Factors affecting the relative abundance of two coexisting aphid species on sugar beet

1 The two most common species of aphid colonizing sugar beet Beta vulgaris L. are Myzus persicae (Sulzer) (Hemiptera: Aphididae) and Aphis fabae Scopoli (Hemiptera: Aphididae). 2 M. persicae colonizes sugar beet earlier than A. fabae but the population of the former also declines earlier. Despite similar numbers of each species migrating at the time of colonization, M. persicae is usually less abundant on the crop than A. fabae, suggesting differences between the species in their selection of, and performance on, sugar beet. 3 The intrinsic rate of increase of both species declines as sugar beet matures, however, at any given plant age the intrinsic rate of increase of A. fabae is one and a half times greater than that of M. persicae. This results in more rapid population growth and a later decline of the population. 4 Intraspecific competition appears to result in M. persicae becoming very restless, but there is no evidence for interspecific competition between the two species on this host. 5 A population growth model which takes account of the decline in host quality of sugar beet shows that the M. persicae population peaks 30 days before that of A. fabae, and, excluding differences in emigration rate, the maximum A. fabae population is 14 times greater than the maximum M. persicae population. These results are compared to field data.     

The influence of size and duration of aphid infestation on host plant quality, and its effect on sugar beet yellowing virus epidemiology

This paper studies the influence of previous infestation on the host quality of sugar beet (Beta vulgaris L.) for aphids and the influence of previous infestation on sugar beet yellowing virus epidemiology. Sugar beet previously infested with Myzus persicae (Sulzer) or Aphis fabae Scopoli (Homoptera: Aphididae) had an improved host quality for subsequently infesting aphids of the same species. There was a significant negative relationship between the number of M. persicae infesting a plant and the proportion of those that died with a dark deposit in their stomachs, and a significant positive relationship between the number that settled on a plant and the number that infested it previously. Nymphs feeding on previously infested plants grew more rapidly than those on control plants. The beneficial effect of previous infestation persisted for at least 2 weeks and prolongation of the infestation beyond 2 weeks was of no further benefit to the aphids. Field grown sugar beet, previously colonised by M. persicae, was more susceptible to natural infestation by M. persicae up to 5 days after exposure. Previously infested plants were also more susceptible to infection with beet mild yellowing virus (BMYV) but not beet yellows virus (BYV), suggesting that the aphids on the previously infested sugar beet settled more readily and were more inclined to feed (and thus transmit BMYV) than aphids on the previously uninfested plants. The consequences for the control of sugar beet yellowing virus vectors are discussed.     

Host quality of different aphid species for rearing Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae)

This study aimed to evaluate the quality of the aphid Myzus persicae (Sulzer), Lipaphis erysimi (Kaltenbach) and Brevicoryne brassicae (L.) as hosts for the parasitoid Diaeretiella rapae (McIntosh). Parasitization by D. rapae was higher on M. persicae than on L. erysimi and B. brassicae. The time of development of D. rapae from egg to mummy or egg to adult male or female were shorter on M. persicae than on L. erysimi and B. brassicae. Moreover, D. rapae showed no significant differences in the emergence rate, sex ratio and longevity when reared on the three aphid species. Myzus persicae was the largest aphid host, with B. brassicae and L. erysimi being of intermediate and of small size, respectively. Diaeretiella rapae reared on M. persicae was larger than when reared on L. erysimi and B. brassicae, and females of D. rapae were significantly larger than males on M. persicae, but males of D. rapae were larger than females when reared on L. erysimi. No difference in size was detected between males and females in parasitoids reared on B. brassicae. Among the aphid species studied, M. persicae was found to be the most suitable to D. rapae.     

THE SPREAD OF BEET YELLOWS AND BEET MOSAIC VIRUSES IN THE SUGAR-BEET ROOT CROP I. FIELD OBSERVATIONS ON THE VIRUS DISEASES OF SUGAR BEET AND THEIR VECTORS MYZUS PERSICAE SULZ. AND APHIS FABAE KOCH

