Biological Control Of Weeds Research Articles

Is Biological Control of Weeds Conservation’s Blind Spot?

Invasive alien species are among the most important threats to biodiversity, with invasive plants ranking among the highest. Classical weed biological control—or biocontrol—reunites exotic plants with host-specific natural enemies from their native range with the aim of controlling the invasive plant. We reviewed the attention classical weed biocontrol has received from scientific publications for the last 30 years, classified according to the area of academia and applied sciences, as well as the region of the world. Biological control journals were excluded from the analyses to avoid bias. This process allowed us to evaluate the support classical weed biocontrol has among the scientific community. We also recorded the number of weed biocontrol agents released from 1900 to date, where they were collected, and where they were released as a way to analyze the evolution of classical weed biocontrol policies in different parts of the world. Classical weed biocontrol releases peaked between 1990 and 1999, but have declined since, probably due to funding issues, increases in regulations, and bad publicity. Researchers in theoretical ecology appear to be more skeptical toward weed biocontrol than scientists in applied and experimental biology. Our synthesis also suggests that despite resistance to classical weed biocontrol in some quarters of the scientific community, the general scientific perception of the discipline has been consistently favorable. This means that the general scientific perception of classical weed biocontrol contradicts its level of current application. The five main objections against classical weed biocontrol—direct nontarget effects, indirect and hidden nontarget effects, evolution of host shifts in biocontrol agents, dispersion to unwanted areas, and disagreements on its level of success in the field—are summarized and analyzed in terms of their relevance and probability of occurrence. We also describe the way classical weed biocontrol practitioners deal with them at present to ensure safety and sustainability. Our analysis suggests the potential of classical weed biocontrol is undervalued in some areas of science and management due to objections that are plausible in theory, although their likelihood is very low and on-ground evidence scant.

The bioherbicidal potential of isolated fungi cultivated in microalgal biomass.

This study evaluated the bioherbicidal potential of wild fungi grown on microalgal biomass from the digestate treatment of biogas production. Four fungal isolates were used and the extracts were evaluated for the activity of different enzymes and characterized by gas chromatography coupled with mass spectrometry. The bioherbicidal activity was assessed by application on Cucumis sativus, and the leaf damage was visually estimated. The microorganisms showed potential as agents producing an enzyme pool. The obtained fungal extracts presented different organic compounds, most acids, and when applied to Cucumis sativus, showed high levels of leaf damage (80-100 ± 3.00%, deviation relative to the observed average damage). Therefore, the microbial strains are potential biological control agents of weeds, which, together with the microalgae biomass, offer the appropriate conditions to obtain an enzyme pool of biotechnological relevance and with favorable characteristics to be explored as bioherbicides, addressing aspects within the environmental sustainability.

When a plant invader meets its old enemy abroad: what can be learnt from accidental introductions of biological control agents.

Accidental introductions of biological weed control (BWC) agents (i) offer opportunities to assess host use of agents with a potentially broader fundamental host-range than those approved for field release directly in target areas; (ii) urge national authorities to rapidly respond as they may threaten native species or crops, and by this (iii) help advancing post-release studies, a neglected aspect of BWC. Through detailed insights gained from studying the recent accidental introduction of the ragweed leaf beetle Ophraella communa into Europe, we derive suggestions for overcoming barriers to adoption of BWC by re-evaluating the predictive power of pre-release studies and, thus, the presently strict criteria for deciding upon their release that might exclude safe and efficient agents. By using the allergenic weed Ambrosia artemisiifolia and the accidentally introduced BWC agent O. communa as study system, we also hope to raise the awareness of authorities to consider biological control more prominently as a key approach for pest management in the 'One Health' concept, which aims to sustainably balance and optimize the health of people, animals, plants and ecosystems. © 2023 Society of Chemical Industry.

