低浓度SO2污染与桃蚜的生长和繁殖

用40或80ppbSO₂熏气处理过的油菜饲养桃蚜(Myzus persicae),研究低浓度SO₂污染对这种蚜虫的影响。与对照组相比,两个处理组若蚜的发育速率显著加快,5天内的平均相对生长速率(MRGR)分别增加22.3%和31.5%。成蚜的繁殖力提高40—90%,导致桃蚜种群的内禀增长率(r_m)分别升高17%和27%。比较了桃蚜和其它3种蚜虫对SO₂污染的反应强度,讨论了SO₂污染促进某些植食性昆虫生长的可能原因。     

Free fatty acids, neutral and polar lipids in Hordeum vulgare exposed to long-term fumigation with SO2

Three 9-day-old cultivars of Hordeum vulgare L. (Barberousse, Gerbel and Panda) were exposed to low levels of SO₂ fumigation (40 ± 5 and 117 ± 20 ppb). After 48 days of treatment the seedlings were harvested for lipid analysis. In comparison to the control (plants exposed to charcoal-filtered air), the total lipid content of fumigated seedlings declined at 40 ppb SO₂ and even more so at 117 ppb in all three cultivars. A large reduction in diacylglycerols. polar lipids and free sterols was also observed after fumigations at both SO₂ concentrations, whereas the treatments resulted in an increase in triacylglycerols and free fatty acids. The percentage composition of total fatty acids and that of each lipid class were changed by the fumigations. resulting in an increase in the degree of unsaturation. No changes in the percentage composition of sterols occurred in the fumigated leaves. These results suggest that even if SO₂ may not directly oxidize unsaturated fatty acids at the low concentrations used here (which do not cause visible injury). it may alter lipid metabolism. This alteration. which was particularly evident in the polar lipids and sterols, could affect the functions associated with membrane stabilization, in which lipids plus sterols play a key part.     

Evaluation of Bt-toxin uptake by the non-target herbivore, Myzus persicae (Hemiptera: Aphididae), feeding on transgenic oilseed rape

As consequence of the concern about the biosafety of genetically modified plants, biological and ecological studies are considered crucial for environmental risk assessment. Laboratory experiments were carried out in order to evaluate the transfer of the Cry1Ac Bt-toxin from a transgenic Bt-oilseed rape to a non-target pest, Myzus persicae Sulzer. Cry1Ac protein levels in plants and aphids were determined using a double sandwich enzyme-linked immunosorbent assay. Phloem sap from (Bt+) and (Bt-) oilseed rape plants was collected from leaves using a standard method of extraction in an EDTA buffer. Bt-toxin was present in phloem sap, with a mean concentration of 2.7 +/- 1.46 ppb, corresponding to a 24-fold lower level than in oilseed rape leaves. Toxin was also detected in aphid samples, with a mean concentration in the positive samples of 2.0 +/- 0.8 ppb. The evidence that Bt-toxin remains in herbivores, in this case an aphid, could be useful to clarify functional aspects linked to possible consequences of Bt-crops on food chains involving herbivore-natural enemy trophic systems. Further studies are needed in order to improve the knowledge on the functional aspects linked to the transfer of the Cry1Ac Bt-toxin from GM-oilseed rape to aphids and their possible consequence.     

EFFECTS OF RAPE GROWN IN SO2-ENRICHED ATMOSPHERES ON PERFORMANCE OF THE APHID,MYZUS PERSICAE (SULZER) *

Abstract Performances of the aphid, Myzus persicae, were monitored during feeding on leaves of the rape, Brassica chinensis, previously fumigated with SO₂ in a range of concentrations between 20 and 160 nl/1 at 25°C. Response of the aphids depended on dose of the air pollutant. Moderate dose of SO₂ treatment on the rape greatly enhanced the aphids' performances while high level of the pollutant heavily suppressed their growth and reproduction. They performed best at about 80 nl/l SO₂, where nymphal mean relative growth rate (MRGR), adult fecundity and intrinsic increase rate(r_m) of the population increased by 31.5%, 89.8% and 42. 7% over those of control aphids, respectively. Determination of the plant chemistry suggests that the altered relative content of methionine induced by So, exposure might be responsible for this response of dosage dependence.     