A survey of aphids and virus diseases of sugar-beet root crops in eastern England was made between 1940 and 1948. Prior to 1943 the observations were made on fertilizer experiments; from 1943 onwards they were made on commercial fields selected for position in relation to beet and mangold seed crops. The incidence of beet yellows increased with increasing numbers of Myzus persicae , but not of Aphis fabae. The relation with M. persicae was sufficiently close to suggest that it is the most important, possibly the only important, vector of beet yellows virus. Beet mosaic virus also increased with increasing numbers of M. persicae , but the relation was not close enough to exclude the possibility of other vectors.
Numbers of A. fabae on sugar beet were slightly, but consistently, depressed by the use of salt as a fertilizer. Other fertilizers had variable effects. Neither aphids nor virus are likely to be greatly affected by fertilizers.
Beet yellows is most prevalent in areas where seed crops are grown, but within these areas nearness to individual seed crops did not appear to increase its incidence. M. persicae were more numerous on sugar beet in seed-crop areas than elsewhere, and this alone might account for the prevalence of yellows. Beet mosaic virus is more closely associated with seed crops than is beet yellows. It is most prevalent near to seed crops within the seed-crop areas.     

Effect of an alternate weed host, hairy nightshade, Solanum sarrachoides, on the biology of the two most important potato leafroll virus (Luteoviridae: Polerovirus) vectors, Myzus persicae and Macrosiphum euphorbiae (Aphididae: Homoptera)

Hairy nightshade, Solanum sarrachoides (Sendtner), is a ubiquitous weed in potato agro-ecosystems and nonagricultural lands of southeastern Idaho and the Pacific Northwest. This weed increases the complexity of the Potato leafroll virus (PLRV) (Luteoviridae: Polervirus)-potato pathosystem by serving as aphid and virus reservoir. Previous field studies showed higher densities of green peach aphid, Myzus persicae (Sulzer), and potato aphid, Macrosiphum euphorbiae (Thomas), the two most important vectors of PLRV, on S. sarrachoides compared with potato plants in the same fields. Some of the S. sarrachoides plants sampled in these surveys tested positive for PLRV. Viral infections can alter the physiology of plant hosts and aphid performance on such plants. To understand better the potential effects of S. sarrachoides on the PLRV-potato-aphid pathosystem, the life histories of M. persicae and M. euphorbiae were compared on virus-free and PLRV-infected S. sarrachoides and potato. Individual nymphs of each aphid species were held in clip cages on plants from each treatment to monitor their development, survival, and reproductive output. Nymphal survival for both aphids across plant species was higher on S. sarrachoides than on potato, and, within plant species, it was higher on PLRV-infected plants than on noninfected plants. With a few exceptions, similar patterns occurred for fecundity, reproductive periods, adult longevity, and intrinsic rate of increase. The enhanced performance of aphids on S. sarrachoides and on PLRV-infected plants could alter the vector population dynamics and thus the PLRV-disease epidemiology in fields infested with this weed.     

Arable weeds identified as new sources of beet mosaic potyvirus in Greece

Field and laboratory studies were carried out between 1992 and 1994 to assess the potential for arable weeds to act as reservoirs of beet mosaic potyvirus (BtMV) in fields where sugar beet is cultivated for seed. 933 weed samples were collected and tested by biological methods, while a representative number of weeds were tested by serological methods. The results showed that 97 samples, representing 14 weed species from eight families, were infected with BtMV. The following weeds were found to be naturally infected with BtMV for the first time: Bilderdykia convolvulus, Nonea pulla, Cerastium glomeratum, Galium aparine, Conyza (Erigeron) spp., Fumaria officinalis, Heliotropium europaeum and Rumex spp. The most common weeds found to be infected with BtMV in high percentage were members of the Papaveraceae.     

Summer weeds as hosts for Frankliniella occidentalis and Frankliniella fusca (Thysanoptera: Thripidae) and as reservoirs for tomato spotted wilt Tospovirus in North Carolina