Ultrastructural studies of the host (Senecio aegyptius L.) responses after the infection by the pathogenic rust fungus, Puccinia lagenophorae Cooke

This study investigated the impact of the rust fungus, Puccinia lagenophorae on its host, Senecio aegyptius using both light (LM) and transmission (TEM) electron microscopy. The chloroplast numbers decreased during the aecial and telial stages of the pathogen (53.7 and 56.6%, respectively). The nucleus volumes were increased during both stages (10.9 and 14.1%, respectively). Infected chloroplasts and nuclei showed changes in their shape and ultrastructure. Instead of the M-haustorium, a collar was created around the D-haustorium. A neck encasing developed in both types of necrotic haustoria. This encasement may serve as the host cell’s protection against toxins created after the death of haustoria. The severe changes in the chloroplasts and nuclei of this host plant after infection by this pathogen may give this pathogen the possibility of controlling this serious weed. Future research in the molecular mechanism may explore the biological control of weeds for local farm agroecology.

Accessing biological control genetic resources: the United States perspective.

The USA has been actively involved in classical biological control projects against invasive insect pests and weeds since 1888. Classical (importation) biological control relies upon natural enemies associated through coevolution with their target species at their geographic origin to also provide long-term, self-sustaining management where the pest/weed has become invasive. Biological control agents are a form of genetic resources and fall under the purview of the 1993 Convention on Biological Diversity (CBD) and its Nagoya Protocol (NP), which entered into force in 2014 to address equitable sharing of benefits arising from utilization of genetic resources. Safe and effective classical biological control agents have historically been shared among countries experiencing problems with invasive species. However, a feature of the Nagoya Protocol is that countries are expected to develop processes governing access to their genetic resources to ensure that the benefits are shared equitably-a concept referred to as "access and benefitsharing" (ABS). Although the USA is not party to the CBD nor the NP, US biological control programs are affected by these international agreements. Surveying, collecting, exporting and importing of natural enemies may be covered by new ABS regulatory processes. Challenges of ABS have arisen as various countries enact new regulations (or not) governing access to genetic resources, andthe processes for gaining access and sharing the benefits from these resources have become increasingly complex. In the absence of an overarching national US policy, individual government agencies and institutions follow their own internal procedures. Biological control practitioners in the USA have been encouraged in recent years to observe best practices developed by the biological community for insect and weed biological control.

Assessment of the inhibitory effect of two local plants on the emergence of four weeds and identification of their secondary metabolites: Case of Parkia biglobosa (Jacq.) R.Br.ex G.Don. and Tephrosia purpurea (L.) Pers.

In Burkina Faso, Senna occidentalis, Ipomoea eriocarpa, Pupalia lappacea and Triumfetta cordifolia are frequent weeds in the maize crop. This work evaluated the inhibitory effect of Parkia biglobosa pods and Tephrosia purpurea leaves and identifies their chemical compounds. Biological and chemical approaches were used to identify the weeds. The inhibitory effect of powders was evaluated on weed germination and growth. Experimental results showed that powders reduced both germination (p<0.001) and growth (p<0.016). Parkia biglobosa pods were rich in total flavonoids (544.2±1.4 µg mg-1) and condensed tannins (182.3±1.5 µg mg-1) than Tephrosia purpurea leaves which contained small amounts of total flavonoids (6.7±1.7 µg mg-1) and condensed tannins (5.7±1.2 µg mg-1). Parkia biglobosa pods could be used in the biological control of weeds. Int. J. Agril. Res. Innov. Tech. 12(2): 74-81, December 2022

Insect and weed biological control in Hawaii: Recent case studies and trends

Hawaii has a long history of classical biological control research and implementation. Many successes have been achieved in suppressing invasive insect species and plants though the introduction of insect and plant pathogenic natural enemies. This review paper details selected recent introductions and discusses selected cases highlighting successes with highly impactful invasive species control in diverse environments. The current state of biological control in Hawaii is discussed, including recent trends in numbers of species released, concerns about non-target impacts, and how these are addressed. Research on the biological aspects is thorough, but the ability to expand research to address continuing invasive species issues is constrained largely by infrastructure limitations. Urgent research needs for continued biological control research are identified.