二氧化硫对墨西哥豆瓢虫的影响

空气污染对害虫的影响,国内尚无研究报道。本文报道了作者在美国农业研究中心植物胁迫实验室进行的部分工作。实验结果表明,在0.30ppmSO_2的作用下,墨西哥豆瓢虫(Epilachna varivestis)的取食量和蛹重增加;与未受污染的寄主植物相比,豆瓢虫偏食受污染的植物;而且有嗜食含较高糖分寄主植物的倾向;在污染空气中长成的成虫可消耗更多的植物物质。     

蚕豆叶片SOD活性监测大气SO2污染的可行性研究

 本文从实验室熏气和野外大气暴露两方面对利用蚕豆叶片SOD活性评价和监测大气SO2污染的可行性进行了研究。低浓度SO2(0.1312、0.2601mg·m-3)处理,引起叶片SOD活性升高,一定时间后,SOD活性趋于稳定,且0.2601mg·m-3SO2处理时,SOD活性较高,表现出SOD活性增量与SO2浓度相关,为利用SOD活性监测和评价SO2污染提供了可能性。大气暴露试验结果表明SOD活性与大气硫酸盐化速率存在极显著的相关性。利用SOD活性和大气硫酸盐化速率分别对大气SO2污染程度进行了评价,结果基本一致,并根据SOD活性估测了大气硫酸盐化速率,符合程度较高,置信分析表明估测结果可信。以上结果表明,利用蚕豆叶片SOD活性监测和评价大气SO2污染是可行的。     

Effect of soil potassium availability on soybean aphid (Hemiptera: Aphididae) population dynamics and soybean yield

Studies were conducted to examine the effect of potassium (K) on soybean aphid, Aphis glycines Matsumura, population growth. A laboratory feeding assay examined the effect of K-deficient foliage on life table parameters of soybean aphids, and field experiments were designed to determine the effect of three soil K treatment levels on aphid populations and their impact on soybean yields. The feeding assay found that life table parameters differed between aphids feeding on the K-deficient and nondeficient soybean leaves. Soybean aphids in the K-deficient treatment exhibited significantly greater intrinsic rate of increase (r(m)), finite rate of increase (lambda), and net reproductive rate (Ro) relative to aphids feeding on nondeficient leaves. No significant difference was observed in mean generation time (T) between the two treatments. However, the field experiment repeated over 2 yr showed no effect of K on soybean aphid populations. Soybean aphid populations were high in unsprayed plots and feeding resulted in significant yield losses in 2002 at all three K treatment levels: when averaged across 2001 and 2002, unsprayed treatments yielded 22, 18, and 19.5% less than the sprayed plots in the low, medium, and high K treatments, respectively. No significant interaction was observed between aphid abundance and K level on soybean yields in either year. This study therefore suggests that although aphids can perform better on K-deficient plants, aphid abundance in the field may be dependent on additional factors, such as dispersal, that may affect final densities within plots.     

Degradation of membrane lipid components and antiovidanl levels in Hordeum vulgare exposed to long-term fumigation with SO2

Hordeum vulgare L. (cv. Barberousse) seedlings were continuosly exposed to SO₂ (40±5 and 117±20 ppb) for 48 days and compared to control plants exposed to charcoal-filtered air. Glyco-and phospolipid amounts were strongly affected by exposure to SO_2:, and decreased with increasing SO₂, fumigation. The chloroplast membranes of fumigated leaves were characterized by lower quantities of rnonogalacto-syldiacylglycerol (MGDG) as well as of sulphoquinovosyldiacylglycerol (SQDG). Among the phospholipids a decrease in the phosphatidylglycerol (PG) content was observed, indicating that the chloroplast membranes are affected even by such low concentrations of SO₂ as used here. As for the other phospholipids, phosphatidylcholine (PC) and phosphatidylinositol (PI) suffered a reduction and phosphatidylethano-lairrine (PE) almost disappeared at the highest SO₂, concentration, whereas phosphatidic acid (PA) followed the opposite trend. The fatty acids of both glyco- and phospholipids fell sharply upon fumigation without any decline in the degree of unsataration. In particuSar, neither linoleic nor linolenic acid showed any evident change in level, suggesting that no lipid peroxidation of polytmsaturated fatty acid tails occurred. Furthermore, the electron spin resonance (ESR) showed no differences in the free radical levels between control and fumigated leaves. The level of malondialdehyde (MDA) decreased, while lipid-soluble antioxidants, as well as superoxide dismutase (SOD; EC 1.15.1.1) and catalase (EC 1.11.1.6) activities increased with the increase in SO₂ concentration, providing evidence that defence mechanisms against oxy-radical action are activated by the plants at low levels of SO₂,. Even if SO₂, at low concentrations may not directly oxidize polyunsaturated fatty acids, it may act as a deesterifying factor on each component of both glyco- and phospholipids.     

