Detecting spatial interactions in the ragweed (<Emphasis Type="Italic">Ambrosia artemissifolia</Emphasis> L.) and the ragweed beetle (<Emphasis Type="Italic">Ophraella communa</Emphasis> LeSage) populations

We observed a weed (Ambrosia artemissifolia)–beetle herbivore (Ophraella communa) system for three years in a spatially continuous field (≈200 ha). We analyzed our field data in the light of two contrasting theories: the resource-concentration hypothesis and reaction–diffusion theory. For the resource-concentration hypothesis, we calculated the correlation coefficients between weed and beetle abundances for every season in each year. Although we found weak support for resource concentration in some seasons, we could not find any clear relationships in other seasons. We discuss a dispersal-based mechanism to explain the differences observed among seasons in lieu of the resource-concentration hypothesis. For the reaction–diffusion theory, we estimated the nonparametric spatial covariance functions for the spatial autocorrelation of weeds and beetles. Although we could not find any strong spatial structure for the individual species, we found evidence of spatial interactions between weeds and beetles using time lagged cross-correlation functions. Weed abundance enhanced local beetle abundance. Through time, there was evidence of beetle spillover to adjacent locations at roughly the one beetle-generation time scale. Sites with large number of beetles did not seem to reduce subsequent weed abundance.     

Weed species in tomato production and their role as alternate hosts of Tomato spotted wilt virus and its vector Frankliniella occidentalis

Tomato spotted wilt virus (TSWV) is an important plant virus that infects a wide range of hosts including weeds making its management difficult. A survey was undertaken to establish the occurrence of weed species in tomato production systems in Kenya and their role as hosts of TSWV and its vectors. Selected weed species were further evaluated for their reaction to TSWV, transmission efficiency by Frankliniella occidentalis and ability to support thrips reproduction. Of the 43 weed species identified in the field, 29 species had been reported as hosts of TSWV, two were non‐hosts and 11 had no record of their status. Among the more common species, Amaranthus hybridus, Solanum nigrum, Tagetes minuta and Datura stramonium were susceptible to the virus and supported high levels of thrips reproduction. The TSWV could not be transmitted to Galinsoga parviflora and Sonchus oleraceus by F. occidentalis despite them being highly susceptible in mechanical transmission tests. There was a significant correlation between feeding damage and number of larvae of F. occidentalis on different weeds. Occurrence of weeds that support thrips reproduction and are good hosts of TSWV is a clear indicator of their role in epidemiology and the importance of their management for disease control.     

The impact of plant associations on Macrosteles quadrilineatus management in carrots

Habitat diversification can influence the interactions of insects with plants and this can be used in agroecosystems for the management of pest populations. Plant diversification can be achieved through planting crops, such as trap crops, or by adjusting weed management. Aster leafhopper, Macrosteles quadrilineatus Forbes (Hemiptera: Cicadellidae), is a polyphagous species that uses cereals, vegetables, and weeds as host plants. The influence of weeds on M. quadrilineatus abundance was investigated experimentally in carrot [Daucus carota L. cv. Canada (Apiaceae)] field plots by adjusting the level of management of two groups of weeds (broadleaf and grass) and by comparing it to weed‐free plots. The preference of M. quadrilineatus for different cereal and weed species relative to carrots was tested in choice test assays. Habitat context influenced the abundance of M. quadrilineatus in the field experiments. The presence of border crops such as oat, rye, barley, wheat, and triticale did not significantly attract or repel this insect to carrot plots compared to the no‐border treatment. However, spelt‐bordered plots had 42% fewer M. quadrilineatus than three treatments, triticale, wheat, and barley, that had the highest insect abundance. The type of weed management affected M. quadrilineatus abundance in carrot plots, but not the frequency of herbicide application. Plots that had carrot growing with broadleaf‐weeds had about 59% fewer M. quadrilineatus compared with those growing with crabgrass or carrot alone. In the greenhouse choice tests, grasses (e.g., cereals) attracted and broadleaf‐weeds repelled M. quadrilineatus relative to carrots. In summary, carrot growers may be able to manage this pest by reducing the interaction of cereal cover crops with carrots and eliminating grassy weeds in commercial production fields.     

