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Background: There is a consensus that the conservation of natural enemies is the most important biological control strategy, but it has also been the least attended. The reason is simple: there is a strong contradiction between modern agriculture and biological control. Various strategies have been proposed for the conservation of natural enemies, among others, protection against pesticides and establishment of nectar plants as alternative food. Less attention has been paid to the conservation of alternative hosts for natural enemies. Main body: Natural enemies are not exclusive to pests, on the contrary, numerous species require alternative prey and hosts for their prevalence. Their conservation is a strategy widely referenced in scientific literature; however, this idea is not consistent with the studies developed. From 1973 to 2021, only 21 studies that emphasized the use of alternative hosts were recorded. Most focused on single phytophagous–natural enemy species, and little attention was given to the plant–phytophagous relationship. For example, Asclepias curassavica (Apocynaceae) hosts more than nine species of specialist phytophagous; and they, in turn, attracted 24 species of natural enemies. Although different studies demonstrate the potential of alternative hosts, some presume an adverse or doubtful effect on pest control; for example, additional vegetation in agroecosystems could act as a source, but also as a sink for natural enemies. This analysis tries to fit biological control to the modern agricultural paradigm, and not the other way around, as suggested by ecological theory. We support the idea that conservation biological control should be directed toward the conservation of multiple species, with the aim of controlling not only pest, but also the self-regulation of the agroecosystem. The path that should be followed by the study and application of alternative hosts as a strategy of biological control by conservation is discussed. Conclusion: The wide diversity of non-pest insect species suggests an enormous potential for their exploitation as alternative hosts. The evaluation of host plants of specialized phytophagous species could improve biological control and reduce the risk of pests for crops. This strategy would partly fill the huge gap that exists in modern agroecosystems in terms of biological diversity. [ABSTRACT FROM AUTHOR]

Since the late 19th century, exotic ladybirds (Coleoptera: Coccinellidae) have been used extensively for suppressing herbivorous insects of economic importance. In recent decades, the introduction of non‐native biological control (BC) agents has been greatly limited due to the awareness of the potential non‐target effects of introductions. Nonetheless, recent episodes of biological invasions of economically important pests have raised the need to carefully consider whether the expected benefits of pest control go beyond the possible environmental risks of introduction. To better understand the factors that contributed to successful BC programs, here we review the literature behind classical and augmentative BC using exotic ladybirds. Additionally, by means of case studies, we discuss the BC efficacy of selected exotic species, e.g., Coccinella septempunctata L., Harmonia axyridis (Pallas), and Hippodamia variegata (Goeze), and their position within the communities of predators in the introduced areas of USA, Canada, and Chile. In Europe, much of the research on exotic ladybirds has been conducted on the undesired impact of H. axyridis. Therefore, we summarize the risk assessment data for this species and review the field research investigating the ecological impact on European aphidophagous predators. According to the BIOCAT database of classical BC programs, 212 ladybird species belonging to 68 genera have been released in about 130 years of BC activity, with 14.6% of introductions having resulted in partial, substantial, or complete control of the target pest. However, because post‐release evaluation of establishment and BC success has not always been conducted, this rate could underestimate the successful cases. Among other factors, ladybird establishment and pest suppression mostly depend on (1) intrinsic factors, i.e., high voracity, synchronized predator‐prey life cycle, and high dispersal ability, and (2) extrinsic factors, i.e., adaptability to the new environment and landscape composition. This review contributes to improved understanding of ladybirds as exotic BC agents. [ABSTRACT FROM AUTHOR]

Medusahead (Taeniatherum caput-medusae, Poales: Poaceae) is an annual grass native to central Asia and the Mediterranean region. It is a noxious, invasive weed in much of western North America. As such, it is the target of a classical biological control programme established by USDA-ARS. During explorations carried out in 2014 a new species of eriophyid mite, Aculodes altamurgiensis de Lillo & Vidovic, 2018 (Acari: Eriophyidae), was discovered on medusahead in southern Italy; it was also collected from medusahead in Bulgaria, Serbia, Turkey, and Iran in subsequent years. In the field A. altamurgensis has consistently been associated with the target weed while never having been detected from sympatric grass (Poales: Poaceae) species (e.g. Stipa austroitalica, Avena sativa, Triticum durum, T. aestivum), suggesting that A. altamurgensis is highly specific to medusahead. An open-field host-specificity test was carried out in Rome, Italy in 2016 in which an Italian population of A. altamurgensis was infested onto 11 different grass genotypes, including five crop species and five different populations of medusahead (two from Italy and three populations that are invasive in the USA). The results supported the previous observations that A. altamurgiensis is highly specific to medusahead and merits further evaluation as a candidate for biological control of this invasive grass. However, the Italian population of A. altamurgiensis showed variable colonisation rates on different medusahead populations, indicating that populations of A. altamurgiensis from other regions should also be tested to determine if they can colonise medusahead at more uniformly high rates, particularly on the targeted invasive populations in the USA. [ABSTRACT FROM AUTHOR]

