Indigenous Natural Enemies Associated with Phyllocnistis citrella (Lepidoptera: Gracillariidae) in Eastern Spain

The incidence of generalist indigenous natural enemies of the citrus leafminer (CLM), Phyllocnistis citrella Stainton (Lepidoptera; Gracillariidae), was monitored during three growing seasons at two different orchards located in the major citrus-growing area of Spain. Composition of the parasitoid complex changed during the study period. However, the eulophids Cirrospilus near lyncus Walker and Pnigalio pectinicornis L. were consistently the predominant species. Despite the varying composition of the parasitoid complex, oviposition, host feeding, and predatory preferences of the natural enemies of the CLM clearly centered on third instar larvae. Incidence of beneficial fauna increased as the season progressed, reaching maximal values up to 70% of susceptible leafminers (mature larvae) at the end of the summer. Parasitism was significantly related to relative host density. However, predation showed no relationship to host availability but did so to flushing in one of the orchards. Incidence of indigenous natural enemies of the CLM should not be ignored when planning any introduction of exotic parasitoids, and their conservation should be taken into account when planning any citrus IPM strategy.     

Invasive Mahonia plants outgrow their native relatives

Invasive populations often grow more vigorously than conspecific populations in the native range. This has frequently been attributed to evolutionary changes resulting either from founder effects, or from natural selection owing to enemy release. Another mechanism contributing to evolutionary change has largely been neglected in the past: Many invasive plant species do actually descend from cultivated plants and were therefore subject to breeding, including hybridization and artificial selection. In a common garden experiment, we compared invasive Central European populations of the ornamental shrub, Mahonia, with native populations of its putative parental species, Mahonia aquifolium and M. repens, from North America. We hypothesized that plants of invasive populations show increased growth and retained high levels of heritable variation in phenotypic traits. Indeed, invasive Mahonia plants grew larger in terms of stem length, number of leaves and above-ground biomass than either of the two native species, which did not differ significantly from each other. Since there are no hints on release of invasive Mahonia populations from natural enemies, it is likely that hybridization and subsequent selection by breeders have lead to an evolutionary increase of plant vigour in the introduced range. Further on, heritable variation was not consistently reduced in invasive populations compared with populations of the two native species. We suggest that interspecific hybridization among the Mahonia species has counteracted the harmful effects of genetic bottlenecks often associated with species introductions. Based on this case study, we conclude that, more attention has to be paid on the role of plant breeding when assessing the mechanisms behind successful plant invasions in future.     

Survey of natural enemies of spider mites (Acari: Tetranychidae) in citrus orchards in eastern Spain

Field surveys were conducted from 2004 to 2007 to determine the species composition and relative abundance of natural enemies associated with colonies of either the citrus red mite, Panonychus citri, or the two spotted spider mite, Tetranychus urticae, in Valencian citrus orchards (eastern Spain). Fourteen species were recorded, six phytoseiid mites and eight insect predators. Two of them are reported for the first time on citrus in Spain and two more are first reports as predators associated with T. urticae. The community of predators associated with T. urticae and P. citri was almost identical, and the Morisita–Horn index of similarity between both natural enemy complexes was close to one, suggesting that predators forage on both pest species. Quantifying the presence of many known spider mites predators in Valencian citrus orchards is an important first step towards spider mite control. A challenge for future studies will be to establish conservation and/or augmentation management strategies for these predators, especially to improve T. urticae biological control.     

