Classical Biological Control Program Research Articles

Integrating ecoclimatic niche modelling methods into classical biological control programmes

Much of the success of a classical biological control programme hinges on identifying effective candidate agents, and once approved for release deploying them in the range invaded by the target organism at site-specific times of the year when they have the best chance of establishing. While suitable ecoclimatic modelling methods are available to guide decision-making, they have not been well integrated into biological control praxis. We present a framework that shows how ecoclimatic modelling techniques can be usefully and cost-effectively integrated into biological control programmes. The framework consists of a range of modelling methods within the CLIMEX software toolbox, differing in their information demands and outputs. To demonstrate the framework, we use different types of invasive plants in Australia: the annual forbs Conyza bonariensis (syn. Erigeron bonariensis) and Sonchus oleraceus, the woody perennial shrub Lycium ferocissimum, and the submerged aquatic Cabomba caroliniana. Simple climate-matching techniques, which only require data on the distribution of the target invasive species, are shown to be useful to identify the regions to search for candidate agents in the native range that are climatically adapted to those in the invaded range where biological control is most wanted. More sophisticated niche models can inform both where and when to search for candidate agents in the native range and when and where to release approved agents in the invaded range so that their hosts are actively growing and at the appropriate life stage at the selected sites. We demonstrate how simple manipulative experiments on the temperature response of the target invasive species can be used to parameterise these more complicated niche models. While the modelling framework has been demonstrated using invasive plants as targets, it is equally applicable to arthropod pests. The modelling has been a valuable component of the current biological control programmes, guiding agent prospecting and future deployment efforts in time and space.

Eco-climatic matching to guide foreign exploration and optimal release strategies for biological control agents of Rastrococcus iceryoides in Africa and Asia

Rastrococcus iceryoides (Green) (Homoptera: Pseudococcidae) is a major invasive pest of several horticultural crops [in Africa and Asia, outside its native range in India], with damage levels ranging from 30% to complete crop failure. Due to lack of effective co-evolved parasitoids in the invaded regions, maximum entropy (MaxEnt) and genetic algorithm for ruleset production (GARP) were used to identify climatically suitable areas in India for foreign exploration. Based on the outcome of the predictive models, an extensive survey was conducted in 15 major mango growing regions in the state of Tamil Nadu, India. Thereafter, both models were used to identify climatic compatibility habitats in the invaded regions of R. iceryoides. Our results revealed ten host plants belonging to eight families with considerably low levels of infestation. The percentage parasitism established using mummified R. iceryoides was relatively high ranging between 16.7 ± 1.4 to 91.3 ± 3.7%. Both old and new host-parasitoid associations were recorded with eleven parasitoid species described. Eight of the parasitoids recorded were new records of R. iceryoides. Among these parasitoids, Praleurocerus viridis Agarwal, Anagyrus chryos Noyes & Hayat and Neoplatycerus tachikawai Subba Rao were the most dominant and widespread parasitoid species, highly specific to R. iceryoides with percent parasitism of 53.2 ± 5.4, 31.3 ± 2.7 and 8.8 ± 2.9%, respectively. Using the occurrence data of the parasitoids, both models successfully identified optimal suitable habitats in Africa and Asia. Both models showed optimal performances with the value of the average area under the curve (AUC) of 0.98 for MaxEnt and 0.95 for GARP. However, the percentage contribution of the predictor variables that influenced the current and future predictions in the native and invaded range varied considerably. These findings demonstrate the importance of predictive modelling as novel tools to support future classical biological control program targeting R. iceryoides in the invaded regions. Our results provide important information to guide strategic planning for future classical biological control programmes.

Antennal Transcriptome Analysis and Identification of Candidate Chemosensory Genes of the Harlequin Ladybird Beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae).

