A study of the dynamics of a natural population of the freshwater crayfish, Austropotamobius pallipes

SUMMARY. 1. Population size, survival and recruitment were estimated from mark—recapture data at frequent intervals.
2. Two types of mortality were identified: (1) moult-associated—an intense but short duration mortality, and (2) overwinter mortality, which operated at a lower estimated weekly rate but over some 30 weeks.
3. Population size reached a mid-summer peak as recruitment into the catchable size classes occurred. Thereafter numbers declined slowly to the end of the growth season, followed by an overwinter decline of some 50% of total.
4. Annual production was estimated at 196.5 kg wet wt ha⁻¹ in 1977, 116.8 kg wet wt ha⁻¹ in 1978 and 87.79 kg wet wt ha⁻¹ in 1979.     

Distribution of second generation European corn borer,Ostrinia nubilalis, egg masses in field corn and relationship to subsequent tunneling damage

The relationship between second generation European corn borer (Ostrinia nubilalis Hübner) egg mass numbers and subsequent field corn damage, as measured by stalk cavity numbers, was studied in 79 fields in northeastern North Carolina over three years. A mean of 0.028 egg masses per plant (645 egg masses/23400 plants) was found over the course of the study. Significant differences in oviposition rate were detected between fields and years. Ca. 85% of egg masses were deposited in a five leaf zone surrounding the primary ear; of these, 89% were found on the lower four leaves in this zone. Egg masses appeared to be distributed randomly within fields but at low rates of incidence, and oviposition was relatively uniform between sampling areas within individual fields. Under moderate to high oviposition pressure (mean number of egg masses per plant over the duration of the oviposition period >ca. 0.02), eggs laid during the early phases of the oviposition period account for more subsequent stalk damage than eggs laid during the later phases of the oviposition period. Variations in second generation egg mass numbers accounted for ca. 70% of variation in stalk cavity numbers.     

Book reviews

Serruya, C. (Ed.) (1978) Lake Kinneret .
Reay, P.J. (1979) Aquaculture .
Neff, J.M. (1979) Polycyclic Aromatic Hydrocarbons in the Aquatic Environment. Sources, Fates and Biological Effects .
Thorp J.H. and Gibbons J.W. (Eds) (1978) Energy and Environmental Stress in Aquatic Systems .
Mordukhai-Boltovskoi, Ph.D. (1979) The River Volga and its Life .
Welcomme, R.L. (1979) Fisheries Ecology of Floodplain Rivers .
Heller, H. (Ed.) (1978) Verhandlungen, Gesellschaft für Ökologie, Kiel 1977 .
Elliott J.M. & Mann K.H. (1979) A key to the British freshwater leeches with notes on their life cycles and ecology .
Merritt R.W. & Cummins K.W. (Eds) (1978) An Introduction to the Aquatic Insects of North America .     

The causes of seasonal changes in numbers of the yellow dung fly, Scathophaga stercoraria (Diptera: Scathophagidae)

ABSTRACT. 1. Counts of adult Scathophaga stercoraria (L.) on cow pats were made in Houghall, County Durham, in 1964 and 1965.
2. A spring peak of numbers was due to adults (overwintered mainly as pupae or larvae) maturing and going to dung to breed. Numbers then dropped, rising to one or more peaks in late June—early July. In 1964 there was then a summer drop in numbers until late September. In 1965 high numbers persisted in summer associated with cooler, wetter weather. Autumn peaks in both years persisted until severe frosts or snow.
3. Mature adults, developed from eggs laid during the spring peak, form the first generation when breeding in mid-late June. No clear generations can be identified after this, due to eggs being laid daily (females have successive gonotrophic cycles). Changes in adult numbers breeding reflects survival of eggs and newly-hatched larvae 5–6 weeks earlier, and lower survival rates of adults in mid-summer compared with spring and autumn.
4. Adult Scathophaga numbers in vegetation rose as numbers on dung dropped. Females dissected to count ovariole tunica dilatations showed that most flies in vegetation were immature, with some parous flies hunting insects to develop the next batch of eggs.
5. Females on dung were dissected and found to range from immature to seven-parous. Those gravid for the first time were grossly under-represented, possibly due to wider dispersal.
6. It is suggested that seasonal changes in this r-strategist cannot be explained simply in terms of generations nor by the occurrence of adult diapause.     

