0.85 mg/g AFDW) and remained constant to predators (0.88 mg/g AFDW). Potassium concentrations were much higher in vegetation (14.28 mg/g AFDW) than in either the prey (1.87 mg/g AFDW) or predators (1.96 mg/g AFDW), which were essentially the same. Sodium and potassium behaved similarly in their movement through arthropod food chains. The low concentrations of calcium in arthropod trophic levels and the rapid elimination of this element from each trophic level suggest that calcium is not as limiting as are sodium and potassium in this arthropod community. Herbivores, the dominant members of the arthropod fauna, attained a maximum standing crop of 927 mg/m2 (Melanoplus = 705 mg/m2, Conocephalus = 200 mg/m2, and the Homoptera—Hemiptera = 22 mg/m2). This trophic level was responsible for 85% of the sodium turnover, 76% of the calcium turnover, and 78% of the potassium turnover by the arthropod component of the ecosystem. The omnivore Pteronemobius fed equally well on fresh vegetation and on litter. It reached a maximum biomass of 194 mg/m2 and utilized 10% of the sodium, 22% of the calcium, and 20% of the potassium which passed through the arthropod community. The predator (Lycosa spp.) biomass reached a maximum of 146 mg/m2 in late fall and was responsible for 5% of the sodium, 2% of the calcium, and 2% of the potassium utilized by the arthropod component of the ecosystem. Wolf spiders consumed 21% of total net secondary production. Absence of other predator species in collections from the arthropod community suggests that Lycosa was the dominant invertebrate predator in this grassland ecosystem.

The Effects of an Acute Insecticide Stress on a Semi‐Enclosed Grassland Ecosystem

The effects of a carbamate insecticide, Sevin, on plant, arthropod, and mammal components within a grain crop grassland ecosystem were investigated. A single application of 2 lb. of the insecticide was applied in July to 1 of 2 comparable and adjacent once—acre fenced enclosures, each planted in a crop of millet (Panicum ramosum) and stocked with three species of small mammals, the cotton rat (Sigmodon hispidus), the house mouse (Mus musculus) and the old—field mouse (Peromyscus polionotus). Intensive and frequent sampling of plants, arthropods, and mammals on both control and treated enclosures provided the data for evaluating the effects of the insecticide on productivity, density, diversity, and equitability of the three components. Sevin residues on plants decreased rapidly from 35 ppm on the first day following spraying to 0.37 ppm on the 16th day. No effect of the insecticide could be detected on producer standing crop or net community primary production which averaged for the two areas 567 g dry wt/m2 for season or 3.96 g/day. A highly significant decrease in litter decomposition in the treated area was measured 3 weeks after spraying, presumed to be the result of a reduction in microarthropods and other decomposers. The total biomass and numbers of arthropods were reduced more than 95% in the treated area and remained well below the control area for 5 weeks; after 7 weeks total biomass but not total numbers returned to the control level. Photophagous insects (Homoptera and phytophagous Hemiptera were dominant at the time of spraying) were more severely affected than predaceous insects and spiders; density of the latter returned to control levels in 3 weeks. Species—numbers diversity in terms of S—1/1nN also was markedly reduced in all orders of insects immediately after treatment, but with the exception of the Hemiptera and Hymenoptera, returned to control levels within 1—2 weeks. Diversity in spiders was not affected by the treatment, even though numbers were reduced. In terms of trophic groupings, species diversity of phytophagous insects, although more severely reduced, "recovered" more quickly than did diversity in predaceous insects. The equitability index of Lloyd and Ghelardi (1964), in contrast to species/numbers diversity, tended to rise 1 to 3 weeks after treatment, especially in the phytophagous insect group. In terms of the seasonal succession, equitability index values for the predator populations increased to about 1.0 while that of herbivores remained at lower levels of 0.5 to 0.6 throughout the study on the control area, suggesting that predators tended to be food limited and to occupy non—overlapping niches. Cotton rat reproduction was delayed with ultimate density reduced in the treated grid; laboratory tests indicated this was a probable direct effect of the insecticide. However the total mammal population, which grew in sigmoid fashion to an asymptotic level of about 180/acre in both grids, was not affected by the treatment because there was a compensatory increase in the house mouse population in the treated grid. In summary, although the insecticide remained toxic in the environment for only a few days, long—term side effects on litter decomposition, arthropod density and diversity, and mammalian reproduction were demonstrated. It is hoped that this study will provide a model for an ecosystem approach to the testing of pesticides.

The Insect Ecology of Red Pine Plantations in Central Ontario: IV. The Crown Fauna

AbstractThe faunal changes in the crown stratum of a newly established red pine plantation were observed during the first five years of growth. The crown faunae of three older stands planted in 1950, 1939, and 1929 were sampled throughout the growing seasons of four consecutive years by a technique employing pyrethrum insecticide.The stands represent four stages in the development of a red pine community over a period of 35 years, and the presence, distribution, density, annual and seasonal fluctuations, species succession, and food relations of arthropod taxa are discussed.Species colonizing trees in the establishment stage are largely replaced in the transition stage by a species-complex that persists throughout the succeeding monoculture and young-forest stages. Arthropod density in relation to crown size increases rapidly until the trees are about 15 years of age, and then declines. The pattern of seasonal abundance is dominated by a few species. The ratio between parasite–predator and prey species remains remarkably stable throughout the three older stages of the community.

Bedeutung der Indifferenten Arthropoden in Obstanlagen

About 50% of all Arthropods living in the crown of untreated apple trees are so called “indifferent” species, that is to say they are neither useful nor noxious to the apple tree. The most frequent and most important of these Arthropods are listed in this paper. These indifferent species however are of great importance in limiting the population density of the noxious Arthropods by interspecific competition and influencing the stability of the biocoenosis. This and also other facts point to a useful tendency of these indifferent species within the fauna of an apple tree. In any case they should not be neglected in investigations on population dynamics.

The Influence of Spray Programs on the Fauna of Apple Orchards in Nova Scotia. VII. Effects on Some Beneficial Arthropods

The toxicities of a large number of spray chemicals to arthropod pests are well known. In most instances, observations on the effects of such materials on natural enemies have beeen incidental to other studies, and little has been published on experiments designed to determine the direct toxicities of the chemicals to beneficial species. The effects of spray chemicals on the predators and parasites of the major pests of apple trees in Nova Scotia have been investigated as part of a broader project on the factors that influence population densities of orchard arthropods, as outlined by Pickett et al. (31).