Genetic diversity in a seed production population vs. natural populations of Sitka Spruce

Isozyme analysis was applied to estimate the level of variation and the genetic structure of a seed-production population (i.e., seed orchard) and 10 range-wide natural populations of Sitka spruce (Picea sitchensis (Bong.) Carr.). Gene diversity and heterozygosity estimates were comparatively high in both the seed orchard and the natural populations studied. The seed orchard population showed a significantly higher number of alleles per locus and percentage of polymorphic loci. Though not significant, mean heterozygosity of the seed orchard was higher than that observed for all natural populations. Genetic distance analysis indicated that the seed-orchard population was genetically similar to three natural populations from which the parent trees were selected. Parent trees sampling breadth has been identified as the major cause for the observed increased level. The impact of recurrent selection and seed orchard biology and management on maintaining the genetic diversity is discussed.     

Population dynamics of the citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae) in Japanese pear orchards

In spring a population of the citrus red mite (Panonychus citri),a non-diapausing species, migrated to a Japanese pear orchard, mainly from nearby Japanese holly trees, but in autumn most of the mites starved to death while the rest returned to the holly trees. In the Japanese holly trees, the population of mites reached their maximum density in late May1993 and in mid-June 1994 on overwintered leaves and moved to newly opened leaves in mid-June 1993 and late June 1994. The mites tended to disperse abruptly in early June or mid-June and again towards the end of June. The mites inhabiting the holly trees appeared to migrate to the Japanese pear trees in June but their densities on pear leaves remained low until mid-August. In the pear orchard, the mites initially tended to increase on pear leaves near the holly trees and then gradually spread to other leaves farther away from the holly trees. Their highest density in the pear orchard occurred in mid-October. When pear leaves were inoculated with two or five female adults at different times from May to September, the leaves inoculated before mid-August showed no increase in the number of mites. A possible cause for the suppression of the population increase on pear leaves from June to mid-August is discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Cross-correlation analysis of fluctuations in local populations of pear psyllids and anthocorid bugs

1. To test whether predatory anthocorids migrate into pear orchards when populations of pear psyllids are building up, a cross-correlation analysis was carried out on their population numbers. Predator and prey population sizes were assessed weekly in 3 consecutive years (1991–93) by sampling pear leaves for eggs and nymphs of psyllids and pear tree branches for adult psyllids, as well as adults and nymphs of predatory anthocorids. The time-series consisted of numbers (per leaf or branch) averaged over preselected pear trees in an orchard and, in addition, over other trees selected along the hedgerows flanking the orchard. 2. The fluctuations in populations of adult and juvenile anthocorids showed strong cross-correlations with those of the eggs and nymphs of pear psyllids, but less correlation with adults of pear psyllids, as expected based on their increased ability to escape from predation. The psyllids always appeared first on the pear trees, resulting in positive phase shifts. The first peak of adult anthocorids on pear trees was always later than the first peak in the hedgerows, and the first peak of nymphal anthocorids on pear trees was always later than the first peak of adults on these pear trees. In each of the 3 years, anthocorids were rarely observed in the pear orchard during the first part of the growing season (April–June), but during the second half of the growing season (July–August) there was a strong numerical response of the anthocorid populations to increasing population densities of pear psyllids. 3. These results provide support for the hypothesis that the numerical response of the predators to prey density is caused initially by migration of anthocorids into the pear orchard and then by a reproductive response. The migrants originate from the hedgerows and other trees elsewhere, where they feed on aphids during the first part of the growing season.     

Gene flow estimation with microsatellites in a Malagasy seed orchard of Eucalyptus grandis

Eucalyptus grandis has a mixed-mating reproductive system. Malagasy Eucalyptus seed orchards were established 15 years ago with two aims both based on panmixia: open-pollinated seed production and genetic improvement. The panmixia hypothesis has never been confirmed in the seed orchard. From a seedling seed-orchard stand comprising 349 trees and using data obtained with six selected microsatellite markers, paternity analysis was performed for 724 offspring collected on 30 adult trees. Paternity assignment, based on exclusion procedures and likelihood-ratio method, was achieved with high accuracy; the exclusion probability value was 0.997. The outcrossing rate was very high (96.7%). More than 50% of potential male trees (199 out of 349) in the seed orchard contributed to pollination for 440 offspring of 30 progenies (8.6% of the basic population). The pollination rate from outside the seed orchard was high (39.2%), but might be due to the small size of this seed orchard. This study showed that "panmixia-like pollination" can be assumed.     