Weed Control Using Allelopathic Properties of Rapeseed Residues and Crop Management

Planting date, density and allelopathic properties are important tools of crop management in controlling weeds in crops. Allelopathy refers to any direct or indirect inhibitory or stimulating effect of one plant on another through the production and release of secondary metabolites in the environment. Two experiments performed separately, in order to investigate the effect of allelopathic properties of rapeseed residues and crop management on the control of rapeseed weeds and its yield. The first experiment was conducted during two agricultural years (2018-2019 and 2019-2020) in a factorial form of a randomized complete block design with 3 replications at the Qarakhil agricultural research station (QaemShahr). The treatments were included: planting date in 3 treatment levels (October 17, November 6 and November 26), seed rate in 3 treatment levels (3, 5 and 7 kg per hectare) and weed management in 2 treatment levels presence of weed (no control) and the absence of weed (control). The second experiment was conducted as a factorial in the form of a completely random design in three repetitions in the research laboratory of the Islamic Azad University, QaemShahr branch in 2020. The experimental treatments included weeds [wild oat (Avena fatua), darnel regrass (Lolium temulentum), phalaris (Phalaris minor)] and charlock mustard (Sinapis arvensis)) different concentrations of rapeseed root and stalk extracts (0, 25, 50, 75 and 100%). The results of the first experiment showed that, in general, the rapeseed seed yield was affected by the planting date and density, so that the rapeseed seed yield on the delayed planting date (November 26) decreased compared to the first planting date (October 17) by 49 and 59 percent, respectively in the first and second year of the experiment, and this decrease was more intense in the second year. Also, the results showed that the highest dry weight of weeds was obtained in both years at a density of three kilograms per hectare and in the cultivation of November 26 (except for the highest dry weight of wild oats that was observed in the cultivation of October 17). While the highest weight of seed yield was obtained in both crop years at a density of 7 kg per hectare. The results of the second experiment showed that the extract obtained from the root and stem of the rape plant had a negative and significant effect on the speed, percentage and inhibition of germination in all weeds. However, no significant difference was observed between the concentration of root and stem extracts at the 5% level. A significant negative linear regression relationship was observed between the concentration of the extract (root and stem) with the percentage and speed of germination. Also, a significant positive linear regression relationship was observed between inhibition percentage and extract concentration (root and stem). Therefore, the germination and seedling growth of the seeds of all three weed species had a negative reaction to the concentration of rapeseed extract, but the highest sensitivity was observed in wild oat seeds. Therefore, according to the results, rapeseed extract can be used in the biological control of weeds. In general, the results of two experiments showed that the planting date, density and rapeseed residues can be used effectively in controlling weeds in rapeseed fields.

Weed biological control with fungi-based bioherbicides

Biological control refers to the use of living beneficial organisms as well as the products of their metabolism in pest control. Weed plants are indispensable companions of cultivated plants, in which they cause substantial damage. Organic food production, human health care and environmental preservation impose a need for the production and application of bioherbicides, particularly in organic systems of plant production. Plant pathogens have significant potential as biological agents in weed control. The aim of the present study was to indicate the most important properties of the weed biological control system, with particular emphasis on the use of fungi-based bioherbicides. According to the organism they suppress, biopesticides are classified into bioinsecticides, biofungicides, bioherbicides, etc. Weed control using plant pathogens can be performed in three ways, by classical, conservation and augmentative biological control. Bioherbicides were initially introduced to the market in 1980, and the majority of them were fungi-based bioherbicides. The most common fungi included in bioherbicides belong to the genera Alternaria, Colletotrichum, Cercospora, Fusarium, Phomopsis, Phytophthora, Phoma, Puccinia, etc. The studies, development and final commercialisation of fungi as biological control agents face many obstacles, ranging from basic biological facts to social and economic factors. There are also challenges in the production, formulation process, environmental friendliness, duration of herbicidal action, and expensive and time-consuming registration procedures. Considering the success in weed suppression with fungi-based bioherbicides, the global market is still dominated by chemical companies manufacturing synthetic herbicides, while there are no such products on the Serbian market yet.