Simple SummaryThe predatory harlequin ladybird Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) has been widely released for classical and augmentative biological control programs of insect herbivores and is now distributed worldwide. Because of its invasive behavior and the threat it can pose to local biodiversity, this ladybird has been adopted as a model species for invasive biocontrol predators. A huge amount of existing literature is available on this species. However, little is known about the mechanisms underlying H. axyridis smell and taste, even though these senses are important in this ladybird for courtship, mating, and for locating suitable habitats for feeding and oviposition. Here we describe the first chemosensory gene repertoire that is expressed in the antennae of male and female H. axyridis. Our findings would likely represent the basis for future functional studies aiming at increasing the efficacy of H. axyridis in biological control or at reducing its populations in those areas where the ladybird has become a matter of concern due to its invasiveness.In predatory ladybirds (Coleoptera: Coccinellidae), antennae are important for chemosensory reception used during food and mate location, and for finding a suitable oviposition habitat. Based on NextSeq 550 Illumina sequencing, we assembled the antennal transcriptome of mated Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) males and females and described the first chemosensory gene repertoire expressed in this species. We annotated candidate chemosensory sequences encoding 26 odorant receptors (including the coreceptor, Orco), 17 gustatory receptors, 27 ionotropic receptors, 31 odorant-binding proteins, 12 chemosensory proteins, and 4 sensory neuron membrane proteins. Maximum-likelihood phylogenetic analyses allowed to assign candidate H. axyridis chemosensory genes to previously described groups in each of these families. Differential expression analysis between males and females revealed low variability between sexes, possibly reflecting the known absence of relevant sexual dimorphism in the structure of the antennae and in the distribution and abundance of the sensilla. However, we revealed significant differences in expression of three chemosensory genes, namely two male-biased odorant-binding proteins and one male-biased odorant receptor, suggesting their possible involvement in pheromone detection. Our data pave the way for improving the understanding of the molecular basis of chemosensory reception in Coccinellidae.

Captive sentinel hosts efficiently measure the establishment, seasonality and dispersal of a parasitoid biological control agent

Introduced biological control agents are used to suppress populations and reduce the damage caused by many exotic herbivorous insects in New Zealand pasture. Understanding the dispersal behaviour of a recently introduced biocontrol agent in its new environment is important as it helps biocontrol practitioners make decisions on the number and location of future releases. In this study, a monitoring device which contained sentinel hosts was developed to monitor the establishment and dispersal of the Irish strain of Microctonus aethiopoides (Hymenoptera, Braconidae) into areas of the South Island of New Zealand where the clover pest Sitona obsoletus Gmelin (Coleoptera, Curculionidae) had recently become established. Field tests of the monitoring device at five sites in Marlborough confirmed that M. aethiopoides would enter the device through a 900 µm mesh and parasitise the sentinel weevils within. In a further trial conducted over 4 years at four sites in North Canterbury, monitoring devices successfully tracked the dispersal and establishment of M. aethiopoides at sites up to 27 km from the original release site. Monitoring devices containing sentinel hosts may help reduce the cost of classical biological control programmes as they enable rapid sampling of numerous sites and largely eliminate the time consuming practice of dissecting field collected hosts to determine the presence of the parasitoid.

Hidden Host Mortality from an Introduced Parasitoid: Conventional and Molecular Evaluation of Non-Target Risk.

Hidden trophic interactions are important in understanding food web ecology and evaluating the ecological risks and benefits associated with the introduction of exotic natural enemies in classical biological control programs. Although non-target risk is typically evaluated based on evidence of successful parasitism, parasitoid-induced host mortality not resulting in visible evidence of parasitism (i.e., nonreproductive effects) is often overlooked. The adventive establishment of Trissolcus japonicus, an exotic parasitoid of the introduced stink bug Halyomorpha halys, provides an opportunity to investigate the total impact of this parasitoid on target and non-target hosts in the field. We developed a new methodology to measure nonreproductive effects in this system, involving a species-specific diagnostic PCR assay for T. japonicus. We applied this methodology to field-deployed eggs of four pentatomid species, coupled with traditional rearing techniques. Nonreproductive effects were responsible for the mortality of an additional 5.6% of H. halys eggs due to T. japonicus, and were even more substantial in some of the non-target species (5.4-43.2%). The observed hidden mortality of native non-target species from an introduced parasitoid could change predictions about direct and indirect ecological interactions and the efficacy of biological control of the target pest.

