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.     

Should the flower bud weevil Anthonomus santacruzi (Coleoptera: Curculionidae) be considered for release against the invasive tree Solanum mauritianum (Solanaceae) in New Zealand?

The invasive tree Solanum mauritianum Scop. has been targeted for biological control in South Africa and New Zealand, by deploying insect agents that could constrain its excessive reproductive output. The flower-feeding weevil Anthonomus santacruzi (Curculionidae) was approved for release in South Africa in 2007 but following the loss of the original culture in quarantine, new stocks were introduced from Argentina in 2008–2009. This study was initiated to confirm that the host range of the new culture was the same as that of the previous one, but also to assess the risks associated with the weevil's release in New Zealand. Different testing procedures, including no-choice tests and multi-choice tests in different arenas, produced inconsistent and ambiguous results. During no-choice tests, oviposition and larval development to adulthood occurred on three non-target species including two native South African and one native New Zealand Solanum species. However, subsequent multi-choice tests and a risk assessment suggested that the risks of anything more than collateral damage to non-target Solanum species are low. Overall, these data do not deviate substantially from the results of the original quarantine tests which facilitated the release of A. santacruzi in South Africa in 2009. Although we argue that none of the New Zealand native and cultivated species are at risk, stronger evidence from open-field trials and chemical ecology studies may be required to convince the regulatory authorities that A. santacruzi is suitable for release in New Zealand.     

Climate constrains the establishment and proliferation of Anthonomus santacruzi,a flower-feeding biological control agent of the invasive weed Solanum mauritianum in South Africa

The flowerbud-feeding weevil Anthonomus santacruzi Hustache (Coleoptera: Curculionidae) was released in South Africa in 2008 for the biological control of the invasive tree Solanum mauritianum Scopoli (Solanaceae). The weevil was widely deployed throughout KwaZulu-Natal province, which supports large S. mauritianum infestations, and has become well established in its warmer coastal regions. The aim of this study was to provide field evidence that climate is constraining the weevil’s distribution in South Africa. Solanum mauritianum populations were sampled at 23 sites across an altitudinal gradient in KwaZulu-Natal to determine A. santacruzi densities in relation to food availability and climatic variables. Despite significantly higher amounts of floral material on S. mauritianum at the higher altitude inland sites, A. santacruzi numbers were significantly higher at the lower altitude coastal sites. There was thus a significant negative relationship between A. santacruzi numbers and altitude and significant positive relationships between A. santacruzi numbers and both temperature and humidity. Neither rainfall nor food availability influenced A. santacruzi numbers, although lower amounts of floral material at the coastal sites may well have been caused by higher weevil densities at these sites. Anthonomus santacruzi was absent at only three sites, all at higher altitudes, further demonstrating that conditions in coastal or low-altitude regions are favourable for establishment and population proliferation. Future release efforts in KwaZulu-Natal, but also in other South African provinces, should thus be focused on coastal regions and inland regions that are below 1000 m above sea level.     

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.     

Assessing the risks of releasing a sap-sucking lace bug, <Emphasis Type="Italic">Gargaphia decoris</Emphasis>, against the invasive tree <Emphasis Type="Italic">Solanum mauritianum</Emphasis> in New Zealand

The South American tree Solanum mauritianum Scopoli (Solanaceae), a major environmental weed in South Africa and New Zealand, has been targeted for biological control, with releases of agents restricted to South Africa. The leaf-sucking lace bug, Gargaphia decoris Drake (Tingidae), so far the only agent released, has become established in South Africa with recent reports of severe damage at a few field sites. To evaluate the insect’s suitability for release in New Zealand, host-specificity testing was carried out in South Africa in laboratory and open-field trials, with selected cultivated and native species of Solanum from New Zealand. No-choice tests confirmed the results of earlier trials that none of the three native New Zealand Solanum species are acceptable as hosts. Although the cultivated Solanum muricatum Aiton and S. quitoense Lam. also proved unacceptable as hosts, some cultivars of S. melongena L. (eggplant) supported feeding, development and oviposition in the no-choice tests. Although eggplant was routinely accepted under laboratory no-choice conditions in this and previous studies, observations in the native and introduced range of G. decoris, open-field trials and risk assessment based on multiple measures of insect performance indicate that the insect has a host range restricted to S. mauritianum. These results strongly support the proposed release of G. decoris in New Zealand because risks to non-target native and cultivated Solanum species appear to be negligible. An application for permission to release G. decoris in New Zealand will be submitted to the regulatory authority. Handling editor: John Scott.     

