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R H Collier

Publications and source records attributed to R H Collier.

12 recordsLinked to original sources
PubMed2002

Evaluating an interpolation approach for modelling spatial variability in pest development.

Air temperatures estimated by partial thin plate spline interpolation, or from the 'nearest station' (Voronoi polygon method), were used to model the phenology of three pests of horticultural crops throughout England and Wales. Temperatures for a particularly hot (1976) and a particularly cold (1986) year were interpolated to a grid resolution of 1 km. Estimates were made of the timing of spring emergence (Cecidophyopsis ribis (Westwood)), the maximum number of generations completed during the summer (Plutella xylostella (Linnaeus)) and the numbers of days when mating was possible (Merodon equestris (Fabricius)). The relative accuracy of the two temperature estimation methods was compared using jack-knife cross-validation. For C. ribis and P. xylostella, modelling with interpolated temperature input data was more accurate than using data from the 'nearest station'. Of the three phenology models used, the one that relied on an activity threshold (M. equestris) was the most sensitive to both types of input data. Spatial variability in the activity of M. equestrisadults was investigated in the two main areas (south-west peninsula and Lincolnshire) where its host crop (Narcissus) is grown. Modelling at cruder scales (up to 25*25 km) masked local variation, but the degree to which this was important varied from region to region and over time, as did the geography of the variability itself. The results indicate that interpolated data, computed to a resolution of 1 km using the UK synoptic network, have the potential for wider use within agricultural decision support systems for horticultural crops.

Animals↗
PubMed2001

Pest insect control in organically-produced crops of field vegetables.

In the UK, the demand for organic vegetable and salad crops is increasing, mainly as a result of the requirements of the multiple retailers. However, approximately 85% of the organic fruit and vegetable produce sold in the UK is imported. A major constraint to growing field vegetable crops, and particularly organically-produced crops, is the reduction in crop yield and quality caused by pest insects. This paper will consider the control techniques currently available to organic growers and other techniques that may become available in the future. Growing plant varieties with complete or even partial resistance to pest insects can be an effective way of reducing crop damage. There are already varieties of carrot, with resistance to carrot fly, and lettuce, with resistance to certain pest aphid species, which are available commercially. Cultural techniques to exclude, deter or avoid pest insects are also being used by some organic growers. Although isolating new crops from sources of infestation can be a highly effective control strategy, many organic growers cannot use it, as the land converted for organic production is still limited. Various crop covers can be used to prevent pest insects from damaging field crops, but to be effective such covers have to be in place before the pests enter the crop. Several researchers have tried to develop techniques to prevent pest insects from finding their host-plants. No technique involving semiochemicals has been sufficiently successful to be used in field vegetable production in the UK. Other studies have shown that the numbers of pest insects found on crop plants are reduced considerably when the crop is allowed to become weedy, is intercropped with another plant species, or is undersown with a living mulch. Hence, work is now needed to select background plant species that will both reduce pest insect numbers and cause the least reduction in yield to the harvested crop plants. There is also a need to obtain a better understanding of "companion planting", a practice used frequently by organic growers. To date, microbial control is the only biological technique that has been used successfully in field vegetable crops in the UK. However, only the toxicant produced by one microbial agent, the bacterium Bacillus thuringiensis, has so far been registered for use. The use of bacteria, fungi and viruses to control pests of field vegetable crops certainly has possibilities. However, in many cases there are still problems to be overcome to select pathogens that are compatible with, or can still be effective in, the wide fluctuations in temperature, humidity and soil moisture that occur under field conditions. Attempts are now being made to use entomopathogenic nematodes and predatory arthropods to control one major pest insect, the cabbage root fly. Techniques developed to improve the timing of application of various crop protection procedures in systems of conventional vegetable production apply equally well to organic production, despite the choice of control options being more limited. In particular, models to forecast the timing of pest insect attacks could be used to great effect, to indicate the best times to plant, protect and harvest a specific crop to minimise pest insect damage.

Agriculture↗
PubMed2001

Cabbage root fly control using non-organophosphorus insecticides.

The need to find non-organophosphorus insecticides to control the cabbage root fly has never been so urgent. Of the six non-OP insecticides tested, fipronil was the most effective but spinosad, diflubenzuron and cyromazine also showed considerable promise. As expected, the transplant drenches (34 mg active ingredient (a.i./plant) were more effective than the module drenches (5 mg a.i./plant), which in turn were more effective than the film-coated seed treatments (0.001 mg a.i./plant), simply because of the different amounts of insecticide applied per plant. One remaining major problem is that, even if effective non-OP insecticides can be found, the manufacturers may still not support their insecticides being applied to minor crops such as field vegetables.

Animals↗
PubMed1972

Nonidentity of the aspartate and the aromatic aminotransferase components of transaminase A in Escherichia coli.

Tyrosine, added to the growth medium of a strain of Escherichia coli K-12 lacking transaminase B, repressed the tyrosine, phenylalanine, and tryptophan aminotransferase activities while leaving the aspartate aminotransferase activity unchanged. This suggested that the aspartate and the aromatic aminotransferase activities, previously believed to reside in the same protein, viz. transaminase A, are actually nonidentical. Further experiments showed that, upon incubation at 55 C, the aspartate aminotransferase of crude extracts was almost completely stable, whereas the tyrosine and phenylalanine activities were rapidly inactivated. Apoenzyme formation was faster, and apoenzyme degradation proceeded more slowly with aspartate aminotransferase than with tyrosine aminotransferase. Electrophoresis in polyacrylamide gels separated the aminotransferases. A more rapidly moving band contained tyrosine, phenylalanine, and tryptophan aminotransferases, and a slower band contained aspartate aminotransferase. A mutant of E. coli K-12 with low levels of aspartate aminotransferase exhibited unchanged levels of tyrosine aminotransferase. Thus, transaminase A appears to be made up of at least two proteins: one of broad specificity whose synthesis is repressed by tyrosine and another, specific for aspartate, which is not subject to repression by amino acids. The apparent molecular weights of both the aspartate and the aromatic aminotransferases, determined by gel filtration, were about 100,000.

Aspartate Aminotransferases↗