Natural Enemy Guilds Research Articles

Inventory and assessment of foliar natural enemies of the soybean aphid (Hemiptera: Aphididae) in South Dakota.

Soybean aphid (Aphis glycines Matsumura) (Hemiptera: Aphididae) is a major pest of soybean in northern production regions of North America, and insecticides have been the primary management approach while alternative methods are developed. Knowledge of arthropod natural enemies and their impact on soybean aphid is critical for developing biological control as a management tool. Soybean is a major field crop in South Dakota, but information about its natural enemies and their impact on soybean aphid is lacking. Thus, this study was conducted in field plots in eastern South Dakota during July and August of 2004 and 2005 to characterize foliar-dwelling, arthropod natural enemies of soybean aphid, and it used exclusion techniques to determine impact of natural enemies and ants (Hymenoptera: Formicidae) on soybean aphid densities. In open field plots, weekly soybean aphid densities reached a plateau of several hundred aphids per plant in 2004, and peaked at roughly 400 aphids per plant in 2005. Despite these densities, a relatively high frequency of aphid-infested plants lacked arthropod natural enemies. Lady beetles (Coleoptera: Coccinellidae) were most abundant, peaking at 90 and 52% of all natural enemies sampled in respective years, and Harmonia axyridis Pallas was the most abundant lady beetle. Green lacewings (Neuroptera: Chrysopidae) were abundant in 2005, due mainly to large numbers of their eggs. Abundances of arachnids and coccinellid larvae correlated with soybean aphid densities each year, and chrysopid egg abundance was correlated with aphid density in 2005. Three-week cage treatments of artificially infested soybean plants in 2004 showed that noncaged plants had fewer soybean aphids than caged plants, but abundance of soybean aphid did not differ among open cages and ones that provided partial or total exclusion of natural enemies. In 2005, plants within open cages had fewer soybean aphids than those within cages that excluded natural enemies, and aphid density on open-cage plants did not differ from that on noncaged plants and those accessible by small predators. In a separate 3-yr experiment, exclusion of ants from soybean plants did not lead to differences in soybean aphid density compared with ant-accessible plants. Overall, these results suggest that the soybean aphid natural enemy guild is unsaturated and could be enhanced to improve biological control of soybean aphid in South Dakota.

Incorporating natural enemy units into a dynamic action threshold for the soybean aphid,Aphis glycines(Homoptera: Aphididae)

Recommended action thresholds for soybean aphid, Aphis glycines, do not adjust for natural enemy impact, although natural enemies contribute important biological control services. Because individual natural enemy species have varied impacts on pest population dynamics, incorporating the impact of a diverse predator guild into an action threshold can be cumbersome. Field surveys identified an aphidophagous natural enemy complex dominated by Orius insidiosus, Coccinella septempunctata, Harmonia axyridis and Aphelinus certus. Functional responses of O. insidiosus were determined in the laboratory, while predation rates of all other natural enemies were obtained from the literature. Natural enemy impacts were normalized using natural enemy units (NEUs), where 1 NEU = 100 aphids consumed or parasitized. A dynamic action threshold (DAT) was developed by combining NEUs with an A. glycines population growth model. With the DAT, an insecticide application was only triggered if natural enemy numbers were insufficient to suppress pest populations. In field experiments, DAT provided equivalent yields to the conventional action threshold and reduced the average number of pesticide applications. The DAT approach has the potential to reduce pesticide use, will help preserve natural enemy populations and can be applied to other pest systems with diverse natural enemy guilds.

