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An experiment on Geescroft field, Rothamsted, from 1951 to 1954, tested the direct and residual effects of BHC, DDT, aldrin and chlordane applied to control wireworms (Agriotes spp.) in wheat.The treatments applied were BHC seed dressing at 2 oz./bushel of a dressing containing 20 per cent. γ isomer of BHC; BHC 3·5 per cent. dust, combine-drilled to give 3·8–4·0 oz. γ isomer per acre; DDT 5 per cent. dust, combine-drilled to give 7·5 lb./acre technical DDT; aldrin 1·78 per cent. dust, combine-drilled to give 3·56 lb./acre technical aldrin, and chlordane 5 per cent. dust, combine-drilled to give 5 lb./acre chlordane.In the year of application, the first out of old grass, when wireworm attack was slight, the plots treated with BHC, aldrin and chlordane, combine-drilled, gave significantly greater yields than the control plots. In the following year, when wireworm attack was heavier, residual effects on yield were observed on plots initially treated with BHC, DDT, aldrin and chlordane, combine-drilled. In the third year, residual effects on yield were observed on the plots initially treated with BHC, aldrin and chlordane, combine-drilled.No direct or residual effect of BHC seed dressing was observed.The residual effects are closely associated with the effect of the treatments on the wireworm population.The results are compared with those of previous experiments and the increases in yield from the various treatments are discussed briefly.

RESP-3788

SUMMARY Several field experiments at Rothamsted have rotations including plots fallowed before sowing to winter wheat each year, which provide ideal conditions for maintaining infestations of wheat bulb fly (Leptohylemyia coarctata). In eight consecutive years of one experiment, a mean of 13% of the eggs laid on fallows in these rotations eventually survived to become adults. There was a considerable variation between years, ranging from a maximum survival of 28 % to a minimum of 7%. Most deaths occur in the larval stage, and although previous work showed that survival of the larvae increases with the number of shoots available for infestation, much of the variability in survival rates between seasons was apparently caused by other factors, possibly climatic. Eggs laid in fallows were sampled in most years from 1953 to 1972. They varied from 3.57 to 0.02 million/acre (8.81–0.05 million/ha), depending on the season and site; the mean was 1.08 million/acre (2.67 million/ha). Egg populations varied in synchrony at all the three sites studied; there were cycles lasting several years between peaks of abundance or scarcity but there was no consistent tendency for populations to increase or decrease. Fewest eggs were laid when the weather was cold and wet during July and August, i.e. when adults are active. Weather was more closely correlated with the number of eggs laid expressed as a fraction of those laid in the previous year (net reproductive rate) than with the number of eggs laid/acre.

SUMMARY The organophosphorus insecticides Bayer 38156 (O-ethyl S-p-tolyl ethyl phosphonodithioate), trichloronate, Stauffer N 2790 (O-ethyl S-phenyl ethyl phosphonodithioate), thionazin and fenitrothion were compared with aldrin, dieldrin and γ-BHC for their effects on soil fauna, particularly wire-worms, and on crop yields in 1964 and 1965. At 1·5 lb active ingredient/acre, none of the organophosphates had as great an effect on wireworms as an aldrin spray at 2·25 lb a.i./acre or a dieldrin seed dressing at 2·25 lb a.i./acre. Some treatments significantly increased and some significantly decreased numbers of mites and Collembola. Except for Allolobophora chlorotica in plots treated with Bayer 38156, earthworm numbers were greater in plots sprayed with Bayer 38156 or aldrin, or sown with dieldrin-dressed seeds, than in untreated plots. In May 1964, one month after sowing, untreated plots had significantly fewer plants than plots sprayed with aldrin, trichloronate or Bayer 38156, or sown with γ-BHC or dieldrin-dressed seeds, but yields from untreated plots at harvest were high for such a large wireworm population and did not differ significantly from yields of treated plots in either year. The persistence of thionazin and Bayer 38156 in treated plots was measured by a bioassay using Collembola. Bayer 38156 was detected in plots 1 month after spraying but not after 6 months. Thionazin left detectable residues 1 month after spraying in the two acid plots but not in the two alkaline plots. More frequent samples taken from thionazin-treated plots in 1965 showed a similar pattern of persistence, and laboratory tests, using soil mixed with various amounts of powdered calcium carbonate, confirmed that thionazin persisted longer in more acid soils.

