Host specificity ofCostesia yakutatensis [Hym.: Braconidae] on lepidoptera in peppermint and alfalfa

Seven species of Lepidoptera, common to alfalfa and peppermint in western Oregon, were tested as potential hosts forCotesia yakutatensis (Ashmead). Laboratory and field studies demonstrated that onlyAutographa californica (Speyer) andTrichoplusia ni (Hubner) were suitable. Percent parasitism, duration of oviposition, and number of parasitoids per host were highest whenC. yakutatensis was associated withA. californica.     

Host specificity testing and suitability of a European biotype of the braconid parasitoid Microctonus aethiopoides as a biological control agent against Sitona lepidus (Coleoptera: Curculionidae) in New Zealand

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.     

Differential attraction of parasitoids in relation to specificity of kairomones from herbivores and their by-products

Infochemicals are used by foraging parasitoids in the host selection process from habitat preference until host recognition. Kairomones from the herbivore host plays a vital role in the attraction of parasitoids, particularly in the micro-habitat. Parasitoids are specifically attracted to their respective herbivore species even when different herbivores are present on the same plant. Chemicals emitted from different stages of host （eggs, larvae, pupae, adult）, host by-products （e.g., frass, exuviae, mandibular gland secretions, defense secretions etc.）, or intra-specific infochemicals （pheromones） can be main signals for the parasitoids. Parasitoids can differentiate between host and non-host, between different hosts and host stages by perceiving specific volatile and contact kairomones from the host itself, host along with its by-product, by-products alone or intra-specific infochemicals; of which frass （by-product） and intra-specific infochemicals are the most reported ones. Adult and larval parasitoids have been reported to be attracted to kairomones of their target stage or byproduct of their host. Pupal parasitoids have been found to utilize kairomones from the preceding host stage while egg parasitoids are known to exploit a variety of host infochemicals, for example, either from eggs themselves or other non-target host stages, especially adults and adult-related by-products. The kairomonal chemicals identified so far include various groups, but mainly hydrocarbons. A high degree of host specificity and host acceptance is important for the parasitoids as any mistake may result in the loss of fitness.     

Avoiding conflicts between insect and weed biological control: selection of non-target species to assess host specificity of cabbage seedpod weevil parasitoids

Abstract:  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.     

多寄主型寄生性天敌昆虫的寄主适应性及其影响因素

寄生性天敌昆虫对不同寄主资源的适应能力是其存活和繁殖的必要条件,它们的寄主选择行为则是其重要的适应结果。多寄主型寄生性天敌昆虫虽然对某种特定寄主资源的利用效率可能不如单寄主型寄生蜂,但却有利于拓展更宽的寄主范围,因此对环境的适应能力更强,更容易在自然界维持其种群的生存。统计结果也表明多寄主型天敌的生物防治效果往往比专食性天敌更高。有时生物防治成功的关键可能并不在于所利用的天敌种类的不同,而在于天敌的不同生物型或地理宗。总结了多寄主型寄生性天敌昆虫的寄主适应能力及其影响因素。寄生性天敌昆虫不仅因地理隔离产生种群分化,也可能因寄生不同的寄主产生种群内的分化,从而更加适应寄主的生活特性和栖境条件。寄主种类、寄主发育阶段、寄主大小、寄主营养、寄主免疫反应、寄主逃避反应、其它天敌的竞争、寄主共生或共栖生物的存在、寄主植物、天敌自身的学习能力及其共生微生物等多种因素对寄生性天敌昆虫的寄主适应性可产生影响。展望了多寄主型寄生性天敌昆虫对新寄主资源的拓展利用能力和适应性在生产上的可能应用前景和途径,以期为明确天敌与寄主间的互作关系,人工驯化寄生性天敌昆虫增强对靶标害虫的控制作用,合理利用天敌提高生物防治效率提供新的思路和理论支持。     

Differential attraction of parasitoids in relation to specificity of kairomones from herbivores and their by‐products

