Interaction among two biological control agents and the developmental stage of their target weed,Dalmatian toadflax,Linaria dalmatica (l.) Mill. (Scrophulariaceae)

An experiment with potted Linaria dalmatica (L.) Mill. was set up to test the effects of root‐feeding by Eteobalea (syn. Stagmatophora) intermediella Riedl (Lep. Cosmopterigidae) and stem‐mining by Mecinus janthinus Germar (Col. Curculionidae), as well as the interaction among the insects and the developmental stage of the host plant. During the summer season, mining by M. janthinus decreased the stem biomass substantially, while E. intermediella did not produce statistically significant effects on the performance of host plant individuals (the experimental conditions represented the effect of the univoltine M. janthinus adequately, but the potentially important effect of mining by the second generation of E. intermediella, at the beginning of the growing season, was not assessed). M. janthinus survived almost exclusively on plants in the flowering stage, although adult females readily used vegetative (younger) plants for oviposition. E. intermediella had a higher chance of survival on vegetative plants. Both species have recently been released as biological control agents on L. dalmatica in North America. For this purpose the complementary survival rates on the two developmental stages of the host plant is advantageous.     

Twenty‐five years after: post‐introduction association of Mecinus janthinus s.l. with invasive host toadflaxes Linaria vulgaris and Linaria dalmatica in North America

Linaria vulgaris, common or yellow toadflax, and Linaria dalmatica, Dalmatian toadflax (Plantaginaceae), are Eurasian perennial forbs invasive throughout temperate North America. These Linaria species have been the targets of classical biological control programmes in Canada and the USA since the 1960s. The first effective toadflax biological control agent, the stem‐mining weevil Mecinus janthinus (Coleoptera: Curculionidae) was introduced from Europe in the 1990s. This weevil has become established on L. dalmatica and L. vulgaris in both countries, although it has shown greater success in controlling the former toadflax species. Genetic and ecological studies of native range M. janthinus populations revealed that weevils previously identified as a single species in fact include two cryptic species, now recognised as M. janthinus, associated with yellow toadflax, and the recently confirmed species Mecinus janthiniformis, associated with Dalmatian toadflax. The results of a comprehensive study characterising haplotype identities, distributions and frequencies within M. janthinus s.l. native range source populations were compared to those populations currently established in the USA and Canada. The presence of both Mecinus species in North America was confirmed, and revealed with a few exceptions a high and consistent level of host fidelity throughout the adopted and native ranges. Genetic analysis based on mitochondrial cytochrome oxidase subunit II gene (mtCOII) defined the origin and records the subsequent North American establishment, by haplotype, of the European founder populations of M. janthinus (northern Switzerland and southern Germany) and M. janthiniformis (southern Macedonia), and provided population genetic indices for the studied populations. This analysis together with existing North American shipment receipt, release and rearing records elucidates probable redistribution routes and sources of both weevil species from initially released and established adopted range populations.     

Biology and host specificity of Aulacobaris fallax (Coleoptera: Curculionidae), a potential biological control agent for dyer’s woad,Isatis tinctoria (Brassicaceae) in North America

Dyer’s woad, Isatis tinctoria, a plant of Eurasian origin is a problematic weed in western North America against which a classical biological weed control programme was initiated in 2004. Three European insect species were selected as candidate agents to control this invasive species, including the root‐mining weevil Aulacobaris fallax. To determine its suitability as an agent, the biology and host specificity of A. fallax were studied in outdoor plots and in the field between 2004 and 2006 in its native European range. Aulacobaris fallax is a univoltine species that lays its eggs from March to August into leaf stalks and roots of dyer’s woad. Larvae mine and pupate in the roots and adults emerge from August to October. Up to 62% of the dyer’s woad plants at the field sites investigated were attacked by this weevil. In no‐choice host‐specificity tests, A. fallax attacked 16 out of 39 species and varieties within the Family Brassicaceae. Twelve of these are native to North America. In subsequent multiple‐choice tests, seven species, all native to North America, suffered a similar level of attack as dyer’s woad, while none of the European species were attacked. Our results demonstrate the importance of including test plant species that have not co‐evolved with the respective candidate agent. In sum, we conclude that the risk of non‐target effects is too high for A. fallax to be considered as a biological control agent for dyer’s woad in the United States.     