Citizen science reveals the establishment of Chamaesphecia empiformis (Esper) (Lepidoptera: Sesiidae), a long-lost biological control agent for Euphorbia cyparissias (Euphorbiaceae), in Ontario, Canada

Abstract The European root-boring moth, Chamaesphecia empiformis (Lepidoptera: Sesiidae), was released in Ontario, Canada, in 1971 and 1989 as a biological control agent for the perennial invasive weed cypress spurge, Euphorbia cyparissias Linnaeus (Euphorbiaceae). Until recently, the moth was believed to have failed to establish. Beginning in 2015, images posted on citizen science platforms, including BugGuide, iNaturalist, and Facebook groups, indicated that C. empiformis was in fact established. We have confirmed its presence in eastern Ontario by morphological and molecular identification of field-collected adults and eggs. This may be the longest-known lapse between the release of a weed biological control agent and confirmation of its establishment. Citizen science may provide valuable records documenting the establishment and dispersal of biological control agents.

Weed control with small ruminants: Exploratory evaluation on Senecio inaequidens

Objective: Carry out an exploratory evaluation of sheep and goats grazing in a temperate pasture invaded by Senecio inaequidens, as a means of biological control of weeds in small-scale dairy systems (SSDS).
 Methodology: Crude protein (CP), neutral detergent fibre (NDF), and acid detergent fibre (ADF) were determined on pasture and Senecio samples. The effect of grazing by sheep and goats on the pasture was assessed by means of the height, density and soil cover of Senecio, and also sward height; and the live weight of the animals, daily weight gain and body condition score were recorded. Statistical analysis was by a 2x2 factorial design, with species (sheep or goat) and two grazing intensities at 28.3 or 50.3 m2/animal per day.
 Results: height, coverage and density of Senecio did not show significant differences (P>0.05), neither did sward height. The chemical composition of the pasture did not show statistically significant differences for the assessed periods either. Animal weight, body condition and daily weight gain did not show significant differences among the evaluated treatments (P>0.05).
 Implications: This is the first report evaluating sheep and goat grazing to control of Senecio invasion in temperate pasture in central Mexico. In addition, knowing the chemical quality of Senecio will allow decisions to be made for supplementation in grazing systems with sheep or goats.
 Conclusions: The grazing of sheep and goats reduced the number of Senecio plants in the assessed pasture, which indicates the possibility of controlling this weed by grazing sheep or goats over longer-term grazing.

The weevil, Hypolixus pica (F.) (Coleoptera: Curculionidae) as a potential biological control agent of Amaranthus species (Amaranthaceae) in Adana Province, Turkey

Amaranthus species (Family) are among the most important weeds in summer crops and orchards in Turkey. The detrimental effects of pesticides on the environment and human health and the development of high levels of resistance to several herbicide classes by Amaranthus species have generate interest in alternative weed control methods. Since the biological control of weeds has gained great prominence recently, this study was carried out to determine the potential biological control agents of Amaranthus spp. in Adana Province. Turkey. For this aim, ten randomly selected fields randomly were in three districts (Yüreğir-Ceyhan-İmamoğlu). In each field, ten Amaranthus plants were collected randomly and dissected, and the numbers of the weevils and theirdifferent stages were recorded. In this study, three Amaranthus species were identified and A. palmeri was the most common, followed by A. retroflexus and A. spinosus. Fifty-nine larvae, 26 pupae and 10 adults were collected from the Amaranthus plants. All adult individuals were identified as H. pica according to their genital organs. Our results show that H. pica could be considered to be a potential biological control agent of A. palmeri and A. retroflexus. More detailed studies are needed to determine its ecology and role as a biological control agent of the target weed species. In addition, it is crucial to develop mass rearing methods for potential beneficial insects such as H. pica.