SUMMARY Water traps examined weekly were used to assess the activity of adult wheat bulb flies during the oviposition period in late July, August and eariy September. Traps were placed at various distances up to 1 mile (1–6 km) from known sources of infestation at Whittlesey, Cambridgeshire and at Rothamsted. Most flies were caught down wind from possible emergence sites and few were caught more than 1/4-1/2 mile (0.4–0.8 km) away. The distribution of flies between traps was similar in both the first and second halves of the trapping period. At Whittlesey there was a significant positive correlation between the number of flies caught in a trap and the number of eggs laid in the field containing the trap.

Certain of the habits of earthworms make them potential pests of crops. The habit of certain species of seizing fallen leaves and pulling them down through the mouth of their burrows, means that if they seize the leaves of growing plants in this way, they damage the plant, sometimes sufficiently to kill it. Zicsi (1954) reported such damage to various crops, and Edwards (unpublished) noted that earthworms destroyed a large part of a lettuce crop in this manner.

The activities of earthworms that have most influence on soil structure are: (1) Ingestion of soil, partial breakdown of organic matter, intimate mixing of these fractions, and ejection of this material as surface or sub-surface casts. (2) Burrowing through the soil and bringing subsoil to the surface.

Earthworms can be kept in culture in almost any large vessel, provided that it is non-porous (otherwise it will be difficult to keep the soil sufficiently moist) and large enough, its actual size depending on the numbers of worms in the culture. Some species of earthworms produce their normal number of cocoons, only if given more space than they require to live and remain healthy.’ stocks’ of earthworms can be kept in large glazed earthenware pots, about 12 cm diameter and 30 cm deep, with the top covered with muslin, although for experimental purposes, smaller vessels are usually preferable, so that the amount of soil required is not excessive. Glass jars, such as ‘Kilner’ jars, having wide mouths are very suitable for earthworm experiments. Evans and Guild (1948) successfully maintained cultures for the study of cocoon production, with three earthworms per 5-pint (2·85-litre) capacity jar (Lumbricus terrestris), five per 3-pint (1·71-litre) capacity jar (Allolobophora longa) and five per 1-pint (450-ml) jar for smaller species such as Allolobophora caliginosa, Allolobophora chlorotica and Allolobophora rosea. Normally cultures should be kept in a cool building or cellar at a temperature between 10°C and 15°C or buried in soil. The ideal culture medium for most of the common pasture and garden species is a friable loam with 25–30% moisture content (such that it will remain in a ball when lightly squeezed in the hand). Food can be any partly-decomposed plant material, such as moist horse or bullock droppings (if these are dried before use, cocoons introduced with the food material will not be viable), partly rotted straw or tree leaves (not beech leaves).

Scanned PDF of THE INVERTEBRATE FAUNA OF THE PARK GRASS PLOTS I. SOIL FAUNA , part of Rothamsted Experimental Station Report for 1974 Part 2

Wild habitats such as woodlands and grassland usually support a diverse flora and fauna. Even these are used for agriculture, this flora is replaced, either by a few species of plants when grassland is reseeded or by a single species when an arable crop is sown; this, in turn, usually causes a decrease both in the total numbers and species diversity of the animals associated with the flora. Such changes have been thoroughly investigated for the insects that live on the aerial parts of plants, but there have been few experimental investigations of the effect of cultivation on populations of soil animals (Edwards and Lofty, 1969). Although it has been assumed that cultivation decreases numbers and diversity of soil animals, such assumptions have been based on relatively sparse data from surveys of the fauna of different habitats, and may be unjustified because most of them have been based on single population estimates and have taken no account of changes in populations with time.

Plant organic material that reaches the soil is subject to many decomposing agents, including both micro-organisms and animals. Very soft plant and animal residues may be decomposed by the microflora but much organic matter, particularly the tougher plant leaves, stems and root material, does not breakdown without first being disintegrated by soil animals and acted upon by enzymes in their intestines. Earthworms have an important role in this initial process of the cycling of organic matter, because a few common species such as L. terrestris seem to be responsible for a large proportion of the fragmentation of litter in woodlands of the temperate zone. Soils with only few earthworms often have a well- developed layer of undecomposed organic matter lying on the soil surface. Edwards and Heath (1963) showed that in two sites earthworms consumed more oak and beech litter than all the other soil invertebrates together. In apple orchards L. terrestris removed more than 90% of the autumn leaf fall, during the course of the winter; this was calculated to be about 1.2 tonnes of dry weight of leaves per ha of orchard (Raw, 1962) (Fig. 46). The effectiveness of L. terrestris in initiating the fragmentation and incorporation of fallen apple leaves was vividly illustrated by comparing the soil profile and structure of an orchard with a large L. terrestris population, with one in which earthworms were almost totally absent (due to frequent and heavy spraying with a copper-based fungicide). The orchard with few earthworms had an accumulated surface mat, 1–4 cm thick, made up of leaf material in various stages of a very slow decomposition and sharply demarcated from the underlying soil, which had a poor crumb structure (Plate 8).