Guiding Classical Biological Control of an Invasive Mealybug Using Integrative Taxonomy

Delottococcus aberiae De Lotto (Hemiptera: Pseudococcidae) is a mealybug of Southern African origin that has recently been introduced into Eastern Spain. It causes severe distortions on young citrus fruits and represents a growing threat to Mediterranean citrus production. So far, biological control has proven unsatisfactory due to the absence of efficient natural enemies in Spain. Hence, the management of this pest currently relies only on chemical control. The introduction of natural enemies of D. aberiae from the native area of the pest represents a sustainable and economically viable alternative to reduce the risks linked to pesticide applications. Since biological control of mealybugs has been traditionally challenged by taxonomic misidentification, an intensive survey of Delottococcus spp. and their associated parasitoids in South Africa was required as a first step towards a classical biological control programme. Combining morphological and molecular characterization (integrative taxonomy) a total of nine mealybug species were identified in this study, including three species of Delottococcus. Different populations of D. aberiae were found on wild olive trees, in citrus orchards and on plants of Chrysanthemoides monilifera, showing intra-specific divergences according to their host plants. Interestingly, the invasive mealybug populations from Spanish orchards clustered together with the population on citrus from Limpopo Province (South Africa), sharing COI haplotypes. This result pointed to an optimum location to collect natural enemies against the invasive mealybug. A total of 14 parasitoid species were recovered from Delottococcus spp. and identified to genus and species level, by integrating morphological and molecular data. A parasitoid belonging to the genus Anagyrus, collected from D. aberiae in citrus orchards in Limpopo, is proposed here as a good biological control agent to be introduced into Spain.     

The role of natural enemies in controllingIcerya purchasi in South Australia

The obscure occurrence of the cottony-cushion scaleIcerya purchasi Maskell in its native country Australia is generally attributed to its natural enemies. Twelve natural-enemy-exclusion experiments were conducted at monthly intervals to confirm the role of natural enemies. Each experiment had uncaged, open-caged, and caged treatments. The natural enemies were active throughout the year. The percentage of scales surviving to adults in the cages was significantly higher than in the open-caged treatments, except the April (first) cohort. In both open-caged and uncaged treatments, the percentage of scales surviving to adults was similar and matched the changes in the numbers of natural enemies, thus confirming their importance in controllingI. purchasi in South Australia.      

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.     

Collections of natural enemies ofLeptinotarsa decemlineata [Coleoptera: Chrysomelidae] in Mexico, 1980–1985

Three trips were taken to central Mexico to search for natural enemies ofLeptinotarsa decemlineata (Say), in 1980, 1983, and 1985. 18 natural enemy species were found associated with 10 species ofLeptinotarsa. Asopine pentatomids dominate the collections, followed by tachnid parasites and hemipteran and coleopteran predators. Natural enemies may play a major role in regulating populations ofLeptinotarsa in Mexico. Their adaptability to northern climates is unclear.      

Interspecific Interactions among Natural Enemies ofBemisiain an Inundative Biological Control Program

Interspecific interactions among insect natural enemies have seldom been investigated experimentally within the context of biological control. Research in this area is needed due to the often contradictory predictions provided by the many theoretical models, the increasing dependence on biological control, and the concern that biological control agents may adversely affect some nontarget organisms. We describe a study whereby the occurrence and dynamics of interspecific interactions among three natural enemies (two parasitoids:Encarsia formosaandEncarsia pergandiella;and one predatorDelphastus pusillus) of the whitefly,Bemisia argentifolii(previously referred to asBemisia tabacistrain “B”), were evaluated in greenhouse cage experiments. Eight populations consisting of all possible combinations of the three natural enemies and one population of whitefly alone were established to test the following hypotheses: (1) Natural enemy introductions are capable of suppressingB. argentifoliipopulations; (2) all interspecific interactions are detrimental to achieving biological control; (3) the likelihood of achieving biological control decreases as the potential number of interspecific interactions increases; and (4) the species composition of biological control agents is of greater consequence than the number of natural enemy species released. In addition, we tested the hypothesis (5) that the frequency of interspecific interactions increases with a decrease in host or prey availability. Our results demonstrate that all combinations of natural enemies provided significant levels of whitefly suppression. While the intensities of interspecific interactions among natural enemy species were frequently positively and significantly correlated with the densities of parasitized whitefly, interspecific interactions among natural enemies were not detrimental to achieving higher levels of biological control. The composition of species released, rather than the number of species released, was of greater importance to accomplishing biological control. Releases ofD. pusillusin combination with one or both of the parasitoids provided the greatest levels of whitefly suppression. These results suggest that the types of interspecific interactions rather than the numbers of interspecific interactions among natural enemies may be important to the outcome of inundative biological control programs.     