Relationships between biodiversity and biological control in agroecosystems: Current status and future challenges

Agricultural systems around the world are faced with the challenge of providing for the demands of a growing human population. To meet this demand, agricultural systems have intensified to produce more crops per unit area at the expense of greater inputs. Agricultural intensification, while yielding more crops, generally has detrimental impacts on biodiversity. However, intensified agricultural systems often have fewer pests than more “environmentally-friendly” systems, which is believed to be primarily due to extensive pesticide use on intensive farms. In turn, to be competitive, less-intensive agricultural systems must rely on biological control of pests. Biological pest control is a complex ecosystem service that is generally positively associated with biodiversity of natural enemy guilds. Yet, we still have a limited understanding of the relationships between biodiversity and biological control in agroecosystems, and the mechanisms underlying these relationships. Here, we review the effects of agricultural intensification on the diversity of natural enemy communities attacking arthropod pests and weeds. We next discuss how biodiversity of these communities impacts pest control, and the mechanisms underlying these effects. We focus in particular on novel conceptual issues such as relationships between richness, evenness, abundance, and pest control. Moreover, we discuss novel experimental approaches that can be used to explore the relationships between biodiversity and biological control in agroecosystems. In particular, we highlight new experimental frontiers regarding evenness, realistic manipulations of biodiversity, and functional and genetic diversity. Management shifts that aim to conserve diversity while suppressing both insect and weed pests will help growers to face future challenges. Moreover, a greater understanding of the interactions between diversity components, and the mechanisms underlying biodiversity effects, would improve efforts to strengthen biological control in agroecosystems.

Two tests of enemy release of commonly co-occurring bunchgrasses native in Europe and introduced in the United States

The popularly cited enemy release hypothesis, which states that non-native species are released from population control by their enemies, has not been adequately tested in plants. Many empirical studies have compared damage to native versus non-native invaders only in the invaded range, which can lead to erroneous conclusions regarding enemy release. Biogeographical studies that have compared natural enemies in native and introduced ranges have typically focused on a small area of the plants’ distributions in each range, only one plant species, and/or only one guild of natural enemies. To test enemy release, we first surveyed both pathogens and herbivores in multiple populations in both the native and naturalized ranges of three commonly co-occurring perennial bunchgrasses introduced to the United States from Europe. We then compared our field results to the number of fungal pathogens that have been documented on each species from published host-pathogen data compilations. Consistent with enemy release, our field survey showed less herbivory and denser populations in the naturalized range, but there was no evidence of release from pathogens. In contrast, the published host-pathogen data compilations produced evidence of enemy release from pathogens. The difference in results produced by the two approaches highlights the need for multiple approaches to testing mechanisms of invasions by introduced species, which can enable well supported theory to inform sound management practices.

Mortality factors affecting Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae) eggs in the native and invaded ranges

An absence of diverse and coevolved natural enemies may explain the high levels of oak mortality caused by an invasive wood boring beetle, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), in California (CA). A field study was conducted to test the enemy release hypothesis for a single guild of natural enemies by comparing mortality factors affecting A. auroguttatus sentinel eggs deployed in both native (southern Arizona [AZ]) and introduced ranges (southern CA). The percentage of eggs attacked by natural enemies did not differ between sites, which does not support the enemy release hypothesis for this life stage. Although the predominant cause of mortality to sentinel eggs deployed in CA and AZ was due to factors other than natural enemy activity, chewed, missing, and parasitized eggs contributed to as much as 16% and 24% of sentinel egg mortality in CA and AZ, respectively. In addition, the first known egg parasitoid of A. auroguttatus was collected during this study from a single egg deployed in AZ, and was identified as Trichogramma sp. using molecular techniques. This parasitoid is a generalist, and therefore not suitable for use in a classical biological control program against A. auroguttatus in CA. A continuation of this study is needed across a larger number of field sites and over a longer period of time to optimize the potential detection of host specific egg parasitoids for potential introduction into CA as part of a future classical biological control program, and to better quantify natural enemy impacts on A. auroguttatus eggs.