Infochemicals are used by foraging parasitoids in the host selection process from habitat preference until host recognition. Kairomones from the herbivore host plays a vital role in the attraction of parasitoids, particularly in the micro‐habitat. Parasitoids are specifically attracted to their respective herbivore species even when different herbivores are present on the same plant. Chemicals emitted from different stages of host (eggs, larvae, pupae, adult), host by‐products (e.g., frass, exuviae, mandibular gland secretions, defense secretions etc.), or intra‐specific infochemicals (pheromones) can be main signals for the parasitoids. Parasitoids can differentiate between host and non‐host, between different hosts and host stages by perceiving specific volatile and contact kairomones from the host itself, host along with its by‐product, by‐products alone or intra‐specific infochemicals; of which frass (by‐product) and intra‐specific infochemicals are the most reported ones. Adult and larval parasitoids have been reported to be attracted to kairomones of their target stage or byproduct of their host. Pupal parasitoids have been found to utilize kairomones from the preceding host stage while egg parasitoids are known to exploit a variety of host infochemicals, for example, either from eggs themselves or other non‐target host stages, especially adults and adult‐related by‐products. The kairomonal chemicals identified so far include various groups, but mainly hydrocarbons. A high degree of host specificity and host acceptance is important for the parasitoids as any mistake may result in the loss of fitness.     

A critical evaluation of host ranges of parasitoids of the subtribe Diabroticina (Coleoptera: Chrysomelidae: Galerucinae: Luperini) using field and laboratory host records

The subtribe Diabroticina is a large group of New World Chrysomelidae that includes corn rootworms, cucumber beetles and other pests. Recent introductions of Diabrotica virgifera virgifera LeConte into Europe, and the development of resistances to current management practices of rootworms in the USA have increased interest in new sustainable options for managing those pests. The only parasitoids that have been shown to consistently target and develop inside the beetle adults are Centistes gasseni Shaw, Centistes diabroticae Gahan (both Hym.: Braconidae), and Celatoria diabroticae Shimer, Celatoria compressa (Wulp), Celatoria bosqi Blanchard, and Celatoria setosa Coquillett (all Diptera: Tachinidae). This review improves our understanding of the realised and potential host range of these known parasitoids by rectifying erroneous references in light of new host records and from laboratory host range tests. Based on this critical review, all tachinid and braconid species studied are considered to be specific at least to the level of subtribe, i.e. Diabroticina. Celatoria setosa, Celatoria diabroticae and C. bosqi, have a narrow realized and potential host range; the former is restricted to the genus Acalymma and the last two to the fucata and virgifera groups of the genus Diabrotica. The braconids Centistes gasseni and C. diabroticae are also specific. The realized host range of C. gasseni includes species in the Diabrotica fucata and virgifera groups; while its potential host range also includes Acalymma species. The realized and potential host range of Centistes diabroticae includes Acalymma species as well as species in the fucata and virgifera groups of Diabrotica. Celatoria compressa has the broadest realised range compared to the other species studied, since it was obtained from species in several genera of Diabroticina; and its potential host range may also include Old World Aulacophora species.     

A modified DNA barcode approach to define trophic interactions between native and exotic pentatomids and their parasitoids

The establishment of invasive Halyomorpha halys (Stål) outside of its native range may impact native species assemblages, including other pentatomids and their scelionid parasitoids. This has generated interest in defining species diversity and host‐parasitoid associations in this system to better understand the impact of invasive alien species on trophic interactions in invaded regions. Information on scelionid–pentatomid associations in natural habitats is lacking, and species‐level identification of these associations can be tenuous using rearing and dissection techniques. Naturally occurring pentatomid eggs were collected in areas where H. halys has established in Canada and were analysed using a modified DNA barcoding approach to define species‐level trophic interactions. Identification was possible for >90% of egg masses. Eleven pentatomid and five scelionid species were identified, and trophic links were established. Approximately 70% of egg masses were parasitized; parasitism and parasitoid species composition were described for each species. Telenomus podisi Ashmead was the dominant parasitoid and was detected in all host species. Trissolcus euschisti Ashmead was detected in several host species, but was significantly more prevalent in Chinavia hilaris (Say) and Brochymena quadripustulata (Fabricius). Trissolcus brochymenae Ashmead and Tr. thyantae Ashmead were recorded sporadically. Parasitism of H. halys was 55%, and this species was significantly less likely to be parasitized than native pentatomids. The scelionid species composition of H. halys consisted of Te. podisi, Tr. euschisti and Tr. thyantae. Although these species cannot develop in fresh H. halys eggs, we demonstrate that parasitoids attempt to exploit this host under field conditions.     