In North Carolina, Tomato spotted wilt tospovirus (family Bunyaviridae, genus Tospovirus, TSWV) is vectored primarily by the tobacco thrips, Frankliniella fusca (Hinds), and the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). TSWV overwinters in winter annual weeds from which it is spread to susceptible crops in spring. Because most susceptible crops are destroyed after harvest before winter weeds emerge in the fall, infected summer weeds are thought to be the principal source for spread of TSWV to winter annual weeds in fall. A survey of summer weeds associated with TSWV-susceptible crops in the coastal plain of North Carolina conducted between May and October revealed that relatively few species were commonly infected with TSWV and supported populations of F. fusca or F. occidentalis. F. occidentalis made up > 75% of vector species collected from 15 summer weed species during 2002. The number of F. occidentalis and F. fusca immatures collected from plant samples varied significantly among plant species. Ipomoea purpurea (L.) Roth, Mollugo verticillata L., Cassia obtusifolia L., and Amaranthus palmeri S. Wats supported the largest numbers of immature F. occidentalis. Richardia scabra L., M. verticillata, and Ipomoea hederacea (L.) supported the largest numbers of F. fusca immatures. TSWV was present at 16 of 17 locations, and naturally occurring infections were found in 14 of 29 weed species tested. Five of the TSWV-infected species have not previously been reported as hosts of TSWV (A. palmeri, Solidago altissima L., Ipomoea lacunosa L., I. purpurea, and Phytolacca americana L.). Estimated rates of infection were highest in I. purpurea (6.8%), M. verticillata (5.3%), and I. hederacea (1.9%). When both the incidence of infection by TSWV and the populations of F. occidentalis and F. fusca associated with each weed species are considered, the following summer weed species have the potential to act as significant sources for spread of TSWV to winter annual weeds in fall: I. purpurea, I. hederacea, M. verticillata, A. palmeri, C. obtusifolia, R. scabra, Ambrosia artemisiifolia L., Polygonum pensylvanicum L., and Chenopodium album L.     

Interactions of two species of the genusChenopodium with two production plants—Sugar beet and spring wheat

TwoChenopodium species (C. album L.,C. suecicum J. Murr) were grown under field conditions with sugar beet to assess the weed-caused crop loss, and with spring wheat in a replacement series experiment. The weeds strongly reduced the growth of sugar beet. Dew's competition indexes for the regressions of sugar beet yield on weed density were 6.81 and 3.78 forC. suecicum andC. album respectively. On the other hand, the yield of spring wheat was not affected by the twoChenopodium species owing to early shading of the weeds by the faster growing crop stand.     

Reproduction and feeding behavior of Myzus persicae on four cereals

Green peach aphid, Myzus persicae (Sulzer), does not overwinter outdoors in Minnesota; it arrives each spring on low-level jet streams from the south. After arrival, anholocylic reproduction occurs on numerous herbaceous species, including many common weeds, before movement to potato, Solanum tuberosum L. In investigating aphid feeding behavior on barrier crops, we observed winter wheat, Triticum aestivum L., colonized by green peach aphid. The Northern Great Plains grows 94,000 ha of potatoes and 20.5 million ha of small grain cereals each year, the latter potentially providing an early emerging and widely distributed green peach aphid host to influence early season potato colonization. Life tables statistics indicated green peach aphid had its highest reproductive potential among cereals on winter wheat, with rye (Secale cereale L.) > barley (Hordeum vulgare L.) > oats (Avena sativa L.). Green peach aphid was found to colonize barley, rye, and winter wheat, but not oats. Mean generation time, net reproductive rate, doubling time, and finite rate of increase were significantly different between host plants. Electrical penetration graph technique indicated mean nonpenetration duration by green peach aphid was significantly different among plant species, and significantly longer on winter wheat than on the other cereals. Mean xylem phase duration was not significantly different among plant species but sieve element salivation was of longest duration on potato. Phloem sap ingestion (E2) was also significantly different among plant species with longest E2 duration on winter wheat. This study demonstrates that this aphid can effectively use key cereals at the vegetative stage.     

Beet leafhopper (Hemiptera: Cicadellidae) transmits the Columbia Basin potato purple top phytoplasma to potatoes, beets, and weeds

Experiments were conducted to determine whether the beet leafhopper, Circulifer tenellus (Baker) (Hemiptera: Cicadellidae), transmits the purple top phytoplasma to potato, Solanum tuberosum L.; beets, Beta vulgaris L.; and selected weed hosts. The beet leafhopper-transmitted virescence agent (BLTVA) phytoplasma was identified as the causal agent of the potato purple top disease outbreaks that recently occurred in the Columbia Basin of Washington and Oregon. The phytoplasma previously was found to be associated almost exclusively with the beet leafhopper, suggesting that this insect is the probable vector of BLTVA in this important potato-growing region. Eight potato cultivars, including 'Russet Burbank', 'Ranger Russet', 'Shepody', 'Umatilla Russet', 'Atlantic', 'FL-1879', 'FL-1867', and 'FL-1833', were exposed for a week to BLTVA-infected beet leafhoppers. After exposure, the plants were maintained outdoors in large cages and then tested for BLTVA by using polymerase chain reaction after 6 to 7 wk. The leafhoppers transmitted BLTVA to seven of the eight exposed potato cultivars. Sixty-four percent of the exposed plants tested positive for the phytoplasma. In addition, 81% of the BLTVA-infected potato plants developed distinct potato purple top disease symptoms. Beet leafhoppers also transmitted BLTVA to beets and several weeds, including groundsel, Senecio vulgaris L.; shepherd's purse, Capsella bursa-pastoris (L.) Medik); kochia, Kochia scoparia (L.) Schrad; and Russian thistle, Salsola kali L. This is the first report of transmission of BLTVA to potatoes, beets, and the above-mentioned four weed species. Results of the current study prove that the beet leafhopper is a vector of the potato purple top disease.     