Seasonal abundance of hemipteran predators in relation to western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae) on weeds in the eastern Mediterranean region of Turkey

Generalist predators and the prey species Frankliniella occidentalis (Pergande) were periodically sampled from 64 weed species to determine their numerical interrelationships in three ecologically different locations in the eastern Mediterranean region of Turkey in 2002–2003. Adult and nymph stages of seven hemipteran predator species were recorded: Deraeocoris pallens Reuter, Geocoris arenarius (Jakovkev), Nabis punctatus Costa, Orius laevigatus Fieber, Orius majusculus (Reuter), Orius niger (Wolff) and Piocoris erythrocephalus (Peletie and Serville). The most common and abundant predator species was O. niger, which was found on 53 weed species in the winter–spring and summer–fall periods; the highest total numbers of O. niger adults per weed species were 139, 275, 266 and 325 on Urtica urens, Sinapis arvensis, Lamium amplexicaule and Mentha aquatica, respectively. Relatively higher numbers of Orius spp. nymphs were detected on the weed species Echium plantagineum, Cichorium intybus, Heliotropium europeum, Mentha aquatica and Polygonum aviculare. Orius spp. were attracted to flowers in significantly higher numbers than to leaves of the investigated weeds. No significant correlation was found between the numbers of Orius spp. and F. occidentalis on the major weed species, except E. plantagineum. These findings suggest that weeds may provide Orius spp. with resources other than prey, such as nectar and pollen, shelter, and breeding sites. The weed species on which relatively higher numbers of Orius adults and nymphs were found may be considered as candidates for studies aiming to include weeds to enhance integrated pest management of F. occidentalis on crops.     

Nitrogen availability and weed invasion in a remnant native woodland in urban Melbourne

Abstract The woodlands of Studley Park, and the greater Yarra Bend Park, are within 4 km of the centre of the city of Melbourne and total more than 200 ha. Weeds are major contributors to the loss of diversity of native species. We examined the hypothesis that an increase in the availability of nitrogen (N) may be responsible for the increase in weed abundance. In a small field trial, nitrogen availability was greater in areas invaded by weeds and weeds had greater nitrate reductase activity than native species. Both invaded and uninvaded areas were well‐supplied with weed seed, although the composition of the seed bank varied greatly between sites. Diaspores of the weed Romulea rosea were abundant in uninvaded sites while those of Ehrharta erecta and Ehrharta longiflora were abundant in invaded sites. The abundance of weed diaspores suggested that increased N availability may be a precondition for invasion. Formation of a dense litter layer by senescent weeds is likely to promote the capture and retention of N added from anthropogenic sources including air pollution and overland flow from nearby roads and drainage channels.     

Nutritional resources used by the invasive maize pest Diabrotica virgifera virgifera in its new South-east-European distribution range

Food utilization by adults of the invasive maize (Zea mays L.) (Poaceae) pest western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte) (Coleoptera: Chrysomelidae) was investigated in the south‐eastern part of its new European distribution range. At weekly intervals over a 10‐week period, 10 beetles per field were collected from six fields that had a high abundance of flowering weeds and six fields with a low abundance of flowering weeds, with the aim of understanding adult feeding behaviour in Europe and comparing this behaviour with North American WCR. Gut content analysis was performed to determine the use of maize tissue and weed pollen with regard to maize phenology. Furthermore, all pollen found within the gut was quantified and identified to plant species level. The use of maize tissue by adult WCR changed over time according to maize phenology. Pollen originating from plants other than maize was used more frequently as the maize matured. Adults fed on pollen from 19 of 25 different plant species found in maize fields and showed a preference for the pollen of specific weeds. Pollen from weed species was found more often in beetles from fields with a high abundance of weeds compared to beetles from fields with a low abundance of weeds. Females consumed greater amounts of pollen than males, the latter feeding on a wider diversity of host plants. The pollen resources used by adult WCR in Hungary were more diverse compared to WCR in the USA, which may contribute to the invasion success of WCR in Europe.     