Life history and laboratory host range of Stenopelmus rufinasus, a natural enemy for Azolla filiculoides in South Africa

The frond-feeding weevil, Stenopelmus rufinasus Gyllenhal, was imported into quarantine for testing as a potential natural enemy for the invasive fern Azolla filiculoides Lamarck in South Africa. Adult S. rufinasus lived for approximately 55 days during which the females produced on average 325 offspring. The developmental period for the immature stages (egg, three larval instars and pupation) was about 20 days indicating the potential for several overlapping generations per year. Both the adults and the larvae caused severe damage to A. filiculoides in the laboratory. Host specificity of this insect was determined by adult no-choice oviposition and larval starvation tests on 31 plant species in 19 families. Adult feeding, oviposition and larval development was only recorded on the Azolla species tested (A. filiculoides, A. pinnata subsp. poss. asiatica R.K.M. Saunders and K. Fowler, A. pinnata subsp. africana (Desv.) R.K.M. Saunders and K. Fowler and A. nilotica De Caisne Ex Mett.). A. filiculoides proved to be significantly the most suitable host for the weevil. The low adult emergence from A. nilotica and A. pinnata subsp. africana would most probably prevent the weevil from establishing on them in the field. A. pinnata subsp. poss. asiatica which supported greater development, is thought to be introduced and has a weedy phenology in South Africa and is thus of low conservation value. Therefore, any damage inflicted on this plant in the field may be an acceptable trade-off for the predicted impact of S. rufinasus on the aggressive exotic weed, A. filiculoides.     

The leafmining Leurocephala schinusae (Lepidoptera: Gracillariidae): not suitable for the biological control of Schinus terebinthifolius (Sapindales: Anacardiaceae) in continental USA

The host range of Leurocephala schinusae Davis & Mc Kay (Lepidoptera: Gracillariidae) was studied to assess its suitability as a biological control agent of Schinus terebinthifolius Raddi (Anacardiaceae), a serious environmental weed in the USA and elsewhere in the world. The host range was determined in the laboratory with adult no-choice oviposition (Argentina and USA) and larval development tests (USA). Seventeen plant species in ten genera were selected based on taxonomic relatedness to S. terebinthifolius, economic importance, and availability. Additional information was obtained by sampling foliage of S. terebinthifolius and six other South American native Anacardiaceae species in north-eastern Argentina. In the laboratory, except for Lithrea molleoides and Spondias mombin, all of the tested species were accepted for oviposition with a marked preference for Rhus aromatica. Incipient mines successfully developed into complete mines, pupae and adults on R. aromatica, Rhus copallinum, Schinus molle, Schinus lentiscifolius and S. terebinthifolius. In the field, although L. schinusae showed a clear preference for S. terebinthifolius, the host range, as determined by samples of host use in the native range, included three other Schinus species (S. lentiscifolius, Schinus longifolius, Schinus weinmannifolius) and one Astronium species (Astronium balansae). In conclusion, L. schinusae will not be considered for the biological control of S. terebinthifolius in continental US. However, the utilisation of this species in other infested areas such as Hawaii and Australia should be further discussed.     

Host specificity assessment and potential impact of Megamelus scutellaris (Hemiptera: Delphacidae) on waterhyacinth Eichhornia crassipes (Pontederiales: Pontederiaceae)

The delphacid Megamelus scutellaris Berg was evaluated for host specificity and potential impact as part of a biological control program targeting Eichhornia. crassipes. Survival and development of adults and nymphs were used as metrics with no-choice, two-choice, nymph transfer, and sustainability tests conducted under quarantine conditions. A total of 69 plant species were tested including 12 from the Pontederiaceae (including E. crassipes). Additionally, 27 native and 5 exotic associated wetland species and 11 economic species were tested. Megamelus scutellaris exhibited a high level of oviposition and developmental fidelity to E. crassipes by failing to sustain populations on any non-target test plant past the F₁ generation. Nymph transfer tests which simulated potential spill-over events found that survival was virtually non-existent on associated wetland plants, regardless of taxonomic relatedness, including on Pontederia cordata, an important and widespread native species. Eichhornia crassipes plants exposed to two consecutive generations of feeding produced 66.9% less biomass and 73.4% fewer leaves than those in the controls. We conclude that Megamelus scutellaris is safe to release on E. crassipes in the United States.     