Persistence of the flowerbud weevil Anthonomus santacruzi in optimal versus marginal areas: implications for the biological control of the invasive tree Solanum mauritianum in South Africa

Anthonomus santacruzi Hustache (Coleoptera: Curculionidae) was released in South Africa to offset the extensive reproductive output of the invasive tree Solanum mauritianum Scopoli (Solanaceae). Widespread establishment has occurred predominantly in the coastal areas of KwaZulu-Natal province, with limited success in higher-altitude inland areas. Irrespective of location, populations exhibit peaks in the austral autumn and decline during winter. In this study, we evaluated the persistence of A. santacruzi populations in climatically-optimal coastal areas versus climatically-marginal inland areas. The weevil’s pre- and post-winter abundance was surveyed at six coastal and six inland sites during 2018, and compared between areas and seasons. The 2018 pre-winter data were also compared to 2016 pre-winter data collected at the same sites. During 2018, pre- and post-winter numbers were six times and 22 times higher, respectively, at optimal sites than at marginal sites, with substantial winter declines at all sites. Post-winter weevil numbers at optimal sites were significantly higher than pre-winter numbers at marginal sites. Pre-winter numbers at optimal sites were not significantly different between 2016 and 2018, but at marginal sites were significantly lower in 2018. Inflorescences of S. mauritianum at marginal sites contained significantly more floral material and fruit than those at optimal sites, during both seasons in 2018. Significant negative correlations between A. santacruzi numbers and floral/fruit production suggest some impact on the reproductive output of S. mauritianum. Since A. santacruzi populations are barely persisting in marginal areas, releases in other South African provinces should target locations that are below 300?m in altitude.     

Inflorescence-inhabiting spiders do not threaten the survival and fecundity of Anthonomus santacruzi (Curculionidae), a florivorous biocontrol agent of Solanum mauritianum (Solanaceae) in South Africa

The florivorous weevil Anthonomus santacruzi is being released in South Africa to reduce the reproductive capacity of the invasive tree, Solanum mauritianum. Initiated to allay concerns about biotic interference, our study suggests that inflorescence-inhabiting spiders pose no risk to the survival and proliferation of A. santacruzi populations in the field.     

Biology and host range of Platyphora semiviridis, a leaf beetle evaluated as a potential biological control agent for Solanum mauritianum in South Africa

The South American tree Solanum mauritianum is a major environmental weed in the high-rainfall regions of South Africa and has been targeted for biological control. Potential agents included five species of the genus Platyphora, which were imported from South America in 1994. Platyphora species associated with Solanaceae reputedly have very specific habitat requirements and host plant preferences in the field. Despite this, host-specificity tests on one species, Platyphora semiviridis, revealed a broad physiological host range. Although laboratory tests showed that P. semiviridis is confined to Solanum species and cannot survive on solanaceous crops outside that genus, it developed on potato and cultivated eggplant (aubergine) as well as on 10 native South African Solanum species. With few exceptions, there were no consistent differences in survival and duration of development on these compared with S. mauritianum. Furthermore, at least six of these non-target species, including potato and eggplant, supported breeding colonies of the beetles in cages. During choice tests in both small and larger cages, P. semiviridis avoided potato but did not consistently discriminate between S. mauritianum, eggplant and six native solanums for larviposition. Despite these findings, P. semiviridis has never been recorded on either potato or eggplant in South America, where it was only observed to feed on S. mauritianum. Although there are several reasons why P. semiviridis is unlikely to attack non-target Solanum species in the field, it will not be released in South Africa because there are other imported agents which have displayed narrower physiological host ranges and which may be more effective.     