Weed species differ in their ability to emerge in no‐till systems that include cover crops

No‐till cropping systems that include cover crops could lead to important changes in weed communities by decreasing some annual weed populations. In this study, we predicted that seed burial depth and the presence of cover crop would affect the emergence and initial growth success of annual weed species. We tested two factors on 14 weed species in a greenhouse: the seed burial depth of weeds (buried versus soil surface) and the presence/absence of a cover crop (ryegrass). We counted the emerged seedlings and measured the height of weeds and cover crops (Hweed, Hcover), the dry matter content of weeds and cover crops (DMCweed, DMCcover) and the number of leaves of weeds (NLweed) on 1433 weed and 390 ryegrass individuals. Emergence of five weed species (AMBEL, ANGAR, BROST, CENCY and EPHHE) was affected by the seed location (?10.3% on average for unburied seeds), five other weed species (ALOMY, CAPBP, SONAS, VERPE and VLPMY) were affected by cover (on average ?9.5% for seeds emerged in the presence of cover crop), and four weed species (GERDI, LAMPU, POAAN and VIOAR) were not affected by either. Weed growth of all weed species also decreased with the presence of a cover crop (on average Hweed: ?49.9%, DMCweed: ?87.2% and NLweed: ?55.4%) and for unburied seeds (on average Hweed: ?33.7%, DMCweed: ?70.6% and NLweed: ?43.3%), with various responses according to species. This study indicates that annual weeds could be disadvantaged by no‐till systems using cover crops.     

Exotic wildland weeds serve as reservoirs for a newly introduced cole crop pest,Bagrada hilaris (Hemiptera: Pentatomidae)

The role of wildland weeds that serve as alternate hosts for insect pests has not been directly examined for the potential to sustain pest populations or facilitate pest outbreaks. The development of weed biological control programmes is also complicated by weed species that are closely related to economically important or native plants, especially rare or special status species. In recent surveys in southern California, USA, we found a newly introduced insect pest of cole crops, Bagrada hilaris Burmeister (Bagrada bug), feeding on Brassicaceae weeds in riparian areas adjacent to agricultural fields where cole crops are routinely grown. Insect populations grew to levels well over action thresholds and caused severe damage to populations of the invasive weed, Lepidium latifolium (perennial pepperweed). The numerical response of B. hilaris on L. latifolium and other Brassicaceae weeds in natural areas may pose a significant challenge to effectively managing pest populations in crops. However, the accidental introduction of this insect provides the opportunity to examine plant–insect interactions with important implications for development of biologically based control methods for weeds.     

川西平原五种水旱轮作模式旱作季杂草群落特征

为明确不同水旱轮作模式对川西平原旱作季杂草群落特征的影响,从而为旱作季杂草的高效防控提供理论依据。基于大蒜-水稻(GR)、小麦-水稻(WR)、蚕豆-水稻(BR)、油菜-水稻(RR)和马铃薯-水稻(PR)五种水旱轮作的长期定位试验,在2022年旱季采用生态学方法探究了不同水旱轮作模式下旱作季农田杂草种类、密度、株高、生物量等杂草群落结构和物种多样性特征。结果表明:(1)五种轮作模式下杂草田间密度表现为WR>BR>RR>GR>PR,生物量表现为WR>BR>GR>RR>PR,物种多样性表现为GR>BR>RR>PR>WR,物种均匀度表现为GR>PR>BR>RR>WR,群落优势度表现为WR>PR>RR>BR>GR,表明GR杂草群落稳定性最高,WR杂草群落稳定性最低且优势物种发生危害的程度最高,RR的杂草种类数少且不易发生危害;(2)五种水旱轮作模式杂草群落相似性较高,相似性指数在0.69-0.84之间,WR杂草生活型以一年生单子叶杂草为主,其余四种模式以一年生双子叶杂草为主;(3)WR优势杂草种类最少,为禾本科棒头草(Polypogon fugax Nees ex Steud),其重要值为59.53%;BR优势杂草种类最多,为棒头草、蔊菜(Rorippa indica (L.) Hiern)、毛茛(Ranunculus japonicus Thunb)和通泉草(Mazus japonicus (Thunb.) O. Kuntze);GR优势杂草为苣荬菜(Sonchus wightianus DC)和猪殃殃(Galium spurium L); RR和PR优势杂草均为三种,都包括为棒头草和蔊菜。因此,以确保旱作季杂草能得到有效控制,不同水旱轮作模式应制定不同的杂草防控措施。GR和PR应重点控制以猪殃殃为代表的双子叶杂草,WR应着重控制以棒头草等为代表的单子叶杂草,BR和RR应注重繁殖力强的单双子叶杂草的综合防治。     

