An evaluation of two cypermethrin-based pour-on formulations on sheep infested with the biting louse, Bovicola ovis

Two synthetic pyrethroid (cypermethrin) based pour-on insecticide formulations, with high cis/trans isomer ratios (80:20) but differing in their respective active ingredient concentrations and solvent component(s), were applied to sheep infested with the biting-louse, Bovicola ovis. All treated sheep were penned with louse-infested sheep 9,12 and 15 weeks after the insecticide was applied. The 2% cypermethrin formulation achieved a higher level of control than the 1.25% cypermethrin formulation at each challenge interval when applied 12 weeks after shearing. The 2% cypermethrin formulation provided 97-100% control of lice from 4 to 16 weeks after application on sheep shorn 6 or 12 weeks prior to treatment. The 1.25% cypermethrin formulation provided 85% control of lice 4 weeks after application on sheep shorn 12 weeks prior to treatment, the level of control increasing to a maximum of 100% by week 9, and declining thereafter. The 2% cypermethrin formulation may provide a better level of control in long-woolled sheep than 1.25% cypermethrin, by compensating for the diluent effect of lipid.     

Virus transmission by aphids in potato crops

This paper reviews the contribution of vector activity and plant age to virus spread in potato crops. Determining which aphid species are vectors is particularly important for timing haulm destruction to minimize tuber infection by potato virus Y (PVY). Alate aphids of more than 30 species transmit PVY, and aphids such asRhopalosiphum padi, that migrate in large numbers before flights of the more efficient vector,Myzus persicae, appear to be important vectors. Differences in methodology, aphid biotypes and virus strains prevent direct comparisons between estimates of vector efficiencies obtained for aphids in different countries in north western Europe. M. persicae is also the most efficient vector of potato leafroll virus (PLRV), but some clones ofMacrosiphum euphorbiae transmit PLRV efficiently toNicotiana clevelandii and potato test plants. The removal of infected plants early in the season prevents the spread of PLRV in cool regions with limited vector activity. The proportion of aphids acquiring PLRV from infected potato plants decreases with plant age, and healthy potato plants are more resistant to infection later in the season. Severe symptoms of secondary leafroll developed on progeny plants of cv. Maris Piper derived from mother plants inoculated with PLRV in June or July of the previous year. Progeny plants derived from mother plants inoculated in August showed only mild symptoms, but the concentration of PLRV in these plants was as high as that in the plants with severe symptoms.     

Interactions among herbivores,microbial insecticides and crop plants

Knowledge of the interactions among lepidopterous insects, microbial insecticides and plants is either lacking or incomplete. In some of the interactions, plant allelochemicals antagonized the insecticidal activity of the microbe by means of feeding reduction. In others, microbe activity was enhanced either by causing insect toxicity or by a potentiation of the crystal protein. Nutritional evaluations of the interactions amongHeliothis virescens. Bacillus thuringiensis crystal protein and tannin showed that microbe toxicity in the larva was antagonized by this phytochemical.     

Nutritional stress in ficea sitchensis plantations in coastal British columbia: The effects of gaultheria shallon and declining site fertility

Examples of nutritional stress in conifer seedlings caused by competing ericaceous species (e.g. Calluna and Kalmia), have been reported in several parts of the world. Nutritional stress (primarily N deficiency) has been reported in Sitka spruce (Picea sitchensis) plantations growing in association with an ericaceous species, salal (Gaultheria shallon), in coastal British Columbia. Nutritional interference by salal was investigated on a chronosequence of sites up to 10 yr after clearcutting and slashburning. No direct evidence for an allelopathic contribution to the N stress was obtained. However, the rapid accumulation of salal fine roots and rhizomes, and the nutrients contained therein, provides a partial explanation for the observed stress symptoms. Soil analyses and seedling bioassays demonstrated a reduction in fertility in the period 8 to 10 yr after clearcutting and slashburning in comparison to the period 2 to 4 yr, which is believed to impose further nutritional stress on Sitka spruce. It is concluded that the nutritional stress in these Sitka spruce plantations is caused by a combination of (1) salal competition for nutrients and their subsequent immobilization in salal biomass, and (2) declining site fertility caused by the termination of the flush of nutrients (the assert period) that occurs in the immediate post-clearcutting and slashburning period. Sustaining good growth of plantations under such circumstances will require site nutrient management as well as vegetation management.     

Growth and erosion of thin solid films

Thin films that are grown by the process of sputtering are, by and large, quite unlike the smooth, featureless structures that one might expect. In general, these films have a complicated surface morphology and an extended network of grooves and voids in their interiors. Such features can have a profound effect on the physical properties of a thin film. The surface irregularities and the bulk defects are the result of a growth instability due to competitive shadowing, an effect that also plays a role in geological processes such as erosion. For amorphous thin films, the shadow instability can be described by a remarkably simple model, which can be shown to reproduce many important observed characteristics of thin film morphology.