A review of <Emphasis Type="Italic">Solanum mauritianum</Emphasis> biocontrol: prospects,promise and problems: a way forward for South Africa and globally

The invasive tree Solanum mauritianum Scopoli remains one of the world’s most widespread environmental weeds. Despite biocontrol providing one of the few viable long-term solutions to tackling S. mauritianum invasions globally, only South Africa and, more recently, New Zealand, have programmes in place. Ongoing biocontrol efforts against S. mauritianum are reviewed here with particular reference to South Africa. The South African programme has suffered a troubled history, with considerable research efforts culminating in the eventual release and establishment of only two insect agents, Gargaphia decoris Drake and Anthonomus santacruzi Hustache. The difficulties experienced have hindered research into new agents, causing apprehension in using biocontrol internationally. However, recent studies have demonstrated that biocontrol may be deserving of renewed investment, particularly within an integrated management context. In this review, we advocate for the revival of the S. mauritianum biocontrol programme in South Africa, and discuss possible avenues for future research internationally.     

Candidates for biocontrol of Macfadyena unguis-cati in South Africa: biology, host ranges and potential impact of Carvalhotingis visenda and Carvalhotingis hollandi under quarantine conditions

Macfadyena unguis-cati (L.) Gentry (Bignoniaceae) was introduced as an ornamental in South Africa, but is fast becoming an important invasive plant in many areas. It is difficult to control the plant chemically and mechanically. The first biocontrol agent, the chrysomelid Charidotis auroguttata (Boheman), has been released. It established at some release sites, but numbers have so far remained low. Additional biocontrol agents were sought to augment C. auroguttata. The potential host ranges of two foliage feeding lace bugs, Carvalhotingis visenda (Drake and Hambleton) and C. hollandi (Drake) (Hemiptera: Tingidae) were evaluated on the basis of nymphal no-choice and adult multi-choice tests involving 23 plant species in 11 families. In no-choice tests, nymphs of both species were able to survive and complete development on M. unguis-cati only, and adults of both species only fed and oviposited on M. unguis-cati during the adult multi-choice tests. Host specificity tests thus confirm that the tingids are highly host specific biocontrol agents, and will not pose risk to any non-target plants in South Africa. A study to determine the potential impact of C. hollandi nymphal feeding on M. unguis-cati showed a significant decrease in the chlorophyll contents of leaves when compared to those of control plants. These studies indicate that, once released, the two lace bug species could contribute significantly to the biological control of M. unguis-cati in South Africa.     

Glandular trichomes ofSolanum berthaultii alter host preference of the Colorado potato Beetle,Leptinotarsa decemlineata

Choice and no-choice studies were conducted to determine how the glandular trichomes of the wild potato,Solanum berthaultii Hawkes, affect host preference of the Colorado potato beetle,Leptinotarsa decemlineata (Say). Given a feeding choice betweenS. tuberosum andS. berthaultii, larvae and adults preferred the foliage ofS. tuberosum, but adults were more discriminating. When foliage ofS. berthaultii was appressed toS. tuberosum leaflets, fewer adults fed on the appressed leaflets. When given a choice between ‘trichome-intact’ and ‘trichome-removed’S. berthaultii foliage, adults preferred to feed on the latter. The preference for ‘trichome-removed’ foliage and the percent of adults initiating feeding, increased with the degree of trichome removal. These studies provide evidence that the resistance ofS. berthaultii is associated with feeding deterrents localized in the glandular trichomes, thatS. berthaultii possesses more than one mechanism of resistance to the Colorado potato beetle, and that the expression of resistance is dependent on the developmental stage of the insect.     