苹果园植被多样化在果树害虫持续治理中的作用

1992-1995年对四个不同类型苹果园进行了系统调查,结果表明引入夏至草、泥胡菜等有益杂草并与树行间种植的紫花苜蓿搭配的生草园,捕食性天敌发生量大,种群稳定,发生高峰期较免耕园、清耕园提前7d左右;害虫发生量低,种群数量变化平稳,无突增现象,生草园在未施用任何杀虫、杀螨剂的情况下,树冠上蚜虫、叶螨和潜叶蛾的平均虫口密度均低于免耕园、清耕稀植园和密植园。生草园寄生性天敌的数量亦明显增加,金纹细蛾的寄生率高达62.7%,分别是免耕园、清耕稀植和密植园的1.34倍、16.9倍和17.9倍。果园植被多样化可使地面植被上的天敌数量逐年成倍提高,生草第3年捕食性天敌的数量是生草当年的12.5倍,树冠上天敌量亦明显增加,益害比大大提高,生草第2年树冠上最大蝽螨比为1∶14.4,与原先油菜与紫花苜蓿搭配生草5年的效果相近。除当年生草果园(1992年)早期施用1次杀螨剂—螨克外,1993、1994年均未施用任何杀虫、杀螨剂,通过天敌的自然控制作用,有效地控制果树害螨、蚜虫和金纹细蛾等次生性害虫的为害。     

Performance of a pyrethroid-resistant strain of the predator mite Typhlodromus pyri (Acari: Phytoseiidae) under different insecticide regimes

An organophosphate pyrethroid-resistant strain of Typhlodromus pyri Scheuten imported from New Zealand was reared on potted apple trees in an outdoor insectary. From 1988 to 1995, the population was selected one to three times per year with a dilute solution (1.7 ppm) of the pyrethroid cypermethrin. Petri dish bioassays with cypermethrin in 1995 indicated that the insectary-reared T. pyri had an LC50 of 81 ppm versus 0.006 ppm for native T. pyri taken from a research orchard. The bioassays suggested that recommended orchard rates of cypermethrin would cause heavy mortality in native populations of T. pyri but only moderate losses in the imported New Zealand strain. Bioassays in 1996 with the organophosphate insecticide dimethoate indicated both New Zealand and native T. pyri were susceptible and that recommended orchard rates of dimethoate likely would cause high mortality of T. pyri in apple orchards. These findings from bioassays were supported by data from orchard trials. In June and July 1993, insectary-reared New Zealand T. pyri were placed on five apple trees in each of eight 38-tree plots in the research orchard. In late August 1994, New Zealand T. pyri from orchard trees that had been sprayed twice by airblast sprayer with the full recommended rate of 50 g (AI)/ha (83 ppm) cypermethrin were placed on the other 33 trees in each of six plots. In the summers of 1994-1996, plots were treated with one of the following insecticide regimes: (1) conventional integrated pest management (IPM) (registered neurotoxic insecticides considered harmless or slightly toxic to T. pyri); (2) advanced IPM (use of newer, more selective insecticides); (3) pyrethroid (at least one full-rate application of cypermethrin); (4) dimethoate; and (5) dimethoate plus pyrethroid. Densities of European red mite, Panonychus ulmi (Koch), were highest in all plots treated with dimethoate and in pyrethroid plots not yet inoculated with New Zealand T. pyri. Densities of apple rust mite, Aculus schlechtendali (Nalepa), and of the stigmaeid predator Zetzellia mali (Ewing) were highest in plots treated with dimethoate and were nearly absent in the IPM plots. Densities of T. pyri were high enough for effective biocontrol in the IPM plots and in the pyrethroid plots 1-2 yr after release of the New Zealand strain, provided pyrethroid was applied just before the resistant strain was released in the orchard. A recurring theme of this study was the generally negative association between densities of phytophagous mites and those of T. pyri, suggesting the ability of this predator to suppress their prey. In contrast, the positive association between phytophagous mites and Z. mali suggests the inability of this predator to regulate their prey at least under the conditions of this study.     