Observations on the host specificity and biology of Lixus salsolae (Col., Curculionidae), a potential biological control agent of Russian thistle, Salsola tragus (Chenopodiaceae) in North America

Abstract:  No-choice host specificity tests were performed on Lixus salsolae Becker (Col., Curculionidae) in a quarantine green house near Montpellier, France. Several varieties of seven species of economic and ornamental plants from six genera of Chenopodiaceae were tested. Adult feeding was observed on almost all test plants and larvae successfully developed on nine of the eleven species/varieties tested. Sex ratio of field-collected overwintering adults was close to 1 : 1. While no-choice tests may indicate a wider host range under field conditions, we no longer consider L. salsolae as a potential biological control agent of Salsola tragus L. (Chenopodiaceae) in North America.     

Biology and host specificity ofChamaesphecia hungarica andCh. Astatiformis (Lep.: Sesiidae) two candidates for the biological control of leafy spurge,Euphorbia esula (Euphorbiaceae) in North America

Leafy spurge (Euphorbia esula (s.1.)) is an herbaceous perennial and serious weed of Eurasian origin that has been accidentally introduced into North America. The two European root-boring mothsChamaesphecia hungarica andCh. astatiformis are univoltine and overwinter as mature larvae. Both species have a lower survival rate on leafy spurge than on their field hosts, and thus are not optimal candidates for the biological control of leafy spurge. However, the rate of larval development and larval growth on the target weed and on the two field hosts is nearly the same. The experimental host range of both species is restricted to a few species in the subgenusEsula within the genusEuphorbia. The two species occupy different habitats in the steppe biome and are targeted for similar leafy spurge habitats in North America.     

Biology and host range of the leafminer,Pseudonapomyza sp. (Diptera: Agromyzidae), a potential biological control agent for Tecoma stans (Bignoniaceae) in South Africa

Tecoma stans (Bignoniaceae), is an evergreen shrub that has a wide natural distribution in the tropical and subtropical parts of the western hemisphere. This shrub is native to Mexico and the southern regions of the USA. This weed is widely distributed in South Africa and neighbouring countries. As part of the biological control initiative, a leafmining fly, Pseudonapomyza sp. (Diptera: Agromyzidae), was imported into South Africa, and was subsequently studied as a potential biological control agent for T. stans. During no-choice tests involving 46 plant species in 16 families, Pseudonapomyza sp. only oviposited and developed on T. stans. Neither oviposition nor larval development was recorded on the closely related and indigenous plant species. When six plant species in the Bignoniaceae family were exposed to Pseudonapomyza sp. during multi-choice tests, oviposition and larval development only occurred on T. stans. It was concluded that Pseudonapomyza sp. was sufficiently host-specific to be released against T. stans in South Africa. Pseudonapomyza sp. also displayed very promising biological attributes that could enhance its effectiveness to control T. stans.     

Biology and host range of Mada polluta,a potential biological control agent of Tecoma stans in South Africa

The host range of Mada polluta Mulsant (Coleoptera:Coccinnellidae) was studied to assess its suitability as a biological control agent of Tecoma stans (L.) Juss ex Kunth var stans (Bignoniaceae), an invasive weed in South Africa. Biology of M. polluta and its host range were determined in the laboratory using no-choice and multi-choice feeding, oviposition and larval survival tests. Out of 36 plant species from 12 plant families (Bignoniaceae, Acanthaceae, Asteraceae, Verbenaceae, Lamiaceae, Oleaceae, Cucurbitaceae, Fabaceae, Scrophulariaceae, Solanaceae, Apiaceae, Chenopodiaceae and Poaceae) within the order Lamiales that were tested during the host specificity testing, M. polluta showed a very strong preference for T. stans, depositing its eggs on T. stans and none on non-target plant species. In no-choice tests, an average of 246 eggs was laid on T. stans, and from these, 133 larvae developed to adulthood. The beetle also showed very promising biological attributes that will contribute to its success as a biological control agent of T. stans. These attributes include highly damaging larvae and adults, high fecundity (532 eggs/female) and a short life cycle (four weeks). The short life cycle will enable multiple generations per year and rapid population increase in the field. It is concluded that M. polluta is sufficiently host-specific to be released against T. stans in South Africa. It is, therefore, strongly recommended that permission be granted to release this beetle from quarantine for biological control of T. stans in South Africa.     

