Weedy Plant Species Research Articles

The effect of different natural enemies on the performance of Cirsium arvense in its native range

Abela‐Hofbauerová I, Münzbergová Z & Skuhrovec J (2011). The effect of different natural enemies on the performance of Cirsium arvense in its native range. Weed Research51, 394–403.SummaryUnderstanding the effects of herbivores on weedy plant performance under different habitat conditions may provide useful information for limiting the spread of these plant species in their native and invaded ranges. A critical drawback to using herbivores to limit the spread of weedy plant species is the limited knowledge regarding the effects of different natural enemies on plant performance under natural conditions and in different habitat types. The aim of this study was to collect information on the degree and types of damage caused by natural enemies and their effects on the performance of the weed species Cirsium arvense, under different abiotic conditions in its native range in the Czech Republic. Damage induced by different natural enemies of C. arvense in four different populations in wet and dry sites was studied. The most common types of damage found in C. arvense were folivory (eaten foliage), external stem damage and leaf necrosis, and their occurrence varied strongly in space and time. Different plant damage types tended to be significantly associated with each other. It was therefore difficult to separate the effects of individual damage types and to study their interactions. Overall, the results indicate that in its native range, C. arvense experiences high levels of herbivory, with stem damage, flower herbivory and folivory having the strongest effects on plant performance. Experimental studies that would separate the effect of single herbivores are, however, needed to confirm this.

Antifungal activity of four weedy plant extracts against selected mycotoxigenic fungi

To investigate the antifungal activity of aqueous and organic extracts of four weedy plant species viz. Tagetes minuta, Lippia javanica, Amaranthus spinosus and Vigna unguiculata against isolates of four agriculturally important fungi, i.e. Fusarium verticillioides, F. proliferatum, Aspergillus flavus and A. parasiticus. Dried powdered aerial parts of the plants were extracted sequentially with hexane, dichloromethane, methanol and water and tested for activity using a serial microdilution assay. Results were read every day over 120 h. All extracts except for the water extracts showed growth inhibitory activity against most isolates of the Fusarium spp. The most active were the methanol and hexane extracts of V. unguiculata and A. spinosus with minimum inhibitory concentration (MIC) values of <0.5 mg ml(-1) after 48 h against Fusarium spp. No inhibition of the Aspergillus spp. tested was observed, but conidium formation was stimulated on plates treated with plant extracts when visually compared to the growth controls. The results obtained from this study indicated that chemical constituents from these plant species may be developed as potential agrochemical fungicides. SIGNIFICANCE AND IMPACT OF THE RESEARCH: Food and feed are subject to infection by a variety of micro-organisms that can induce spoilage and/or produce metabolites that are toxic to humans and animals. Extracts of V. unguiculata and A. spinosus were most active and maybe developed into environmentally friendly fungicides, which are affordable to rural farmers in developing countries.

No interaction between competition and herbivory in limiting introduced Cirsium vulgare rosette growth and reproduction

Both competition and herbivory have been shown to reduce plant survival, growth, and reproduction. Much less is known about whether competition and herbivory interact in determining plant performance, especially for introduced, weedy plant species in the invaded habitat. We simultaneously evaluated both the main and interactive effects of plant neighbors and insect herbivory on rosette growth and seed reproduction in the year of flowering for Cirsium vulgare (bull thistle, spear thistle), an introduced Eurasian species, in tallgrass prairie in 2 years. Effects of insect herbivory were strong and consistent in both years, causing reduced plant growth and seed production, whereas the effects of competition with established vegetation were weak. The amount of herbivore damage inflicted on rosettes did not depend on the presence of neighbor plants. We also found no interaction between competition and herbivory on key parameters of plant growth and fitness. The results of this study contradict the hypothesis that competitive context interacts with insect herbivory in limiting the invasiveness of this introduced thistle. Further, the results provide additional, experimental evidence that high levels of herbivory on established rosettes by native insects exert significant biotic resistance to the invasiveness of C. vulgare in western tallgrass prairie.