Movement of adult pecan weevils Curculio caryae within pecan orchards

1 The pecan weevil Curculio caryae (Horn) (Coleoptera: Curculionidae) is an indigenous pest of pecan Carya illinoinensis (Wangenh.) K. Koch, in North America. Understanding the movement of this pest from the orchard floor to host trees could lead to pest management practices that exploit weevil behaviour and thus reduce insecticide application to the entire orchard canopy. Furthermore, no information exists on diel periodicity of pecan weevil movement. 2 Movement of adult pecan weevils crawling and flying to the host trunk, flying to the host canopy, crawling within the host canopy and flying between host trees was studied using four types of passive traps over four seasons. Each type of trap was used to capture weevils at different locations on or near the tree and to discriminate flying versus crawling behaviour. 3 More pecan weevils crawl to the trunk than fly and a proportion of the population flies directly from the orchard floor into the pecan canopy. The majority of this movement occurs at dusk. 4 The vertical distribution of weevils was generally uniform throughout the canopy but more weevils were captured in suspended traps nearest tree tops, rather than traps near the ground, when flying between trees and this was significantly so for two of 4 years. 5 The results of the present study are contrary to previous reports suggesting that most adult pecan weevils fly to the pecan trunk after emergence from the soil; however, our results did indicate that a proportion of the population flies directly from the orchard floor into the pecan canopy and thus would circumvent strategies that attempt to control weevils moving up the trunk.     

Phylloplane fungi: an extrinsic factor of tetranychid population growth?

In a study on leaf-inhabiting tetranychid mites (Tetranychus urticae Koch–TSSM and Panonychus ulmi (Koch)–ERM) we investigated the effects of an extrinsic factor on the mites environment, namely phylloplane fungi. In a research orchard four trees were selected and treated with an aerosol application of a phylloplane fungus (Alternaria alternata) in a tap-water emulsion. Applications were made immediately after each sampling, with the exception of the last sample date. Two tap water controls for each treated tree were also sampled: a nearest neighbour (< 3 m from the treated trees) and a distant neighbour (> 30 m from the treated trees with other apple trees in between). Due to possible migration from the treated trees to near neighbours, the distant control best reflected normal orchard conditions. Eight samples were taken throughout the 1994 growing season; however, appreciable mite populations were only observed on the last four sample dates. On the treated trees, the ERM maintained a steady low population (less than ten per leaf) whereas the TSSM showed a population outbreak (up to 44 mites per leaf). Conversely, on the distant trees, the TSSM maintained a low population (less than ten per leaf) while the ERM showed an outbreak (up to 33 per leaf). Observing on a leaf by leaf basis, when tetranychids were present on a leaf, either one species dominated or the other, suggesting mutual competitive exclusion, the outcome of which was reversed to favour TSSM on trees that received an application of fungus. We concluded that the application of additional or supplemental amounts of A. alternata to apple leaves enhanced the population growth of TSSM compared to that of ERM. Possible mechanisms are discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Life cycle of a non-diapausing population of the two-spotted spider mite,Tetranychus urticae Koch in a pear orchard

The life cycle of a non-diapausing T. urticae population was studied in a pear orchard in the southern part of Okayama Prefecture, western Honshû, Japan. The mites overwintered only on biennial weeds in the orchard without entering diapause, started to increase in number in early spring on them and then moved to other weeds as they emerged. The occurrence of the mites on pear began in early May several weeks after the unfolding of pear leaves and the population on pear was initiated by the migrants from the weeds around the base of pear trees. The population on pear showed two distinct peak occurrences, one in June and the other in mid-autumn. After pear leaves dropped in late autumn, the mites returned to biennial weeds for overwintering.     