秸秆还田对甘蔗地土壤优先流运动特征的影响

秸秆还田措施可改变田间土壤环境,在一定程度上影响作物生长.为探究不同秸秆还田措施对田间土壤优先流的影响,以秸秆覆盖(CM)、秸秆焚烧覆盖(BM)和无秸秆覆盖(CK)3种处理方式下的甘蔗地为研究对象,通过野外染色示踪试验,结合图像解析技术和生态学景观格局分析方法对广西不同秸秆还田措施下的甘蔗地土壤优先流运动特征进行研究....     

The use of water and some inorganic salt solutions to advance sugar beet seed. II. Experiments under controlled and field conditions

The effect of seed advancement on the early growth of sugar beet was determined in two experiments made under controlled conditions and eight field experiments made between 1974 and 1978. The experiments in the growth room suggested that seed advancement increased the rate of emergence and seedling dry weight over a wide range of soil moisture contents but seedling numbers were only greater under sub-optimal moisture conditions. Similarly, in most field experiments, seed advancement resulted in more rapid emergence and larger seedlings. In four field experiments, seed advancement gave up to 16% more plants, and in three experiments a significant increase in final sugar yield of up to 0–7 t h^-1 was detected. The plants were hand-singled to a uniform stand and had the crops been drilled to a stand, some yield responses would have been larger. Seed advancement did not decrease the plant stand or final yield in any experiments. Results in 1977 and 1978 provided some evidence that seed advancement may help reduce the damage caused by field mice and the number of plants which bolt and, by making emergence more rapid, be particularly beneficial on soils prone to slumping or capping. There might, however, be a slightly increased risk of frost injury if advanced seed is used for early sowings.     

Film Reviews

Book reviewed in this article:
Discovering Country and Western Music . 1977. Produced by Bernard Wilets.
Full of Life A-Dancin' . 1978. Produced by Robert Fiore and Richard Nevell and directed by Robert Fiore.
Guitar Craft . 1977. Produced by Rob Williams.
Gypsy Yodeler . 1978. Produced by Ron Taylor.
Homemade American Music . 1980. Produced by Carrie Aginsky and Yasha Aginsky.
New England Fiddles . 1984. Produced and directed by John M. Bishop.
Nimrod Workman: To Fit My Own Category . 1975. Directed by Scott Faulkner and Anthony Slone and produced by Appalshop
Oaksi . 1979. Directed by Anthony Slone and produced by Appalshop
Ralph Stanley's Bluegrass Festival . 1982. Produced and directed by Jim Kent.
Sourwood Mountain Dulcimers . 1976. Produced by Gene DuBey.
Sprout Wings and Fly . 1982. A film by Les Blank, Cece Conway , and Alice Gerrard.
Tough, Pretty or Smart: A Portrait of the Patoka Valley Boys . 1981. Produced by Richard Kane and Dillon Bustin.     

Reproductive performance of the Bald Ibis Geronticus calvus in relation to rainfall and grass-burning

Reproductive performance of the Bald Ibis Geronticus calvus was studied during three consecutive nesting seasons (1978–80) at a single large breeding colony in Natal, South Africa. A focal sample of 22 nest sites (out of a total of 60 in the colony) was inspected at frequent intervals to determine clutch sizes, egg survival, hatching success, nestling mortality and fledgling production in each year. Mean clutch size was slightly lower in 1980, compared to the two previous years, although survival and hatching success of eggs were similar in all three years. However, nestling mortality was significantly higher in 1980, largely as a result of parental nest desertion and nestling starvation, so that the proportion of breeding pairs producing at least one fledged offspring, and the average brood size at fledging, were lower compared to 1978 and 1979.
The 1978 and 1979breeding seasons were both preceded by 12 months of above average rainfall, and Bald Ibises fed extensively on small invertebrates obtained in burnt grassland in the study area during the nesting period. By contrast, the onset of nesting in 1980 followed 11 consecutive months of sub-normal rainfall. As a result of the drought, and the consequent lack of controlled burning by landowners in the study area in 1980, very little burnt grassland was available during the Bald Ibis' breeding season, and the birds fed primarily in cultivated pastures during the customary burning period. The lower reproductive performance of Bald Ibises at the study site in 1980 is discussed in relation to the possible effects of drought on the abundance of invertebrate prey and the extent of controlled burning in the species' grassland biotope.     