Biology and host specificity ofWeiseana barkeri (Col.: Chrysomelidae): A biological control agent forAcacia nilotica (mimosaceae)

The leaf-feeding beetleWeiseana barkeri Jacoby feeds onAcacia nilotica (L.) Willdenow ex Delile in Kenya. Host specificity tests show it is host specific toA. nilotica and approval has been given for its field release in northwest Queensland. A novel rearing and host specificity-testing technique is reported whereA. nilotica foliage stimulates oviposition into strips of corrugated cardboard.     

Host range of the European,rhizome-stem feeding scale Rhizaspidiotus donacis (Hemiptera: Diaspididae), a candidate biological control agent for giant reed,Arundo donax (Poales: Poaceae) in North America

The armored scale Rhizaspidiotus donacis (Leornardi) was evaluated as a potential biological control agent of the invasive reed grass Arundo donax in North America. No-choice tests, native range field surveys and non-target host exposures were used to determine the fundamental host range of the scale collected from Caloma, Spain and Perpignan, France. Thirty-five species, including two genotypes of A. donax and seven ecotypes of Phragmites australis, along with closely related grasses, economic grasses and habitat associates were tested. In quarantine no-choice testing using releases of 200 crawlers per plant, normal development of R. donacis was observed on A. donax and A. formosana, with very limited survival to the adult stage on Spartina alterniflora and Leptochloa spp. In follow-up studies using 1000 crawlers per plant, 10 live adult females were found on Leptochloa virgata, and one adult female on Spartina alterniflora, but average adult female abundance per plant was (2580%) 26-times lower on L. virgata and over (39,090%) 100-times lower on S. alterniflora than on A. donax. Field surveys were conducted at five locations in Spain and France at which A. donax infested with R. donacis, co-occurred with two non-target species of concern and R. donacis was only found on A. donax. Six-month field host exposures in Spain using potted Leptochloa plants entwined with heavily infested A. donax confirmed that R. donacis is specific to Arundo under field conditions. Based on our results, the scale R. donacis appears to be specific to the genus Arundo and is unlikely to harm native or cultivated plants in the Americas.     

Distribution, biology and host range of Rhembastus sp. (Coleoptera: Chrysomelidae), a candidate for the biological control of Bryophyllum delagoense (Crassulaceae) in Australia

The biology and host range of a leaf-beetle, Rhembastus sp. (Coleoptera: Chrysomelidae: Eumolpinae) from Madagascar, was studied under quarantine laboratory conditions in South Africa to determine its potential as a biological control agent of Bryophyllum delagoense (Ecklon & Zeyher) Schinz (Crassulaceae) in Australia. Favourable attributes of the beetle include relative ease of culturing, multiple generations per year, and high levels of damage inflicted by adults, which feed on the plantlets produced at the end of each leaf, and root feeding larvae. The adults therefore have an impact on the reproductive potential of the plant and larval feeding on the roots hampers the uptake of water and may even facilitate secondary infections by pathogens. Despite indications from field surveys in Madagascar that Rhembastus sp. has a narrow host range, preliminary no-choice and multiple-choice trials in quarantine revealed that it could complete its development on five non-target species in the family Crassulaceae. Extensive host range trials still have to be undertaken in Australia before the beetle can be considered for release.     

The biology and host specificity of the onion weed rust, Puccinia barbeyi, a potentially useful agent for biological control in Australia

Onion weed, Asphodelus fistulosus L., (Liliaceae) a weed of Mediterranean and Middle Eastern origin is widespread in southern Australia where it invades pastures making them unsuitable for grazing. A program of research is underway to discover natural enemies of this plant and to study their possible role in the biological control of onion weed. A rust fungus Puccinia barbeyi (Roum.) Magnus has been found to severely attack A. fistulosus . Observations on the biology of the rust confirmed that it is monoecious and microcyclic and multiplied essentially by aecial and telial stages, although occasionally urediniospores also appeared among teliospores. Several members of the Liliaceae exposed to the aeciospores of the rust remained unattacked indicating that it is most probably specific to Asphodelus spp. and thus its potential for the biological control of A. fistulosus in Australia should be studied further.     