The status ofBemisia tabaci (Hom.: Aleyrodidae),Trialeurodes vaporariorum (Hom.: Aleyrodidae) and their natural enemies in Crete

The non «B» biotype ofBemisia tabaci (Gennadius) is recorded for the first time in Crete in 1992, in the north east and south east of the island.Trialeurodes vaporariorum (Westwood) is the predominant whitefly on plants in the north and west of the island. Three surveys of Crete were made in 1992 and 1993 for natural enemies ofB. tabaci andT. vaporariorum and resulted in the collection of 4 species ofEncarsia, (plus a number of species that are unidentifiable at this time), anEretmocerus sp. (unidentifiable at this time) and a fungal pathogen,Paecilomyces farinosus (Dickson Ex Fries) Brown &; Smith.Encarsia adrianae was identified fromT. vaporariorum; which constitutes its most westerly distribution point and a new host record respectively.B. tabaci andT. vaporariorum were found on horticultural crops, ornamentals and weeds. Populations of both whitefly species were severely depleted on field hosts throughout the island during the winter of 1992/93. Climatic constraints, competition withT. vaporariorum in otherwise suitable niches, effective natural enemies and an observed low level of polyphagy may explain the present limited distribution of the non «B» biotype ofB. tabaci in Crete.     

Assessment of interspecific interactions among parasitoids on the outcome of inoculative biological control of leafminers attacking chrysanthemum

Indigenous natural enemies occur within field grown crops at varying densities dependent upon a variety of other biotic and abiotic parameters. This natural control often does not provide adequate suppression, which results in the application of other pest management solutions including augmentative biological control. When releasing mass-reared natural enemies into a backdrop of existing natural enemy populations, competitive interactions are likely to occur. To assess the influence of these interspecific interactions on the outcome of such biological control practices studies were conducted in a simulated, field cage grown, cut chrysanthemum production system. Competitive interactions of two commercially available parasitoids were studied both in terms of parasitoid-host population dynamics and the impact of interspecific interactions on crop quality at harvest. The parasitoids Diglyphus isaea and Dacnusa sibirica attacking the leafminer Liriomyza langei were used as the model insect system. Both parasitoids are cosmopolitan and are known to occur in many ornamental production areas. Treatment comparisons included single species releases with complimentary releases of both species either simultaneously or with 2-week time lags, as well as a no release control to measure the background effects of natural mortality. Conclusions drawn from results of population-level studies replicated within and among years were that levels of interspecific competition among parasitoid species were undetectable at leafminer densities typical of field-grown ornamental crops (low densities), and thus, the efficacy of one species released into a backdrop of potentially competing parasitoids did not negatively or positively affect the outcome of the augmentative biological control, nor was there a positive outcome; however, crop quality at harvest was influenced.     

