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The phenology and some aspects of the biology of the clover weevil Sitona lepidus Gyll. were studied in the field and the laboratory. Oviposition and hatching were temperature dependent. Most eggs were laid in September and October, although there was also an oviposition period in early summer. Hatching was largely confined to late spring and early summer. The relevance of this to control strategies is discussed. Most eggs were laid on the plant but(were very easily dislodged and probably usually hatch on the ground. In no-choice tests, there were as many eggs laid on more cyanogenic as on less cyanogenic plants and cultivars. There was no evidence that the cyanogenic ability or any other cultivar characteristic would be useful in control strategies.

Slugs of three species, Deroceras reticulatum, Arion fasciatus and A. subfuscus, which had fed on sclerotia or apothecia of Sclerotinia trifoliorum, transmitted the disease to water agar plates. In the case of Arion spp., transfer of excreta also produced infection. After feeding on apothecia D. reticulatum transmitted the disease to white clover plants, although the direct transfer of apothecia produced higher levels of infection. The visible symptoms of the disease were reduced when slugs were allowed to remain on the plants, apparently owing to a feeding preference of D. reticulatum for diseased leaf tissue.

Seedling ryegrass and oat plants in various proportions were exposed to oviposition by frit fly in the laboratory. The growth stage of the ryegrass ranged from single-leaved (unattractive as oviposition sites) to three-leaved (almost immune to serious damage). Oat plants attracted most oviposition and their inclusion usually reduced oviposition on ryegrass, by up to 90%. Where the frit fly population density was so high that potential oviposition exceeded the availability of oviposition sites, inclusion of oats did not reduce the number of eggs laid on ryegrass. This approach does not, therefore, show promise of a reliable control method against severe primary attack in the field, but is potentially useful over an important range of population densities at which further control measures might otherwise be required. The inclusion of oats would also provide an early warning of damage.

Invertebrate numbers were studied in two white clover cultivars trials, grown with perennial ryegrass Weevils (Sitona spp.), slugs, lucerne flea, leatherjackets and as were more common (at least at some life stage) in cultivars of lower cyanogenic potential. Damage to clover foliage by the first three species was also negatively related to cyanogenesis. The production of HCN ranged from 0.025 mg to about 1.8 mg g−1 fresh leaf. There was no evidence of any other factor influencing cultivar preference. Cyanogenesis had most effect on numbers of weevil larvae and leatherjackets. The effect on weevil larvae was attributed partly to intercultivar differences in oviposition, but it was also suspected that larvae had fed on cyanogenic parts of the plant before reaching the root. Leatherjacket numbers developed inter-cultivar differences during larval growth. In one case these differences were detectable by December. By March in the second experiment there were approximately three times as many leatherjackets at the low as at the high end of the cyanogenic range. Approximately four times as many Sitona larvae were found at the lower as at the higher end of the scale. There was some evidence that a higher clover content in the sward was attractive to ovipositing Tipula paludosa but not in recently harvested cultivars of high cyanogenic potential

In plots of perennial ryegrass and white clover, regular treatment with chlorpyrifos and methiocarb more than trebled the clover content of the sward, compared with untreated plots, in just over 2 years from sowing. Chlorpyrifos alone accounted for most of the effect, which was attributed mainly to the control of Sitona lepidus. Combined treatment increased total herbage dry matter yield by 4·24 t ha−1 during this period but had little effect on grass-only plots. Methiocarb appeared to have contributed by assisting earlier establishment of clover, but otherwise had little effect until slugs, which were initially uncommon, became more abundant in the later stages of the experiment. The effect of slug control was most noticeable in a cultivar of low cyanogenic potential. This factor did not influence the effect of chlorpyrifos.

SUMMARY In years of relatively high frit fly activity the control of all generations produced increases averaging 0×44 t d.m. ha-1 in annual yield of Italian and hybrid ryegrass. A cutting programme designed to make the sward especially vulnerable to frit fly attack did not increase the total annual effect of pesticide treatment but accentuated the periods at which damage occurred. The annual yield increase was almost entirely obtainable by controlling the second and third frit fly generations, but even one treatment for this purpose was of doubtful economic justification. The prospect of augmenting the response to control of later-occurring pests, such as leatherjackets or eriophyid mites, by including the part of the frit fly response which is recoverable by the same treatment, was a more probable justification for pesticide usage. There was some evidence that a Westerwold and a hybrid cultivar suffered more damage than an Italian ryegrass cultivar, but pesticide treatment did not improve the persistence of any cultivar.