Temperature and host-plant effects on development and population growth of Mecinus janthinus (Coleoptera: Curculionidae), a biological control agent for invasive Linaria spp.

Mecinus janthinus Germar is a European stem-mining weevil that has been established in North America as a biological control agent against the invasive European weeds Linaria vulgaris P. Mill. and Linaria dalmatica (L.) P. Mill. (Scrophulariaceae). Establishment success and impact of the weevil have varied widely among sites. We investigated the hypothesis that some of this variation may be due to a lack of sufficient time for M. janthinus to develop to the adult (overwintering) stage in less favorable climates. Development time of M. janthinus was measured in L. vulgaris and L. dalmatica at four constant temperatures, and logistic regression was used to derive a model for the effect of temperature on development. Development rates were simulated using historic climate data for a site in central Alberta (where establishment was marginal on L. vulgaris) and one in southern British Columbia (where outbreaks occurred, resulting in heavy damage to L. dalmatica). The model showed that, on average, the British Columbia site had 50 more days available for the weevil to lay eggs that could reach the adult stage in time for overwintering than did the Alberta site. This may explain the more rapid population buildup at the British Columbia site. This model could be used to predict the climatic suitability of other areas for establishment of M. janthinus. An unexplained result was the very low survival rate of eggs laid in L. dalmatica under the same experimental conditions.     

Biology, host specificity and risk assessment of the leaf-mining flea beetle, Acallepitrix sp. nov., a candidate agent for the biological control of the invasive tree Solanum mauritianum in South Africa

The South American tree Solanum mauritianum, a major environmentalweed in the high-rainfall regions of SouthAfrica, has proved to be a difficult target forbiological control. Artificially expanded hostranges of candidate agents during quarantinehost-specificity tests, have resulted in therelease of only one agent species which has sofar had a negligible impact on the weed. Thenecessity for additional agents resulted in theimportation of a leaf-mining flea beetle, anunidentified species of Acallepitrix,from Brazil in 1997. No-choice tests inquarantine showed that potential host plantsare confined to the genus Solanum.Although several non-target plants, includingcultivated eggplant (aubergine) and some nativeSouth African Solanum species, sustainedfeeding, oviposition and the development oflarval leaf mines, most of these were inferiorhosts. These results were confirmed by pairedchoice tests, where Acallepitrix sp. nov.displayed significant feeding and ovipositionpreferences for S. mauritianum and where,with few exceptions, more larval leaf mineswere initiated on S. mauritianum.Interpretation of the host-specificity testswas facilitated by a risk assessment matrixwhich suggested that the risk of feeding andoviposition on non-target Solanum plants,including eggplant cultivations, was relativelylow. These and other considerations, such asthe lack of evidence of damage inflicted oncultivated Solanaceae in South America, suggestthat Acallepitrix sp. nov. could beconsidered for release against S. mauritianum in South Africa. However, the results of the host-specificity tests remain ambiguous and until more compelling evidence is obtained from field surveys and open-field trials in Brazil, an application for permission to release the flea beetle in South Africa will not be considered.     

Biology, life table and host specificity of the mushroom pest, Brennandania lambi (Acari: Pygmephoroidea)

Biology and life table parameters of Brennandania lambi (Krczal) were studied at different temperatures while feeding on white mushroom (Agaricus bisporus) mycelium cultured on mushroom compost. The duration of egg and larva development, preoviposition and oviposition period, female longevity, and the time to 50% mortality declined as temperature increased from 16 to 28°C. The threshold temperature of development (female) was 9°C and the thermal constant for completion of development (female) was 195 day-degrees. At 16, 20, 24 and 28°C, the total fecundity (eggs/female) was 71, 67, 66 and 57, respectively and the daily fecundity rate (eggs/female/day) was 5.6, 8.7, 8.7 and 9.1, respectively. The sex ratio (female/male) ranged from 1.9 to 2.1 at 16–28°C. At 16, 20, 24 and 28°C, the intrinsic rate of natural increase (r _m) was 0.11, 0.18, 0.22 and 0.27, respectively, and the population doubling time was 6.1, 3.9, 3.2 and 2.5 days, respectively. All life stages of the mite died when exposed to 35°C constant temperature for 24h, or to 32°C constant temperature for 12 days or to 31–35°C (average 32.9°C) ambient temperature for 4 days. Brennandania lambi completed development only when fed on Ag. bisporus mycelium growing on mushroom compost. It could not survive on mushroom mycelia of Auricularia auricula, Au. polytricha, Ganoderma lucidum, Hericium erinaceus, Lentinus edodes, Pleurotus ostreatus, P. sajor-caju and Tremella fuciformis.     