Natural enemy interactions constrain pest control in complex agricultural landscapes

Biological control of pests by natural enemies is a major ecosystem service delivered to agriculture worldwide. Quantifying and predicting its effectiveness at large spatial scales is critical for increased sustainability of agricultural production. Landscape complexity is known to benefit natural enemies, but its effects on interactions between natural enemies and the consequences for crop damage and yield are unclear. Here, we show that pest control at the landscape scale is driven by differences in natural enemy interactions across landscapes, rather than by the effectiveness of individual natural enemy guilds. In a field exclusion experiment, pest control by flying insect enemies increased with landscape complexity. However, so did antagonistic interactions between flying insects and birds, which were neutral in simple landscapes and increasingly negative in complex landscapes. Negative natural enemy interactions thus constrained pest control in complex landscapes. These results show that, by altering natural enemy interactions, landscape complexity can provide ecosystem services as well as disservices. Careful handling of the tradeoffs among multiple ecosystem services, biodiversity, and societal concerns is thus crucial and depends on our ability to predict the functional consequences of landscape-scale changes in trophic interactions.

A mechanistic model for a tritrophic interaction involving soybean aphid, its host plants, and multiple natural enemies

Soybean aphid (Aphis glycines) is a severe pest of soybean in North America with a diverse natural enemy guild. A large body of literature exists examining aspects of the biology and ecology of this species, but these studies have not been synthesized in a quantitative context, limiting the understanding of the relative importance of environmental and ecological factors in the population dynamics of this species. Existing models for population dynamics of A. glycines are geographically restricted, and do not incorporate host plant phenology or natural enemy impact on aphid population dynamics and phenology. In this paper, a mechanistic tritrophic population and phenology model is developed for this species, incorporating environmental cues, host plant cues and natural enemy dynamics. Individual natural enemy species differ with respect to prey consumption rates and foraging behaviours and may occur at different times in the lifecycle of a prey species in response to environmental cues, densities, or the availability of alternate prey. Additionally, the natural enemy complex of A. glycines differs in composition and abundance in different parts of the aphids range. Because of these factors, we developed a strategy to quantify impact of the natural enemy guild that would facilitate the incorporation of natural enemy complexes occurring at multiple locations. In order to standardize the impact of natural enemy guilds on prey species, we used the Natural Enemy Unit (NEU), where NEU is defined as the number of individuals of a predatory species that can kill 100 individual prey in 24h. After calibration of the NEU calculation to incorporate a type III functional response to prevent natural enemies from driving aphid populations to local extinction, the model performed very well in predicting the dynamics between populations of natural enemies and A. glycines when compared to field observations. Simulations suggest that natural enemy abundance impacts A. glycines abundance more strongly than environmental conditions, but host plant phenology also dramatically influences dynamics of this species.

Predicting Activity Patterns from Resource Exploitation in Guilds of Digger Wasps' Natural Enemies

Predicting Activity Patterns from Resource Exploitation in Guilds of Digger Wasps' Natural Enemies

Quantitative food webs of herbivore and related beneficial community in non-crop and crop habitats

Quantitative food webs were constructed from the data collected, using visual observation technique, from May to July in 2005 and 2006 to describe separately the trophic relationships between the community of aphids and their natural enemies of predators and parasitoids in agricultural and semi-natural habitats in Gembloux, Belgium. In the web, a total of six aphid attacked by six parasitoid and 21 predator species were recorded in this study; 50 and 33 links between aphid and natural enemy species were respectively observed in 2005 and 2006. Aphid density varied seasonally and among years, and three species of aphid were particularly common in different habitats. The ratios of the number of aphid species to the number of species of either predators or parasitoids changed also seasonally. Most communities of insect herbivores are likely to be structured by apparent competition mediated by shared natural enemies more than to be structured by resource competition. The potential of two guilds of natural enemies to contribute in structuring aphid community through indirect interactions was assessed. The potential strengths of apparent competition between hosts mediated by parasitoids and predators were assessed using quantitative parasitoid/predator overlap diagrams. Symmetrical links were uncommon, and rare species were severely influenced by the presence of common aphids with which they shared parasitoids or predators or both. The study’s results suggest that (i) stinging nettle aphids, acting as potential sources of apparent competition mediated by natural enemies, may be important in these highly connected communities and can control whole-community dynamics, and (ii) stinging nettle habitats, in providing an important alternative prey for natural enemies, are likely to play a key role in conservation biological control.