Prey availability,pesticides and the abundance of orchard spider communities

In a 4 year study, in southern England, the abundance of apple orchard canopy spiders and their potential prey was manipulated using two pest management strategies based on broad spectrum (highly toxic both to spiders and pests) and selective (moderately toxic to spiders but highly toxic to pests) insecticides in the first part of the growing season. The spider community was left to develop freely afterwards. Apple orchard plots untreated by pesticides served as control.The effect of insecticides was detrimental to spider populations as the treatments coincided with the peak abundance of adults in May and early June. Within adults, the treatments were harmful to female spiders, whereas, male spiders were much less affected. As a result the proportion of males increased in all of the sampled spider families.The use of selective insecticides resulted in a higher spider abundance compared to the use of broad spectrum compounds while the highest spider abundance was found in the pesticide free trees, i.e. three significantly different spider abundance levels were produced in spring. Spider abundance began to increase unequally between the treatments afterwards and became identical in the two pesticide treated plots due to the immigration of juveniles from surrounding habitats. However, a similar equalisation of abundance was not observed between the pesticide treated plots and untreated control. Analysing the abundance pattern of potential prey in the plots of the studied orchard we concluded that the post-disturbance increase in spider abundance was regulated by prey availability.     

A ten-year study of population dynamics of citrus pests in the pesticide-reduced orchard

To determine the effectiveness of a pest management system that uses pesticides at a low level, we censused populations of seven insect pests and three plant diseases from 1980 to 1989 in a citrus orchard which was managed with a pesticide-reduced and pesticide-free protocols, in Wakayama Prefecture, Japan. In the orchard, we controlled the pests solely by spraying petroleum oil once a year from 1980 to 1985, by not spraying insecticide in 1986, and spraying only germicide in 1987. The arrowhead scale population remained much lower level at which citrus trees begin to wither when petroleum oil was sprayed, whereas it rapidly increased and began to wither trees during the years without spraying petroleum oil. The Indian wax scale population rapidly increased only during a 2-year period and then declined. Although the infection level of the sooty mold was unusually high on the trees where the density of the scale was high, this pathogen did little damage to citrus trees. The population of the red wax scale gradually increased throughout the census period but did not reach the level at which citrus trees begin to be damaged. Other pests also caused negligible damages to citrus trees. The results indicated that the pesticide-reduced pest management system which was proposed by Inoue and Ohgushi (1976, 1977) is valid for the prevention of the outbreak of the arrowhead scale, and that is has the sufficient control efficiency for the other pests in citrus orchards.     

Simultaneous estimation of pollen contamination and pollen fertilities of individual trees in conifer seed orchards using multilocus genetic data

Seed orchards of forest trees are established to produce genetically-improved seed for reforestation. Genetic efficiency requires seed orchards to be (1) reproductively isolated form surrounding trees, (2) that there be similar fertilities among all orchard trees, and (3) minimum inbreeding. Each aspect of seed orchard reproduction can be simultaneously estimated using the observed frequency of each multilocus gametic type contributed through fertilizing pollen and the expected multilocus gametic segregation frequencies of orchard tree and of the contaminating population. These genetic estimates are directly relevant to the genetics of the tree breeding program. The flexibility of sampling seed — the basic data for these techniques — allows great scope for hypothesis testing, including tests of the accuracy of predictions of biophysical models of pollen movement. A simple example and a white spruce seed orchard case study are presented to illustrate the estimation technique and to investigate its sensitivity.     

The Speciation History of Drosophila Pseudoobscura and Close Relatives: Inferences from DNA Sequence Variation at the Period Locus

Thirty-five period locus sequences from Drosophila pseudoobscura and its siblings species, D. p. bogotana, D. persimilis, and D. miranda, were studied. A large amount of variation was found within D. pseudoobscura and D. persimilis, consistent with histories of large effective population sizes. D. p. bogotana, however, has a severe reduction in diversity. Combined analysis of per with two other loci, in both D. p. bogotana and D. pseudoobscura, strongly suggest this reduction is due to recent directional selection at or near per within D. p. bogotana. Since D. p. bogotana is highly variable and shares variation with D. pseudoobscura at other loci, the low level of variation at per within D. p. bogotana can not be explained by a small effective population size or by speciation via founder event. Both D. pseudoobscura and D. persimilis have considerable intraspecific gene flow. A large portion of one D. persimilis sequence appears to have arisen via introgression from D. pseudoobscura. The time of this event appears to be well after the initial separation of these two species. The estimated times since speciation are one mya for D. pseudoobscura and D. persimilis and 2 mya since the formation of D. miranda.     