Host range and risk assessment of Zygogramma bicolorata,a defoliating agent released in South Africa for the biological control of Parthenium hysterophorus

Parthenium hysterophorus (parthenium) is a weed of international importance and is spreading rapidly in sub-Saharan Africa. Consequently, it has been targeted for biocontrol in South Africa since 2003. Based on precedents elsewhere in the world, the defoliating beetle Zygogramma bicolorata was prioritised as a candidate agent. Although no-choice tests, involving some 48 test plant species, indicated a significant preference for parthenium, significantly reduced feeding and oviposition was recorded on some species. Multiple-choice tests resolved many of these non-target results; however, Helianthus annuus (sunflower) was still selected for oviposition and feeding. Of the 12 sunflower cultivars tested, four were selected for oviposition, while two were selected for oviposition and feeding. These six cultivars were then subjected to larval development trials, together with three native and two weed species (in the Asteraceae). These trials showed high levels of complete development on parthenium, significantly reduced development on sunflower cultivars, and partial development on only one of the weed species. Finally, a risk assessment was conducted on the six sunflower cultivars to quantify Z. bicolorata feeding and reproductive performance. Feeding risk calculations revealed these cultivars to have an extremely low risk (<0.2%) of supporting Z. bicolorata feeding and development. Similarly, reproductive risk calculations showed a very low risk (<0.16%) of supporting viable Z. bicolorata populations. These data are supported by findings from both the native (Mexico) and introduced ranges (Australia, India) of Z. bicolorata, where it has never been recorded as a pest of sunflower. These considerations were accepted by the regulatory authorities and in August 2013, Z. bicolorata became the second insect agent to be released in South Africa for the biocontrol of parthenium.     

Host-size preference of the parasitoidAnisopteromalus calandrae [Hym: Pteromalidae] onSitophilus zeamais (Col.: Curculionidae) larvae with a uniform age distribution

First generationAnisopteromalus calandrae (Howard) collected from commercial stored maize in South Carolina were exposed to a mixture of all sizes of immatureSitophilus zeamais Motschulsky, representative of a uniform age distribution, in shelled maize. Eighty-seven percent of parasitism is expected on larvae with tunnel diameters of 0.9 to 1.8 mm and 6% on prepupae and pupae, given this host-size distribution. Preference was greatest for large host larvae (1.6 mm diameter), intermediate for other larvae in the range 0.9 to 1.8 mm, and least for pupae and small larvae. Host-stage preference is discussed with respect to Chesson's (1983) parameters for preference, α_i, probability of parasitism, P_i, and electivity index, ?_i.     

Rapid preliminary characterisation of host specificity of leaf-beetles (Coleoptera: Chrysomelidae)

Rapid characterisation of host specificity is important both in biological control of weeds and studies in ecology and evolution. A means for doing this was developed and tested on four species of leaf beetles of interest for biological control of the weed Mimosa pigra (Mimosaceae). We identified the most promising for the more detailed tests necessary to obtain release approval. The impact of time-dependent effects and effects of experience were also investigated as part of this study but were not detected. Short-term host specificity tests on adult feeding accurately predicted the results of longer term trials. The long-term trial showed that survival on a plant species depended on feeding on it. Hence short-term feeding trials can predict the longer term survival of adults on other plant species. Different feeding results were obtained in cut foliage versus entire plants but no consistent pattern was shown: of the two insect species tested, one species ate more of the cut material while the opposite was demonstrated for the second species. Species in order of priority for further consideration as biocontrol agents were Syphrea bibiana, Genaphthona sp., Syphrea sp. and Paria sp. The latter three species were probably not sufficiently specific for release. The tests done here allow the identification of the most likely species upon which to conduct the more laborious and difficult larval developmental tests, saving considerable resources.     