Parasitoids of the painted apple moth Teia anartoides Walker (Lepidoptera: Lymantriidae) in Australia

Painted apple moth Teia anartoides Walker (Lepidoptera: Lymantriidae), a native to Australia, was discovered in Auckland, New Zealand in late 1999 and eradicated by 2006. It was recognised in 2002 that biological control would be the most effective long-term control strategy if eradication was unsuccessful, and a search was initiated for potential biocontrol agents in Australia. In 2003, autumn and spring surveys were undertaken in Victoria, Tasmania and South Australia of the guild of parasitoid natural enemies of T. anartoides. Eggs, larvae and pupae were collected and held to rear out any parasitoids. In addition, localised searches were made in Queensland in late 2003 early 2004 and laboratory-reared juvenile stages of T. anartoides were released for recapture in both Victoria and Queensland. Acacia dealbata Link (Fabales: Fabaceae) was the main plant from which T. anartoides was recovered, followed by apple. Most T. anartoides samples were collected from Victoria and Tasmania. Eighteen species from 13 genera of egg, larval and pupal parasitoids were reared and included Diptera (Tachinidae) and Hymenoptera (Braconidae, Encyrtidae, Eulophidae and Ichneumonidae). Of the seven Hymenopteran genera recovered from the larval stage, the most common in Victoria and Tasmania was a previously unidentified larval parasitoid Cotesia Cameron (Hymenoptera: Braconidae) sp. Echthromorpha intricatoria (Fabricius) (Hymenoptera: Ichneumonidae) was the dominant pupal parasitoid. The survey showed that the parasitoid complex associated with T anartoides is structurally very similar to that on other pest Lymantriidae in the northern hemisphere such as gypsy moth (Lymantria dispar L.) (Lepidoptera: Lymantriidae). Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae) was recorded for the first time in Australia.

Insects and a pathogen suppress Melaleuca quinquenervia cut-stump regrowth in Florida

Utilization of multiple natural enemy species in weed biocontrol programs has often been advocated. Herein, we tested the hypothesis that multiple guilds of natural enemies, rather than individual species, would result in greater levels of damage to target host plants. This was investigated by evaluating the herbivorous insects Oxyops vitiosa (weevil) and Boreioglycaspis melaleucae (psyllid) and rust fungus Puccinia psidii separately and together when attacking cut-stump coppices of the invasive tree Melaleuca quinquenervia (melaleuca). We felled 120 trees in each of three mature melaleuca stands and assigned 6–13 coppicing stumps to each of the four treatments: control (insects and rust fungus excluded); insect herbivory; rust-fungus-infection; and combination of insect herbivory and rust fungus infection. We repeated the experiment once in adjacent plots located within the same stands as above. Coppices were harvested annually for three years and evaluated for damage, height, branching, mortality, and biomass. Three treatments: insects, rust fungus, and their combination caused higher levels of coppice damage and mortality compared to controls; these three treatments also reduced plant height, branching, and biomass of surviving coppices. These impacts of insects and rust-fungus-combination were additive on cut-stump and coppice stem mortality, and reduction in height, branching, leaf biomass, and total biomass of coppices. The rust fungus and psyllid showed better ability to co-attack the same leaf tissues compared to the rust fungus and the weevil. In conclusion, overall effects of the three natural enemies led to markedly reduced performance of the invasive tree melaleuca.