Evaluation of dry-adapted strains of the predatory mite Neoseiulus californicus for spider mite control on cucumber, strawberry and pepper

The goal of this study was to evaluate spider mite control efficacy of two dry-adapted strains of Neoseiulus californicus. Performance of these strains were compared to a commercial strain of Phytoseiulus persimilis on whole cucumber, pepper and strawberry plants infested with Tetranychus urticae at 50 +/- 5% RH. Under these dry conditions predators' performance was very different on each host plant. On cucumber, spider mite suppression was not attained by any of the three predators, plants 'burnt out' within 4 weeks of spider mite infestation. On strawberry, all predators satisfactorily suppressed spider mites yet they differed in short term efficacy and persistence. Phytoseiulus persimilis suppressed the spider mites more rapidly than did the BOKU and SI N. californicus strains. Both N. californicus strains persisted longer than did P. persimilis. The BOKU strain was superior to SI in population density reached, efficacy in spider mite suppression and persistence. On pepper, in the first 2 weeks of the experiment the BOKU strain was similar to P. persimilis and more efficacious in spider mite suppression than strain SI. Four weeks into the experiment the efficacy of P. persimilis dropped dramatically and was inferior to the SI and BOKU strains. Overall, mean predator density was highest on plants harbouring the BOKU strain, lowest on plants with P. persimilis and intermediate on plants with the SI strain. Implications for biocontrol of spider mites using phytoseiid species under dry conditions are discussed.     

Population Characteristics and Dosage Trajectory Analysis for Mesocriconema xenoplax in California Prunus Orchards

The Mesocriconema xenoplax population increased exponentially in a newly planted peach orchard. The rate of increase was greater on Nemaguard than on Lovell rootstock and was reduced by postplant nematicides. Population levels were more stable in an established almond orchard on Nemaguard rootstock. All life stages of the nematode were present year round; lower ratios of juveniles to adults in summer suggested adverse effects of temperature and dry soil. Also in summer, there was a smaller proportion of the population in the upper 30 cm of soil than at greater depths. Nematode dosage, average nematode density multiplied by accumulated degree-days (physiological time) of the sampling interval, was useful in quantifying nematode stress on trees and as an indicator of the nematode management effectiveness. The annual trajectory of the nematode dosage could be determined by two samplings, one in spring and one in fall. A nematode predator, the parasitic fungus Hirsutella rhossiliensis, did not regulate ring nematode populations in the newly planted orchard; a recovery period was necessary for increase in the prevalence of parasitism.     

Complex patterns of mating revealed in a Eucalyptus regnans seed orchard using allozyme markers and the neighbourhood model

The neighbourhood model apportions offspring of individual mother plants to self-fertilization, outcrossing to males within a circumscribed area around the mother plant (the neighbourhood), and outcrossing to males outside the neighbourhood. Formerly the model was applied only to haploid pollen gametes in the offspring of conifers, but is extended so that it can be used with genotypic data from diploid offspring of both angiosperms and gymnosperms. In addition, it is shown that the mating parameters can be estimated without independent estimates of allele frequencies in the pollen pools outside the neighbourhood; thus the model might be applied effectively to natural populations exposed to unknown external pollen sources. Parameters of the neighbourhood mating model were estimated for a 10-year-old seed orchard population of the insect-pollinated tree, Eucalyptus regnans, in southeast Australia, which contained a mixture of two geographical provenances (Victoria and Tasmania). The mating patterns revealed were complex. Crosses between trees of the same provenance occurred three times more often than crosses between trees of different provenances. Levels of self-fertilization and patterns of mating within neighbourhoods were influenced by provenance origin, crop fecundity and orchard position (central vs. edge) of mother trees. Gene dispersal, however, was extensive, with approximately 50% of effective pollen gametes coming from males more than 40 m away from mother trees (average distance between neighbouring trees was 7.4 m). Thus, insect pollinators are efficient promoters of cross-fertilization in this orchard, with the result that the effective number of males mating with each female is large.     