Biology and host specificity of Spurgia capitigena (Bremi) (Dipt., Cecidomyiidae), for the biological control of Euphorbia esula L. in North America

Abstract: Spurgia capitigena (Bremi) was evaluated as a potential biological control agent of leafy spurge, Euphorbia esula L. (species complex) in North America. To ascertain the host specificity of this gall midge, tests were conducted in the field at Cavaillon, France, and at laboratories located in Rome, Italy and Bozeman, Montana, USA, in 1994 and 1995. Twenty-nine plant species, including eight native North American euphorbias and biotypes of E . esula , were evaluated. In the laboratory, the gall-midge was able to induce galls on seven species of spurges (all belonging to the subgenus Esula) and the three accessions of leafy spurge. In field tests, S . capitigena infested only E . esula . The biology and host specificity of S . capitigena from France appears to be similar to that observed for Spurgia esulae Gagné from Italy (= Bayeria capitigena Bremi). In France, this gall-midge was commonly observed from early May until October in habitats of very heavy and moist soils located along water channels, roadsides and in fruit orchards. Galls were induced on meristematic tissues, and thereby prevented flowering.     

Preliminary host specificity testing of Endophyllum osteospermi (Uredinales, Pucciniaceae), a biological control agent against Chrysanthemoides monilifera ssp. monilifera

Chrysanthemoides monilifera ssp. monilifera, indigenous to the Western Cape Province of South Africa, is a serious invader of native vegetation in south-eastern Australia. The rust fungus Endophyllum osteospermi causes witches' brooms on C. monilifera ssp. monilifera in South Africa, and is associated with a reduction in growth and seed production of its host under natural conditions, as well as mortality of severely infected bushes. This rust fungus is considered to be a potential biological control agent for use against C. monilifera ssp. monilifera in Australia. Endophyllum osteospermi has a long latent period, typically between 6 and 24 months between infection and the initiation of witches' brooms. This long latent period makes the logistics of doing traditional host specificity testing, in which all test plant species are inoculated and observed for symptom development, unfeasible for this rust fungus. Germination of aecidioid teliospores and penetration by basidiospores were observed on the surface of excised leaves of 32 test plant species at 4 days after inoculation, and compared to that on C. monilifera ssp. monilifera. Germinating aecidioid teliospores aborted on 14 test plant species, whilst no penetration was attempted on a further 12 test plant species. Penetration only occurred on nine of the 32 test plant species, in addition to C. monilifera ssp. monilifera. Inoculating whole plants of nine selected test plant species confirmed the above results. Therefore, only the test plant species in which penetration occurred, or at least was attempted, need to undergo comprehensive host specificity testing. Pending these results, E. osteospermi may be suitable for release in Australia for the biological control of C. monilifera ssp. monilifera.     

Biology of Polypedilum n. sp. (Diptera: Chironomidae), a promising candidate agent for the biological control of the aquatic weed Lagarosiphon major (Hydrocharitaceae) in Ireland

