Field boundaries play an important role as refuges, food sources and corridors for invertebrates and vertebrates, and increasing farmland fragmentation impacts on these functions. However, hedgerows and other structures can also impede dispersal by flying insects. The current work uses the pollen of Phacelia tanacetifolia in hover fly guts as a marker to assess hover fly movement in farm landscapes. In the United Kingdom and New Zealand, Phacelia pollen was found in the guts of Ephisyrphus balteatus and Metasyrphus corollae (United Kingdom) and Melanostoma fasciatum (New Zealand) at distances up to 200 m from the source, when there were no barriers between the flowers and the traps used to catch the flies. The rate of decline over distance in the proportion of flies containing pollen was similar for the two countries. The extent to which four replicated field boundary types impeded hover fly movement was tested using post-and-wire fences, lines of poplars (Populus spp.) with gaps, dense poplars and controls (no potential barriers). Phacelia was planted on one side of each boundary, and along the centre of the control plots. The relative presence of the pollen in flies on both sides of the barriers showed that both types of poplar boundary restricted the movement of the flies, but the fence had no effect. In a separate experiment, gravid females of M. fasciatum were captured at a greater height on a shade-cloth fence than were non-gravid females and males. The implications of this work include the functioning and persistence of metapopulations and the influence of field boundaries on population recovery of beneficial invertebrates following pesticide-induced mortality. If field boundaries contribute to a temporal asynchrony between pest and natural enemy populations, this needs to be considered along with the well-established roles of boundaries as refugia for, and sources of, beneficial arthropods.

There has been little study on the growth and morphology of individual plants constituting the population of white clover in mixed swards under grazing. Such information is required if the mechanisms governing plant productivity and persistence are to be understood.Intact white clover plants were sampled from intensively sheep-grazed pastures under set stocking, rotational grazing, and a combination of both systems, by taking turves (250 x 250 mm), and washing out the plants, every month for a year. Characters measured for every stolon of each plant were: presence of a growing point; numbers of leaves, roots and axillary buds; stolon length. Total plant leaf and stolon dry weight were also recorded. Plants were classified according to degree of branching, and the contribution of each branching order to the population determined.There were strong seasonal variations in plant size (leaf and stolon dry weight, stolon length, and numbers of stolons and leaves per plant) which showed a significant decrease in spring with recovery over the following summer. This was paralleled by a rapid increase in the proportion of less branched plants (1st and 2nd branching order) in the population from 60 to 80% in spring, as higher-order plants broke up into smaller-and lower-ordered plants at this time. Numbers of roots per plant increased over winter to peak in early spring then declined in the following summer-autumn. While system of grazing management had no significant effect on branching structure of plants, it had a large effect on plant dry weight; rotationally grazed plants were 2-5 times larger than set stocked plants (0-182 cf. 0073 g respectively).Other general features of plant morphology were that each successive order of branch stolons was shorter and length before branching was less than that of their preceding parent stolon. The highest branching order observed was 6th order. There was no relationship between branching and numbers of roots; in branched plants only 55% of stolons were rooted regardless of plant order, but rooted stolons accounted for 85% of total stolon length and carried 62, 48 and 90% of the leaves, growing points and axillary buds per plant, respectively.Comparison with other studies suggests that the processes outlined in this report may be common to white clover growth under grazing over a wide range of favourable environments.

No abstract

Four methods are presented for calculating the number of plants needed, with a specified high probability, to recover a given number of plants possessing a trait, given that the trait occurs with a known probability.

S U M M A R YProgeny of perennial ryegrass (PRG) plants selected for low and high leaf shear strength were sown in a spaced-plant field experiment and were shown to differ in leaf strength in the same direction, confirming this to be a heritable trait. Selection for low leaf shear strength also reduced weight per leaf length, but had no effect on dry-matter (D.M.) percentage, growth score, rust score or tendency towards aftermath heading.Rates of D.M. consumption (g D.M./min) and ruminal degradation of D.M. using the polyester bag technique, were then determined with small quantities of the two PRG selection lines, and also white clover, using sheep fed a basal diet of fresh ryegrass/white clover pasture. Selecting PRG for low leaf shear strength slightly reduced concentrations of cellulose and hemicellulose, slightly increased total N concentration and increased rate of D.M. consumption by sheep (17%) but had no effect on rates of ruminal D.M. degradation. The selection thus moved the nutritional characteristics of PRG in the direction of white clover.The first nutritional response to the selection appears to be a faster rate of D.M. consumption, and it is considered that leaf shear strength has potential for selecting PRG with increased rates of voluntary intake by ruminants.Sinclair (1982) deduced that slow degradation and I N T R O D U C T I O N outflow rates were the principal factors causing long Feeding value defined as the live-weight gain of young rumen retention time and reduced voluntary intake in sheep grazing New Zealand (NZ) temperate forage s h e e P f e d perennial ryegrass. and expressed in relative units, is higher for white Although breeders of temperate forage plants have clover (Trifolium repens: 100) than for perennial selected to improve apparent digestibility (Cooper ryegrass (Lolium perenne: 52), with annual ryegrasses et al. 1962;Dennis & Frandsen, 1986), there has been and other legumes being intermediate (Waghorn & no selection for improving feeding value once maxi- Barry, 1987). Both voluntary intake measured in field mum apparent digestibility has been attained. When studies (Ulyatt, 1971) and rate of D.M. consumption maintained in the vegetative state, most forage measured under controlled indoor conditions (Ulyatt cultivars used in New Zealand would be close to et al. 1986) are much lower for sheep fed fresh maximum digestibility (75-80%). We wished to test perennial ryegrass than fresh legumes, and there is the hypothesis that selecting perennial ryegrass for thus a need to improve the voluntary intake and reduced leaf toughness, using leaf shearing strength as hence feeding value of perennial ryegrass for rumi-the testing criterion, would increase the rates of D.M. nants. consumption and rumen degradation by sheep. The Long retention time of digesta in the rumen experiments reported examine this hypothesis: Expt 1 of forage-fed animals reduces voluntary intake examines whether leaf-shear strength is an heritable (Thornton & Minson, 1973) and hence feeding value, characteristic t...