Comparative study on elemental composition and DNA damage in leaves of a weedy plant species, Cassia occidentalis, growing wild on weathered fly ash and soil

Open dumping of fly ash in fly ash basins has significant adverse environmental impacts due to its elevated trace element content. In situ biomonitoring of genotoxicity is of practical value in realistic hazard identification of fly ash. Genotoxicity of openly disposed fly ash to natural plant populations inhabiting fly ash basins has not been investigated. DNA damage, and concentrations of As, Co, Cr, Cu and Ni in the leaves of natural populations of Cassia occidentalis growing at two contrasting sites-one having weathered fly ash (fly ash basin) and the other having soil (reference site) as plant growth substrates-were assessed. The foliar concentrations of As, Ni and Cr were two to eight fold higher in plants growing on fly ash as compared to the plants growing on soil, whereas foliar concentrations of Cu and Co were similar. We report, for the first time, based upon comet assay results, higher levels of DNA damage in leaf tissues of Cassia occidentalis growing wild on fly ash basin compared to C. occidentalis growing on soil. Correlation analysis between foliar DNA damage and foliar concentrations of trace elements suggests that DNA damage may perhaps be associated with foliar concentrations of As and Ni. Our observations suggest that (1) fly ash triggers genotoxic responses in plants growing naturally on fly ash basins; and (2) plant comet assay is useful for in situ biomonitoring of genotoxicity of fly ash.

Ethnomedicine in South Africa: The role of weedy species

Some weedy plant species have competitive advantage over other species found growing in the same habitat due to their efficient utilization of mineral resources, adaptability to the environment and comparative high fecundity. They are often caught in the web of conservation policy which causes the indiscriminate eradication of these species without consideration for other potential economic importance. This review elucidates the medicinal importance of weedy species found growing in South Africa. Twenty four plant families and 34 species were implicated in the treatment of twenty one diseases and sicknesses by the different natives of South Africa. The importance of this work on the future management of weedy species is briefly discussed.

Evolved glyphosate‐resistant weeds around the world: lessons to be learnt

Glyphosate is the world's most important herbicide, with many uses that deliver effective and sustained control of a wide spectrum of unwanted (weedy) plant species. Until recently there were relatively few reports of weedy plant species evolving resistance to glyphosate. Since 1996, the advent and subsequent high adoption of transgenic glyphosate-resistant crops in the Americas has meant unprecedented and often exclusive use of glyphosate for weed control over very large areas. Consequently, in regions of the USA where transgenic glyphosate-resistant crops dominate, there are now evolved glyphosate-resistant populations of the economically damaging weed species Ambrosia artemissifolia L., Ambrosia trifida L., Amaranthus palmeri S Watson, Amaranthus rudis JD Sauer, Amaranthus tuberculatus (Moq) JD Sauer and various Conyza and Lolium spp. Likewise, in areas of transgenic glyphosate-resistant crops in Argentina and Brazil, there are now evolved glyphosate-resistant populations of Sorghum halepense (L.) Pers and Euphorbia heterophylla L. respectively. As transgenic glyphosate-resistant crops will remain very popular with producers, it is anticipated that glyphosate-resistant biotypes of other prominent weed species will evolve over the next few years. Therefore, evolved glyphosate-resistant weeds are a major risk for the continued success of glyphosate and transgenic glyphosate-resistant crops. However, glyphosate-resistant weeds are not yet a problem in many parts of the world, and lessons can be learnt and actions taken to achieve glyphosate sustainability. A major lesson is that maintenance of diversity in weed management systems is crucial for glyphosate to be sustainable. Glyphosate is essential for present and future world food production, and action to secure its sustainability for future generations is a global imperative.