Climate and seasonal effects on phenology and biological control of giant whitefly Aleurodicus dugesii (Hemiptera: Aleyrodidae) with parasitoids in southern California, USA

The invasive giant whitefly Aleurodicus dugesii Cockerell (Hemiptera: Aleyrodidae), a pest of many important crops and ornamentals, has established throughout southern California, USA. The parasitoids Encarsia noyesi Hayat (Hymenoptera: Aphelinidae), Idioporous affinis LaSalle and Polaszek (Hymenoptera: Pteromalidae), and Entedononecremnus krauteri Zolnerowich and Rose (Hymenoptera: Eulophidae) were introduced as part of a classical biological control program against giant whitefly. Populations of giant whitefly can still reach high numbers, however, despite biological control efforts. Seasonal variation in giant whitefly population densities and parasitoids' species-specific parasitism rates across three climates types in southern California were examined by repeated censuses during 2015–2016 in order to identify potential underlying factors influencing giant whitefly population dynamics. Giant whitefly population densities did not vary between southern California climate types, but varied seasonally, with the highest observed population densities in the spring. Parasitism rates of all three parasitoids also varied seasonally, with total parasitism reaching a peak in late summer and declining until the start of spring. Only I. affinis parasitism rates varied between climate types. Parasitism rates of I. affinis were the highest of the three parasitoid species observed, followed by E. noyesi and E. krauteri. Potential explanations for these findings and their impact on giant whitefly control are discussed.

Shared enemies exert differential mortality on two competing parasitic wasps

Abstracta Classical biological control programs introduce primary parasitoids into new geographic regions, often exposing them to existing populations of hyperparasitoids. Hyperparasitoids are frequently implicated in the failure of parasitoid biological control agents to establish and provide control of insect pests. The outcome of competition among two or more parasitoid species may be altered if the parasitoids are differentially attacked by the same hyperparasitoids. A reliable assessment of the hyperparasitoid community is needed to understand how top-down trophic interactions influence the effectiveness of introduced parasitoids. We examined the diversity of hyperparasitoids attacking Cotesia glomerata in Colorado (USA), where the congener C. rubecula is absent. We compared this diversity with the hyperparasitoid community of C. glomerata and C. rubecula from Maryland (USA) where both wasps co-occur and use the imported cabbageworm (Pieris rapae) as their main host. Field collected C. glomerata broods were analyzed to examine the relationship between brood sizes and the adult sex ratio and the likelihood of attack by different hyperparasitoid species. A total of nine hyperparasitoid species were found in Colorado, of which four species also occurred in Maryland. While larger C. glomerata broods experienced increased odds of hyperparasitism, C. glomerata developing in larger broods had higher per capita survivorship than those developing in smaller broods. The proportion of adult male C. glomerata in a brood increased with brood size in both non-hyperparasitized and hyperparasitized broods, suggesting that female C. glomerata were not preferentially hyperparasitized. Hyperparasitoids inflicted greater mortality on C. rubecula than on C. glomerata. This differential hyperparasitism may enable the coexistence of C. glomerata with its congener C. rubecula, which usually outcompetes and displaces C. glomerata.

Prospects for classical biological control of Marchalina hellenica in Australia

The giant pine scale, Marchalina hellenica Gennadius (Hemiptera: Marchalinidae), is a sap-sucking insect native to South-East Europe that was recently introduced in Australia where it threatens the pine forestry industry. To initiate a classical biological control programme, a literature review and field surveys were carried out in Greece to investigate the natural enemy complex of the scale. While no parasitoids were found, M. hellenica was attacked by several predators, most notably Neoleucopis kartliana Tanasijtshuk (Diptera: Chamaemyiidae). N. kartliana was present at all sites investigated and is presumably specific to Marchalina. This highlights its potential as a biological control agent for M. hellenica. This predatory fly has already been used to control M. hellenica on the Italian island of Ischia. Interestingly, molecular analyses of Greek samples revealed other Chamaemyiidae predatory flies that can be potentially included in the Australian classical biological control programme of M. hellenica.

Post-release monitoring in classical biological control of weeds: assessing impact and testing pre-release hypotheses.

While various aspects of classical biological control (CBC) of weeds, including non-target risk assessment, have been continuously improved in the past few decades, post-release monitoring remains neglected and underfunded. Detailed assessments of the population, community and ecosystem outcomes of CBC introductions, including reasons for success/failure and absence or evidence of non-target effects are generally lacking or fragmentary. Here we review recent advances in understanding the demography of biological control agents released into a novel environment, their impact on the target weed and on non-target species, and the consequences for the resident plant and animal communities and ecosystem functioning, including the restoration of ecosystem services. We argue that post-release monitoring of CBC programs offers unique but largely underutilized opportunities to improve our understanding of CBC outcomes and to inform management and decision-makers on when and how CBC should be integrated with other management options to enhance ecosystem restoration.