5种茶园秋冬季天敌与假眼小绿叶蝉空间关系密切程度的差异

为了明确与假眼小绿叶蝉空间关系密切的天敌种类,为合理利用和保护天敌提供科学依据。运用地学统计学分析方法计算白毫早茶园、黄山大叶种茶园、农抗早茶园、平阳特早茶园和乌牛早茶园秋冬季假眼小绿叶蝉和其主要6种天敌地统计学半变异函数的变程。使用灰色系统分析方法对计算结果进行灰色关联度分析,并对分析结果进行标准化。以标准化后的密切指数大小评判天敌与假眼小绿叶蝉空间关系的密切程度。结果是：1）、黄山大叶种茶园和农抗早茶园与假眼小绿叶蝉空间关系密切的前3位天敌是粽管巢蛛、鳞纹肖蛸和斜纹猫蛛,但位次不同。2）、白毫早茶园前3位天敌是鳞纹肖蛸、斜纹猫蛛和锥腹肖蛸,前2种与黄山大叶种和农抗早茶园相同。3）、平阳特早茶园前3位天敌是鳞纹肖蛸、粽管巢蛛和草间小黑蛛,前2种与黄山大叶种和农抗早茶园相同。4）、乌牛早茶园前3位天敌是粽管巢蛛、草间小黑蛛和三突花蟹蛛,只有粽管巢蛛与黄山大叶种和农抗早茶园相同。根据5种茶园同种天敌密切指数之和以及同种天敌位次之和评判,与假眼小绿叶蝉空间关系密切的天敌均是鳞纹肖蛸、粽管巢蛛和斜纹猫蛛。天敌位次的变化主要是害虫和天敌数量之比的比值变化。害虫个体数与某种天敌个体数之比的比值越小,天敌与害虫的跟随关系则越密切。密切原因与食饵资源短缺有关。     

Incidence of natural enemies of the Colorado potato beetle,Leptinotarsa decemlineata [Coleoptera: Chrysomelidae] on a native host in Mexico

In central Mexico, the center of origin forLeptinotarsa decemlineata (Say) and its principal host plants,L. decemlineata is associated with a diverse complex of natural enemies. Observations during 2 years in Morelos, Mexico revealed 4 species of asopine pentatomids, 7 species of foliar searching carabids, and 2 coccinellids among the predators ofL. decemlineata. Parasitoids include 3 species of tachinids andEdovum puttleri Grissel, an eulophid egg parasitoid. These natural enemies include several predators that have not previously been reported attackingL. decemlineata. University of Maine Agriculture Experiment Station No. 1553     

Landscape-scale forest cover increases the abundance of Drosophila suzukii and parasitoid wasps

Agricultural landscapes rich in natural and semi-natural habitats promote biodiversity and important ecosystem services for crops such as pest control. However, semi-natural habitats may fail to deliver these services if agricultural pests are disconnected from the available pool of natural enemies, as may be the case with invasive species. This study aimed to provide insights into the relationship between landscape complexity and the abundance of the recently established invasive pest species Drosophila suzukii and a group of natural enemies (parasitoid wasps), which contain species that parasitize D. suzukii in native and invaded ecosystems. The importance of landscape complexity was examined at two spatial scales. At the field scale, the response to introduction of wildflower strips was analysed, while the relationship with forest cover was assessed at the landscape scale. Half of the surveys were done next to blueberry crops (Vaccinium corymbosum), the other half was done in landscapes without fruit crops to examine effects of D. suzukii host presence. As expected, the number of observed parasitoid wasps increased with amount of forest surrounding the blueberry fields, but the number of D. suzukii individuals likewise increased with forest cover. Establishment of wildflower strips did not significantly affect the abundance of D. suzukii or parasitoid wasps and insect phenology was similar in landscapes with and without blueberry crops. This suggests that D. suzukii is enhanced by landscape complexity and is largely unlinked from the species group that, in its native range, hosts key natural enemies. Although management practices that rely on enhancing natural enemies through habitat manipulations can contribute to the long-term stability of agroecosystems and to control agricultural pests, other control measures may still be necessary in the short term to counteract the benefits obtained by D. suzukii from natural habitats.     

Indirect cost of a defensive trait: variation in trichome type affects the natural enemies of herbivorous insects on <Emphasis Type="Italic">Datura wrightii</Emphasis>

The costs and benefits of defensive traits in plants can have an ecological component that arises from the effect of defenses on the natural enemies of herbivores. We tested if glandular trichomes in Datura wrightii, a trait that confers resistance to several species of herbivorous insects, impose an ecological cost by decreasing rates of predation by the natural enemies of herbivores. For two common herbivores of D. wrightii, Lema daturaphila and Tupiocoris notatus, several generalized species of natural enemies exhibited lower rates of predation on glandular compared to non-glandular plants. Lower rates of predation were associated with reductions in the residence time and foraging efficiency of natural enemies on plants with glandular trichomes, but not with direct toxic effects of glandular exudate. Our results suggest that the benefit of resistance to herbivores conferred by glandular trichomes might be offset by the detrimental effect of this trait on the natural enemies of herbivores, and that the fitness consequences of this trichome defense might depend on the composition and abundance of the natural-enemy community.     