Knowledge and perceptions of invasive plant biocontrol in Europe versus the rest of the world

Biological control (BC) of invasive alien plants (IAP) can be an effective environmental management approach. It has only very recently been adopted in Europe and is underutilized compared to other continents where this method has been successfully implemented for over a century. This is in sharp contrast to the BC of invertebrate pests, which has been taken up widely within Europe. It has been suggested that this is related to the risk-adverse attitude of Europeans towards weed BC. Scientific and public perception have a major influence on environmental policy actions. Public perception and knowledge regarding BC is an understudied subject despite its relevance for the application of this management alternative. We aimed to assess the knowledge and perception of BC of IAP among European professionals compared with their peers from other continents. To this end we conducted an online survey including multiple choice and open questions among over 700 people professionally engaged with managing the natural environment, of which approximately half were from Europe (EU) and the others from outside (non-EU). We assessed relationships between the geographical location of the respondents and their knowledge, and perceptions of BC of weeds versus BC of invertebrate pests. We found that respondents’ location influenced both perceptions and knowledge of BC for weeds. Compared to non-EU respondents, EU professionals showed less appreciation for BC (e.g., regarding safety, sustainability, and cost-effectiveness), and perceived it as a riskier method, particularly in the case of practitioners and researchers. More profoundly insect pest BC tended to be considered less safe than weed BC for non-EU respondents. Confidence in weed BC as a method, as well as in the validity of the associated pre-release risk assessments, strongly increased with the level of expertise in weed BC. While a much higher proportion of non-EU respondents were correctly aware of the presence/absence of BC in their own countries and identified successful examples of BC accurately, both groups of respondents were similarly aware of unsuccessful BC examples, including BC agents against animals, stressing the bias of EU respondents towards examples of BC failure. The appreciation of weed BC in Europe could be elevated by a combination of increasing knowledge of the technique and pre-release risk assessment and promoting successful examples of weed BC, which may bring major benefits for the management of IAP across the region.

Application of Three Weed Pathogenic Fungi on Bok choy (Brassica rapa subsp. chinnensis)

Weed pathogenic fungi play an important role in biological control of weeds. Weeds grow a lot among cultivated plants, the role of weed pathogenic fungi to cultivated plants is not yet known. This research aimed to determine the effect of weed pathogenic fungi on bok choy. The research was carried out in Tambaksogra Village, Sumbang District, Banyumas Regency at an altitude of 100 m above sea level. Randomized block design was used with treatments of weed pathogenic fungi (Fusarium sp., Curvularia sp., Chaetomium sp., Fusarium sp. + Curvularia sp., Fusarium sp. + Chaetomium sp., Curvularia sp. + Chaetomium sp., and Fusarium sp. + Curvularia sp. + Chaetomium sp.) repeated four times. The observed variables included symptoms, incubation period, disease intensity, disease incidence, infection rate, AUDPC, number of leaves, plant height, and plant fresh and dry weight. Results showed that Weed pathogenic fungi of Curvularia sp. and Chaetomium sp. alone or in combination did not affect bok choy indicated by disease intensity of 0 %, and did not affect plant height, number of leaves, and plant fresh weight. The weed pathogenic fungi can be used as a bioherbicide in bok choy. To control weeds in bok choy plantations, both weed pathogenic fungi are recommended to be used. The further application of weed pathogenic fungi needs to be continued to other cultivated plants besides bokchoy.

Detection of Parthenium Weed (Parthenium hysterophorus L.) and Its Growth Stages Using Artificial Intelligence