Non-crop vegetation associated with chili pepper agroecosystems promote the abundance and survival of aphid predators

Habitat manipulation has long been used as strategy to enhance beneficial insects in agroecosystems. Non-crop weed strips have the potential of supplying food resources to natural enemies, even when pest densities are low. However, in tropical agroecosystems there is a paucity of information pertaining to the resources provided by non-crop weeds and their interactions with natural enemies. In this study we evaluated (a) whether weeds within chili pepper fields affect the diversity and abundance of aphidophagous species; (b) whether there are direct interactions between weeds and aphidophagous arthropods; and (c) the importance of weed floral resources for survival of a native and exotic coccinellid in chili pepper agroecosystems. In the field, aphidophagous arthropods were dominated by Coccinellidae, Syrphidae, Anthocoridae, Neuroptera and Araneae, and these natural enemies were readily observed preying on aphids, feeding on flowers or extrafloral nectaries, and using plant structures for oviposition and/or protection. Survival of native Cycloneda sanguinea (Coleoptera: Coccinellidae) differed between plant species, with significantly greater survival on Ageratum conyzoides and Bidens pilosa. However, no evidence was gathered to suggest that weed floral resources provided any nutritional benefit to the exotic Harmonia axyridis (Coleoptera: Coccinellidae). This research has provided evidence that naturally growing weeds in chili pepper agroecosystems can affect aphid natural enemy abundance and survival, highlighting the need for further research to fully characterize the structure and function of plant resources in these and other tropical agroecosystems.     

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.     

Prospects for the Management of Invasive Alien Weeds Using Co-Evolved Fungal Pathogens: A Latin American Perspective

Invasive alien weeds pose a serious threat to the biodiversity of natural ecosystems and a significant constraint to agricultural production worldwide. The use of co-evolved natural enemies, a strategy referred to as classical biological control (CBC), has proven to be a potentially efficacious, cost-effective, and safe option for the management of alien weeds. An analysis of CBC of invasive weeds in Latin America is presented, which shows that only 5% of the worldwide releases of agents, overwhelmingly arthropod, have been in this region. Fungal pathogens are increasingly being considered in CBC programmes, and there are now 11 examples of Latin American fungi having been released as biocontrol agents in other regions of the world. In contrast, only three weed pathogens have been deliberately released in the region. Possible reasons for the paucity of CBC programmes in Latin America are presented, despite the presence of a significant number of alien weed species (60 are listed). An analysis of these weeds reveals that many of them could be amenable to control using natural enemies, including nine weed species for which CBC programmes have been successfully implemented elsewhere in the world. In addition, for many of these 60 species, a co-evolved and damaging mycobiota has already been recorded. The prospects for management of invasive alien weeds in Latin America, using co-evolved fungal pathogens, are assessed with particular reference to selected species from the genera Ambrosia, Broussonetia, Calotropis, Commelina, Cyperus, Dichrostachys, Echinochloa, Pittosporum, Rottboellia, Rubus, Sonchus and Ulex. This revised version was published online in July 2006 with corrections to the Cover Date.     