转Bt基因抗虫棉田棉铃虫消长规律及危害特点

通过对转 Bt基因抗虫棉田棉铃虫的系统调查研究表明 :(1)转 Bt基因抗虫棉对棉铃虫蛾、卵无抗性表现 ,田间落卵量与常规棉田无明显差异 ,相反 ,二代棉铃虫百株累计卵量倒比常规棉处理区增加了 2 16～ 2 74粒 ,增长幅度为 30 %～ 38% ;(2 )转 Bt基因抗虫棉对二代棉铃虫幼虫的抗性及控制作用较强 ,基本不用进行药剂防治 ,但对三代棉虫幼虫的抗性控制效果明显下降 ,田间 3龄以上幼虫平均达2 0～ 4 0头 /百株 ,多者达 6 0头以上 ,仍需进行必要的药剂防治 ;(3)棉铃虫在转 Bt基因抗虫棉株上的危害特点与常规棉株有明显的差异 ,表现在幼虫和危害症状均较隐蔽 ,不易被发现。     

Abundance and survival of a seed-infesting weevil, Pseudanthonomus hamamelidis (Coleoptera: Curculionidae), on its variable-fruiting host plant, witch-hazel (Hamamelis virginiana)

Abstract. 1. The relative importance of seed abundance and of mortality factors in the population biology of Pseudanthonomus hamamelidis , a hostspecific predispersal seed predator on Hamamelis virginiana , is evaluated by analysis of weevil life tables and abundance estimates in three years with markedly different magnitudes of fruit production.
2. Fruit production of marked Hamamelis individuals averaged 336 m^-2 in 1978, increased three- to four-fold in 1979, and declined again in 1980. More individuals fruited in 1979 than in the other two years.
3. The early larval stage of P.hamamelidis incurred the greatest mortality, with 42–58% dying from often undeterminable causes. Losses in the egg stage ranged from 22% to 31%. Three parasitoid species each accounted for minor mortality. Generation survival was similar in all three years, ranging from 21% to 28%.
4. The percentage of Hamamelis fruit crops infested by P.hamamelidis was high in 1978, averaging 76%, but was much lower in 1979, the year of abundant fruit. In 1980, when fruit were less abundant again, infestation was nearly complete. Egg densities on fruits were lower in 1979 than in the other two years.
5. The fluctuating fruit crops of Hamamelis are responsible for limitation of P.hamamelidis numbers during poor fruiting years. The occasional highly productive fruiting year results in satiation of weevil populations and concomitant seed escape by Hamamelis . Mortality factors appear less important in influencing weevil population dynamics.     

Trade-off in oviposition strategy: choosing poor quality host plants reduces mortality from natural enemies for a salt marsh planthopper

Abstract.  1. Both host plant nutrition and mortality from natural enemies have been predicted to significantly impact host plant selection and oviposition behaviour of phytophagous insects. It is unclear, however, if oviposition decisions maximise fitness.
2. This study examined whether the salt marsh planthopper Pissonotus quadripustulatus prefers higher quality host plants for oviposition, and if oviposition decisions are made so as to minimise mortality at the egg stage.
3. A controlled laboratory experiment and 4 years of field data were used to assess the rates of planthopper oviposition on higher quality 'green' and lower quality 'woody' stems of the host plant Borrichia frutescens . The numbers and percentages of healthy eggs and eggs that were killed by parasitoids or the host plant were recorded.
4. In all years, including the laboratory experiment, Pissonotus planthoppers laid more eggs on lower quality woody stems than on higher quality green stems. While host plant related egg mortality was higher in woody stems, the percentage of eggs parasitised was much greater in green stems. This resulted in a lower total mortality of eggs on woody stems.
5. The results of this study demonstrate that, although Pissonotus prefers lower quality host plants for oviposition, this actually increases fitness. These data seem to support the enemy free space hypothesis, and suggest that for phytophagous insects that experience the majority of mortality in the egg stage, oviposition choices may be made such that mortality is minimised.     