Interaction effects of Allium spp. residues, concentrations and soil temperature on seed germination of four weedy plant species

Soil in laboratory microcosm experiments was amended with dried and milled crop residues of onion ( Allium cepa L. cv. Mission) or garlic ( A. sativa L. cv. California Early). The amendments, along with the additional factors of amendment concentration (0, 1 or 3% (w/w)) and soil temperature (23 or 39 °C), were evaluated with respect to germination of seeds of the weedy annual plants Echinochloa crus-galli (L.) Beauv. (barnyardgrass), Portulaca oleracea L. (common purslane), Sisymbrium irio L. (London rocket) and Solanum nigrum L. (black nightshade). Deleterious effects of seed exposure to 39 °C versus 23 °C were demonstrated in ECHCG, POROL, and SSYIR; and to increasing amendment concentration and the [concentration × temperature] interaction in all four plant species tested ( P < 0.05). The effect of garlic versus onion amendment was significant only in SOLNI, where garlic residues demonstrated more herbistatic and/or herbicidal activity. The results of these experiments showed that the garlic and onion plant residues were capable of causing significant reductions in seed germination during their decomposition in soil, but only at elevated (39 °C versus 23 °C) soil temperature. At the agricultural level, activity of these residues could be exploited as a component of integrated weed management using appropriate crop sequencing, and may extend utility of soil heating treatments (e.g. solarization) for weed control to cooler climates or seasons, or for shorter treatment durations.

Ranking Nonindigenous Weed Species by Their Potential to Invade the United States

Because of the large number of potentially invasive species, and the time required to complete weed risk assessments (WRAs) with the use of the current, mandated system in the United States, species need to be prioritized for assessment and possible listing as Federal Noxious Weeds. Our objective was to rank the potential invasiveness of weedy or pest plant species not yet naturalized in the United States. We created a new model of invasiveness (hereafter the U.S. weed-ranking model) based on scoring factors within four elements: (1) invasiveness potential, or likelihood to exhibit invasive behavior; (2) geographic potential, or habitat suitability; (3) damage potential, or likely impact; and (4) entry potential, or likelihood to be introduced. The ranking score was the product of the four elements. We scored 250 species satisfactorily, from a list of 700 +. We analyzed model sensitivity to scoring factors, and compared results to those from a WRA model for Hawaii. For species not in cultivation in the United States, the top 25 species included a mix of annuals, perennials, sedges, shrubs, and trees. Most had exhibited invasive behavior in at least several other countries. Because of greater entry potential scores, the highest-scoring species were weeds in cultivation. Twenty-nine such species, out of 44 total, had scores greater than the highest scoring species not in cultivation. In comparison to the Hawaii WRA model, correlation and regression analyses indicated that the U.S. weed-ranking model produced similar, but not exact, results. The ranking model differs from other WRAs in the inclusion of entry potential and the use of a multiplicative approach, which better suited our objectives and United States regulations. Two highly ranked species have recently been listed as Federal Noxious Weeds, and we expect most top-tier species to be similarly assessed.

Restoration of Stipa kryloviisteppes in Inner Mongolia of China: Assesment of seed banks and vegetation composition

The landscapes of Inner Mongolia are widely known for the vast Stipa krylovii steppes. However, overgrazing and other improper land uses have extensively degraded the Stipa krylovii steppe ecosystem in recent decades. Knowledge about the soil seed banks and the remaining vegetation in these damaged ecosystems is crucial for guiding the restoration efforts. Using a germination method, this study examined the size, composition, and species richness of the soil seed banks in three field types: overgrazed steppe, enclosed steppe and abandoned crop field. The abandoned crop field had the largest soil seed bank with mostly annual and weedy plant species. Seeds of desirable perennial grass species were impoverished by the intensive cultivation in the abandoned crop field. The lack of desirable perennial species in the abandoned field was a critical limiting factor for restoration. Grazing decreased the size of the seed bank in the overgrazed steppe. But seeds of desirable grassland species were present in both the overgrazed and the enclosed steppes. As indicated by the Sorenson's indices of community similarity (50–67%), plant species abundance and composition in the soil seed banks were closely related to the corresponding vegetation for each of the three sites.