Behavioural responses of the vine weevil, Otiorhynchus sulcatus, to semiochemicals from conspecifics, Otiorhynchus salicicola, and host plants

The vine weevil Otiorhynchus sulcatus is a parthenogenetic reproducing species which forages for suitable host plants at night, but is found congregated in dark places during the day. Frass of this weevil species is suspected to contain attractive compounds that are host‐plant related. Using a still‐air olfactometer, we tested adult vine weevils at night for their behavioural response to odours from conspecifics, feeding on a mixture of spindle tree (Euonymus fortunei) and yew (Taxus baccata), and to a sexually reproducing related species (Otiorhynchus salicicola), feeding on a mixture of ivy (Hedera helix) and cherry laurel (Prunus laurocerasus). Their attraction to conspecifics and O. salicicola appeared to be related to frass production. Freshly collected frass from O. sulcatus and from O. salicicola males and females was attractive. Prunus laurocerasus and H. helix have not been observed to be hosts of the vine weevil in the field. However, our tests showed that the vine weevil was attracted to mechanically damaged leaves of both plant species, whereas undamaged leaves were not attractive. Only undamaged young unfolding leaves of H. helix were also attractive. The attraction to odours from mechanically damaged host and non‐host plants suggested the involvement of compounds that are commonly found in many plant species. The involvement of plant compounds and/or aggregation pheromones in attraction to frass of the vine weevil and frass of the related weevil species O. salicicola is discussed.     

Behavioural responses of the Colorado potato beetle to trichomes and leaf surface chemicals of Solanum tarijense

Wild Solanum species constitute a source of resistance to several pests and diseases of potato. Several species of wild tuber‐bearing potato have been identified as resistant to the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), including Solanum tarijense Hawkes (Solanaceae). Our objective was to determine the mechanism of resistance of S. tarijense to the Colorado potato beetle and, because the resistance is limited to the adult stage of the insect, to study the host selection behaviour on resistant plants. In the field, Colorado potato beetles demonstrated a unique behaviour when in contact with S. tarijense, abandoning the plant by falling to the ground after a few minutes. The abundant trichomes on the leaves of S. tarijense induced the falling behaviour. However, on S. tarijense feeding remained low even after the trichomes were mechanically removed. Observations demonstrated that the normal sequence of behaviour leading to feeding was interrupted before adult beetles fed on S. tarijense leaves. Feeding experiments using volatile and non‐volatile fractions of leaf surface extracts identified a phagodeterrent effect of the volatile fraction. Our results contrast with a similar evaluation of the mode of resistance of Solanum berthaultii Hawkes, a close relative of S. tarijense, on which some feeding occurred and adults did not show falling behaviour. This study presents information on S. tarijense as a new source of resistance to the Colorado potato beetle that can be used for potato breeding.     

Host Specificity of the Argentine Root-Boring Weevil, Heilipodus ventralis (Coleoptera: Curculionidae), a Potential Biocontrol Agent for Snakeweeds (Gutierrezia: Asteraceae) in Western North American Rangelands—U.S. Quarantine Tests

Native snakeweeds, especially Gutierrezia sarothrae (Pursh) Britton and Rusby and Gutierrezia microcephala (DC.) A. Gray, are among the most widespread and damaging weeds of rangelands in the western United States and northern Mexico. The genus long ago spread to southern South America, where further speciation occurred. We have found several species of insects in Argentina that damage other species of snakeweeds there and are possible candidates for biological control in North America. The first of these, the root-boring weevil, Heilipodus ventralis (Hustache), was tested in Argentina and then sent to the USDA-ARS Insect Quarantine Facility at Temple, Texas, for host specificity testing on North American plants. We tested H. ventralis on 40 species of the family Asteraceae, in 19 tests of five types, using 686 adults and 365 larvae. Host specificity increased from adult feeding, to ovipositional selection, to larval development. At Temple, adults fed mostly on 6 species of the closely related genera Grindelia, Gutierrezia, and Gymnosperma, but with substantial feeding on four other genera of the two preferred subtribes Solidagininae and Machaerantherinae and on Baccharis in the tribe Baccharidinae, with lesser feeding on the subtribe Asterinae, all in the tribe Astereae, and on 1 species in the tribe Anthemideae. Females oviposited primarily on the same 6 species but very little on plants outside the 2 preferred subtribes. Larvae developed only on 9 of the 29 U.S. plant species tested, 6 within the two preferred subtribes and on Brickellia and Aster in other tribes. Only 5 species of three genera appear to be potential true hosts of H. ventralis in North America, on which all stages of the life cycle, adult feeding, oviposition, and larval development, can take place; these are Gymnosperma glutinosum (Spreng.) Less., Gutierrezia grandis Blake, Gut. microcephala, Gut. sarothrae, and Grindelia lanceolata Nutt. None of these genera contain species of economic or notable ecological value; the few rare species appear to be protected by habitat isolation from attack by H. ventralis. H. ventralis, therefore, appears sufficiently host specific for field release in North America. This is the first introduced biocontrol agent to be approved for release in a continental area to control a native weed.     

