Stig Larsson

Effects on growth of simulated and induced shoot pruning by Tomicus piniperda as related to carbohydrate and nitrogen dynamics in Scots pine.

With the combination of field survey and EPIC modeling,this paper simulated the restoration effect of soil moisture in different alfalfa (Medicago sativa)-grain rotation systems in semi-arid and drought-prone regions of Loess Plateau. In perennial alfalfa field and in grain crop field after alfalfa,the correlation coefficients between the simulated and observed values of soil moisture content in 0-10 m layer were larger than 0.9 (P0.01),and their relative root mean square errors were between 0.05 and 0.16,with the relative errors less than 10%. The dynamic changes of the simulated soil moisture contents in different soil layers were consistent with those of the observed values. In the study regions,it was difficult for the restoration of soil moisture in the deep soil layers of alfalfa field. During the cultivation of alfalfa,the soil moisture content in the layers at 8-10 m depth should not be less than 5.7%. Considering the sustainable development of agricultural production,the appropriate cultivation duration of alfalfa should be 4-6 years and no more than 8 years. For the restoration of soil moisture after alfalfa cultivation in the study regions,the rotation system potato (Solanum tuberosum) → potato → spring wheat (Triticum aestivum) could be adopted,and alfalfa could be cultivated again after 32-33 years.

Histochemical observations on the pancreatic islets in normal and obese-hyperglycemic mice

SummaryIn the islets of Langerhans in mice with the American variety of the obese-hyperglycemic syndrome (AO) and their thin litter mates (AN) the following observations were made:1.In cryostat sections of fresh pancreatic tissue from AN-mice, both more centrally situated islet cells with yellowish white granules, and peripherally situated cells with brighter silver white granules were found with dark field microscopy. While the central cells were considerably degranulated in the AO-mice, the peripheral cells were also well filled with granules in these animals. The technique described offers, especially in the AO-mice, better possibilities of differentiation of the islet cells than with the granule staining methods of fixed pancreatic material, which are now generally used.2.After intravenous injection of dithizone, abundant orange yellow zinc dithizonate granules were found in all islet cells with dark field microscopy of cryostat sections from fresh pancreatic tissue of AN-mice. By dissolving out these granules, the zinc content could be related to the different types of islet cells. It was possible in this way to show that the zinc in the islets of the AO-mice was mainly situated in the peripheral cells, containing the silver white granulation typical of untreated animals in dark field. The occurrence of a lower zinc content in the centrally situated islet cells in the AO-mice was also evident from the so-called “sulphide-silver method”.3.A positive islet reaction to both acid and alkaline phosphatases was obtained in the AN-mice. The alkaline phosphatase activity was high in the peripheral parts of the islets of AN-mice, but much lower in the AO-mice. While the majority of islet capillaries were strongly positive as regards alkaline phosphatases in the AN-mice, in the AO-mice they were for the most part completely negative.4.In spite of the existence of a prolonged hyperglycemia, no storage of glycogen could be demonstrated in the islets of the AO-mice. With fluorescence microscopy, the occurrence of masked lipids in the islets was observed in the AN-mice, and to an even higher degree in the AO-mice. On the other hand the sudanophilic reaction was negative throughout. The raised functional activity in the islet B-cells of the AO-mice was reflected in an enlargement and fragmentation of the Golgi apparatus.

Utilization of dry matter and bioelements in larvae of Neodiprion sertifer Geoffr. (Hym., Diprionidae) feeding on Scots pine (Pinus sylvestris L.)

SummaryIn the laboratory the consumption (C), egestion (F), assimilation (A) and assimilation efficiency (A/C) of dry matter and of the bioelements C, N, P, K, Ca, Mg, S and Na were studied weekly during the whole feeding stage. The larvae were reared in clusters of 10 individuals (on average 3.5 ♂♂ and 6.5 ♀♀), fed one-year-old needles. The average values of (C), (F) and (A) were 2,950, 2,530 and 414 mg dw per cluster, respectively, implying a dry matter assimilation efficiency of only 14.0%. The mean production of tissue (P) per cluster amounted to 250 mg dw. The concentration of bioelements in faeces (in order as above) was 51.2, 0.80, 0.08, 0.36, 0.41, 0.11, 0.10 and 0.02% of dw, and in larval tissue 57.5, 7.60, 0.64, 0.85, 0.24, 0.22, 0.24 and 0.06% of dw, respectively. The concentration of N and P in larval tissue was 5.8 and 4.9 times higher than in food, that of K, Mg, S and Na about twice, that of C and Ca about equal or less. The assimilation efficiency of the bioelements was estimated at 14.5, 59.3, 47.4, 20.9, 4.6, 12.5, 13.8 and 44.4%, and the energetics (C), (F), (A), (P) and (R=A-P) at 61,900, 53,600, 8,320, 6,710 and 1,610 J per cluster, respectively. It is argued that in N. sertifer the high consumption rate, low efficiency of dry matter assimilation and low nitrogen accumulation, in all attained at a low maintenance cost, are adaptations to a food low in nitrogen content (1.3% of dw). The study is part of an investigation on the interaction between insect consumption and pine growth, performed within the Swedish Coniferous Forest Project.

Growth in Scots pine (Pinus silvestris L.): A hypothesis on response to Blastophagus piniperda L. (Col., Scolytidae) attacks

Abstract The purpose of this paper is to suggest an explanation of the long-lasting and drastic growth rate reduction in stands of Scots pine, caused by a common pine shoot beetle attack. Based on an evaluation of nitrogen economy and canopy growth it is hypothesized that the growth reduction is primarily an effect of removal of needle biomass and secondarily an effect of decreased rate of nitrogen uptake. Consequences of this hypothesis are discussed and experiments aimed at testing it are suggested.

Production of larvae of Phyllobius piri L. (Col. Curculionidae) in an abandoned field

The abundance of the larvae of Phyllobius piri L. and P. viridicollis F. (Col. Curculionidae) was investigated in an abandoned field in central Sweden. On the basis of the individual growth curve and the life table of the larvae the production of P. piri was calculated to be 4.6 ± I.9 g dw per m2 or 25 ± II kcal per m2 (mean ± 95 per cent c.i.). The population of the hibernating pupae of P. piri was about 500 per m2 during three successive years. During the same period the abundance of hibernating larvae of P. viridicollis was I00-250 per m2. Notes are given on the life history of the two species. The larvae are described by B. Lekander in an appendix.