[Display omitted] • We evaluate host specificity of a native and an accidentally introduced parasitoid. • The native parasitoid attacks several non-target species in the laboratory. • The introduced species shows affinity for the target pest and a related non-target. • The parasitism rate of each parasitoid was evaluated in three greenhouses. • Both species show potential as biological control agents against Tuta absoluta. New strategies are urgently needed to control Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), one of the most destructive pests of tomato crops. Originating from South America, it is spreading rapidly and has evolved resistance to most common insecticides making it highly challenging to control. Regarding biological control, the parasitoid Necremnus tutae Ribes & Bernardo (Hymenoptera: Eulophidae) is widely present around the Mediterranean basin and has adapted to the invader playing a substantial role in its control. In addition, the neotropical parasitoid Dolichogenidea gelechiidivoris Marsh (Hymenoptera: Braconidae) has established accidentally following its host in Spain and Algeria and a classical biological control program using this species is ongoing in Sub-Saharan Africa. Understanding the trophic connections between D. gelechiidivoris , N. tutae , the targeted host T. absoluta and potential non-target hosts is essential to assess their value as augmentative or classical biological control agents and to promote their establishment in conservation biocontrol. We conducted host-specificity tests in the laboratory using four European leafminer species to evaluate the specificity of these two parasitoids to T. absoluta. We then assessed their affinity for T. absoluta by exposing sentinel plants with the alternative host Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) inside and around greenhouses and measuring each parasitoid species' field parasitism rate. Our results show that of the four non-target species tested in the laboratory, N. tutae attacked three, while D. gelechiidivoris attacked only P. operculella. In the greenhouse, N. tutae did not prefer P. operculella or T. absoluta, whereas D. gelechiidivoris preferred the latter. The mean parasitism rate of T. absoluta over the three-month monitoring period in the greenhouses reached 27 % for N. tutae and 35 % for D. gelechiidivoris. We discuss the importance of host affinity for understanding potential non-target effects and the value a natural enemy can have as biological control. [ABSTRACT FROM AUTHOR]

Highlights • Species distribution models based on bioclimatic variables are useful for predicting natural enemies' distribution. • Climate constrains the distribution of Ibalia leucospoides and Megarhyssa nortoni in the Southern Hemisphere. • The distribution of Rhyssa persuasoria is limited by other factors besides climate. • M. nortoni distribution model correctly predicted the regions where the species failed to establish. • I. leucospoides distribution largely overlaps with the range invaded by Sirex noctilio. Abstract Classical biological control is a pest management practice frequently deployed against invasive insects. However, introduced natural enemies too often fail to establish, and this has been partly explained by climatic mismatching. We evaluate climate matching (using MaxEnt) for three parasitoids, Megarhyssa nortoni, Ibalia leucospoides and Rhyssa persuasoria , released in classical biological control programmes of the pine pest Sirex noctilio in the Southern Hemisphere and explore how climatic factors can influence parasitoid establishment success. Model predictions are compared against data on historical releases in this region. The main results show that for I. leucospoides and M. nortoni the eco-climatic distribution model successfully predicted the establishment in all the regions where the species are currently present. Additionally, for M. nortoni, the model also correctly predicted the regions where the species was released and failed to establish, as is the case of the south of Brazil and the Western Cape, South Africa. However, R. persuasoria established only in some of the regions where the model predicted its presence. These results highlight the usefulness of climatic matching techniques as an effective way to prioritize suitable areas to release specific biological control agents. However, climatic matching modelling does not always guarantee establishment, and likely, several other factors explain failures in establishing populations after releases. Further understanding of the factors affecting success in biological control programs of forest insects at a broad spatial scale may contribute to improve pest management skills of new and established populations of non-native forest insects. [ABSTRACT FROM AUTHOR]

The intentional introduction of exotic species through classical biological control programs provides unique opportunities to examine the consequences of population movement and ecological processes for the genetic diversity and population structure of introduced species. The weevils Neochetina bruchi and N. eichhorniae (Coleoptera: Curculionidae) have been introduced globally to control the invasive floating aquatic weed, Eichhornia crassipes, with variable outcomes. Here, we use the importation history and data from polymorphic microsatellite markers to examine the effects of introduction processes on population genetic diversity and structure. We report the first confirmation of hybridization between these species, which could have important consequences for the biological control program. For both species, there were more rare alleles in weevils from the native range than in weevils from the introduced range. N. eichhorniae also had higher allelic richness in the native range than in the introduced range. Neither the number of individuals initially introduced nor the number of introduction steps appeared to consistently affect genetic diversity. We found evidence of genetic drift, inbreeding, and admixture in several populations as well as significant population structure. Analyses estimated two populations and 11 sub‐clusters for N. bruchi and four populations and 23 sub‐clusters for N. eichhorniae, indicating divergence of populations during and after introduction. Genetic differentiation and allocation of introduced populations to source populations generally supported the documented importation history and clarified pathways in cases where multiple introductions occurred. In populations with multiple introductions, genetic admixture may have buffered against the negative effects of serial bottlenecks on genetic diversity. The genetic data combined with the introduction history from this biological control study system provide insight on the accuracy of predicting introduction pathways from genetic data and the consequences of these pathways for the genetic variation and structure of introduced species. [ABSTRACT FROM AUTHOR]