In two experiments in established swards of perennial ryegrass and white clover, plots were treated with pesticides to control slugs, leather-jackets, weevil larvae and lucerne flea as selectively as possible. Other plots were treated to control ail of these pests. Chlorpyrifos application in early summer (to control weevil larvae) and methiocarb pellets (to control slugs) also gave partial control of leather-jackets. Other effects on non-target species were considered to be unimportant, as pest status could not be attributed to the species. A high level of control of lucerne flea by methiocarb pellets, noted previously, was confirmed. At both sites combined treatment against insect pests and slugs produced large increases in clover content and yield over a 3-year period, in comparison with untreated plots, although clover tended to decline In alt plots. At one site, where the clover content of untreated plots reached 33% at one stage, specialist clover herbivores such as weevils and lucerne flea were more common. Treatments directed against weevils and slugs gave the highest clover yields, and leatherjacket control may also have contributed, particularly when the population reached 0.9 m ha−1 in the final year. At the other site, where the clover content was low (ultimately 01.1–6%), leather-jacket populations reached 2.1 m ha−1 and slug numbers were also relatively high. Control of these species contributed most to the relative increase in clover content and yield.

To determine whether leatherjackets might be controlled by application of a pesticide in summer, before oviposition by crane flies, chlorpyrifos was applied to perennial ryegrass (Lolium perenne) swards on dates from July to September in anticipation of leatherjacket infestation. Subsequent winter population estimates showed that leatherjacket numbers had been reduced by at least 85% by 0·72 kg chlorpyrifos ha-1 applied on 13 July, and by 0·60 kg ha-1 applied on 3 August or later. The significance of leatherjacket control by pesticide application on these dates is discussed in relation to previously recorded effects of pesticide treatment on other known pests. It is concluded that control of all common arthropod pests of proven significance in established grassland may be achieved with one application of pesticide.

In laboratory experiments to clarify earlier field observations, Sitona lepidus larvae caused significant damage to established clover plants at infestations of approximately 1–2 per plant. When eggs were placed on the soil, cultivars of differing cyanogenic capacity were damaged equally. The plants did not recover when larval feeding ended. Leatherjackets, slugs and ‘lucerne flea’ fed most on the least cyanogenic cultivars, even where no choice was offered. Plants ultimately recovered from damage by leatherjackets. Deroceras reticulatum caused more damage than did Arion fasciatus. The proportion of leaves damaged by lucerne fiea was highest in the least cyanogenic eultivar but also tended to increase in the most cyanogenic cultivar, confirming a field observation. At high population densities lucerne flea was capable of killing some seedlings but was not tested against established plants.

SUMMARY Three cultivars of Italian or hybrid ryegrass were exposed to frit fly attack at varying frequency in the laboratory. Initially a Westerwolds and a hybrid cultivar showed greater yield reductions than an Italian ryegrass cultivar, although they did not usually suffer a higher proportion of damaged tillers. The differing effect on yield appeared to be due mainly to greater impact of first or infrequent attacks on cultivars producing fewer tillers. After two to six attacks in approximately 7 months the Westerwolds and hybrid cultivars appeared to become tolerant to attack and were subsequently the least affected, although continuing to suffer tiller damage at a rate at least as high as the Italian ryegrass. All cultivars recovered fully when attack ceased, and their exclusion from attack did not improve their persistence.

Laboratory experiments gave useful indications of the effectiveness of insecticide treatments to control larvae of frit fly (Oscinella frit L.). Lightly infested field experiments provided confirmatory evidence. Several seed treatments, insecticide granules combine-drilled with the seed and post-emergence sprays were very effective. The feasibility of delivering granules with seed must be confirmed for each granular formulation. Post-emergence sprays were most effective if applied at approximately the time of oviposition but several also gave a strong residual effect if applied earlier and a remedial effect if applied after larval establishment in the seedlings. More detailed conclusions are discussed.

SUMMARY In four experiments from 1981 to 1983 August-sown perennial (Lolium perenne) and Italian (L. multiflorum) ryegrass were exposed to frit fly attack by oviposition on the seedlings. Responses to pesticide treatment were detected at autumn harvests. Even at low sowing rates pesticide application did not ultimately establish a better sward and, owing to a tendency towards spring reversal of autumn yield responses, even temporary returns were negligible. As frit fly numbers were unusually low the autumn response to pesticide was sufficient to suggest that frit fly is always likely to be an influential factor in ryegrass sown in early August in this area. Later sowings are less likely to be affected. The yield response was related to the numbers of adult flies present 2–7 wk after sowing. Neither grass species was consistently more affected than the other. Additional seed (compared with a sowing rate below normal commercial rates) and the inclusion of fertiliser at sowing also gave only small temporary returns and failed to establish a better sward. It is suggested that routine protection against frit fly attack is of at least equal value to the other two variables in an early August sowing.