Host stage preference and performance of Dolichogenidea gelechiidivoris (Hymenoptera: Braconidae), a candidate for classical biological control of Tuta absoluta in Africa

Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is native to South America but has invaded the Afro-Eurasian supercontinent where it is currently the most devastating invasive arthropod pest of tomato. As a part of the first classical biological control programme against T. absoluta in Africa, a larval parasitoid, Dolichogenidea gelechiidivoris Marsh. (Syn.: Apanteles gelechiidivoris Marsh) (Hymenoptera: Braconidae), of T. absoluta was imported from Peru into the quarantine facility of the International Centre of Insect Physiology and Ecology, Kenya. We report on the host larval preference of D. gelechiidivoris and the host suitability, and the parasitoid’s reproductive strategy, including lifetime fecundity and egg maturation dynamics. Dolichogenidea gelechiidivoris females preferentially oviposited in early (1st and 2nd) larval instars of T. absoluta but parasitized and completed development in all four instars of the host. Host instar did not affect D. gelechiidivoris sex-ratio but females reared on the first instar had significantly fewer eggs than when reared in late larval instars (3rd and 4th). Females of the parasitoid emerged with a high mature egg load which peaked 2 d post eclosion. The females of D. gelechiidivoris survived 8.51 ± 0.65 d and produced 103 ± 8 offspring per female at 26 ± 4 °C (range: 24 to 29 °C) and 50–70% relative humidity (RH) with males present and fed honey-water (80% honey). Increasing maternal age decreased the proportion of female offspring. Under the aforementioned laboratory conditions, the Gross and Net reproductive rates were 72 and 39.5 respectively, while the mean generation time was 20 d. The potential intrinsic rate of natural increase was 0.18. This study shows that D. gelechiidivoris is a potential biological control agent of T. absoluta and should be considered for release in Kenya and across Africa following host specificity testing and risk assessments.

Determining Optimal Parasitoid Release Timing for the Biological Control of Emerald Ash Borer (Coleoptera: Buprestidae)

The emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), quickly established itself as an invasive species in North America after it was first detected near Detroit, Michigan, USA, in 2002. Just 1 yr later, emerald ash borer was introduced accidentally into Maryland, USA, on imported ash nursery stock. After quarantine and eradication efforts failed, a classical biological control program was initiated in Maryland in 2009 with the release of 2 larval parasitoids: Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae) and Spathius agrili Yang (Hymenoptera: Braconidae), and 1 egg parasitoid, Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae). Timing is critical to the success, efficiency, and cost-effectiveness of classical biological control programs where release of parasitoids must coincide temporally with that of susceptible stages of the host. In 2017, periodic field surveys at 2 sites in central Maryland were conducted to assess emerald ash borer phenology using green funnel traps to sample adults, and debarking infested ash trees to sample larval stages. Adult emerald ash borer first appeared in traps on 18 May 2017 (479 growing degree d base 10 [GDD10]), peaked on 15 Jun (823 GDD10), and were absent from 13 Jul (1,301 GDD10) through 12 Oct (2,598 GDD10) when surveys were terminated. Larval sampling in early Aug (1,698 GDD10) found all larval instars present, the most common being the second instar (46%), followed by the third instar (28%), fourth instar (20%), first instar (5%), and prepupal J-shaped larvae (J-larva) (0.5%). J-larvae are so called because after excavating a pupal chamber, the head is bent down 180 degrees to the rest of the body, resembling the shape of the letter J. Larval sampling in late Oct (2,710 GDD10) found J-larvae to be the dominant stage present (92.2%), followed by fourth instar (4.8%), third instar (2.4%), and second instar (0.6%). We found that emerald ash borer was univoltine, and that nearly 50% of emerald ash borer larvae had developed to stages susceptible to parasitism (third and fourth instar) by early Aug (1,698 GDD10). By late Oct (2,710 GDD10), 92% had developed beyond parasitoid susceptible stages (J-larvae). These findings suggest that egg parasitoid releases are best targeted from early May to late Jun at an approximate GDD10 range of 300 and 1,100 with larval parasitoid releases best targeted between 1,400 and 2,500 GDD10.