Evaluation of hairy nightshade as an inoculum source for aphid-mediated transmission of potato leafroll virus

Potato leafroll virus (PLRV) causes one of the most serious aphid-transmitted diseases affecting yield and quality of potatoes, Solanum tuberosum (L.), grown in the United States. The green peach aphid, Myzus persicae (Sulzer), is considered to be by far the most efficient vector of this virus. Even the most strict aphid control strategy may not prevent the spread of PLRV unless measures also are taken to keep virus source plants within and outside the crop at a minimum. Hairy nightshade, Solanum sarrachoides (Sendtner), is one of the preferred weed hosts for green peach aphid. The potential of this weed as an aphid reservoir and virus source and its spread or perpetuation were investigated. With the use of double antibody sandwich enzyme-linked immunosorbent assay, it was confirmed that green peach aphid can transmit PLRV to hairy nightshade and that aphids can become viruliferous after feeding on infected hairy nightshade plants. Transmission from hairy nightshade to potato is 4 times the rate of potato to potato or potato to hairy nightshade. The green peach aphid preferred hairy nightshade over potato plants and reproduced at a higher rate on hairy nightshade than on potato. Therefore, a low level of PLRV-hairy nightshade infection could enhance the disease spread in the field.     

Yield of glyphosate-resistant sugar beets and efficiency of weed management systems with glyphosate and conventional herbicides under German and Polish crop production

In sugar beet production, weed control is one of the most important and most expensive practices to ensure yield. Since glyphosate-resistant sugar beets are not yet approved for cultivation in the EU, little commercial experience exists with these sugar beets in Europe. Experimental field trials were conducted at five environments (Germany, Poland, 2010, 2011) to compare the effects of glyphosate with the effects of conventional weed control programs on the development of weeds, weed control efficiency and yield. The results show that the glyphosate weed control programs compared to the conventional methods decreased not only the number of herbicide applications but equally in magnitude decreased the dosage of active ingredients. The results also showed effective weed control with glyphosate when the weed covering was greater and sugar beets had a later growth stage of four true leaves. Glyphosate-resistant sugar beets applied with the glyphosate herbicide two or three times had an increase in white sugar yield from 4 to 18 % in comparison to the high dosage conventional herbicide systems. In summary, under glyphosate management sugar beets can positively contribute to the increasingly demanding requirements regarding efficient sugar beet cultivation and to the demands by society and politics to reduce the use of chemical plant protection products in the environment.     

Effect of dodecanoic acid on the colonisation of sugar beet by aphids and the secondary spread of virus yellows

The effect of dodecanoic acid, a behaviour-controlling chemical which alters aphid feeding behaviour and virus transmission efficiency, was studied under field conditions. In a first experiment, dodecanoic acid reduced the level of natural colonisation of sugar beet by Aphis fabae. A second experiment revealed no significant influence of dodecanoic acid on the secondary spread of the semi-persistent beet yellows virus and the persistent beet mild yellowing virus.     