Forgotten natural enemies: Interactions between coccinellids and insect-parasitic fungi

The role of predators and parasitoids in the regulation of insect populations is widely reported in the context of both pest and non-pest insects. However, this is not the case for pathogens (entomopathogens). Indeed, most studies on insect life history refer only to predators and parasitoids when considering natural enemy guilds, even though naturally occurring entomopathogens are undoubtedly more diverse and widespread. This is certainly the case with the Coccinellidae; the natural enemies of coccinellids have been the subject of a number of review articles but pathogens receive only brief mention. In this review we attempt to address the balance and consider the interactions of natural populations of Coccinellidae with entomopathogenic fungi. Most research on ento- mopathogens and Coccinellidae focuses on the non-target impact of biorational insecticides against coccinellids and the impact of fungal infections upon aggregations of overwintering coccinellids; with the former overwhelmingly dominating the literature. Given the prominence of coccinellids in classical and conservation biological control, it is surprising that studies have not measured the natural impact of pathogenic fungi upon introduced species or natural populations of Coccinellidae, as has been done with numerous insect pest species. Here we review the literature on the intriguing interactions between coccinellids and fungal pathogens. We examine the literature on direct infection (sub-lethal and lethal) of coccinellids by pathogenic (Beauveria bassiana, Metarhizium ani- sopliae, Paecilomyces fumosoroseus) or parasitic (Hesperomyces virescens). We also consider the role of intra-guild predation (on the aphid-specific fungus Pandora neoaphidis and Beauveria bassiana) and finally indirect interactions such as coccinellids dis- persing P. neoaphidis. We suggest that fungal pathogens are all too often forgotten natural enemies and future research should address the profound absence of knowledge in this field.

The effectiveness of field margin enhancement for cereal aphid control by different natural enemy guilds

Studies demonstrating the empirical impact of natural enemies on pests and the effect of habitat manipulation are required if farmers are to be persuaded to adopt conservation biocontrol. The relative abundance of different natural enemy guilds were manipulated to investigate their impact on grain aphids ( Sitobion avenae) and whether the establishment of wider field margins increased levels of control. The impact of epigeal and flying aphid predators, in isolation and together, on cereal aphids was tested in five fields with standard field margins ( ca. 2 m wide) and in five fields with wide margins ( ca. 6 m wide). Flying predators alone were as effective as all predators in controlling the grain aphid and reduced aphids by 90% and 93%, whereas epigeal predators alone achieved a reduction of only 40% and 18% in fields with standard and wide margins respectively. Levels of parasitism measured by counts of aphid mummies were relatively low (⩽12%) on all sampling occasions. There was no evidence that the wide field margins increased natural enemies within the adjacent field as measured using pitfall traps, suction sampling and sticky traps. The wide field margins were considered to have no benefit for biocontrol because flying predators capable of moving between fields were primarily responsible or the amount of uncropped land suitable for natural enemies was not a limiting factor in the landscape.

Integration of endemic natural enemies and Bacillus thuringiensis to manage insect pests of Brassica crops in North Korea

Brassica crops, principally varieties of Brassica oleracea and Brassica campestris, account for over half the total vegetable production in the Democratic People's Republic of Korea (DPRK). The crops are attacked by a complex of insects and the two major pest species, Plutella xylostella L. (Lepidoptera: Plutellidae) and Pieris rapae L. (Lepidoptera: Pieridae) represent the principal constraints to Brassica crop production. On co-operative farms pests are managed by scheduled application of broad spectrum insecticides and there is no attempt to conserve or utilize endemic natural enemies. The natural enemy complexes attacking P. xylostella and P. rapae in summer white cabbage ( Brassica oleracea var. 6–21) on three co-operative farms in the south west of DPRK were studied. The hymenopteran parasitoids Cotesia vestalis Haliday (= plutellae Kurdjumov) (Braconidae), Oomyzus sokolowskii Kurdjumov (Eulophidae) and Diadromus collaris Gravenhorst (Ichneumonidae) attacked P. xylostella while Cotesia glomeratus L. (Braconidae), Cotesia rubecula Marshall (Braconidae) and Pteromalus puparum L. (Pteromalidae) and an unidentified species of Exorista (Diptera: Tachinidae) attacked P. rapae. The generalist epigeal predatory fauna was dominated by Lycosidae (most abundant species: Lycosa t-insignata) and Carabidae (most abundant species: Chlaenius naeviger Morawitz, C. pallipes Gebler, Calathus helensis Schaller). Larval and pupal parasitism rates of both P. xylostella and P. rapae increased during the early summer months but natural enemy exclusion experiments showed that generalist predators were the most important natural enemy guild attacking P. xylostella populations in the agro-ecosystem. In a step towards the development of conservation biological control strategies, field experiments compared current pest management practice with pest threshold based interventions using commercial formulations of Bacillus thuringiensis var. aizawai ( Bt). The Bt-natural enemy strategy significantly increased crop yields and the impact of both parasitoid and predator natural enemies on pest populations. However, even under the threshold based Bt regimes, natural enemy impact remained relatively low. The ecology of the major pests and their natural enemies is discussed and recommendations for improved biological control and more effective management of key Brassica pests are made within the constraints posed by current agricultural circumstances in DPRK.