Parasitic wasp assemblages associated with native and weedy plant species in an agricultural landscape

Abstract The establishment and maintenance of suitable habitat on‐farm or in the surrounding landscape can enhance the survival of beneficial parasitic Hymenoptera, thus improving the control of pest species. Both endemic and weedy non‐crop plant species across a highly modified agricultural landscape supported species‐rich and abundant parasitic wasp assemblages with diverse biology and host associations. It was also shown that isolated, recently planted, single‐species stands of plants can rapidly accumulate diverse assemblages of parasitoids. Chalcidoidea was the most species‐rich and abundant group, egg and larval parasitoids were the most speciose and abundant guilds, and parasitoids of herbivorous insects feeding on and inside plant tissue were the most species‐rich and abundant functional groups. The hymenopteran assemblages associated with the majority of plant species were dominated by three parasitoid species: a Trichogrammatidae, a Scelionidae (Telenomus sp.) and a Eulophidae (Ceranisus sp.), all genera that contain many important biocontrol agents of pest Lepidoptera, Hemiptera and Thysanoptera. Results show that both native and weedy plant species may potentially provide an important reservoir of mobile parasitic wasps of benefit to crop protection.

New weed threats: extent, origins, and proper management.

Abstract Weed problems continue to be an obstacle in plant protection and in natural areas, causing high costs of control and asking for adequate prevention measures. New weed problems in any given area (risk area) may arise from three basic sources: by introduction and naturalization of new weedy plant species, by increasing spread of weedy taxa that are already present in the risk area, and by the evolution of new weedy taxa in the risk area. Introduction and subsequent naturalization of new plant species is taking place worldwide and the number of alien plant species being introduced is steadily increasing. Newly recorded alien plant species prevail in disturbed sites and semi-natural habitats, increasing the risk for new plant invasions into areas of high conservation value. New weed problems in agroecosystems are associated with recently naturalized species, with adaptation and evolution of plant species, but also due to land use change, global warming, and changes in the environmental conditions. These may affect the dynamics of weed populations, triggering sudden range expansion and abundance increase. Evolution of new weedy taxa involves crop/weed hybridization, hybridization between native and alien plants in the risk area, and hybridization between formerly separated taxa that co-occur in the risk area. Evolution of herbicide resistance is another source of new weed taxa. A literature survey revealed more than 40 new weed species of agroecosystems within the last 20 years and about 35 new plant species invading natural and semi-natural habitats during the last ten years. Measures towards mitigating problems associated with new weeds includes regular monitoring and risk assessments, aiming at preventing entry of new weeds and prioritizing weed species for control.

Concurrent Management of an Exotic Species and Initial Restoration Efforts in Forests

Abstract One of the proximate results of forest fragmentation, and a cause of continued microenvironmental change and exacerbation of ecological problems, is increased invasions by weedy plant species. One such example is Alliaria petiolata (Brassicaceae), a serious pest threatening much of eastern North America. Alliaria petiolata impedes mitigation of fragmentation and restoration efforts because it tends to outcompete and possibly extirpate much of the native understory species on localized scales. As part of a strategy to address the problems of fragmented habitats, an experiment was conducted to determine whether Sanguinaria canadensis (Papaveraceae) could outcompete A. petiolata. Using an additive design, I transplanted S. canadensis at densities of 0, 1, 2, 3, 5, 7, 9, 11, 15, and 20 ramets/m2 in 1997 and allowed them to interact with initial A. petiolata densities of 128 seedlings and 31 rosettes/m2. As of 2000, multivariate analyses of variance with repeated measures and simple analyses of variance indicated that initial S. canadensis densities of as little as 5 ramets/m2 suppressed A. petiolata. Initial S. canadensis densities of 9 and 11 ramets/m2 resulted in the lowest numbers of late‐spring seedlings, numbers and sizes of year 1 and 2 rosettes, numbers and gross areas of stem leaves, numbers of flowering individuals, number of flowers, number of fruits (siliques), and height at flowering. While it remains to be tested whether this will continue and if the reestablishment of S. canadensis will help reassemble forest ecosystems, the experiments indicated that transplanting S. canadensis was effective at mitigating the spread of A. petiolata.