Open field evaluation of Aculodes altamurgensis, a recently described eriophyid species associated with medusahead (Taeniatherum caput-medusae)

ABSTRACTMedusahead (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.

Nontarget Host Risk Assessment of the Egg Parasitoid Trichogrammatoidea cryptophlebiae (Hymenoptera: Trichogrammatidae) for Classical Biological Control of the False Codling Moth (Lepidoptera: Tortricidae) in Israel.

The false codling moth Thaumatotibia leucotreta (Meyrick), is an invasive species in Israel. In order to carry out a classical biological control program, the African egg parasitoid Trichogrammatoidea cryptophlebiae (Nagaraja) was recently introduced into Israel, and nontarget host risk assessment was performed as required. In no-choice tests we determined that T. cryptophlebiae was unable to develop in eggs of four nontarget Lepidopteran species: Pectinophora gossypiella (Saunders), Spodoptora littoralis (Boisduval), Ephestia kuehniella (Zeller), and Belenois aurota (Fabricius). Conversely, it developed in three Lepidopteran species eggs of the Tortricidae family: Cydia pomonella (Linnaeus), Lobesia botrana (Denis and Schiffermüller), and Epiblema strenuana (Walker). Epiblema strenuana eggs showed the lowest parasitism level among all tested moth eggs of the Tortricidae family. The progeny production of parasitized false codling moth eggs was similar to that of C. pomonella eggs, but smaller than that of L. botrana eggs. However, moth egg and parasitoid clutch sizes were smallest on L. botrana eggs and largest on C. pomonella eggs. In choice bioassays, T. cryptophlebiae significantly preferred to parasitize T. leucotreta eggs over the eggs of C. pomonella, L. botrana, and E. strenuana. Moreover, the choice of T. leucotreta eggs over the eggs of L. botrana was not affected by the parasitoids' rearing histories. Our data support the assumption that T. cryptophlebiae develops only in moth species of the Tortricidae family. Thus, the risk that it may attack nontarget species is low.

Endophytic fungi in the invasive weed Impatiens glandulifera: a barrier to classical biological control?

SummaryThe rust fungus, Puccinia komarovii var. glanduliferae, has been introduced into the UK for biological control of the invasive weed, Impatiens glandulifera (Himalayan balsam). However, establishment of the pathogen has differed across the country, which may be partly explained by variation in plant genotype. The aim of this study was to examine whether there is a further layer of phenotypic resistance, provided by indigenous foliar endophytic fungi. Culturable endophytes were isolated from a number of different balsam populations, and the commonest species were inoculated into ‘clean’ balsam plants, to test their interactions with the rust. We found that endophyte communities within balsam are low in diversity and become more dissimilar with increasing distance between populations. Three endophytes (Colletotrichum acutatum, Alternaria alternata and Cladosporium oxysporum) were common and appeared to be antagonistic to the rust, reducing pustule number and mitigating the effect of the pathogen on plant biomass. I. glandulifera thus partially conforms to the endophyte‐enemy release hypothesis, in that as an introduced species, it has an impoverished endophyte complement, acquired from the local environment. However, these endophytes represent a potential barrier to effective biological control and future weed control strategies need to find strains of rust that can overcome plant genetic resistance and the overlaying phenotypic resistance, conferred by endophytes. Future classical biological control programmes of weeds must therefore take into account the fungal bodyguards that invasive species may acquire in their introduced ranges.

Evaluation of the rust fungus Puccinia rapipes for biological control of Lycium ferocissimum (African boxthorn) in Australia: Life cycle, taxonomy and pathogenicity