Biological control of insect pests in apple orchards in China

Apple is one of the most important fruits in China, and both yield and quality are greatly affected by insect pests. According to surveys, there are more than 200 species of natural enemies in apple orchards. Few, however, have been closely studied. Major natural enemies including parasitoids, predators and pathogens are briefly described in this review, especially focusing on two parasitoids of Trichogramma dendrolimi Matsumura and Aphelinus mali Haldeman, predatory mites and a pathogenic fungus of Beauveria bassiana (Balsamo) Vuillemin as case studies. Augmentation, one important strategy of biological control, supplements the natural control provided by the existing natural enemy community in apple orchards, and greatly increases their efficiency in controlling pests. Conservation biological control is also widely applied in four major apple-producing areas. Based on habitat manipulation, the ground cover planting system helps regulate the microclimate and enhance the biodiversity of apple orchards, effectively conserving the richness and diversity of beneficial insect species. Certain achievements have been made in the main biological control strategies including successful introduction of some exotic natural enemies such as A. mali and Typhlodromus occidentalis Nesbitt, augmentative production and application of biological control agents such as T. dendrolimi, B. bassiana and Bacillus thuringiensis, and further research in conservation of establishing adaptive ground cover planting patterns to local environment. Challenges, however, still exist. Biological control of insect pests in apple orchards is an important part of integrated pest management programs, requiring more research and application in China.     

A molecular phylogeny of the genus Lygodium (Schizaeaceae) with special reference to the biological control and host range testing of Lygodium microphyllum

Lygodium microphyllum, first naturalized in the 1960s, has aggressively invaded forest-dominated wetlands in southern and central Florida. The indeterminate growth of this invasive climbing fern creates thick rachis mats which climb over shrubs and trees smothering the underlying growth and carrying ground fires into the forest canopy. Foreign surveys for natural enemies identified 20 species of insects and two species of mites. Host range testing of three insect species and one mite included five Lygodium species (L. palmatum, L. volubile, L. cubense, L. venustum, and L. oligostachyum) native to the United States and the West Indies. A molecular phylogeny of the genus was conducted using the trnL intron and the trnL-F intergenic spacer of chloroplast DNA to determine the relationship of L. microphyllum to other Lygodium species. Three major clades appeared, one with L. palmatum and L. articulatum (the most basal), a second with L. reticulatum and L. microphyllum, and a third comprising the other species examined. Lygodium microphyllum appeared at the end of a long branch approximately equidistant from all species of interest preventing the correlation of genetic distance and host range behavior. However, inspection of the results of host range experiments showed a relationship between the presence of a related biotype or species of the insect on a related alternate host and the ability of that insect to develop on that alternate host. Ancestral host usage and ecological fitting are examined as possible explanations for the acceptance of L. palmatum by the tested musotimine insects.     

Gringos En El Bosque: Introduced Tree Invasion in a Native Nothofagus/Austrocedrus Forest