Faunistic Study of the Agromyzidae (Diptera) on Weeds of Marginal Areas in Northern Italy Agroecosystems

Extensive surveys of weedy plant species among hedgerows of different complexity and floristical composition were conducted with the aim to evaluate the role of weeds as reservoirs of agromyzids and to study the trophic relationships between these Diptera and noncrop plants. Field samplings were carried out weekly collecting foliage infested by leafminers from the representative weedy plants in three sites located in Bologna province, Italy. During 1998–1999, a total of 646 agromyzid specimens were reared, representing eight genera and 24 species. The most abundant species were Chromatomyia horticola (Goureau), Phytomyza lappae Goureau, Phytomyza ranunculi Schrank, Phytomyza plantaginis Robineau-Desvoidy, Liriomyza trifolii (Burgess), and Ophiomyia pulicaria (Meigen). C. horticola was the dominant species accounting for 35.76% of adults reared. Agromyzids mined 25 plant species belonging to nine families. The Asteraceae, in particular Cirsium arvense (L.) Scopoli and Sonchus asper (L.) Hill, were the most important sources of leafminers considering both species richness and population densities. Shannon–Weaver (H′), Simpson (D), and Berger–Parker (d) indices all pointed out that agromyzid species diversity was higher in the site characterized by the highest floristic richness, the highest complexity of ecological net and nonintensive agriculture. Most of the weeds sampled proved to be reservoirs for noneconomically important agromyzids in open-field crops in Italy.

Spatial patterns of light gaps in mesic grasslands

The spatial pattern of light gaps in mesic grasslands in central Texas with contrasting disturbance histories was assessed using patch-based landscape metrics determined from a threshold level (25% of full sunlight), as light intensities below this threshold substantially decrease survival of honey mesquite (Prosopis glandulosa var. glandulosa Torr.) seedlings. The spatial pattern of light gaps, with the exception of edge density, were significantly different between annually-disturbed and non-disturbed grasslands on all sample dates (2 April, 30 April, 29 May, and 26 June 1998). Differences in patch metrics did not occur between non-disturbed grasslands despite contrasting vegetation composition [perennial forbs and perennial bunch (tussock) grasses]. Patch-based landscape metrics of light gaps did vary temporally in both annually-disturbed and non-disturbed grasslands. The structure and spatial configuration of light gaps were distinctly different between annually-disturbed and non-disturbed grasslands: a low density of large patches characterized light gaps in annually-disturbed grassland, whereas non-disturbed grasslands had a high density of small patches. Our findings demonstrate that the current disturbance regime is the principal environmental driver influencing species dominance and composition, and indirectly vegetation structure, which collectively contribute to the observed dynamics of light gap patches in these mesic grasslands. Incorporating spatially explicit consideration of light gap structure and dynamics into experimental studies addressing invasion of weedy plant species such as honey mesquite may be an effective approach to address mechanisms and the ecological significance of disturbance operating as a driver facilitating woody plant invasions in mesic grasslands.