阔叶丰花草对荔枝园杂草群落特征及物种多样性的影响

【目的】明确阔叶丰花草在荔枝园定植对杂草群落特征及物种多样性的影响,为阔叶丰花草在果园应用提供参考依据。【方法】通过调查广东茂名高州荔枝国家现代农业产业园的荔枝园中90个有、无阔叶丰花草样方中杂草群落组成、群落高度以及物种多样性,探究阔叶丰花草定植对荔枝园杂草群落结构及物种多样性的影响。【结果】阔叶丰花草在荔枝园定植后,杂草种类减少,由对照样方的42种减少到试验样方的30种;杂草群落结构显著改变,牛筋草、白花鬼针草等恶性杂草重要值降低,薇甘菊、香附子、火炭母等杂草消失;阔叶丰花草的重要值与杂草群落高度和物种多样性指数为显著性负相关(P0.001),且均呈显著三项式回归关系。阔叶花草在荔枝园定植后可建立结构较为单一,且低矮的杂草群落。【结论】阔叶丰花草有望成为荔枝园生草的有益草种。     

Mitigating impacts of weeds and kangaroo grazing following prescribed fire in a Banksia woodland

Banksia woodlands are renowned for their flammability and prescribed fire is increasingly employed to reduce the risk of wildfire and to protect life and property, particularly where these woodlands occur on the urban interface. Prescribed fire is also employed as a tool for protecting biodiversity assets but can have adverse impacts on native plant communities. We investigated changes in species richness and cover in native and introduced flora following autumn prescribed fire in a 700‐hectare Banksia/Tuart (Eucalyptus gomphocephala) woodland that had not burnt for more than 30 years. Effectiveness of management techniques at reducing weed cover and the impacts of grazing by Western Grey Kangaroo (Macropus fuliginosus) postfire were also investigated. Thirty plots were established across a designated burn boundary immediately before a prescribed fire in May 2011, and species richness and cover were measured 3 years after the fire, in spring of 2013. Fencing treatments were established immediately following the fire, and weed management treatments were applied annually in winter over the subsequent 3 years. Our results indicate that autumn prescribed fire can facilitate increases in weed cover, but management techniques can limit the establishment of targeted weeds postfire. Postfire grazing was found to have significant adverse impacts on native species cover and vegetation structure, but it also limited establishment of some serious weeds including Pigface (Carpobrotus edulis). Manipulating herbivores in time and space following prescribed fire could be an important and cost‐effective way of maintaining biodiversity values.     

Impact of mowing and weed control on broadleaf weed population dynamics in turf

Abstract

Various turf management activities may influence weed population dynamics and interfere with weed control. The effects of a biocontrol agent, Sclerotinia minor, a chemical herbicide, Killex?, and mowing height on broadleaf weed dynamics were examined in two turfgrass stands for two consecutive years. Mowing did not reduce the population densities of dandelion or the ground cover of broadleaf weeds. In the second year, mowing significantly reduced white clover density, but significantly increased broadleaf plantain density, particularly at the closest mowing height (3–5 cm). Apart from the close height, the S. minor and Killex? treatments were equally effective in suppression of dandelion, white clover, broadleaf plantain, and prostrate knotweed in the second year. Common mallow increased in the herbicide treated plots and other species including yellow woodsorrel, yellow toadflax and lambsquarters increased in abundance in plots mowed at the 3–5 cm height and in plots treated with Killex?. Significant differences between the Killex? and S. minor treatments on dandelion population dynamics were rarely present and did not favour either treatment. S. minor did not damage the turfgrass, but Killex? reduced turf quality in 25% of the plots. The application of S. minor with a regular, medium height (～7 cm) mowing regime was highly effective in controlling broadleaf weeds in temperate Kentucky bluegrass turf.     

Response of the waterbird community to floating pennywort (Hydrocotyle ranunculoides) cover at Ngamo dam,Antelope Park,Zimbabwe.

Little is known on the influence of invasive aquatic weeds on afro‐tropical waterbird communities. We used bird counts in sites of varying floating pennywort Hydrocotyle ranunculoides cover to explore the relationship between the weed and the waterbird community dynamics at Ngamo dam, Antelope Park, Zimbabwe. Waterbird communities in low‐to‐medium weed cover sites were more diverse and abundant compared to sites of high weed cover. In addition to supporting birds such as African Jacana which are able to forage within dense aquatic plants, high weed cover sites were associated with birds whose diets include invertebrates and fish which are likely more abundant and diverse in these sites. In contrast, low‐to‐medium weed cover sites were associated with bird species such as Common Moorhen, Great Egret, Pied Kingfisher and African Fish Eagle which require accessible open water and forage for diving, swimming or wading. The increased bird abundance in low‐to‐medium weed cover sites also likely increases prey for predatory birds. Thus, the negative changes in the waterbird community composition, abundance and diversity in response to increasing floating pennywort cover reflects species‐specific tolerances to floating pennywort and its influence on accessible open water, foraging sites and prey availability.     