Liriomyza spp. leafminer flies (Mik; Diptera: Agromyzidae), are economically important quarantine pests that puncture and mine leaves and fruits of various horticultural crops worldwide, affecting yield and trade. Halticoptera arduine (Walker; Hymenoptera: Pteromalidae), a key parasitoid from the pests' areas of origin in South America, was introduced as a potential alternative management strategy. Prior to H. arduine release, its potential interactions with the dominant local ectoparasitoid, Diglyphus isaea (Walker; Hymenoptera: Eulophidae), were assessed. Halticoptera arduine and D. isaea were released in single, sequential and simultaneous combinations on Liriomyza huidobrensis (Blanchard; Diptera: Agromyzidae) to evaluate possible effect on the parasitism rate, reproduction and host mortality. The combination of both parasitoids did not significantly affect the specific parasitism rates of either of them, an indication that H. arduine and D. isaea can coexist. Parasitism rates of the exotic H. arduine were significantly superior to the indigenous D. isaea in all release combinations except when both species were released simultaneously. While 50 individuals of D. isaea resulted only in 21.23 ± 2.1% parasitism, 50 parasitoids composed of 25 H. arduine and 25 D. isaea caused 53.27 ± 4.99%. Both parasitoids further induced significant nonreproductive host mortalities. Both parasitoids' F1 progenies sex ratios were female-biased in all parasitoid release combinations except in single release of D. isaea with a balanced sex ratio. The improvement in D. isaea 's sex ratio induced by the presence of H. arduine suggests a synergetic effect on D. isaea 's reproductive performance. The introduction of H. arduine in horticulture production systems may therefore improve natural control of Liriomyza leafminers in East Africa. [ABSTRACT FROM AUTHOR]

Abstract: Classical biological control programmes rely on mass production of high‐quality beneficial insects for subsequent releases into the field. Psyttalia lounsburyi (Silvestri) (Hymenoptera: Braconidae) is a koinobiont larval–pupal endoparasitoid of tephritid flies that is being reared to support a classical biological control programme for olive fruit fly in California. The mass‐rearing system for a P. lounsburyi colony, initiated with insects originally collected in Kenya, was evaluated with the goal of increasing production, while at the same time reducing time requirements for rearing in a quarantine facility. We tested the effect of exposure time of a factitious host Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), on parasitization, adult production, superparasitism, and sex ratio of P. lounsburyi and survival of the host. Parasitization rates were highest (31%) at 3‐ and 4‐hr exposure times, while adult production (i.e., emergence of wasp progeny) was highest (16%) at the 2‐hr exposure time. Superparasitism over the course of the study was 1.5% and did not appear to be a factor affecting parasitoid production. The sex ratio of wasp progeny was male‐biased and did not vary significantly over different exposure times. The rate of stings on host larvae increased with exposure time and was consistent with decreases in pupal eclosion from larvae and emergence rate of adult flies. When compared to current rearing procedures, the 2‐hr exposure time resulted in an overall 2.8‐fold increase in P. lounsburyi production when standardized for time. [ABSTRACT FROM AUTHOR]

Classical biological control involves introducing natural enemies to new locations, and can often be limited by the expense, and technical and logistical complexity, of collecting, culturing and releasing natural enemies. Our study investigated the potential of mass-emergence devices, which are designed to confine hosts, but not adult parasitoids, for reducing these limitations in a classical biological control programme. The programme introduced a parasitoid from Europe, Microctonus aethiopoides (Hymenoptera, Braconidae), to assist management of an invasive Palearctic weevil that feeds on white clover, Sitona obsoletus Gmelin (Coleoptera, Curculionidae), in New Zealand. M. aethiopoides is an endoparasitoid of the adult stage of S. obsoletus. Laboratory evaluations of device design confirmed that the devices confined S. obsoletus adults, but not M. aethiopoides adults. They also showed both that parasitised S. obsoletus lived long enough in the devices for immature parasitoids to complete their development, eclose and exit the devices, and that M. aethiopoides adults would enter devices and oviposit in unparasitised hosts. In the field, three approaches to using the devices were tested: populating devices with parasitised hosts cultured in the laboratory; populating devices with parasitised hosts collected from the field; and populating devices with unparasitised hosts, placing them in field locations where the parasitoid was established, allowing them to become parasitised by wild parasitoids, then transferring the devices to new release sites. All three approaches were effective for establishing M. aethiopoides at new locations, and offered advantages over standard release methods. [ABSTRACT FROM AUTHOR]

Aphelinid parasitoids are widely known natural enemies of Bemisia tabaci (Gennadius), a serious pest of agriculture globally. Here we examine pest–parasitoid interactions and dynamics in Arizona cotton from 1996 to 2010, during which a classical biological control program was implemented. Two native species, Eretmocerus eremicus Rose and Zolnerowich and Encarsia meritoria (Gahan) were either largely or completely displaced by exotic Eretmocerus sp. (Ethiopia) and Encarsia sophia (Gahan) in the early 2000s. Further, E. sophia became the dominant parasitoid of B. tabaci in cotton after many years of predominance by native and exotic Eretmocerus . Apparent rates of parasitism were highly variable within and between years and averaged ≈17% overall. In some years there was evidence that B. tabaci populations declined as apparent parasitism increased. Lower pest abundance was associated with higher rates of apparent parasitism over the entire 15-year period but this pattern was not supported by long term life-table based measurements of parasitism. Detailed life table studies within the entire agro-ecosystem will be needed to fully assess the impact of the classical biological control program. [ABSTRACT FROM AUTHOR]