Spatial patterns of light gaps in mesic grasslands

The spatial pattern of light gaps in mesic grasslands in central Texas with contrasting disturbance histories was assessed using patch-based landscape metrics determined from a threshold level (25% of full sunlight), as light intensities below this threshold substantially decrease survival of honey mesquite (Prosopis glandulosa var. glandulosa Torr.) seedlings. The spatial pattern of light gaps, with the exception of edge density, were significantly different between annually-disturbed and non-disturbed grasslands on all sample dates (2 April, 30 April, 29 May, and 26 June 1998). Differences in patch metrics did not occur between non-disturbed grasslands despite contrasting vegetation composition [perennial forbs and perennial bunch (tussock) grasses]. Patch-based landscape metrics of light gaps did vary temporally in both annually-disturbed and non-disturbed grasslands. The structure and spatial configuration of light gaps were distinctly different between annually-disturbed and non-disturbed grasslands: a low density of large patches characterized light gaps in annually-disturbed grassland, whereas non-disturbed grasslands had a high density of small patches. Our findings demonstrate that the current disturbance regime is the principal environmental driver influencing species dominance and composition, and indirectly vegetation structure, which collectively contribute to the observed dynamics of light gap patches in these mesic grasslands. Incorporating spatially explicit consideration of light gap structure and dynamics into experimental studies addressing invasion of weedy plant species such as honey mesquite may be an effective approach to address mechanisms and the ecological significance of disturbance operating as a driver facilitating woody plant invasions in mesic grasslands.

DISTRIBUTIONAL RANGE SIZE OF WEEDY PLANT SPECIES IS CORRELATED TO GERMINATION PATTERNS

For plant species adapted to disturbances, the germination niche breadth (the time span within a year during which the species is able to germinate) may be a key in understanding the variability of range sizes across species. Species that are able to germinate throughout the year should be able to use more disturbances and build up large local populations. As population size is correlated to distribution, one would expect a correlation between the temporal germination pattern and distributional range sizes. For a test of this hypotheses, we used germination patterns and local abundance data from 31 weedy plant species from an abandoned field in eastern Germany. In cross-species and phylogenetically controlled analyses, the germination niche breadth was correlated to range size on the national, as well as the continental scale. However, significant correlations between ger- mination niche breadth and abundance, as well as abundance and range size, appeared only in a phylogenetically controlled analysis. In multiple regression analyses, the germination niche breadth turned out to be the most important predictor of distributional range sizes for our subset of weedy species. These results suggest that, for weedy species, the ger- mination niche breadth influences distributional range size. However, the detailed process behind these relationships remains elusive. Nevertheless, the regeneration niche of plants may be a useful concept for exploring macroecological relationships in plants.

Permeability of ancient forest edges for weedy plant species invasion

Within highly fragmented forest landscapes, the flux of matter, energy and species from the landscape matrix into the forest fragment interior is an important ecological phenomenon. We studied the invasion of ancient forest edges by weedy plant species, which are normally confined to the agricultural landscape matrix. We related this to edge orientation and to the occurrence of natural and anthropogenical environmental edge gradients like microclimate and soil chemistry. The plant community composition of the forest edge zone differed significantly from the community composition of the forest core area, and is characterized by a relatively high number of competitive and light demanding species. The maximal width of this edge zone is more extensive at south facing (maximum ca. 20–23 m) than at north facing edges (ca. 0–3 m). However, most of the weedy plant species were unable to penetrate the forest and were confined to the boundary between forest and arable land. We found no negative edge effects on the more stress tolerant ‘true’ forest species going further than 0–3 m (only at south facing edges). The invasion pattern generally fitted the edge gradient for photosynthetically active radiation (PAR). The negative effects of fertilizer misplacement from adjacent arable land on forest soil chemistry (and community composition) are also restricted to the boundary of the forest edge zone. Based on the derived penetration distances of the edge effects and on the shape index of a forest patch it is possible to derive the minimal required forest patch area for forest plant species conservation.

The importance of sexual and asexual reproduction in the recent evolution of Allium vineale.

