Increase of pest populations to abnormal levels following application of pesticides is a well-known phenomenon which has been turned to advantage in work on host-plant resistance to insect pests. For example, increases in numbers of aphids followed treatment of potato with carbaryl (Sevin), DDT and other chemicals which killed aphid predators (Peterson, 1963) and carbaryl has been used where enhancement of populations of Myzus persicae was achieved deliberately (Radcliffe & Lauer, 1971; Tingey & Van de Klashorst, 1976). Interest in the possibility of breeding for resistance to cereal aphids, especially Sitobion avenae (F), has increased as more examples of differences between varieties have been reported (e.g. Kolbe, 1969; Hinz & Daebeler, 1974; Lowe, 1978, 1980; Stokes, Lee & Wratten, 1980). This aphid occurs sporadically in the field and natural enemies, notably predaceous and parasitic insects, may contribute significantly to this variation (Vickerman & Wratten, 1979), so the use of insecticides to reduce the effects of the latter appears a promising technique in the development of reliable field screening methods for plant breeding.

The addition of superphosphate increases the legume content of grass-legume pastures and the growth rate of beef cattle (Shaw, 1978). It has generally been assumed that the increase in beef production following the application of superphosphate is related directly to greater amounts of legume in the pasture consumed (Norman, 1970; Shaw, 1978) but there is no direct evidence on this subject. This paper reports a study of the influence of small quantities of superphosphate on preference for legume by cattle grazing Stylosanthes-native grass pastures.

Environmental conditions (Clark & Quin, 1949; Daws & Squires, 1974; Degen & Young, 1980) and total feed intake (Clark & Quin, 1949; Forbes, 1968; Degen & Young, 1980) influence the water intake of sheep. In general, high temperatures increase the requirements for water needed for evaporative cooling and high feed intakes necessitate more water for excretion of waste products. This study was designed to measure water intake and estimate the partition of water output in sheep maintained at four air temperatures and offered four levels of a ration.

Estimates of the degradability of protein in the rumen are essential for the application of new systems which have been suggested for the evaluation of the protein requirements of ruminants (Agricultural Research Council, 1980). The effective percentage degradability (P) of protein supplements in the rumen is dependent not only on the course of degradation of the protein particles in the rumen, but also on the time distribution of their stay in the rumen, and will decrease if there is an increase in the rate of passage of the particles. It was shown by Ørskov & McDonald (1979) that if the percentage protein disappearance (p) from samples incubated for time t is described by the equation and if k is the fractional rate of passage from the rumen, then the effective degradability can be calculated as . The calculation depends on the equation for p remaining valid from t =0 (time of ingestion) until a time when all the particles have passed beyond the rumen. It has been found that for some protein supplements, linseed meal for example, the equation for p does not hold true for low values of t. The present note proposes a modification to the formula for effective degradability so that it may remain valid under these circumstances.

Research has shown that it is now possible to control the oestrous cycle of ewes with a high degree of precision (Robinson et al. 1967; Gordon, 1975; Boland, Kelleher & Gordon, 1978). There is general agreement that a high concentration of progestagen, followed by rapid withdrawal and adequate ovarian stimulation is necessary for acceptable fertility (Robinson et al. 1967; Gordon, 1975; Colas, 1975). Application of artificial insemination in France has involved the use of a 40–45 mg Cronolone sponge (Cognie, Mariana & Thimonier, 1970; Colas et al. 1973) while controlled breeding in sheep in Ireland has been used in conjunction with a 30 mg Cronolone pessary (Gordon, 1975; Smith, Boland & Gordon, 1978, 1981). The present experiment was designed to compare the relative effectiveness of two doses of Cronolone (30 or 45 mg) when administered in conjunction with two quantities(375 or 750 i.u.) of pregnant mare serum gonadotrophin (PMSG), given by intramuscular injection.

Several plants are cultivated for medicinal and aromatic purposes. Foxglove (Digitalis lanata) has been introduced into India from Western Europe and is cultivated for medicinal use. The leaves of D. lanata contain various glycosides, namely digoxin, gitoxin and gitalin, which are of medicinal value. This crop is cultivated throughout the year but not much information is available about

seasonal influence on the glycoside content. Hence, attempts are made to assess the effect of seasonal variation on total glycoside content and to arrive at an optimum season for harvesting the crop.