As well as being planted for wind breaks, landscape trees, and fuel wood, eucalypts are also widely used as urban street trees in California. They now are besieged by exotic insect herbivores of four different feeding guilds. The objective of the current analysis was to determine the return on investment from biological control programs that have targeted these pests. Independent estimates of the total number of eucalypt street trees in California ranged from a high of 476,527 trees (based on tree inventories from 135 California cities) to a low of 190,666 trees (based on 49 tree inventories). Based on a survey of 3,512 trees, the estimated mean value of an individual eucalypt was US$5,978. Thus, the total value of eucalypt street trees in California ranged from more than US$1.0 billion to more than US$2.8 billion. Biological control programs that targeted pests of eucalypts in California have cost US$2,663,097 in extramural grants and University of California salaries. Consequently, the return derived from protecting the value of this resource through the biological control efforts, per dollar expended, ranged from US$1,070 for the high estimated number of trees to US$428 for the lower estimate. The analyses demonstrate both the tremendous value of urban street trees, and the benefits that stem from successful biological control programs aimed at preserving these trees. Economic analyses such as this, which demonstrate the substantial rates of return from successful biological control of invasive pests, may play a key role in developing both grass-roots and governmental support for future urban biological control efforts. [ABSTRACT FROM AUTHOR]

Biological control is an underlying pillar of integrated pest management, yet little focus has been placed on assigning economic value to this key ecosystem service. Setting biological control on a firm economic foundation would help to broaden its utility and adoption for sustainable crop protection. Here we discuss approaches and methods available for valuation of biological control of arthropod pests by arthropod natural enemies and summarize economic evaluations in classical, augmentative, and conservation biological control. Emphasis is placed on valuation of conservation biological control, which has received little attention. We identify some of the challenges of and opportunities for applying economics to biological control to advance integrated pest management. Interaction among diverse scientists and stakeholders will be required to measure the direct and indirect costs and benefits of biological control that will allow farmers and others to internalize the benefits that incentivize and accelerate adoption for private and public good. [ABSTRACT FROM AUTHOR]

Highlights: [•] The host range of four Aphidius spp. introduced for biological control was reassessed. [•] No-choice and choice tests were compared with field literature records. [•] Aphidius eadyi and A. sonchi were confirmed as largely specific to target (control) aphids. [•] A. ervi and A. rhopalosiphi parasitized some native aphids at a low rate. [•] Tests on newly discovered native aphids would be required to change historic regulatory decisions. [Copyright &y& Elsevier]

Highlights: [•] Rodolia cardinalis is a specific predator of Icerya purchasi. [•] This predator was released on the Galápagos Islands for biological control of I. purchasi. [•] Pest populations have been reduced substantially by R. cardinalis. [•] Non-target impacts were not observed. [•] It is concluded that the first biological control program in the Galápagos was successful. [Copyright &y& Elsevier]

Abstract: Simulated herbivory experiments in weed biological control have been used to predict the type and level of damage needed to suppress invasive plant growth and reproduction in the introduced range. Prior to host-specificity testing, this information is used to prioritize potential biological control agents based on their feeding guild and habit. In the current study, two levels of leaf cutting and terminal clipping damage to kudzu, Pueraria montana var. lobata (Fabaceae), were applied to plants over a 2year period near the center (North Carolina) and edge (Delaware) of kudzu’s invasive range. Damage type and levels were selected to imitate feeding by two herbivore guilds found on the plant in its native range. Above- and belowground biomass, total vine length and average internode length were significantly reduced by 75% leaf cutting for plants grown over a single season in Delaware. In North Carolina, several treatments reduced plant biomass, but only 75% leaf cutting was consistent in significantly reducing above- and belowground biomass compared to the control for one- and two-year-old plants. These findings suggest that damage to aboveground plant parts can reduce the ability of newly established plants to produce and store carbohydrates, which can contribute to successful biological control. Therefore, insects in the leaf-feeding guild should be investigated for potential host-specific biological control agents of kudzu in China. [Copyright &y& Elsevier]

Abstract: Oriental fruit fly, Bactrocera dorsalis (Hendel), invaded French Polynesia in 1996. In 2002 a natural enemy, Fopius arisanus (Sonan), was released and established. By 2009 mean (±SD) F. arisanus parasitism for fruit flies infesting Psidium guajava (common guava), Inocarpus fagifer (Polynesian chestnut) and Terminalia catappa (tropical almond) fruits on Tahiti Island was 64.8±2.0%. A second parasitoid, Diachasmimorpha longicaudata (Ashmead), was released and established in 2008. Although widespread, parasitism rates have not been higher than 10%. From 2003 (parasitoid establishment) to 2009 (present survey) numbers of B. dorsalis, Bactrocera tryoni (Froggatt), Queensland fruit fly, and Bactrocera kirki (Froggatt) emerging (per kg of fruit) declined. For example, for P. guajava there was a decline of 92.3%, 96.8%, and 99.6%, respectively. Analysis of co-infestation patterns (1998–2009) of B. dorsalis, B. tryoni, and B. kirki, suggest B. dorsalis is now the most abundant species in many common host fruits. Establishment of F. arisanus is the most successful example of classical biological control of fruit flies in the Pacific outside of Hawaii and can be introduced if B. dorsalis spreads to other French Polynesian islands, as was the recent case when B. dorsalis spread to the Marquesas Islands. These studies support F. arisanus as a prime biological control candidate for introduction into South America and Africa where Bactrocera carambolae Drew and Hancock and Bactrocera invadens Drew, Tsuruta, and White, respectively, have become established. [Copyright &y& Elsevier]