In the weedy plant species Allium vineale (wild garlic), individuals may simultaneously produce sexually and asexually derived offspring, by seed and bulbils, respectively. In this study, genetic and genotypic diversity was determined in samples from 14 European A. vineale populations using nuclear (RAPD) and cytoplasmic (PCR-RFLP of cpDNA) markers to investigate the importance of the different reproductive modes. In the whole sample, 77 nuclear multilocus genotypes and four chloroplast haplotypes (chlorotypes) were found. Populations exhibited a high degree of subdivision for nuclear and cytoplasmic markers as estimated from hierarchical F-statistics; at the same time, identical chlorotypes could be found in populations separated by large distances. Genotypic diversity was significantly lower than expected under free recombination in almost all populations, indicating that recruitment into populations is mostly by asexually produced offspring. Nevertheless, within each chlorotype, the distribution of markers from pairs of nuclear loci was incompatible with a purely clonal structure, suggesting that many multilocus genotypes have originated by sexual recombination rather than by mutation within asexual lineages. It is argued that the weedy habit of A. vineale is likely to have favored bulbil reproduction, whereas sexually generated genotypes may have facilitated local adaptation during the species' expansion across Europe.

Allelopathic Effects of Volatile Cineoles on Two Weedy Plant Species

The volatile monoterpene analogs, 1,4-cineole and 1,8-cineole, have been identified as components of many plant essential oils, but relatively little is known about their biological activities. We compared the effects of 1,4- and 1,8-cineole on two weedy plant species by monitoring germination, mitosis, root and shoot growth, chlorophyll content, and photosynthetic efficiency. 1,4-Cineole severely inhibited growth of roots and shoots, causing cork-screw shaped morphological distortion, whereas 1,8-cineole caused a decrease in root growth and germination rates. Chlorophyll fluorescence data (yield and F v / F m) indicated that 1,4-cineole caused significantly higher stress (P ≤ 0.001) to photosynthesis when compared to controls. Mitotic index data showed that 1,8-cineole severely decreased (P ≤ 0.001) all stages of mitosis when compared with controls, while 1,4-cineole only caused a decrease in the prophase stage (P ≤ 0.05). Although superficially similar in structure, these two cineoles appear to have different modes of action.

Leafminers in vegetables, ornamental plants and weeds in Indonesia: Surveys of host crops, species composition and parasitoids

Extensive surveys of vegetable, ornamental and weedy plant species were conducted in highland and lowland vegetable production areas in Indonesia with the aim of recording leafminer species present and their associated natural enemies. The most common dipterous species reared from samples was the pea leafminer, Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae). This introduced pest was particularly serious in highland vegetables in Java, Sumatra and South Sulawesi, causing yield losses as high as 60-70%. Another alien species, the vegetable leafminer, Liriomyza sativae Blanchard, contributed to problems in lowland areas on the north coast of West Java, where cucumbers were heavily damaged. An Asian leafminer species, Chromatomyia horticola Goureau, was more common in snow peas (Pisum sp.). Intensive sampling of leafminer-infested leaves from surveyed host plants yielded 11 species of hymenopteran parasitoids: 10 eulophids (Asecodes sp., Chrysocharis sp., Cirrospilus ambiguus (Hansson and LaSalle), Closterocerus sp., Hemiptarsenus varicornis (Girault), Neochrysocharis formosa (Westwood), Neochrysocharis sp., Pnigalio sp., Quadrastichus sp., Zagrammosoma sp.) and 1 eucoilid (Gronotoma sp.). The most abundant parasitoid species was H. varicornis. Levels of parasitism varied among crops and growing seasons, but were usually low, especially on potato (< 3%). Surveys revealed that most farmers (63%) attempted to control leafminers by applying insecticides twice weekly although these applications were neither effective nor economical according to responses of about 72% of the farmers. An integrated pest management approach is suggested that emphasizes IPM training for vegetable farmers and includes reductionor elimination of broad spectrum chemicals that would adversely affect parasitoids that may already be present as well as those that may be introduced. The initiation of a classical biological control programme is recommended to enhance the limited parasitoid complex present in Indonesia and increase levels of biological control.