SOME PROPERTIES OF FOUR STRAINS OF CUCUMBER MOSAIC VIRUS

Different strains of cucumber mosaic virus differ in their host range, symptoms caused, virulence towards different plants, transmissibility by aphids, dilution end-point and thermal inactivation point.
There are seasonal variations in the susceptibility of some host species; French bean is apparently immune during the summer but during the winter produces countable local lesions suitable for quantitative assays.
Different host species differ in the ease with which cucumber mosaic virus is transmitted to and from them; systemic infection in beet rarely occurs unless the virus is introduced into young tissues. Inhibitors of infectivity in sap of sugar beet and Phytolacca sp. make mechanical transmission from these to other hosts difficult; the inhibitors interfere less with the infection of hosts in which they occur than with the infection of tobacco.
Cucumber mosaic virus has a low temperature coefficient of thermal inactivation and much infectivity is destroyed by heating at temperatures below the thermal inactivation point.
Myzus persicae (Sulz.) is a more efficient vector than M. ornatus Laing which is more efficient than Macrosiphum euphorbiae (Thomas); although individual aphids can cause more than one infection, most cease to be infective in feeding periods of from one to five minutes.     

HOST FINDING BY APHIDS IN THE FIELD: APHIS FABAE SCOP. (GYNOPARAE) AND BREVICORYNE BRASSICAE L.; WITH A RE-APPRAISAL OF THE ROLE OF HOST-FINDING BEHAVIOUR IN VIRUS SPREAD

Aphis fabae gynoparae occurred in the same large proportion in simultaneous collections of all aphids alighting and probing on, and taking off from, a host plant (spindle) and a non-host (peach), and behaved similarly when approaching and leaving them in the same conditions. Most alighters took off again from leaves of both kinds within a few minutes, staying longer and probing more times on the host. In atmospheric conditions favouring local 'hovering' instead of dispersal, flying and alighting aphids became concentrated around host plants, not through any specific attraction to them, but apparently because more aphids had accumulated upon them and were now taking off.
Brevicoryne brassicae occurred in the same large proportion in simultaneous collections of aphids alighting on a host plant (cabbage) and a non-host (sugar beet). No satisfactory evidence was found of preferential alightment on cabbage and there were indications of preferential alightment on the non-host. A very small minority of the A. fabae and B. brassicae that alighted on their hosts stayed there long enough to larviposit. This minority was rather larger among alighters late in the day, but in the absolute sense, more colonization occurred during earlier periods when more aphids arrived.
The intensely dispersive type of host-finding behaviour in Myzus persicae, A. fabae and B. brassicae may be common among Aphididae. It seems ideal for the dissemination of non-persistent plant viruses, more particularly among the less-favoured host plants of each aphid. The tendency to commensal association between virus and vector provides an ecological framework which may govern the incidence of virus-vector specificity and symbiosis.     

Curly Top of Cultivated Plants and Weeds and Report of a Unique Curtovirus from Iran

The incidence of curly top disease on cultivated plants and weeds was investigated in Kerman Province (southeastern Iran) from October 2003 to November 2004. A total of 1186 samples were collected in fields of sugar beet and other crops as well as within commercial plastic houses. Curtovirus infection of four field crops, three vegetables and 11 weeds was verified by indirect enzyme‐linked immunosorbent assay (ELISA) using a polyclonal antibody. An undescribed curtovirus, tentatively designated Iranian beet curly top virus (IBCTV), was isolated from three symptomatic beet samples collected randomly in widely separated regions of south‐eastern, southern and central Iran and used for molecular studies. A 672 bp segment of the coat protein (CP) gene of each isolate was amplified by PCR and sequenced. The results showed that the three isolates shared 98.5–98.7% nucleotide homology with each other but only 72.1–76.5% with other members of the genus Curtovirus. IBCTV was also detected by PCR using specific primers in other samples of sugar beet, tomato, spinach, turnip and several weed species collected in different parts of Iran. These results indicated that IBCTV is the dominant curtovirus in Iran.     

FACTORS AFFECTING THE SPREAD OF APHID-BORNE VIRUSES IN POTATO IN EASTERN SCOTLAND: I. OVERWINTERING OF POTATO APHIDS, PARTICULARLY MYZUS PERSICAE (SULZER)

Three species of potato aphids, Myzus persicae (Sulzer), Macrosiphum euphorbiae (Thomas) and Aulacorthum solani (Kltb.), overwinter in eastern Scotland, primarily as apterae on perennial, glasshouse, frame and brassica crops. Brassica crops are the commonest hosts of overwintering Myzus persicae , the principal vector of potato leaf roll and Y viruses, and these crops are concentrated in the market-gardening areas of the Lothians and Moray. Although crops of savoy cabbage and brussels sprout often carried numerous M.persicae during the winter, spring cabbage, cabbage for seed and broccoli seem the most important overwintering hosts because they usually persist until mid-May, long enough to allow the development and dispersal of alatae to spring-planted crops. Many alatae dispersed during July and August from crops colonized in spring. Although M. persicae overwintered as eggs on peach and viviparously on plants in glasshouses, the influence of such sites, which are generally distributed throughout the main seed-potato growing areas of Angus, Perth and Fife, was local and unless numerous M. persicae survive the winter on weeds, the market-garden area of the Lothians is probably the most important source from which this aphid disperses in spring and early summer to colonize potato crops in eastern Scotland.     