The development of an action threshold for cabbage aphid (Brevicoryne brassicae) in oilseed rape in the UK

Replicated small plot field experiments were done at two sites growing winter oilseed rape (ADAS Boxworth, Cambridgeshire and ADAS High Mowthorpe, North Yorkshire) and two sites growing spring oilseed rape (ADAS Bridgets, Hampshire and ADAS Rosemaund, Herefordshire) to investigate the effect of cabbage aphid (Brevicoryne brassicae) on crop yield and quality. All four sites were included in the first 2 yr of the experiment in 1994 and 1995 but only those with winter oilseed rape were continued into the final year in 1996. Plots were artificially inoculated with cabbage aphids at either five aphid 4 m^-2 or 5 aphids 16 m^-2 or left uninoculated to become naturally infested. In 1995 and 1996 the naturally infested treatment was omitted. Sprays of the aphicide pirimicarb at GS 3.3, 3.7, 4.5, 4.9 and 5.5 were used to manipulate aphid populations. Once a plot had been treated at a target growth stage it was sprayed on all subsequent occasions to prevent recolonisation. Aphid numbers were assessed prior to each spray date and their effect on the crop measured in terms of yield of seed and oil and glucosinolate content. Artificial inoculation of aphids was often successful in establishing different populations of the pest at a range of growth stages. Results showed that cabbage aphid sometimes reduced both crop yield and quality. Yield responses to insecticide treatment tended to be larger in spring oilseed rape than in winter oilseed rape mainly because it became more heavily infested at an early growth stage. Tentative thresholds are proposed for control of the pest in both winter and spring oilseed rape. It is stressed that cabbage aphid is a sporadic pest and rarely likely to reach these threshold levels in field crops.     

How does the host‐specialized aphid deal with food deficiency?

Aphis gossypii Glover shows obvious host specialization, with cucurbit‐ and cotton‐specialized biotypes or host races in many regions. Because its annual natal host crops senesce earlier the cucurbit‐specialized biotype may suffer food deficiency. The method this biotype uses to overcome this challenge is still poorly understood. In order to understand the potential of the cucurbit‐specialized biotype aphids in host shift and usage, the performance of this biotype on cotton (Gossypium hirsutum), a common but poor quality host plant, was explored in this study. The cucurbit‐specialized aphids could establish populations on cotton only when these plants had at least nine leaves, and subsequent populations developed rather slowly. The presence of whitefly populations on cotton improved the success rate of cucurbit‐specialized aphids. The cucurbit‐specialized aphids were mainly distributed on the older leaves of cotton, with only a few settling on the upper leaves. The cucurbit‐specialized aphids reared on cotton for 40, 54 and 61 days still maintained strong preference for their natal host plant, cucumber (Cucumis sativus), rather than cotton, and their net reproductive rates and intrinsic rates of natural increase were dramatically lower when they were transferred onto new six‐leaf cotton plants or detached leaves. Therefore, we concluded that the cucurbit‐specialized aphids have the potential to utilize mature or whitefly‐stressed cotton plants, but that this feeding experience on cotton did not alter their specialization for cucurbits. Some cotton plants could act as a temporary host for the cucurbit‐specialized aphids to overcome food deficiency arising from senescing cucurbits.