Seasonal changes in activity of subterranean termite species (Isoptera) in Western Australian wheatbelt habitats

Subterranean termite assemblages in woodland, mallee and heath habitats of the Western Australian wheatbelt were sampled for seasonal changes in species richness and species abundance. The study was carried out in Durokoppin and Kodj Kodjin Nature Reserves between January and November 1988, and a trench method was used to sample termites. Species richness changed over time, with monthy means of: woodland 10 species (range: 5–15), mallee 8 species (range: 4–15), heath 8 species (range: 5–15). Species richness was highest in autumn and spring when termite activity in the soil was also highest due to favourable soil moisture. Amitermes neogermanus and Tumulitermes petilus were the most abundant species in woodland and mallee in all seasons. During summer, the pooled observations of these two species accounted for 50% (woodland) and 82% (mallee) of all observations. Their predominance may be due to greater tolerance of low soil moisture and a more diverse diet than obligate wood-feeders (e.g. Rhinotermitidae). The latter were generally absent near the soil surface in summer, possibly because food sources deeper within the soil were utilized. Four species were abundant in heath: Tumulitermes dalbiensis (monthly mean 20% of all species observations), T. comatus (13%), Amitermes. sp.‘R’ (18%)and Drepanotermes rubriceps (12%). These four species showed no seasonal change in their relative abundance, possibly because their diet restricted them to surface-foraging.     

The effects of Phoma macrostoma on nontarget plant and target weed species

Phoma macrostoma 94-44B was evaluated against 94 plant species in 34 botanical families, of economically important agricultural, horticultural and ornamental species, as well as target and nontarget weeds. Fifty-seven species from 28 families were found to be resistant to P. macrostoma, while 38 species from 12 families, six of which also contained resistant species, were found to be susceptible. Those families comprising both susceptible and resistant species included the Asteraceae, Brassicaceae, Fabaceae, Lamiaceae, Plantaginaceae and Rosaceae with the foremost three containing the largest numbers of susceptible species. P. macrostoma was pathogenic to many dicotyledonous plant species, but nonpathogenic to monocots. Commercial applications for weed management in turfgrass, agriculture, horticulture and forestry seem probable, while domestically management of weeds in lawns, transplanted ornamental and annual flowering species may provide alternative markets.     

The occurrence of leafminers and their parasitoids on vegetables and weeds in Hangzhou area, Southeast China

Leafminers are the mostimportant insect pests of vegetables inHangzhou area, Zhejiang province, SoutheastChina as well as in the rest of China, but havenever been investigated for speciescomposition, relative abundance and theirassociated parasitoids. A survey was conductedin four localities of Hangzhou area during 1998–2000to determine the distribution ofleafminers and their parasitoids on vegetablecrops and weeds in the field. Over 20,000leafminers were collected and reared. Theleafminer species found were Liriomyzasativae, L. chinensis and Chromatomyia horticola, with C.horticola and L. sativae the mostabundant in spring and autumn, respectively.About 11,000 parasitoid adults were reared fromthe leafminers collected. In total 14hymenopteran species of four families (onebraconid, 10 eulophids, one megaspilid and onepteromalid) were found. Eleven species werereared from C. horticola, nine from L. sativae and seven from L. chinensis.Opius caricivorae and Chrysocharispentheus were the dominant species. Sevenspecies were recorded from L. chinensisfor the first time. Eleven parasitoid specieswere reared from leafminers on two weeds (Veronica undulata and Sonchusoleraceus). Parasitoids caused 48.5–68.8%parasitism on leafminers on crops and 83.7%parasitism on leafminers on weeds in the latergrowing season of vegetable crops. The resultssuggest that leafminer populations areregulated to a certain extent by their naturalenemies in the field.