Ailanthus altissima (Mill.) Swingle, tree-of-heaven, is an invasive species native to Asia. It first was introduced into the United States in the 1700s and now is distributed throughout much of North America. Mechanical and chemical controls are current suppression tactics, however, implementation is costly. A weevil, Eucryptorrhynchus brandti (Harold), was identified in China and imported for quarantine testing in ²004 as a potential biological control agent. Host specificity tests on adult feeding, larval development, and oviposition of this weevil were conducted from ²007 to ²011 on A. altissima and ²9 nontarget species. Eucryptorrhynchus brandti adults fed significantly more on A. altissima foliage when compared with all test species. Range of means for feeding on A. altissima was 3².5-106.5 mm²/adult/d. In no-choice tests, Simaroubaglauca DC, Leitneriafloridana Chapm., and Citrus limon (L.) Burm. F., had feeding rates of only 10, 49, and 10%, respectively, compared with the level of feeding on A. altissima. The mean range of adult feeding by E. brandti on all other test species was <7% of feeding on A. altissima (0.0-3.3 ± 5.0 mm²/adult/d). In the no-choice larval inoculation tests, larval development only occurred in two of 10 L. floridana seedlings compared with seven of 10 A. altissima seedlings. In the no-choice oviposition tests, oviposition and subsequent larval development did not occur in L. floridiana, whereas all seven A. altissima seedlings supported oviposition and subsequent larval development. The weevil did not appear to be a threat to L. floridana or any other nontarget species tested. Therefore, we conclude that Eucryptorrhynchus brandti is highly host specific to A. altissima. [ABSTRACT FROM AUTHOR]

Abstract: Laricobius nigrinus (Coleoptera: Derodontidae) was first collected near the coastal city of Victoria, British Columbia, Canada for release as a biological control agent to suppress tree-killing densities of hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae), in the eastern United States. Beetles established in warm areas of the invaded range of A. tsugae, but had a low probability of establishment in cold areas. With the goal of locating beetles with greater cold-tolerance, we collected hundreds of adults in the northern Rocky Mountains. To support planned releases of these inland L. nigrinus, the cold tolerance of field-collected coastal (Seattle, WA) and inland (Coeur d’Alene and Moscow, ID) adults and climate match index scores (CLIMEX v.2) of these collection areas and parts of the eastern United States were compared. We found that individuals of inland L. nigrinus were more cold tolerant than those of coastal L. nigrinus, based on higher survival in a winter field cage study in Massachusetts and a lower supercooling point in a laboratory assay. Inland L. nigrinus also had higher survival than coastal L. nigrinus after an 18h exposure to sub-zero temperatures in another laboratory assay. Areas of the eastern United States infested with A. tsugae and receiving L. nigrinus releases matched the climate of Seattle and Coeur d’Alene reasonably well, but Coeur d’Alene had higher index values over a considerably larger area than Seattle. Accordingly, inland L. nigrinus appears preferable for release in the colder portions of A. tsugae’s invaded range in the eastern United States. [Copyright &y& Elsevier]

Abstract: The safe practice of biological control relies, in part, on an accurate evaluation of a potential agent’s host-specificity via testing through a “filter of safety”. The results of laboratory tests may differ from those obtained in open field host-specificity tests, where agents are able to use their full range of host-selection behaviors. It was hypothesized that Rhinoncomimus latipes (Coleoptera: Curculionidae), the biological control agent released against mile-a-minute weed, Persicaria perfoliata (Polygonaceae), would not feed or oviposit on nontarget plants in a two-phase, open field setting. Ten weevils were placed at the base of each of 13 test plant species in a randomized complete block design with six replicates. Weevils placed at the base of mile-a-minute weed were marked with yellow fluorescent dust, and yellow weevils were subsequently found only on mile-a-minute. Weevils placed at the base of nontarget plants (marked with red fluorescent dust) rapidly colonized mile-a-minute weed. Three hours after release, the number of R. latipes found on mile-a-minute weed was significantly higher than predicted by a random distribution of weevils on all test plants. The likelihood of finding more weevils on mile-a-minute compared to nontarget plant species was 31.0% at 3h and increased to 96.5% at 44h after release. Whereas prerelease studies showed feeding at low levels on 9 of the 13 plant species tested here, under open field conditions R. latipes did not feed on any nontarget plant species and dispersed from these plants. In an open field setting, where the weevil was able to use its full range of host-selection behaviors, there was no observed risk of nontarget effects for any species tested. [ABSTRACT FROM AUTHOR]

Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae) is a pupal parasitoid under consideration for introduction into Canada for the control of the invasive leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae). Since study of the parasitoid outside of quarantine was not permitted in Canada at the time of this project, we assessed its efficacy via field trials in its native range in central Europe. This was done by simulating introductory releases that would eventually take place in Canada when a permit for release is obtained. In 2007 and 2008, experimental leek plots were artificially infested with pest larvae to mimic the higher pest densities common in Canada. Based on a preliminary experiment showing that leek moth pupae were suitable for parasitism up to 5-6 days after pupation, D. pulchellus adults were mass-released into the field plots when the first host cocoons were observed. The laboratory-reared agents reproduced successfully in all trials and radically reduced leek moth survival. Taking into account background parasitism caused by naturally occurring D. pulchellus, the released agents parasitized at least 15.8%, 43.9%, 48.1% and 58.8% of the available hosts in the four release trials. When this significant contribution to leek moth mortality is added to previously published life tables, in which pupal parasitism was absent, the total pupal mortality increases from 60.1% to 76.7%. This study demonstrates how field trials involving environmental manipulation in an agent's native range can yield predictions of the agent's field efficacy once introduced into a novel area. [ABSTRACT FROM AUTHOR]