Eustenopus villosus (Coleoptera: Curculionidae) Feeding of Herbicide-Resistant Yellow Starthistle (Centaurea solstitialis L.)

A population of yellow starthistle (Centaurea solstitialis L.) near Dayton, Washington developed herbicide resistance in response to repeated applications of picloram and other auxin-type herbicides. Laboratory and field experiments were conducted in 1998 to determine host acceptability and suitability of this herbicide-resistant yellow starthistle population to the biological control weevil Eustenopus villosus (Boheman) (Coleoptera: Curculionidae). In choice and no-choice feeding and oviposition experiments using excised buds, the weevil did not demonstrate a consistent preference for either herbicide-resistant (R) or -susceptible (S) yellow starthistle. When caged on buds of intact plants, the E. villosus feeding rate of 97% did not differ between R and S types. Host plant suitability, measured as larval damage and development to adult weevils, was equivalent in R and S types, with weevils maturing in 46% of the R and in 32% of the S capitula bearing oviposition scars. The number of viable achenes per capitulum was reduced by 87% due to larval feeding, with no difference between R and S types. Observations at the field site where resistance was found revealed oviposition scars on 78% of the late-bud-stage capitula on 23 June 1998 and 73% of the flowering and postflowering capitula on 15 August 1998. Selection for herbicide resistance has not created host incompatibility for E. villosus nor reduced the effectiveness of E. villosus as a biological control agent.     

Resistance of three wild tuber-bearing potatoes to the Colorado potato beetle

The resistance of Solanum okadae Hawkes & Hjert. (PI 458367), Solanum oplocense Hawkes (PI 473368), and Solanum tarijense Hawkes (PI 414150) to the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Chrysomelidae: Chrysomelini), was studied. In replicated field trials all three accessions showed a high level of resistance to the beetle. No significant genetic variability between genotypes of the same species was found. Results from host acceptance behavior experiments, suitability for larval development tests, foliage consumption tests, and adult survival and oviposition tests supported the hypothesis that the mode of resistance differs between the three wild Solanum species. Solanum okadae and S. oplocense affected host acceptance and consumption. Because the beetle reacted differently to these two species it was hypothesized that the antifeedant chemical(s) differed in nature or quantity. S. tarijense contrasted with the other two species by affecting mostly adult colonization and oviposition.     

Role of larval host plant experience and solanaceous plant volatile emissions in Tuta absoluta (Lepidoptera: Gelechiidae) host finding behavior

The tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae), is considered to be a major pest that damages tomato (Solanum lycopersicum L; Solanaceae) crops in South American, European, and Mediterranean countries. This insect species is polyphagous (i.e., feeds on many types of food); hence, it could also develop on other cultivated host plants, principally solanaceous plants, such as potato (S. tuberosum L.; Solanaceae) and eggplant (S. melongena L.; Solanaceae). Therefore, we tested the hypothesis that host plant choice by adult T. absoluta is influenced by plant volatile organic compounds and larval host plant experience. One tomato cultivar (cv.) ‘Moneymaker’ and three potato cv. ