SUMMARYVapour components emanating from disrupted cauliflower, turnip, radish, wallflower and brown mustard tissue were assessed for their effects on the cabbage root fly (Delia brassicae). Of about 20 vapour components detected and separated by gas chromatography, six elicited sufficiently large electroantennal responses to warrant further testing, but of these only allyl isothiocyanate and hexyl acetate markedly affected the behaviour of gravid flies in an olfactometer. In wind‐tunnel tests at a wind speed of 1–2‐1‐7 m/s, the numbers of females caught was increased when allyl isothiocyanate vapour was released at 32–130 mg/h but decreased at higher evaporation rates. The only effect of hexyl acetate vapour released at 40–140 mg/h was a reduction in the numbers caught at the highest concentration.In a cabbage crop, yellow water traps fitted with allyl isothiocyanate sources, each evaporating 2–3 g/day, caught 11 times as many female and seven times as many male flies as unmodified traps during the early period of the third generation but the improvement in trap efficiency later diminished. Trap efficiency was slightly reduced when the rate of evaporation of allyl isothiocyanate from a trap was decreased from 2–3 to 0–51 g/day. On fallow ground, allyl isothiocyanate improved trap performance in catching female flies by about seven‐fold, but along a hedgerow adjacent to Brussels sprouts the improvement was barely two‐fold. Hexyl acetate did not improve the performance of traps in a cabbage crop.
During this study, anglers caught over 580 kg of fish, comprising over 29 500 individuals of 14 species. Nine times as many gudgeon, Gobio gohio, as roach, Rutilus rutilus, were caught. Gudgeon represented 35.94% of the total catch weight compared with 44.64% for roach. The mean total catch per man-hour was 8.9 fish and the mean catch rate was 176 g per man-hour. Population estimates for fish longer than 12 cm for all species other than gudgeon and bleak, Alburnus alburnus, gave fish densities of 0.21 fish m-2, the roach population was 0.15 m-2, and that for dace Leuciscus leuciscus, 0.02 m-2. The population density for all sizes ofall species caught was estimated to be 2.25 fish m-2.The fish biomass available to the angler was 447 kg ha-2. The rate of exploitation of the fishery over the period ofsampling was high at 17%, representing an annual exploitation rate of94%.
Six species of earthworms from an arable soil were analysed for residues of aldrin, dieldrin, DDT and y-BHC. The ratios between the concentrations of y-BHC, aldrin + dieldrin and p,p'-DDT + p,p'-DDE in the earthworms and in the soil (concentration factors) were similar but the residue concentrations were consistently higher in the smaller more shallow-living species Allolobophoru caliginosa, A. chlororicu and A . roseu than in the larger deeper-living species Lumbricus terresrris, A. longu and Ocfolasion cyaneuni.In arable field plots, dieldrin residues in A. longu and A. chlorotica increased with increasing concentrations in the soil but the concentration factors decreased. The concentrations of residues in earthworms ( W ) appear to be related to those in the soil ( S ) by an equation of the form W = uSb where u and b are constants, the latter being about 0.79 for a wide range of residue data embracing the uptake of aldrindieldrin, DDT components, and y-BHC by earthworms. IntroductionThe relatively low concentrations of organochlorine insecticide residues present in many arable soils in central England172 are unlikely to have directly adverse effects on earthworm populations.3-8 As earthworms are eaten by a wide range of vertebrates, however, and may thus introduce residues into certain food chains,9JO information on their residue content in different environments is of value in assessing their potential as residue vectors.Several quantitative field investigations of DDT uptake by earthworms have been reported*~gJl but these related to situations where relatively high concentrations of insecticide occurred, or would be expected to have occurred, at or near the soil surface or in superficial herbage and debris. In arable fields, such conditions will normally occur infrequently, and then for only a few months after insecticides have been applied, because subsequent ploughing and other cultivations will dilute and re-distribute the residue throughout the cultivated layer of the soil.From two fields treated with aldrin (in fertiliser), Raw12 found concentrations of dieldrin in earthworms to be several times greater than those in the soil itself, and Davis 8c Harrison2 reported that concentrations of dieldrin in four samples of earthworms of mixed species from arable sites were two to ten-fold greater than those in corresponding soil samples. However, different species of earthworms can apparently accumulate both dieldrin and DDT residues to different extent~.'~J~ The results of more detailed investigations into the uptake
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