We studied invasion into native Nothofagus/Austrocedrus forest by many introduced tree species planted between 1910 and 1940 in plantations near the center of Isla Victoria, in northern Patagonia. We located virtually all individuals of these species in 30 ha of forest in two series of transects at increasing distances from the plantations. Although these species included many reported as highly invasive elsewhere, we found little evidence for invasion on Isla Victoria, with many invasive species utterly failing to invade native forest. There was a notable decline with distance in number of introduced individuals, but wind direction appeared to be unimportant. Pseudotsuga menziesii and Juniperus communis were the only 2 species represented by many individuals, while 4 pine species plus Araucaria araucana were far less numerous and 6 other species were found fewer than 10 times each. Even those species found repeatedly were represented overwhelmingly by small individuals, and the great majority of introduced individuals were found not in native forest proper, but in somewhat open areas such as road verges, small remnant pastures, and deer trails. Invasion may be occurring, but too slowly to be clearly evidenced yet because of the longevity of the dominant native trees. Factors that may be stopping or slowing invasion include competition in gaps with native species, browsing by introduced deer, unfavorable soil, allelopathy, and natural enemies or other idiosyncratic factors for particular species. The absence of substantial invasion so far is no guarantee against future invasion, particularly if some major natural or anthropogenous disturbance were to occur.     

Natural enemy spectrum ofAphis spiraephaga (Hom.: Aphididae), an exotic immigrant aphid in Central Europe

Aphis spiraephaga Müller, an aphid of Central Asian origin, dispersed west-wards and reached Central Europe probably before 1956. It now occurs in most European countries. Research undertaken in the Czech Republic mainly in 1991–1993, revealed that the aphid is attacked by a variety of natural enemies, including both parasitoids (Aphelinidae, Aphidiidae) and predators (Anthocoridae, Chrysopidae, Hemerobiidae, Cantharidae, Coccinellidae, Chamaemyidae, Itonididae, Syrphidae). All the natural enemies were identified to species. Attendance by ants (Lasius sp.) was common.A. spiraephaga was also successfully utilised as a new alternate host of two newly introduced parasitoid biocontrol agents (Aphidius colemani Viereck,Lysiphlebus testaceipes (Cresson).     

Colonization of apple orchards by predators of <Emphasis Type="Italic">Dysaphis plantaginea</Emphasis>: sequential arrival,response to prey abundance and consequences for biological control

Episyrphus balteatus (DeGeer) (Diptera: Syrphidae), Adalia bipunctata (L.) (Coleoptera: Coccinellidae) and Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) are the three most abundant natural enemies of Dysaphis plantaginea Passerini (Homoptera: Aphididae) in Asturian (NW Spain) apple orchards. They attack this aphid in sequence: E. balteatus arrived first, followed by A. bipunctata and then by A. aphidimyza. The cecidomyiids arrived too late to have a regulating effect. The syrphids laid an average of 2.3 ± 1.7 eggs per aphid colony and the coccinellids 18.4 ± 9.9 regardless of the degree of the infestation rates of the apple shoots. This value corresponds to the size of an egg batch laid by one female. Therefore, these aphid predators did not respond numerically to the abundance of the pest. The results of this study indicate that natural populations of syrphids and ladybird beetles are unable to control D. plantaginea, and therefore a more complex strategy than waiting for natural enemies is required.     

Increased chemical resistance explains low herbivore colonization of introduced seaweed

The success of introduced species is often attributed to release from co-evolved enemies in the new range and a subsequent decreased allocation to defense (EICA), but these hypotheses have rarely been evaluated for systems with low host-specificity of enemies. Here, we compare herbivore utilization of the brown seaweed, Fucus evanescens, and its coexisting competitors both in its native and new ranges, to test certain predictions derived from these hypotheses in a system dominated by generalist herbivores. While F. evanescens was shown to be a preferred host in its native range, invading populations supported a less diverse herbivore fauna and it was less preferred in laboratory choice experiments with important herbivores, when compared to co-occurring seaweeds. These results are consistent with the enemy release hypothesis, despite the fact that the herbivore communities in both regions were mainly composed of generalist species. However, in contrast to the prediction of EICA, analysis of anti-grazing compounds indicated a higher allocation to defense in introduced compared to native F. evanescens. The results suggest that the invader is subjected to less intense enemy control in the new range, but that this is due to an increased allocation to defense rather than release from specialized herbivores. This indicates that increased resistance to herbivory might be an important strategy for invasion success in systems dominated by generalist herbivores.