THE EFFECT OF CERTAIN PREDATORS ON THE NUMBERS OF CABBAGE ROOT FLY (ERIOISCHIA BRASSICAE (BOUCHÉ)) AND ON THE SUBSEQUENT DAMAGE CAUSED BY THE PEST

To determine the importance of beetle predators on the natural control of cabbage root fly, experiments were carried out in 1958 and 1959 using various types of barriers to obtain different levels of beetle populations on cauliflower plots. A barrier of DDT-treated straw, placed in the soil around some plots, decreased the numbers of beetles within them and allowed a greater number of eggs and larvae of cabbage root fly to survive than on the untreated plots, resulting in a greater crop damage. Another type of barrier allowed the beetles to enter plots but made it difficult for them to leave. On these, fewer cabbage root-fly eggs and larvae survived and the crop damage was much less than on the plots surrounded by straw barriers. Where plants were treated with insecticide the root-fly population was reduced to a minimum and crop yields were considerably increased. The insecticide, however, caused a reduction in the numbers of predatory beetles.     

An ant—treehopper mutualism: effects of Formica subsericea on the survival of Vanduzea arquata

Abstract. 1. The numbers of Formica subsericea (Say) were positively correlated with those of the treehopper, Vanduzea arquata Say on branches of black locust.
2. The mean numbers of V.arquata on branches were greater in the second than in the first generation. However, the mean number of ants tending them was significantly lower in the second compared to the first generation.
3. Defoliation of branches resulted in a reduction in the number of mem-bracids on branches and ant numbers declined similarly.
4. Survival of V.arquata was significantly greater when tended by F.subsericea than when ants were exciuded.
5. Ant attendance significantly reduced the number of predators on branches with _Karquata compared to branches lacking both ants and treehoppers. This, in part, explains the greater survival of V.arquata nymphs tended by ants.     

棉红铃虫田间产卵规律的进一步研究

在棉株结铃前,红铃虫一代卵主要分布于棉株新展开叶上。在棉花单株结铃达2．5个左右时,红铃虫卵均集中分布于棉青铃上。红铃虫二、三代卵分别以由外到内第二、三和第三、四大铃圆锥体位上的青铃卵量分布最多,分别占全株卵量的58．56％和67．19％红铃虫在10天以上日龄的青铃上均可产卵,其中在20～34天日龄的青龄上产卵量最大,占青铃上总卵量的55．02％。一代和二、三代红铃虫卵常分别1～8粒和1～13粒聚产成堆,单个青铃上可同期产卵1～16粒。     

Forecasting barley mildew development in West Scotland

Observations on plots of spring barley cv. Golden Promise during May-July 1973–79 showed that escalation of mildew commenced in mid-June 1976, in late June in 1973 and 1974, in early July in 1978 and 1979, and failed to develop in 1975 and 1977. By mid-July there was 40% infection in 1976, and 13–21% infection in 1973, 1974, 1978 and 1979. Less than 2% mildew occurred in 1975 and 1977. Using as a basis the method of mildew forecasting formulated by Polley & King (1973), it was found that once mildew was established in the crop there was moderately good association between the incidence of high mildew risk according to the Polley weather criteria and the major peaks of spore concentration above the crops. It was not possible to correlate these two features during May and early June each year because of a lack of inoculum, but it is considered that the failure of mildew to develop during the entire growing seasons of 1975 and 1977, in spite of frequent high risk periods, was due in part to low atmospheric humidity during the early part of the season. The relative number of accumulated Polley factors satisfied on days when the relative humidity approx. 1 m above ground was 78% or more (at 0900 GMT) during the period mid-May to mid-June, separated the low mildew years of 1975 and 1977 from the moderate ones of 1973, 1974, 1978 and 1979, and the severe mildew year of 1976. This procedure may provide a practical means of forecasting the level of mildew build-up during the later growth stages of the barley crop.     

Fire and recovery of resting egg bank: an experimental study in paddy fields in Pathum Thani province,Thailand

The effects of straw burning, exposure conditions and exposure durations on the diversity of zooplankton resting eggs were examined by hatching resting eggs in sediment collected from rice fields in Pathum Thani province, Thailand. Well-mixed surface sediment samples from with- and without straw burning paddies were stored under three conditions, (4°C and darkness; 28–40°C and darkness; and 28–40°C and light), for different periods of time (0, 2, 4, 6, 8, 10 and 12 months). Thirty zooplankton species were identified from hatching experiments. Of these, 25 species were Rotifera, 3 were Cladocera, 1 was Ostracoda and 1 was Copepoda. Repeated Measurement analysis showed that straw burning significantly decreased the number of zooplankton species, the zooplankton abundance and zooplankton diversity (P = 0.000, 0.019 and 0.004, respectively). A significant effect of storage conditions on the number of species was also present (P = 0.016), whereas zooplankton abundance and zooplankton diversity were not affected (P = 0.583 and 0.180). In addition, exposure time had an effect on number of zooplankton species and diversity (P = 0.001 and 0.033) but not on zooplankton abundance (P = 0.676). The traditional practice of residue burning post harvest therefore has a substantially negative effect on zooplankton biodiversity.     