Fungal plant pathogens are increasingly recognised as being among the most effective and safe agents in classical weed biological control programs worldwide. Suitability of the rust fungus P. rapipes as a classical biological control agent for Lycium ferocissimum (African boxthorn) in Australia was assessed using a streamlined agent selection framework. Studies with P. rapipes were undertaken to elucidate its life cycle, confirm its taxonomic placement and determine its pathogenicity to L. ferocissimum and seven closely-related Solanaceae species that occur in Australia. Field surveys in the native range of South Africa, experiments in a containment facility in Australia and DNA sequencing confirmed that P. rapipes is macrocyclic and autoecious, producing all five spore stages on L. ferocissimum. The stages not previously encountered, spermogonia and aecia, are described. Sequencing also confirmed that P. rapipes is sister to Puccinia afra, in the ‘Old World Lineage’ of Puccinia species on Lycieae. Two purified isolates of the fungus, representing the Eastern and Western Cape distributions of P. rapipes in South Africa, were cultured in the containment facility for use in pathogenicity testing. L. ferocissimum and all of the Lycium species of Eurasian origin tested ‒ Lycium barbarum (goji berry), Lycium chinense (goji berry ‘chinense’) and Lycium ruthenicum (black goji berry) – were susceptible to both isolates of P. rapipes. The Australian native L. australe and three more distantly related species in different genera tested were resistant to both isolates. The isolate from the Western Cape was significantly more pathogenic on L. ferocissimum from Australia, than the Eastern Cape isolate. Our results indicate that P. rapipes may be sufficiently host specific to pursue as a biological control agent in an Australian context, should regulators be willing to accept damage to the Eurasian goji berries being grown, albeit to a limited extent, in Australia.

Classical biological control of the African citrus psyllid Trioza erytreae, a major threat to the European citrus industry

Citrus greening or huanglongbing (HLB) is the main threat to the European citrus industry since one of its vectors, the African citrus psyllid, Trioza erytreae, has recently become established in mainland Europe. In this context, classical biological control programmes should be implemented to reduce the spread of the psyllid. The aims of this study were to: i) disentangle the parasitoid complex of T. erytreae combining morphological and molecular characterization; and ii) to study the biology of its main parasitoids in its area of origin in South Africa for their future importation into Europe. The main citrus producing areas of South Africa were surveyed during 2017. In contrast to previous studies, the parasitoid complex of T. erytreae included three species of primary parasitoids: Tamarixia dryi, Psyllaephagus pulvinatus and another parasitoid of the genus Tamarixia. Molecular analysis showed that it is a new species closely related to T. dryi. Tamarixia dryi was the most abundant parasitoid but its relative abundance varied among sampling sites. The sex ratio (males/females) of T. dryi and Tamarixia sp. decreased with T. erytreae size and became female biased when psyllid nymphs were larger than 0.6 and 1.2 mm2, respectively. These parasitoids were attacked by three species of hyperparasitoids, Aphidencyrtus cassatus, Marietta javensis and a species of the genus Aphanogmus. Aphidencyrtus cassatus, the most abundant hyperparasitoid, tended to emerge from large nymphs, and adult females lived as long as those of T. dryi. The implications of these results are discussed within the framework of the introduction of T. dryi into Europe.

Host range testing of Tamarixia dryi (Hymenoptera: Eulophidae) sourced from South Africa for classical biological control of Trioza erytreae (Hemiptera: Psyllidae) in Europe

The African citrus psyllid, Trioza erytreae, vectors citrus greening or huanglongbing (HLB) disease. The psyllid has been reported from mainland Europe, where it is rapidly spreading from the northwest to the southwest of the Iberian Peninsula. In order to reduce its spread and population levels, a classical biological control program with the parasitoid Tamarixia dryi is under development in Spain. We evaluated the host specificity of T. dryi using 11 non-target psyllid (NTP) species, including five species of the genus Trioza. The psyllids were selected based on phylogenetic and ecological criteria. Tamarixia dryi exhibited a high host specificity. Females did not parasitize any of the 11 NTPs tested, except for one nymph of a gall-forming Trioza species closely related to Trioza montanetana. Tamarixia dryi only laid one egg on a nymph when it was removed from the gall on Convolvulus canariensis and exposed directly to the parasitoid. However, the immature parasitoid died before emerging. We further confirmed that T. dryi did not parasitize a representative triozid species, Trioza laurisilvae, of the endemic Canarian fauna after long time exposure. Our results demonstrate that T. dryi is a highly specific parasitoid and its introduction, release and establishment in Europe within the classical biological control program of T. erytreae should not affect other psyllid species. Therefore, no significant environmental impact is expected.