Scanned PDF of 7. INSECT PESTS ON BROADBALK, part of Rothamsted Experimental Station Report for 1968 - Part 2

During the summer of 1956, a quantitative study of a field population of Wheat Bulb Fly, Leptohylemyia coarctata (Fall.), was carried out at Rothamsted.The work consisted principally of a study of the development and decline of a population of adult flies. This was supplemented by observations on the populations of the immature stages.Emergence was investigated by the use of a cage of fine terylene netting, 24 ft. long, 12 ft. wide, and 6 ft. high. This was erected in an infested wheat field shortly before flies were expected to appear, and was searched twice daily, at 10 a.m. and shortly before sunset.A total of 293 male flies was caught during the 26 days from 24th June to 19th July. Of these, 186 appeared between 1st and 6th July. The highest day's catch was 40 flies on 6th July, by which date (inclusive) about 84 per cent, of the final total had emerged.A total of 258 female flies was caught during the 35 days from 21st June to 25th July. Of these, about half emerged between 6th and 10th July. The highest day's catch was 37 flies on 8th, by which date (inclusive) 66 per cent, of the final total had emerged.Population decrease was investigated by the method of marking and recapture. The newly emerged flies caught in the cage were marked with Artist's oil colours and released in the cage. The colour of the mark was changed daily so that the age of marked flies could be ascertained. A search was made for marked flies every three days and their numbers, marks and sex were recorded. From the recapture figures, estimates of the numbers of flies surviving at different times after marking were obtained. Mortality during the first day was very high, but after this numbers decreased at a steady rate. This initial high mortality was believed to be due to marking. The length of life of marked flies which survived this immediate effect was, however, not impaired, therefore the rate of population decrease was estimated from the recapture figures alone, that is, without reference to the numbers originally marked. The half-life of male and female populations was estimated as 7·3 and 11·1 days, respectively.Application of the estimated rate of population decrease to the observed emergence figures enabled a general picture of the size and structure of the population to be obtained. The predominance of males over females during the early part of the season and the later predominance of females over males were explained.Observations on the populations of the various stages showed that the mortality between pupation and maturation of adults was high, and that the egg populations inside the cage during the autumn of 1956 was only about 1/7th of that of the previous year. This reduction was not observed outside the cage and may have been due to the survival rate and fecundity of the flies being affected by the experiment. Further work will be necessary before this can be elucidated.

It is now well established that grassland usually contains more earthworms than arable land (Tables 5, 7 and 10). This could be due to mechanical damage during cultivation, to the loss of the insulating layer of vegetation, or to a decreased supply of food as the organic matter content gradually decreases. Many workers have considered that these differences are largely due to mechanical damage during cultivation. When old grassland is ploughed, the number of earthworms in it steadily decreases with time after ploughing (Graff, 1953). In one such study (Evans and Guild, 1948), five years after grass was ploughed, the earthworm population had declined by 70%, although the population was unchanged by the first ploughing of the sward, so it is unlikely that mechanical damage was a primary cause of the decreased numbers of worms. Hopp and Hopkins (1946) also reported that cultivation of arable land in late spring did not decrease earthworm numbers. Indeed, it would be surprising if mechanical damage by ploughing was very important, because the plough merely turns the soil over, and probably has little effect on worms with deep burrows. Preparation of seed beds by rotary cultivation, harrowing, disking or rolling can be expected to damage more earthworms, but the regenerative powers of earthworms are so great that only a few would be killed outright. Edwards and Lofty (1971) investigated the effects of maximal and minimal cultivation of grass plots, on earthworm populations. They compared plots ploughed and cultivated in spring with others that were unploughed. The more the soil was cultivated during the first two seasons, the greater was the number and weight of earthworms in the soil (Table 20).