Parthenium weed (Parthenium hysterophorus L. (Asteraceae)), native to the Americas, is in the top 100 most invasive plant species in the world. In Australia, it is an annual weed (herb/shrub) of national significance, especially in the state of Queensland where it has infested both agricultural and conservation lands, including riparian corridors. Effective control strategies for this weed (pasture management, biological control, and herbicide usage) require populations to be detected and mapped. However, the mapping is made difficult due to varying nature of the infested landscapes (e.g., uneven terrain). This paper proposes a novel method to detect and map parthenium populations in simulated pastoral environments using Red-Green-Blue (RGB) and/or hyperspectral imagery aided by artificial intelligence. Two datasets were collected in a control environment using a series of parthenium and naturally co-occurring, non-parthenium (monocot) plants. RGB images were processed with a YOLOv4 Convolutional Neural Network (CNN) implementation, achieving an overall accuracy of 95% for detection, and 86% for classification of flowering and non-flowering stages of the weed. An XGBoost classifier was used for the pixel classification of the hyperspectral dataset—achieving a classification accuracy of 99% for each parthenium weed growth stage class; all materials received a discernible colour mask. When parthenium and non-parthenium plants were artificially combined in various permutations, the pixel classification accuracy was 99% for each parthenium and non-parthenium class, again with all materials receiving an accurate and discernible colour mask. Performance metrics indicate that our proposed processing pipeline can be used in the preliminary design of parthenium weed detection strategies, and can be extended for automated processing of collected RGB and hyperspectral airborne unmanned aerial vehicle (UAV) data. The findings also demonstrate the potential for images collected in a controlled, glasshouse environment to be used in the preliminary design of invasive weed detection strategies in the field.

Synoptic catalogue of insect parasitoids associated with Lixinae (Coleoptera: Curculionoidea: Curculionidae)

The first host-parasitoid catalogue for Lixinae is presented. This survey is based on literature search (~300 references) and followed by two parts, firstly one of the Lixinae, and secondly one of parasitoids with distinguishing numbers of their Lixine hosts. There are at least 221 species recorded as parasitoids on 108 lixine species. Records on 12 host-parasitoid associations seem to be questable or based on misidentifications. Most common hosts are species of two genera: Lixus (112 parasitoid species) and Larinus (43). All actually known parasitoids of Lixinae are dipterans (belonging to three families) and hymenopterans (15 families). The latter listed as parasitoids of no less than 102 lixine species (94.4%) and 22 hosts (19.4%) associated with Diptera. Six lixine species associated with dipterans only. Most common parasitoids are braconids. Four parasitoid species have the most extensive list of the hosts: Exeristes roborator (at least 29 host species), Cerceris tuberculata (12), Bracon urinator (11) and Zeuxia cinerea (10). Parasitoid complex of some hosts can include more than 10 (to 44!) species. Information contained in catalogue will be helpful for programs of effective biological control of economic important pests and weeds.

Competitive interactions affect larval survival of two root-boring weed biological control candidates of Rumex spp

In weed biocontrol, the release of multiple candidates has been proposed as a way to increase herbivore load and thus impact on the target weed. However, the use of multiple herbivorous species may reduce overall herbivore load due to interspecific interactions. We assessed whether a combined application of two Pyropteron spp. (Lepidoptera: Sesiidae) with root-boring larvae can increase larval infestation rate and impact on two Rumex weeds (Caryophyllales: Polygonaceae). In a laboratory assay (‘behavioural experiment’), interference competition was assessed by comparing the survival of a single larva (no competition), of four conspecific larvae (intraspecific competition) and of two larvae of each species (interspecific competition). In a common garden study (‘infestation and impact experiment’), the outcomes of competitive interactions were assessed on potted plants with single and mixed species applications of the two Pyropteron species using a replacement design. In the behavioural experiment, larval survival was similarly reduced under intra- and interspecific competition compared to no competition, suggesting strong interference competition among larvae independent of the Pyropteron species. In the infestation and impact experiment, mixed application did only scarcely increase herbivore load. Increased herbivore load was found to increase root decay when applied in an inundative approach by placing eggs directly on Rumex plants. However, a joint application of two Pyropteron species did not increase the impact. We propose that detailed behavioural and impact studies be conducted to assess the likely outcome of using multiple candidates in biocontrol programs to minimize associated risks with multiple species introductions.

The benefits to sub-Saharan Africa of the biological control of weeds: already considerable, but could be far greater.

Sub-Saharan Africa (SSA) is climatically diverse, with many biomes. Many species of invasive alien plants (IAPs) are present, with severe negative impacts that largely remain unquantified. Importation biological weed control (IBWC) has been practiced on the continent since the early 20th century, with some notable successes. Weed biocontrol agents (WBA) (141 species) have been released in 30 countries on 69 weed species, and spread to a further eight countries. South Africa has the most active IBWC program, while several projects are underway in other countries, involving either the release of WBA or monitoring of their spread and impact. However, given the large and increasing footprint of IAPs, and the poor prospects for their successful management using other control methods, we discuss reasons for therelatively low uptake of IBWC in SSA, and suggest ways to increase this.