Effects of floral resources on the efficacy of a primary parasitoid and a facultative hyperparasitoid

AbstractResources added to agroecosystems to enhance biological control are potentially available to multiple members of the resident insect community—not only the biological control agents for which the resources are intended. Many studies have examined the effects of sugar feeding on the efficacy of biological control agents. However, such information is lacking for other, interacting species such as facultative hyperparasitoids, which may contribute to pest suppression but can also interfere with introduced biological control agents. Under greenhouse conditions, we tested the direct effects of sugar and nectar provisioning on the longevity, host‐killing impact and offspring production of two pupal parasitoids associated with leek moth, Acrolepiopsis assectella: the introduced biological control agent, Diadromus pulchellus, and the native facultative hyperparasitoid, Conura albifrons. Adding sucrose, buckwheat or a combination of buckwheat and common vetch to a sugar‐deprived system (potted leek plants in cages) increased parasitoid longevity and resulted in higher leek moth parasitism and mortality compared to water or common vetch treatments. However, the two parasitoid species exhibited a distinct temporal response to the treatments, likely influenced by differences in their life histories. This study provides insight into how integrating conservation biological control techniques could affect the success of a classical biological control programme.

Organic mulch can increase the survival of a weed biological control agent during laboratory mass rearing

ABSTRACTMass rearing agent organisms is a critical component to classical biological control programmes. Maximising survival of each life stage necessitates that ideal, stage-specific conditions are available in the rearing protocol. We investigated a method to improve pupal survival of Pseudophilothrips ichini Hood (Thysanoptera: Phlaeothripidae), a proposed biological control agent of the highly invasive Brazilian peppertree, Schinus terebinthifolia Raddi (Sapindales: Anacardiaceae). Specifically, we tested the effect of organic mulch on the number of adults emerging. Either compressed coconut fibre, dried Brazilian peppertree leaves, or dried sphagnum moss were added to the soil surface of potted Brazilian peppertrees. Nothing was added to untreated control plants. Each plant was sealed in a clear acrylic cylinder and 50 s instar thrips were added. The number of adults emerging was compared between mulch treatments. The greatest number of adults emerged from plants with sphagnum moss, with no differences among the other mulches and the control. We confirmed that the majority of thrips pupated in the moss rather than in the soil. Relative humidity was higher in the mulch layers compared to the plant canopy. Sphagnum moss likely provided the most ideal harbourages for thigmotactic pupae and the humid microhabitat minimised desiccation. We discuss the use of organic mulches in ecological contexts and emphasise the benefits of organic mulch in captive rearing operations that involve insects with soil-dwelling stages.

Biological control of Gonipterus: Uncovering the associations between eucalypts, weevils and parasitoids in their native range

The study was initiated by the relative failure of the parasitoid Anaphes nitens in controlling the eucalypt weevil Gonipterus platensis on the Iberian Peninsula. Our aim was to gain insight into the community of Gonipterus egg parasitoids occurring in Tasmania. During surveys in 2016 and 2017, adult weevils and egg pods were collected from Eucalyptus trees in Tasmania. The weevils were identified using male genital structure and DNA extracted from hatched larvae. Parasitoids that emerged from the egg pods were identified, and trophic associations of egg parasitoids, weevils and host plants were analyzed. Five species of the Gonipterus scutellatus complex, to which G. platensis belongs, were found, including Gonipterus sp. 2, which is reported for the first time from Tasmania. Molecular analysis corroborated previous phylogenetic studies of this group of species. A sixth species, G. notographus, was also collected. Most species were found to overlap in distribution in Tasmania and, despite being oligophagous, to display selectivity among Eucalyptus species used as hosts: G. platensis and G. pulverulentus were mainly found on E. ovata, Gonipterus sp. 1 on E. nitens and E. globulus and G. notographus on ‘peppermint’ species (E. amygdalina and E. pulchella). Five egg parasitoid species were found associated with these Gonipterus species: Anaphes inexpectatus, A. nitens, A. tasmaniae, Cirrospilus sp. and Euderus sp., with no apparent host specialization. Anaphes nitens, Cirrospilus sp. and Euderus sp. were more frequently found on E. ovata, possibly associated with G. platensis and G. pulverulentus, which were dominant on this host species. Conversely, A. inexpectatus was dominantly found on peppermints (43%), suggesting a main association with G. notographus. Anaphes nitens was found at 23 locations out of 117 and in 2017 was the most abundant parasitoid obtained, with an average 20% parasitism rate, indicating that this species is undergoing a geographical and population expansion since its first report from Tasmania in 2012. These findings contribute to the understanding of the parasitoid-Gonipterus-Eucalyptus trophic relationship and stand to improve future classical biological control programs against G. platensis and other invasive Gonipterus species.