Patterns and Drivers of Scattered Tree Loss in Agricultural Landscapes: Orchard Meadows in Germany (1968-2009)

Scattered trees support high levels of farmland biodiversity and ecosystem services in agricultural landscapes, but they are threatened by agricultural intensification, urbanization, and land abandonment. This study aimed to map and quantify the decline of orchard meadows (scattered fruit trees of high nature conservation value) for a region in Southwestern Germany for the 1968 2009 period and to identify the driving forces of this decline. We derived orchard meadow loss from 1968 and 2009 aerial images and used a boosted regression trees modelling framework to assess the relative importance of 18 environmental, demographic, and socio-economic variables to test five alternative hypothesis explaining orchard meadow loss. We found that orchard meadow loss occurred in flatter areas, in areas where smaller plot sizes and fragmented orchard meadows prevailed, and in areas near settlements and infrastructure. The analysis did not confirm that orchard meadow loss was higher in areas where agricultural intensification was stronger and in areas of lower implementation levels of conservation policies. Our results demonstrated that the influential drivers of orchard meadow loss were those that reduce economic profitability and increase opportunity costs for orchards, providing incentives for converting orchard meadows to other, more profitable land uses. These insights could be taken up by local- and regional-level conservation policies to identify the sites of persistent orchard meadows in agricultural landscapes that would be prioritized in conservation efforts.     

苹果园主要害虫生态调控体系的研究

通过在果园地面种植牧草或花生、油菜等覆盖作物,改善了生态环境,为天敌种群提供了良好的栖息条件和充足猎物,促进天敌群落的早期发展,在4－6月份使树上天敌总量增加60％,地面捕食性天敌增加20倍以上,不仅使苹果蚜、螨高峰期推迟,并使高峰值分别降低39％和1倍以上,使前中期害虫得很好控制。良好的果园生态环境也可促 使周围农田生态系中的天敌因季节性变动向果园迁移,并通过不同生态系之间的运动,扩大天敌种群,达到控制中后期害虫的效果,对优势天敌因季节性变动向果园迁移,并通过不同生态之间的运动,扩大天敌种群,达到控制中后期害虫的效果,对优势天敌在果园生态系中的作用亦做了研究和评价,认为在天敌－害虫相互作用系统中,天敌群落的综合功能是最重要的,针对不同害虫,小花蝽、草蛉、六点蓟马、赤眼蜂等也具有各自的重要作用。通过天敌的人工操纵和补充释放技术以及选择性药剂的筛选运用,在地面覆草,增强天敌功能的基础上,建立起果园主要害虫的生态调控体系,每年可使苹果园比通常减少用农药40％－50％,使果园生态逐步形成良性循环。     

Growth of Artenia franciscana and A. persimilis (Crustacea, Anostraca) under controlled conditions

Growth (length) was compared in A. franciscana populations from Utah, United States of America, and Yape, Chile, and A. persimilis (population from Salinas de Hidalgo, Argentina), cultured under controlled conditions (24 degrees C, seawater 35 g/l, fed with Chaetoceros calcitrans). There were significant differences among all stages of A. franciscana (Utah) and A. persimilis, whereas we found significant differences only in two stages of A. persimilis and A. franciscana (Yape); both A. franciscana had similar total lengths in all stages analyzed. Habitat adaptations could explain these results.     

荔枝-牧草复合系统节肢动物群落多样性与稳定性分析

1997年9月到1998年9月在广东东莞对荔枝－牧草复合系统和单一系统的节肢动物群落进行了比较研究,结果表明,荔枝－牧草复合系统同单一系统相比节肢动物群落数量,物种丰富度及均匀性增加,多样性提高,复合系统中各类群的多样性几乎在一年中的任何时期都比单一系统要高,但不同系统各类群的多样性对夏季高温和荔枝树生长阶段的反应极不一致。利用3个指数来评价群落的稳定性,结果都说明复合系统中的节肢动物群落显得较为稳定,看来,荔枝－牧草复合系统是荔枝园中维持,保护和利用节肢动物群落多样性的一种很好的模式,用有序样品的最优分割方法,把荔枝－牧草复合系统的节肢动物群落最优划分为了5个阶段,各个阶段节肢动物各类群的多样性特征及主要害虫和天敌状态的明确能对复合系统中荔枝害虫综合防治措施的适时采用起指导作用。