Abstract: Hybridization between introduced biological control agents and native species is a nontarget effect of biological control. However, the genetic impacts related to introduced insects, especially from the viewpoint of post-release evaluation, remain largely unexplored. Torymus sinensis (Hymenoptera: Torymidae) is a parasitoid wasp introduced from China into Japan to control the invasive Asian chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae). After T. sinensis was first released in 1982, the damage caused by D. kuriphilus fell greatly. Previous studies showed that hybridization between T. sinensis and indigenous Torymus beneficus (the early-spring strain) was rare in the field, but individuals morphologically intermediate between T. sinensis and T. beneficus then appeared in the field. Here, we examined the frequency of hybridization between T. sinensis and the late-spring strain of T. beneficus by using the internal transcribed spacer 1 (ITS1) region of nuclear rDNA. Increasing numbers of F1 hybrids were detected every year from 1993 to 1996, reaching 22%. It seems that T. sinensis can hybridize more easily with the late-spring strain of T. beneficus. Morphological indices of the F1 hybrid type ranged between indices of the late-spring strain of T. beneficus and T. sinensis, with considerable overlap. Simultaneous with the occurrence of the F1 hybrids, the indigenous late-spring strain of T. beneficus was rapidly displaced by T. sinensis. [Copyright &y& Elsevier]

Abstract: A large-scale biological control program against saltcedars (Caryophyllales: Tamaricaceae) has been implemented in the western United States. Repeated releases of the biological control agent, Diorhabda elongata (Coleoptera: Chrysomelidae), have resulted in delayed establishment success in northern California. Evidence that the target weed species at northern California release sites is a lower ranked host led us to test for shifts in host preference of D. elongata, by comparing the field-established population to its source laboratory colony. In greenhouse experiments, laboratory-colony D. elongata exhibited ovipositional preference for Tamarix ramosissima over Tamarix parviflora, whereas D. elongata reared from the field population had no significant preference between the two host plants. In an open-field host choice experiment conducted prior to widespread field-establishment (2006), higher oviposition and number of adult beetles over time was found in T. ramosissima treatments when compared to T. parviflora-only and mixed-host treatments. We repeated the open-field host choice experiment in 2008 for the laboratory colony and beetles reared from the field-established population. Field-established beetles remained longer than laboratory-colony beetles, irrespective of host. Significantly more laboratory-colony D. elongata remained on T. ramosissima treatments, but there was no treatment effect on field-established beetles. Our findings suggest the relaxation of a host acceptance threshold by field-established D. elongata, which may have improved performance on the target weed, T. parviflora. If such trait shifts are common, then strategies implementing repeated releases may not improve establishment, and studies comparing pre- and post-release realized host use by biological control agents may be useful to detect novel host use patterns. [Copyright &y& Elsevier]

The article presents a study which investigates the distributional activities of Pseudacteon parasitoids which is related with the Solenopsis saevissima complex in South America. The study organizes a record for Pseudacteon species to locate the geographical arrays of species related with the imported fire ants in the native range in South America. The results show that there are no differences in the size of geographical ranges among Pseudacteon linked with various host composites of fire ants.

1. A possible explanation for low success rates when introducing natural enemies to new regions for biological control of insect pests is that they fail to adapt to their new conditions. Therefore it has been widely recommended that biological control practitioners increase the probability of local adaptation by maximizing the genetic variation released. An alternative recommendation is to use climate matching to identify native populations that may already possess traits suited to the new region. However, support for these recommendations is weak through lack of empirical evidence that local adaptation is important to biological control. 2. This study examined how genetic drift and selection influenced the population frequencies of two asexually reproducing, genetically differentiated parasitoid biotypes that were introduced to New Zealand from South America for biological control. Other than by mutation, the biotypes were genetically fixed due to the absence of recombination both within and between biotypes. This meant that adaptive evolution could occur only if selection acted on any traits that varied between the biotypes introduced from South America. 3. The two parasitoid biotypes were released simultaneously at 14 sites and their frequencies were monitored for up to 10 years. Changes in biotype frequency were consistent with strong directional selection favouring one of the South American biotypes, thus generating established parasitoid populations that were better adapted to New Zealand conditions than those that had originally been released. This local adaptation of the control agent contributed to greater mortality of the pest. 4. Synthesis and applications. This study provides the first clear demonstration of the importance of releasing natural enemy genetic variation in new regions to foster adaptive evolution and improve success rates in classical biological control. However, the benefit to biological control of maximizing the genetic variation released needs to be balanced against possible risks to non-target species. The results do not support the concept of choosing sampling sites for putative biological control agents based solely on climatic similarities between the source location and the intended region of introduction. [ABSTRACT FROM AUTHOR]

Classical biological control of insect pests and weeds may lead to potential conflicts, where insect pests are closely related to weed biological control agents. Such a conflict may occur in the classical biological control of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) in North America, which belongs to the same subfamily, Ceutorhynchinae, as a number of agents introduced or proposed for introduction against non-indigenous invasive weed species. We propose a step-by-step procedure to select non-target species and thereby to develop a non-target species test list for screening candidate entomophagous biological control agents of a herbivore pest insect in a way that would simultaneously evaluate non-target potential on weed biological control agents and other non-target species. Using these recommendations, we developed a non-target test list for host specificity evaluations in the area of origin (Europe) and the area of introduction (North America) for cabbage seedpod weevil parasitoids. Scientifically based predictions on expected host–parasitoid interactions and ecological information about the ecological host range in the area of origin can help avoid conflicts, while still allowing the introduction of safe and effective agents against both insect pests and weeds. [ABSTRACT FROM AUTHOR]