Behavior of bird cherry-oat aphid and green peach aphid in relation to potato virus Y transmission

Potato virus Y is transmitted to potato in a nonpersistent manner by many aphid species, some of which do not colonize this crop. The behavior of bird cherry-oat aphid, Rhopalosiphum padi (L.) on potato, Solanum tuberosum L., a plant species that is not colonized by this aphid, was described and compared with that of the potato-colonizing green peach aphid, Myzuspersicae (Sulzer). A higher proportion of winged morph of R. padi than M. persicae left the plant, but aphids that stayed in contact with the plant took the same mean time to initiate the first probe and it lasted the same mean time compared with M. persicae. Electronic penetration graph technique was used to study the probing behavior of the aphids during Potato virus Y (family Potyviridae, genus Potyvirus, PVY) transmission tests. Transmission rate decreased from 29 to 8% when the acquisition time increased from 5 min of continuous probing to 1 h with M. persicae, but it remained low (2 and 1%) with R. padi. Most of the difference in transmission rate between acquisition time with M. persicae and between aphid species was related to the change in the time and behavior taking place between the last cell puncture of the acquisition phase to the first cell puncture of the inoculation phase. Results presented here clearly demonstrated the importance of host plant selection and probing behavior in the transmission of nonpersistent plant viruses. They also stress the need to consider the behavior of the aphid in the design of laboratory tests of virus vector efficacy.     

Aphids from mangold clamps and their importance as vectors of beet viruses

Mangold clamps are over-wintering sources of the aphid-transmitted beet mosaic, beet yellows and beet mild yellowing viruses, and of several species of aphid, three of the most common in clamps being Myzus persicae, Rhopalosiphoninus staphyleae tulipaellus and R. latysiphon. This study attempted to assess the relative importance of the different species in spreading viruses from clamps. Compared with M. persicae, R. s. tulipaellus and R. latysiphon are seldom trapped in flight, except near large infestations. Alatae of M. persicae and R. s. tulipaellus become common in clamps in April, but few fly below 15d? C., a temperature seldom reached in eastern England in early spring. Flight muscle autolysis, which occurs later in R. s. tulipaellus and R. latysiphon than in some aphid species, also probably prevents many alatae in clamps from flying. We confirmed the importance of clamps as sources of beet viruses, the percentage of infected plants decreasing with increasing distance from infested clamps. M. persicae is shown to be a better vector of beet viruses than the other clamp aphids, and is probably responsible for most virus spread from clamps. R. s. tulipaellus did not transmit beet mosaic virus, but it is a fairly efficient vector of beet yellows and beet mild yellowing viruses, and, although we did not find this species on sugar beet in the field, it probably spreads these viruses from clamps. R. latysiphon did not transmit any of the viruses, and the role of Macrosiphum euphorbiae, Aulacorthum solani and Myxus ascalonicus is probably small.     

南京市春季外来杂草调查及生态位研究

利用样方法调查了南京市不同生境下外来杂草的种类、盖度、密度情况,探讨了不同生境中外来杂草对杂草群落的影响,同时分析了10种主要外来杂草和本地伴生种的生态位特点.结果表明,南京市春季外来杂草有36种,在74个样点中外来杂草出现的频率达到98.65%;外来杂草的入侵对生物多样性有不利影响;外来杂草平均优势度在不同生境中大小次序为:水边>菜地>荒地>路旁>景区>田埂>草坪>果茶园>墙缝>农田>宅旁>山坡.生态位的研究结果表明:野塘蒿 Conyzabonariensis L. Cronq. 、野老鹳草 GeraniumcarolinianumL. 和阿拉伯婆婆纳 VeronicapersicaPoir. 是生态位宽度最高的外来杂草,其入侵性最强;具有较高生态位宽度的外来杂草与其它杂草的生态位重叠较大,具有相似形态特征的杂草间的生态位重叠较大.