SUMMARY In laboratory tests concentrations of dieldrin in soil, below that required to control cabbage root fly, were found to be toxic to several species of carabid beetles which prey on the immature stages of this pest. These results confirm previous findings from field experiments that dieldrin residues in soil can, by reducing the populations of predaceous beetles, increase the survival of the cabbage root fly and the subsequent crop damage caused. The toxicity of selected organophosphorus insecticides to these beneficial insects was studied in soils of different moisture content. Thionazin was found to be highly toxic at all moisture levels as was diazinon in moist soil. Chlorfenvinphos and azinphos-methyl and, in dry soil diazinon, were very much less toxic.

In the stretch receptors of Lepidoptera there are normally two giant nuclei, but supernumerary giant nuclei are frequently present. In a study on Samia cynthia supernumerary giant nuclei have been found to occur most frequently in the first, second, third, and fourth abdominal segments. They are present in the larva, pupa, and adult. Small nuclei in the muscular component of the receptors are infrequent in the larva and in the fourth, fifth, and sixth abdominal segments of the adult; but in the first, second, and third abdominal segments there is an increase in small nuclei at metamorphosis. Small nuclei also multiply in the receptors of the eighth and ninth segments but these receptors degenerate. The muscular component of the receptors that metamorphose at first becomes reduced and loses its striations and then differentiates anew. In those receptors that disappear (eighth and ninth) dedifferentiation is succeeded by histolysis. A third category of nucleus, larger than the small nuclei but smaller than the giant nuclei, was found in a few receptors of larva, pupa, and adult. Such nuclei appear to be absent from the fifth and sixth segments, but they were too rare for reliable statistics to be obtained.

Summary The percentage of winter wheat seeds killed by slugs was measured, together with various risk factors, at 93 sites throughout the UK from 1987 to 1990. Estimates of slug populations at each site were obtained from traps baited with methiocarb pellets. The peak number of slugs trapped during the period from July until just before cultivation accounted for 26% of the variability in seed damage, more than any other single risk factor. A combined function of the number of slugs trapped at drilling and the percentage of fine soil aggregates in the seed-bed accounted for 21% of the variability in seed damage. Both (i) the peak number of slugs trapped before drilling, and (ii) the combined function of number of slugs trapped at drilling and the percentage of fine soil aggregates in the seed-bed, have potential for identifying fields with a negligible risk of slug damage to wheat seeds. However, further research is needed to improve the accuracy of forecasting slug damage. In particular, other forms of trap should be tested for their potential use in providing more accurate estimates of slug numbers and biomass at drilling, and techniques of assessing seed-bed conditions should be improved. The percentage of seedlings grazed by slugs was correlated with the numbers of slugs trapped before drilling, at drilling and after crop emergence.

Elimination of shooly larvae increased grass yields daring the September feeding period. Increases were usually less than 10% bat in one case, where growth was abnormally slow, die increase was over 30% and in another, where the larval population was atypically dense, it was almost 60%. The effects of damage were not cumulative daring the feeding period; and at the end of this period insecticidreated plots sometimes gave lower yields than untreated plots. Fertilizer increases had a much greater effect on yield than did control of larvae and, where N was applied at 75 kg/ha (67 lb/ac) in spring, the additional effect of larval control was usually negligible. It is suggested that shoot-fly damage may be more serious in other localities. When turf containing shoot-fly larvae was ploughed, Oscinella spp. re-established themselves more successfully than others in seedling ryegrass bat did not damage the new sward appreciably.

SUMMARY of the damage and the value of control measures depend on the abundance of the pest and the vulnerability of the seedlings when attacked. Vulnerability to attack may be influenced by the size of the plant and its acceptance and suitability as a host. As plants would be expected to suffer most from damage at a very early stage, the characteristic pattern of frit fly damage-the sudden deterioration of a new sward after a period of satisfactory seedling growth-suggests that very young seedlings may be unacceptable host plants. Vickerman (1978) has demonstrated an oviposition preference for tillering grasses. An aversion to smaller- plants, if sufficiently strong in the absence of choice, would imply a period of immunity to attack after seedling emergence which could be of considerable significance to the nature and timing of control measures. This paper describes the results of experiments designed to examine frit fly oviposition on very young ryegrass seedlings and the growth stage at which they first become

A study of the economic importance of the dipterous shoot-flies in Northern Ireland grassland was undertaken from 1967 to 1972. This comprised several experiments to determine the effect of overwintering shoot-fly larvae on grass growth, the distribution of shoot-flies on the farm where these experiments were carried out and the prevalence of shoot-flies in grassland throughout a wide area of Northern Ireland. The study involved the examination of many swards of different botanical composition under different management systems and in different environments and the effect of these factors on the distribution of shoot-flies is described below.