The role of natural enemy guilds in Aphis glycines suppression

Generalist natural enemy guilds are increasingly recognized as important sources of mortality for invasive agricultural pests. However, the net contribution of different species to pest suppression is conditioned by their biology and interspecific interactions. The soybean aphid, Aphis glycines (Hemiptera: Aphididae), is widely attacked by generalist predators, but the relative impacts of different natural enemy guilds remains poorly understood. Moreover, low levels of A. glycines parasitism suggest that resident parasitoids may be limited through intraguild predation. During 2004 and 2005, we conducted field experiments to test the impact of different guilds of natural enemies on A. glycines. We contrasted aphid abundance on field cages with ambient levels of small predators (primarily Orius insidiosus) and parasitoids (primarily Braconidae), sham cages and open controls exposed to large predators (primarily coccinellids), and cages excluding all natural enemies. We observed strong aphid suppression (86- to 36-fold reduction) in treatments exposed to coccinellids, but only minor reduction due to small predators and parasitoids, with aphids reaching rapidly economic injury levels when coccinellids were excluded. Three species of resident parasitoids were found attacking A. glycines at very low levels (<1% parasitism), with no evidence that intraguild predation by coccinellids attenuated parasitoid impacts. At the plant level, coccinellid impacts resulted in a trophic cascade that restored soybean biomass and yield, whereas small natural enemies provided only minor protection against yield loss. Our results indicate that within the assemblage of A. glycines natural enemies in Michigan, coccinellids are critical to maintain aphids below economic injury levels.

Food web structure of three guilds of natural enemies: predators, parasitoids and pathogens of aphids

1. Most communities of insect herbivores are unlikely to be structured by resource competition, but they may be structured by apparent competition mediated by shared natural enemies. 2. The potential of three guilds of natural enemies (parasitoids, fungal entomopathogens and predators) to influence aphid community structure through indirect interactions is assessed. Based on the biology, we predicted that the scope for apparent competition would be greatest for the predator and least for the parasitoid guilds. 3. Separate fully quantitative food webs were constructed for 3 years for the parasitoid guild, 2 years for the pathogen guild and for a single year for the predator guild. The webs were analysed using standard food web statistics designed for binary data, and using information-theory-based metrics that make use of the full quantitative data. 4. A total of 29 aphid, 24 parasitoid, five entomopathogenic fungi and 13 aphid specialist predator species were recorded in the study. Aphid density varied among years, and two species of aphid were particularly common in different years. Omitting these species, aphid diversity was similar among years. 5. The parasitoid web showed the lowest connectance while standard food web statistics suggested the pathogen and predator webs had similar levels of connectance. However, when a measure based on quantitative data was used the pathogen web was intermediate between the other two guilds. 6. There is evidence that a single aphid species had a particularly large effect on the structure of the pathogen food web. 7. The predator and pathogen webs were not compartmentalized, and the vast majority of parasitoids were connected in a single large compartment. 8. It was concluded that indirect effects are most likely to be mediated by predators, a prediction supported by the available experimental evidence.