Phenotypic plasticity in host-plant specialisation in Aphis fabae

Abstract.  1. The study of phenotypic plasticity in host utilisation is crucial for predicting evolutionary patterns of insect – plant interactions. The presence of sufficient variation in plasticity may facilitate host race formation and sympatric speciation.
2.  Aphis fabae genotypes showed high levels of phenotypic plasticity in the intrinsic rate of natural increase ( r _m), relative growth rate (RGR), birth weight (BW), adult weight (AW), fecundity ( F ), and development time (1/ d ).
3. Thirteen A. fabae genotypes reared both on broad bean and nasturtium exhibited statistically significant genotypic variability in phenotypic plasticity.
4. Some genotypes displayed fitness improvement on novel host plants.
5. Differences in genotypic correlation among fitness components between the two hosts and increased variance on nasturtium indicated different genomic expression on nasturtium.
6. The results indicated that phenotypic plasticity in a novel environment may be a major determinant of the evolutionary trajectory of a parasitic species and might support the idea that speciation starts with phenotypic plasticity.     

Host specificity and seasonal distribution of Alloxysta pleuralis, a cynipoid hyperparasitoid of aphids in India

Abstract. 1. Alloxysta pleuralis (Cameron) is a cynipoid (Hymenoptera) hyperparasitoid of aphids (Homoptera) through their aphidiid (Hymenoptera) parasitoids.
2. It was recorded attacking five aphidiids, Lysiphlebus delhiensis (Subba Rao & Sharma), Trioxys indicus Subba Rao & Sharma, Aphidius uzbekistanicus Luzhetzki, Lipolexis scutellaris Mackauer and Lysiphlebia mirzai Shuja-Uddin (in order of preference) out of eight species of aphidiid parasitoids tested.
3. Percentage of hyperparasitism of aphids infesting cucurbits, cereals and pulses is higher than in solanaceous crops. Maximum hyperparasitism was recorded on the T. indicus/Aphis gossypii Glover/cucurbit complex.
4. The aphid host as well as the food plants significantly influence its efficiency.
5. A.pleuralis is abundant in northeastern Uttar Pradesh in winter (December–March) when large areas of pulses, cereals and cucurbits are infested with aphids serving as hosts for the primary parasitoids.     

Host use evolution in Chrysochus milkweed beetles: evidence from behaviour, population genetics and phylogeny

In two sister species of leaf beetles with overlapping host associations, Chrysochus auratus and C. cobaltinus, we established diet breadth and food preference of local populations for evaluation together with genetic differentiation between populations. While C. auratus turned out to be monophagous on the same plant wherever we collected the beetles, the studied populations of C. cobaltinus fed on three different plant species in the field. Plant preference and ranking of the potential host plants significantly differed between these populations. The amount of genetic differentiation between populations was measured by a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay of a 1300 bp mitochondrial DNA (mtDNA) sequence. In addition, the dominant genotypes of all populations were sequenced. No genetic differentiation between the populations of C. auratus could be detected in the RFLP assay and sequence divergence was low (= 0.3%). In C. cobaltinus, on the other hand, genetic differentiation between populations was high, revealing a lack of gene flow over a much smaller scale and a maximum of 1.3% sequence divergence. C. cobaltinus thereby has the prerequisites for host race formation on different plants from the original host spectrum. Our sequence-based phylogeny estimate allows us to reconstruct historical diet evolution in Chrysochus. Starting from an original association with Asclepiadaceae, the common ancestor of C. auratus and C. cobaltinus included Apocynaceae in its diet. The strict specialization on Apocynum and the loss of acceptance of Asclepiadaceae observed in C. auratus could have resulted from a process similar to that displayed by C. cobaltinus populations.     

Host selection behaviour of the banded pine weevil,Pissodes castaneus (Coleoptera: Curculionidae)

1. Pissodes castaneus represents an emerging pest species for Pinus spp. production in Latin America. This species attacks all the cultivated pine species in Patagonia Argentina causing wood damage and tree death. The objectives of this work were to describe the host preference behaviour of P. castaneus and the influence of wood damage by conspecifics on its host selection.
2. In two-choice bioassays, P. castaneus showed a feeding preference for Pinus contorta over P. ponderosa. However, percent weight gain when feeding on either species was similar.
3. In other bioassays, P. castaneus spent more time in areas with twigs on which other conspecifics had recently fed, although they were able to successfully feed on twigs without previous damage.
4. These results show that while P. castaneus can successfully colonize different pine species, P. contorta may be more susceptible to attack than P. ponderosa. Silvicultural management should be prioritized considering the weevil's preference for attacking damaged hosts.