Plant pathogens as introduced weed biological control agents: Could antagonistic fungi be important factors determining agent success or failure?

Mycoparasitic interactions are common in nature, form part of the microbiota of plants, and are considered significant contributors to fungus-fungus antagonism. Mycoparasites kill plant pathogens, protect the plant from abiotic and biotic stressors, and reduce disease incidence and severity at the plant population level. Their exploitation as biocontrol agents in agriculture is well documented. However, mycoparasites may potentially affect classical fungal biocontrol agents of invasive weed species. Classical biological control, or biocontrol, of invasive weeds involves the intentional introduction of exotic, usually co-evolved plant pathogens and insects, for permanent establishment and long-term control of the target plant. Agent establishment, effectiveness, and safety are the critical elements for a successful weed biocontrol programme. Establishment and effectiveness of agents on the invasive plant often vary throughout the invaded range with about two-thirds of weed biocontrol agents failing to suppress their target weed. There are many documented reasons why weed biocontrol agents do not establish or are ineffective when they do, and the presence and accumulation of natural enemies in the invaded range is one of them. Endophyte-enriched, invasive weeds and those forming mutualistic associations with indigenous, native endophytes could explain the lack of consistency of some classical biological control introductions. However, another variable could be factored into the mix: mycoparasitism, where one fungus parasitises another, the natural enemies of the plant's natural enemies. In this review article, we introduce the concept of invasive weed biocontrol and the history of using plant pathogens as biocontrol agents. We discuss the success and failure of fungal agent programmes and delve into the patterns of success or failure, with a focus on the potential antagonistic role of endophytes and mycoparasites.

Predicting parasitoid accumulation by potential Brazilian peppertree biological control agents from assessments in the native and invaded ranges

During their initial releases, classical biological control agents may benefit from enemy-free-space as they are introduced to new habitats with relatively low attack rates by natural enemies. The benefits of classical biological control may be reduced by natural enemies that exploit new agents in the introduced range. Estimates of agent vulnerability to natural enemies prior to release could assist in predicting attack rates and prioritization of proposed agents. Additionally, release of vulnerable biological control agents could have unintended consequences that disrupt native food webs. Our goal was to predict the vulnerability of potential agents to attack by natural enemies by determining parasitism rates in the native range of the weed Brazilian peppertree, Schinus terebinthifolia. Furthermore, we conducted assessments of the rate of attack of ecological analogues in the invaded range in North America, where the agents are to be released, to assist in predicting post release vulnerability. Potential agents and analogues were assigned to four feeding niches, leaf folders, cryptic feeders, thrashers, and sap feeders. Cryptic members were generally most common in the invaded range. However, compared with the other niches, leaf folders were most common in at least one region of the native range. Surveys of potential agents of Brazilian peppertree in their native range of South America indicated parasitism rates were generally <20% for leaf folders (10.5 ± 6.3%; n = 485), cryptic feeders (17.6 ± 3.7%; n = 495), thrashers (12.1 ± 1.2%; n = 381), and sap feeders (2.5% ± 1.1%; n = 200). With exceptions, parasitism rates of the ecological analogues of North America were similar to those from South America for leaf folders (19.2 ± 7.9%; n = 19), cryptic feeders (16.5 ± 5.2%; n = 285), and sap feeders (0.2 ± 0.2%; n = 1247). Thrashers were not included in the analysis as a single parasitoid was found from few (n = 9) hosts recovered in North America. These results suggest that if species of these defoliating leaf folder or cryptic feeder niches are released for biological control in North America they will be parasitized at these same levels. However, if sap feeders are released, these results predict very low parasitism would result. These pre-release assessments of parasitism may assist in the prioritization of potential agent species for biological control of weeds and reduce the likelihood of indirect effects impacting native communities.