Oviposition avoidance of parasitized aphid colonies by the syrphid predator Episyrphus balteatus mediated by different cues

Abstract Oviposition decisions made by members of a guild of natural enemies can have evolved to avoid intraguild predation, potentially avoiding the disruption of the extraguild prey control. We have studied the oviposition preference of the aphidophagous predator Episyrphus balteatus De Geer (Diptera: Syrphidae) within colonies of Myzus persicae Sulzer (Hemiptera: Aphididae) in the presence of two developmental stages of the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae). Results from a greenhouse choice experiment showed that E. balteatus females lay significantly fewer eggs in colonies with mummified aphids than in unparasitized colonies. Colonies of parasitized, but not yet mummified did not contain significantly fewer eggs than colonies with unparasitized aphids. In three no-choice experiments, we assessed stimuli coming from aphid honeydew, from the aphids themselves and also from extracts of the aphid bodies, and all of these stimuli mediate the discrimination of mummified aphids from healthy aphids. To a lesser extent these stimuli also contribute to the discrimination against aphids that are parasitized but not yet mummified. These results suggest that the effects of these two species could be complementary for the control of M. persicae, since the species that acts as an intraguild predator, E. balteatus, avoids ovipositing on aphid colonies parasitized by the intraguild prey, A. colemani.

Fallopia japonica, an increasingly intractable weed problem in the UK: Can fungi help cut through this Gordian knot?

A new approach to the management of one of the UK's alien superweeds, Japanese knotweed ( Fallopia japonica), is currently being investigated. The classical biological control strategy is based on the premise that those neophytes which become invasive and problematic are depauperate in natural enemies, both coevolved and new encounter species. Surveys have confirmed the absence of any significant natural enemy pressure in the UK, and the presence of an extensive guild of specialist arthropod and fungal natural enemies in Japan. The results of these surveys and the follow-up studies in the UK with selected fungi are discussed.

Comparing Invasive Plants from Their Native and Exotic Range: What Can We Learn for Biological Control?1

Abstract This article reviews and summarizes data sets that attempt to compare performance, population dynamics, and herbivory of invasive plant species. Specifically, we review results from studies comparing (1) individual and population parameters of plant invaders in their native and exotic range, (2) herbivore pressure and natural enemy guilds associated with plant invaders in their native and exotic range, and (3) performance and defense levels of native and exotic populations of the invasive under standardized conditions and the performance of selected herbivores. We found a total of 39 published and 2 unpublished studies, investigating 40 plant species. The majority of studies within the first category showed that invaders form larger populations, grow denser, have higher reproductive output, larger seed banks, and higher regeneration rates in the exotic compared with the native range. In contrast, plant vigor was not always greater, presumably because of increased intraspecific competition. Nearly...

Which role do lacewings and ants play as predators of the citrus leafminer in Spain?

In a study about the impact of natural enemies of Phyllocnistis citrella Stainton conducted in Spain, predation appeared as the most important mortality factor. Predators responded to changes in flushing, and this was attributed to continuous availability of preferential prey feeding on tender flushes. In this paper the role of aphid-mutualists and generalist predators feeding on aphids as well as on P. citrella (ants and lacewings, respectively), has been investigated. In the laboratory, Chrysoperla carnea Stephens could complete its development when fed on P. citrella third instars only. In the field, highly statistically significant regressions were obtained between prey indicators (aphid density and flush) and C. carnea densities. Nevertheless, using P. citrella density resulted in a negative relationship. In another field trial, predation rates did not change when ants were excluded from P. citrella-infested trees. Therefore, neither ants, nor lacewings could be identified as key-predators of P. citrella. Although we could not prove the efficiency of these predators, these studies have given us the chance to become aware of the existence of an important guild of unidentified generalist natural enemies.