The European biotype of the parasitoid Microctonus aethiopoides Loan (Hymenoptera: Braconidae) is being considered for release against Sitona lepidus Gyllenhal (Coleoptera: Curculionidae) in New Zealand. Host specificity was evaluated in the laboratory using both endemic and introduced weed biological control curculionid species, with 12 no-choice and three choice experiments carried out comparing the S. lepidus and test weevils. Two further no-choice tests used the Moroccan M. aethiopoides biotype to compare attack rate between European and Moroccan M. aethiopoides, the latter released in 1982 to control the lucerne pest S. discoideus. Across all experiments, total parasitism of S. lepidus was 69% compared with 15% for the test weevils. European M. aethiopoides was able to develop in the native weevils Irenimus aequalis, Nicaeana cervina, Catoptes cuspidatus, Protolobus porculus and Steriphus variabilis with parasitism rates of 13, 28, 2, 7 and 8%, respectively. These levels were significantly less than those in the corresponding S. lepidus control. Total parasitism of I. aequalis and C. cuspidatus increased significantly in the presence of S. lepidus than recorded under no-choice conditions. The presence of European M. aethiopoides caused minor, if any, test weevil mortality prior to the onset of prepupal emergence and there was no significant reproductive suppression in parasitoid-exposed test weevils. Parasitism of the introduced weed control agent R. conicus by European M. aethiopoides was significantly lower (1.1%) compared to the Moroccan biotype (47.5%). Based on these and other experiments, should the European M. aethiopoides be released as a biological control agent of S. lepidus, its ecological impacts are likely to be less severe than those already exhibited by the Moroccan M. aethiopoides . [ABSTRACT FROM AUTHOR]

Melaleuca quinquenervia(Cav.) S.T. Blake, Australian broad-leaved paperbark, has become a serious weed in southern Florida.Poliopaschia lithochlora(Lower) is a promising candidate as a potential biological control agent, and this study describes laboratory and field observations of the life history of this moth. Eggs are laid in small batches, mainly on the surface of leaves, and larvae are voracious leaf feeders, concealed in tubes that are usually found in small colonies attached to leaves and stems. Larvae move from these tubes to feed on surrounding leaves, and saplings and suckers are frequently defoliated. Prepupae form sealed bulbs in the larval tubes in which they pupate. Adult females are mainly active and oviposit at night. Development from egg to adult occurs in approximately 80 d. Field populations appear to be regulated by several egg and larval parasites. Because this moth severely damages saplings and suckers ofM. quinquenervia, prefers low-lying humid sites, and can be successfully mass reared, it is rated highly for its potential as a biological control agent. [ABSTRACT FROM AUTHOR]

The annual vine Polygonum perfoliatum L. (mile-a-minute weed) is an invasive weed in natural areas and has been targeted for biological control in the United States. Host specificity of the Asian weevil Rhinoncomimus latipes Korotyaev, a potential biological control agent of mile-a-minute weed, was evaluated in China using qualitative laboratory choice and no-choice tests on 28 plant species in 18 families outside of the Polygonaceae and on 21 species within the Polygonaceae. An open-field choice-test was also conducted in China. In addition, quantitative assessments of adult and larval no-choice tests and adult-choice tests were conducted in a quarantine laboratory in the United States on 23 species of Polygonaceae (including five also tested in China) and five species in three other plant families. Adult weevils did not eat any plant species in families outside of the Polygonaceae in choice or no-choice tests. In no-choice tests with Polygonaceae, adults fed and survived for up to 30 days on a few species in the tribes Persicarieae, Polygoneae, and Rumiceae, but females did not oviposit on any plant except P. perfoliatum, and in choice tests adults almost exclusively ate P. perfoliatum. Neonate larvae placed on alternative hosts did not survive longer than 36 h, while 80% of neonates placed on P. perfoliatum survived and completed development at least to pupation. Of all plant species tested, only P. perfoliatum fell within the physiological host range of R. latipes. Our tests indicate that R. latipes is a host specialist with minimal potential for non-target effects if released in the United States. [Copyright &y& Elsevier]

In 1980, two species of parasitoid wasps ( Aphytis yanonensis DeBach et Rosen and Coccobius fulvus Compere et Annecke) were introduced to Japan from China as biological control agents to combat the arrowhead scale ( Unaspis yanonensis Kuwana). These introductions represent one of the most successful projects in the history of biological control in Japan. To examine whether density dependent parasitism was inevitable for success of biological control, we tried to detect temporal and spatial density dependence in parasitism rates using time-series data of scale density, as well as parasitism, over a 16-year period. The work was conducted in a Satsuma mandarin orange ( Citrus unshiu Marc.) orchard in which we previously demonstrated that the system appeared to have stabilized after a decline in scale density following the introduction of the parasitoids. Earlier work also indicated that C. fulvus contributes most to the reduction in, and the stability of, scale density. In this study, we examined: (1) the relationship, on a whole-orchard basis, between scale density and the rates of parasitism by A. yanonensis, C. fulvus, and a combination of the two species; (2) whether parasitism was positively correlated to scale density on a single-tree basis among generations and (3) whether spatial density dependence was detectable within generations on an individual-tree basis. Parasitism by A. yanonensis was temporally density-dependent on scale population density at the whole-orchard level, while parasitism by C. fulvus was not. Parasitism by A. yanonensis or by C. fulvus was rarely positively correlated to scale density at the single-tree level, and spatial density-dependence was hardly detected at all at this level. Most analyses of combined parasitism rates were similar to rates of parasitism by C. fulvus alone. Contrary to conventional wisdom of biological control theory, this study demonstrates that density dependence is not necessarily detected, even in a system in which a natural enemy has long held pest density stable at low levels. [ABSTRACT FROM AUTHOR]