SUMMARY Of sixteen compounds applied to soil in laboratory tests, azinphos-ethyl, P2188 (O,O-diethyl S-chloromethyl phosphorothiolothionate), ‘Dursban’ (O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate), P1973 (S-(N-methoxycarbonyl-N-methylcarbamoylmethyl) dimethyl phosphorothiolothionate), B77488 (O,O-diethylphosphorothioate O-esterwith phenylglyoxylonitrile oxime) and R42211 (O,O-diethyl O-(2-diethylamino-6-methyl-pyrimidin-4-yl) phosphorothioate) killed wireworms when first tested, but in second tests with the same soils only ‘Dursban’, P2188 and B77488 did so. Treating seeds with ‘Dyfonate’ (O-ethyl S-phenyl ethyl phosphonodithioate) or with ethion/γ-BHC mixtures killed few wireworms. Three field trials compared the organophosphorus insecticides ‘Dursban’, ‘Dyfonate’ and phorate with organochlorine standards. In trials with barley and potatoes the standard was 3 lb a.i./acre (3·36 kg/ha) of aldrin. The organophosphorus compounds increased plant stands of barley almost as much as aldrin, although they killed fewer wireworms; and they protected fewer potato tubers from wireworm damage. The third trial compared the organophosphorus compounds with 0·5 lb a.i./acre (0·56 kg/ha) γ-BHC sprayed on a site drilled with sugar beet seed dressed with dieldrin. The γ-BHC increased plant stands almost as much as did 3 lb a.i./acre of the organophosphorus insecticides, and killed as many wireworms.

(1) Earthworm populations in direct drilled and ploughed plots were assessed twice annually for 5 years in a continuous cereal experiment at Woburn. (2) In two other experiments, on continuous cereals at Rothamsted and Boxworth, populations of earthworms were assessed twice annually from the fourth to eighth years of cropping. The cultivations compared were deep ploughing, chisel ploughing and direct drilling. (3) Populations of the deep burrowing earthworms Lumbricus terrestris and Allolobophora longa became much greater in direct drilled than in ploughed plots and, after 8 years of direct drilling, were 17.5 and 37.3 times more numerous than in ploughed plots, at Boxworth and Rothamsted, respectively. Populations of deep burrowing species in chisel ploughed plots were intermediate between those in direct drilled and ploughed plots. By contrast, differences between populations of the shallow working earthworms A. caliginosa and A. chlorotica were much less, the greatest increase in direct drilled plots over ploughed ones being 3.4 times. (4) A survey on Lee Farm in Sussex, of earthworm populations in seven fields that had been direct drilled with cereals for several years and seven fields that had been ploughed and sown with cereals, showed significant differences in populations of L. terrestris and A. longa between ploughed and direct drilled fields but not of A. chlorotica or A. caliginosa. (5) There were significant negative correlations between populations of L. terrestris and A. longa and between those of A. chlorotica and A. caliginosa in the survey.

(1) Intact profiles of soil from a field that had been direct drilled for 5 yr and from the same soil that had been regularly ploughed were sterilized with dichloropropane-dichloropropene (D-D?). (2) After aeration, profiles from the direct drilled soil were inoculated with either Lumbricus terrestris, Allolobophora longa, a mixture of A. caliginosa and A. chlorotica, or a mixture of soil arthropods, in numbers similar to average populations. Two sterilized profiles from direct drilled soil and two from ploughed soil were left without animals. (3) Barley seeds were sown in slits to simulate direct drilling. The numbers of seedlings emerging, heights of plants and oven-dry weights of roots were all greater in the profiles from ploughed soil, and in those from direct drilled soil inoculated with animals, than in those with no animals. (4) Root distributions were closely correlated with the characteristic zones of activity of the animals.

SUMMARY (1) Normal field populations of deep-burrowing or shallow-working earthworms were inoculated into small plots that had been sterilized with dichloropropanedichloropropene (D.D. ?), on a site that had been directly drilled with cereals for six successive years. Inoculation with deep-burrowing species (Lumbricus terrestris and Allolobophora longa) significantly increased barley plant populations and the weight and depth of roots and height and amount of foliage. Most of the straw debris on the soil surface was incorporated into the soil in the earthworm-inoculated plots, compared with very little in plots with no earthworms. Yield was also increased significantly by earthworm inoculation. (2) In box experiments, comparing the influence of natural and simulated earthworm burrows on root growth, it was shown that, although the provision of channels for roots to grow was important, the improved root growth was also partially due to the lining of the burrows with more available nutrients than the surrounding soil. Other experiments demonstrated that the nitrogen from dead earthworms was insufficient to account for increased root growth. Ways of encouraging the build-up of earthworm populations in direct drilled land are discussed.

Fields at Rothamsted were sampled for several years to assess populations of wheat bulb fly eggs and larvae, and populations of wheat plants and shoots. The results were fitted to the regression equation $\log_{10}(S^2) = \log_{10} a + b \log_{10} m$, where $S^2$ is the variance, $a$ is a sampling factor, $b$ the 'index of aggregation' and $m$ is the mean. Randomly-distributed populations have $b = 1$, aggregated populations have $b > 1$, and populations with a tendency towards regular distribution have $b < 1$. Most of the variates had $b$ slightly greater than one, i.e. the populations were only slightly aggregated, and a square root transformation is appropriate for analysis of data from infested fields.