Inhibition of DNA synthesis by diflubenzuron in pupae of the stable fly Stomoxys calcitrans (L.)

Biochemical assays of stable fly pupae treated with diflubenzuron at the white prepupal stage and then injected with either [³H]thymidine or [¹⁴C]thymidine showed no differences in uptake of the thymidine at 0–4, 0–24, 20–21, or 22–24 hr after injection of the radiolabeled thymidine. However, at 32–36 hr the diflubenzuron pupae incorporated only 10–11% of the amount of labeled thymidine incorporated by the untreated pupae. Autoradiographs taken from diflubenzuron-treated pupae at 22–24 and 32–36 hr after injection of the labeled thymidine showed that a reduction in DNA synthesis had occurred in cells originating from the imaginal epidermal histoblasts. The reduction in DNA synthesis at 22–24 hr was not detectable by the biochemical assay since the number of proliferating epidermal cells was too small a proportion of the total number of cells undergoing histogenesis at this time period. Thus, the insect growth regulator, diflubenzuron, appears to be cell specific in this species of fly in that the reduction in DNA synthesis is observed only in cells originating from the imaginal epidermal histoblasts. However, it is not known at this time whether this effect is primary or secondary.     

Hemochromatosis in Salers Cattle

Two 2-year-old Salers cattle from different herds raised on pasture were evaluated for retarded growth and diarrhea. Increase of liver enzyme activities and prolonged sulfobromophothalein (BSP) half life (T1/2) indicated liver disease with impaired liver function. Histopathologic examination of liver biopsies revealed a micronodular cirrhosis with marked deposition of hemosiderin in hepatocytes, Kupffer cells, and arterioles. Transferrin saturation (TS) and liver iron content were markedly increased, consistent with a diagnosis of hemochromatosis. Both animals were euthanatized due to deterioration in their condition. Necropsy findings included hepatomegaly and hemosiderin accumulation in the liver, lymph nodes, pancreas, spleen, thyroid, kidney, brain and other glandular tissue. Continued surveillance of the second herd (serum iron, total iron binding capacity [TIBC], unsaturated iron binding capacity [UIBC], and TS), identified a heifer as a hemochromatosis suspect in a subsequent generation. Liver biopsies from that animal revealed the same histopathologic changes as the previous 2 animals, and similar increases in liver iron content (8,700 ppm, normal range 45 to 300 ppm). The 3 affected cattle were all products of line breeding programs and shared a common ancestor. The absence of dietary iron loading in conjunction with the histopathologic and metabolic findings were consistent with a diagnosis of primary hemochromatosis. The reported disease is similar to idiopathic hemochromatosis in human beings in which there is a hereditary defect in iron metabolism.     

Cytosine Arabinoside as a Single Agent for the Induction of Remission in Canine Lymphoma

Cytosine arabinoside (AraC) was administered as a continuous IV infusion to 15 dogs with malignant lymphoma at a dose of 300 mg/m²/d for 2 consecutive days. Dogs were re-examined 7 d after treatment for response to therapy and for hematologic toxicity. Regardless of response, all dogs were started on combination chemotherapy at this time. Other toxicities were reported by owners. No dog responded objectively to Ara-C treatment, although 1 dog with circulating lymphoblasts had partial regression of lymphadenopathy but persistent blastemia. Thrombocytopenia (platelet count < 200,000/μL) 7 days posttreatment was the most commonly encountered hematologic toxicity, occurring in 10 of 14 dogs. Three of these 10 dogs were also mildly neutropenic (neutrophil counts of 2000 to 3000 cell/μL). Nonhematologic toxicity occurred in 8 of 15 dogs and was principally gastrointestinal in nature and mild in severity. Cytosine arabinoside at a dose of 300 mg/m²/day was not considered an active drug for the induction of remission in dogs with lymphoma.     

Plant growth regulators and the physiological limitations to yield in sugar beet

Improvements in seed germination, the early establishment of leaf cover, storage root development and the control of bolting would all increase the yield of sugar beet in the UK. Plant growth at these stages of development is controlled by genotype and by climatic factors acting through endogenous growth substances and is potentially capable of modification by applied growth regulators. For example, sugar beet responds to changes in daylength and spectral quality of light at the end of the day by increasing lamina and petiole growth, light interception and plant growth rate. Changes in endogenous gibberellins in young leaves of plants growing in different photoperiods and the responses of these leaves to applied gibberellic acid are presented as evidence for the involvement of gibberellins in leaf expansion in sugar beet.     

Spray drift from a tractor-powered field sprayer

Amounts of spray drifting downwind from a field sprayer applying picloram or paraquat were determined and compared with the damage done to bean and barley plants. Measurements downwind of a stationary spray-boom showed that drift increases rapidly with both wind speed and boom height. It was concluded that it is possible to set a safe distance downwind for the application of a herbicide which affects plants only in the wetted areas but with a sensitive crop and many growth-regulating materials this will be very difficult.     

The effect of drop size and velocity on the performance of agricultural sprays

The sizes and velocities of drops in sprays from farm sprayers are considered in relation to their impaction on plant surfaces. Examples from a study being carried out at the National Institute of Agricultural Engineering (NIAE) are given. The results showed that young leaves of barley (cv Mazurka) and wild oats (Avena fatua L.) were difficult to wet, only the smallest drops applied (about 100 um diameter) being readily retained. In the context of weed control in cereals the importance of detrmining the effect of the form of plant deposits on herbicidal activity is discussed, and examples of results of a joint study between the NIAE and the Agricultural Research Council Weed Research Organization are given.     

A laboratory device for producing single drops in uniform sizes of 150–450 μm diameter

A device is described which can produce single drops of liquids in uniform sizes. Drop size can be adjusted, and with an aqueous solution of a non-ionic surfactant (“Agral”; 1 ml/litre) sizes 160–490 μm diam. were produced. Suitable techniques of calibration are given. The device is a useful research tool for study of the effects of form of deposit on herbicide performance.     

Systems thinking—Some fundamental aspects

The systems approach is evolving on three fronts. First is the development of general systems theory, second is the development of methodology and third is the application of theory and methodology to practical problems. This paper concentrates on the first topic—the development of a general systems philosophy—and focuses on two ideas. The first is the need for balance between qualitative and quantitative analysis in systems studies and the fact that systems theory provides a framework in which to balance generality and detail. The second is that the systems approach is based on classical inductive/deductive scientific method and requires both imaginative and analytical reasoning.