The predator and parasitoid fauna associated with cereal aphids is described, emphasizing the fauna associated with classical biological control efforts against the greenbug and Russian wheat aphid. We focus on literature from North America and include work from Europe and elsewhere when it is desirable to draw contrasts between approaches that affect cereal aphid biological control. Effects on natural enemies of cereal aphids are described that appear associated with plant traits that are innate, bred, or induced by aphid feeding. Examples of habitat manipulations, within and bordering cereal fields and within the broader landscape in which cereal production resides, affecting predators and parasitoids of cereal aphids are presented. These mediating effects of host plant and habitat manipulations on cereal aphid biological control provide significant and underexplored avenues to optimize cereal aphid management. [ABSTRACT FROM AUTHOR]

The eulophid Quadrastichus sp. was released in Spain in 1996 and 1997 to control the recently introduced citrus leafminer, Phyllocnistis citrella Stainton. Although this parasitoid became established, it did not exert any substantial control of P. citrella compared to the native Cirrospilus brevis Zhu, LaSalle and Huang which clearly predominated. To critically evaluate the results of the classical biological control program developed against P. citrella in Spain, we decided to test whether the observed field results concerning the exotic parasitoid Quadrastichus sp. and the indigenous C. brevis could have been forecasted from laboratory assays. An assay focusing on competition between Quadrastichus sp. and C. brevis was executed. The results obtained indicated that Quadrastichus sp. was an intrinsically superior competitor compared to C. brevis, the latter species becoming extinct in the laboratory competition trial. Environmental factors, not present in the conducted laboratory study, probably account for the outcome in the field. Although our laboratory results could be considered misleading, more post-colonization studies are warranted in classical biological control programs and, in any case, pre-introduction studies should still be conducted. [Copyright &y& Elsevier]

Simple Summary: Halyomorpha halys is a severe agricultural pest of Asian origin, which threatens cultivation of vegetables and fruits worldwide. Classical biological control is foreseen as the most effective approach to reduce populations of H. halys. The egg parasitoid Trissolcus japonicus is the most important candidate biological control agent. Adventive populations of T. japonicus are already present in limited distributions in North America and in Europe. Trissolcus mitsukurii is a second Asian species that attacks H. halys and has been found in Northern Italy. Efficient laboratory rearing procedures of these biological control agents are needed for release programs to help control the pest. We present data that will help to optimize progeny production with minimal effort. Halyomorpha halys is a severe agricultural pest of Asian origin that has invaded many countries throughout the world. Pesticides are currently the favored control methods, but as a consequence of their frequent use, often disrupt Integrated Pest Management. Biological control with egg parasitoids is seen as the most promising control method over the long-term. Knowledge of the reproductive biology under laboratory conditions of the most effective candidates (Trissolcus japonicus and Trissolcus mitsukurii) for optimizing production for field releases is strongly needed. Rearing of these egg parasitoids was tested by offering three different host supply regimes using new emerged females and aged, host-deprived females in different combinations. Results showed a mean progeny per female ranging from 80 to 85 specimens for T. japonicus and from 63 to 83 for T. mitsukurii. Sex ratios were strongly female biased in all combinations and emergence rates exceeded 94% overall. Cumulative curves showed that longer parasitization periods beyond 10–14 days (under the adopted rearing regimes) will not lead to a significantly increase in progeny production. However, ageing females accumulate eggs in their ovaries that can be quickly laid if a sufficient number of host eggs are supplied, thus optimizing host resources. Our data showed that offering H. halys egg masses to host-deprived female Trissolcus once a week for three weeks allowed its eggs to accumulate in the ovary, providing the greatest number of offspring within a three week span. [ABSTRACT FROM AUTHOR]

The hemlock woolly adelgid (HWA) is an invasive insect species native to Japan causing significant hemlock mortality in the eastern United States. Laricobius spp. have been targeted as biological control agents because they are adelgid specialists. Laricobius osakensis Montgomery and Shiyake is native to the same region of Japan from which the strain of HWA found in the eastern United States originated. Studies in Japan found that it is phenologically synchronous with HWA. Following approval to release L. osakensis from quarantine in 2010, approximately 32,000 were released at a total of 61 sites starting in 2012. In winter of 2014 and 2015, periods of extreme cold temperatures throughout the eastern USA, as well as the polar vortex, resulted in extensive mortality to HWA, which likely delayed the establishment of L. osakensis. The ability of the beetle to survive and establish in the eastern United States is reported here. In the first year of this study (2015–2016), limited numbers of L. osakensis were recovered, as HWA populations were still rebounding. In the second year (2016–2017), 147 L. osakensis were collected at 5 of 9 sites sampled, coinciding with rebounding HWA populations. Larval recovery was much greater than adult recovery throughout the study. HWA density was directly correlated with warmer plant hardiness zones and recovery of Laricobius beetles was significantly correlated with HWA density. Our results suggest that L. osakensis is successfully establishing at several of the sampled release sites and that the best predictor of its presence at a site is the HWA density. [ABSTRACT FROM AUTHOR]