Lagarosiphon major (Ridl.) Moss ex Wager (Hydrocharitaceae), an aquatic macrophyte native to Southern Africa that has become invasive in several countries worldwide, is a potential target for biological control. Biology studies were conducted on Polypedilum (Pentapedilum) n. sp. near reei Oyewo & Sæther (Diptera: Chironomidae), a midge whose larvae were discovered mining the plant's shoot tips in its native range. Field surveys indicated that the midge occurred only at a small number of sites but attained high densities (up to 370 shoots damaged/m²) that prevented further growth from the shoot tips. A population of the midge was imported into quarantine in Ireland to evaluate its potential as a candidate biological control agent. The adult stage is terrestrial and short-lived (4–5 d), with females depositing one–two egg packets into the water bodies. First-instar larvae fed externally on the stems and leaflets. Later instars fed on the apical meristems and burrowed into the shoot tips, with resultant damage stunting the apical growth. Larvae moved readily between shoots to complete their development and pupated within the tunnels excavated by the late instar larvae. Developmental time to adulthood ranged from 31 to 49 days at 20.7°C and a 15 L:9-D cycle. This is the first time that a chironomid has been imported and successfully cultured for consideration as a classical biological control agent. Several aspects of the midge's biology suggest that host specificity testing is warranted to determine its potential as a biocontrol agent of L. major.     

Biology, host specificity and risk assessment ofGargaphia decoris, the first agent to bereleased in South Africa for the biological control ofthe invasive tree Solanum mauritianum

The South American tree Solanummauritianum is a major environmental weed in thehigh-rainfall regions of South Africa and has beentargeted for biological control since 1984. Althoughhost ranges of imported agents determined duringquarantine tests have resulted in the rejection ofeight of the 11 candidate agents tested so far, theleaf-sucking lace bug Gargaphia decoris,imported from Argentina in 1995, displayed anacceptably narrow host range in captivity. No-choicetests showed that G. decoris is confined to Solanum species and cannot survive on solanaceouscrops outside that genus. Although these tests alsoindicated that G. decoris colonies could surviveand reproduce on cultivated eggplant (aubergine) andat least five native South African Solanumspecies, all but one native species proved to beinferior hosts in terms of adult survival andoviposition potential. During paired choice andmultichoice tests in small and larger cagesrespectively, G. decoris displayed very strongfeeding and oviposition preferences for S. mauritianum. Analyses of the risk of attack onnon-target Solanum plants revealed that, withone possible exception, none were likely to suffermore than incidental damage in the field. Host recordsfrom South America have also indicated that G. decoris has not been recorded on any Solanumspecies other than S. mauritianum, providingfurther evidence of its host specificity. The resultsof this study were accepted by the regulatoryauthorities and in February 1999, G. decorisbecame the first agent to be released in South Africafor the biological control of S. mauritianum.     

Host specificity testing,release and establishment of Urophora solstitialis (L.) (Diptera: Tephritidae), a potential biological control agent for Carduus nutans L., in Australia

The seed‐fly Urophora solstitialis was imported into Australia from southern France. Previous workers had shown that this seed‐fly limited its attack to selected members of the genus Carduus. Host specificity studies revealed that no native Australian plant tested from the family Asteraceae was a suitable host plant. Permission to release the fly was granted, and it was released in three regions of the New South Wales tablelands. The fly underwent a second generation at two of the release sites, and reasons for its failure to do so at the third are suggested. It has successfully established itself in all three regions, having completed a full seasonal cycle in the field.     

Biology, herbivory, and host specificity of Antiblemma leucocyma (Lepidoptera: Noctuidae) on Miconia calvescens DC. (Melastomataceae) in Brazil

Miconia calvescens DC. (Melastomataceae) is an invasive tree considered one of the greatest threats to natural ecosystems of Hawaii and other Pacific islands. The potential for using the defoliator Antiblemma leucocyma (Lepidoptera: Noctuidae) as a biological control agent of M. calvescens was evaluated in the native habitat of the insect in Brazil. Impact assessment in the field showed that 37.2% of leaves presented damage by A. leucocyma, and among damaged leaves, 1.5-51.9% of the leaf area (16.3% on average) was affected. Damage was found in young to fully expanded leaves (28-915 cm² in area). Individual A. leucocyma developing as third through sixth instars in the laboratory consumed an average of 1348 cm² of M. calvescens leaf material in about 11 days. Populations of A. leucocyma in the field were heavily impacted (up to 83% parasitism) by a braconid parasitoid. Observations in the field and single- and two-host choice tests in the laboratory indicated that A. leucocyma has a narrow host range restricted to M. calvescens. Usefulness of this herbivore for biological control in Hawaii appears low, however, because of its probable susceptibility to generalist parasitoids.