浙江稻田稻秆潜蝇为害损失与防治指标研究

2000-2004在浙江较系统地研究了山区和半山区稻田稻秆潜蝇的种群动态与为害损失的关系,组建了田间自然种群生命表。结果表明：自然条件下,1、2代稻秆潜蝇的卵、幼虫、蛹、成虫死亡率分别为42.7%、14.5%、4.4%、12.6%和32.8%、16.5%、18.9%、15.6%。水稻秧苗期、大田期稻秆潜蝇卵（虫）量与株为害率、为害损失率的关系分析表明,随着卵（虫）量增加,株为害率上升,产量损失率加大,两者呈显著正相关。成虫盛发至卵孵盛期为防治适期,稻秆潜蝇防治指标为秧苗期平均每百株有卵10粒,株为害率1%以上;大田期平均每丛水稻有卵1粒,株为害率3%～5%。     

华北棉区玉米田三代棉铃虫种群动态及其对棉田发生为害的作用分析

本文通过玉米田、棉田中对棉铃虫(Heliogyis armigera)种群动态的系统调查和自然种群生命表的分析,明确了玉米田是三代棉钰虫的重要栖境。并且棉铃虫在玉米田的幼期死亡率显著高于棉田。通过棉田三代棉铃虫的影响指数分析,在9个变量中,玉米田与棉田种植面积的比值被确定为主动因素,而棉田二代棉铃虫卵量被确定为关键因素。最后通过当地1973-1991年共19年的资料对上述结果进行了检验,获得了满意的结果。     

The influence of ants and water availability on oviposition behaviour and survivorship of a facultatively ant-tended herbivore

1. The lycaenid butterfly Hemiargus isola associates facultatively with the ant species Formica perpilosa in arid areas of south-western North America. Ants solicit liquid food rewards from butterfly larvae as larvae feed on the host plant, Acacia constricta . Previous studies have shown that tending by F. perpilosa enhances larval growth and pupal survivorship.
2. The effects of ants and plant water content on oviposition behaviour and survivorship to the last larval instar were tested by excluding ants and supplementing water to host plants in a two-way factorial experiment.
3. Butterflies, which lay eggs singly on host plant inflorescences, laid significantly higher egg numbers and densities (eggs/inflorescence) on plants with ants than on plants without ants. This is the first report of a facultative, generalized ant-associate using ants as oviposition cues. Water supplements increased the number, but not the density, of eggs laid on plants. Therefore, it appears that egg-laying butterflies responded to number of inflorescences, rather than plant tissue water per se .
4. Plants with ants had significantly greater numbers of inflorescences during the experiment than plants without ants. Water supplements increased number of inflorescences slightly, but not significantly.
5. Ants increased larval survivorship. Twice as many fourth-instar larvae survived per egg laid on plants with ants than on plants without ants. Ants did not reduce the number of predators present on acacias, but may have reduced predator effectiveness. Ants also did not reduce the numbers of potential H. isola competitors present.
6. Water supplementation affected neither the survivorship of H. isola larvae, nor the intensity of ant tending. Water supplementation did not affect the abundance of predators on plants, but did increase the abundance of several herbivorous insect taxa.     

The effect of weeds on the numbers of hoverfly (Diptera: Syrphidae) adults and the distribution and composition of their eggs in winter wheat

The abundance and species composition of syrphid adults in herbicide-treated and untreated headlands was recorded in a replicated within-field experiment conducted over a two-year period. The highest numbers of the most abundant syrphid species, Episyrphus balteatus, were recorded in the untreated headland strips. Analysis of the behaviour of the adult flies showed that they were retained in the untreated strips because they were foraging on the flowering non-crop plants. The distribution of syrphid eggs between herbicide treated and untreated headland replicates was examined. A significant positive relationship between the numbers of eggs per aphid and weed density was detected during June in the second year of the study. This is in part attributed to the tendency of Melanostoma females to oviposit on non-crop plants. The implications of the implementation of a modified herbicide regime in the headlands of cereal fields for the biological control of cereal aphids by syrphid larvae is discussed.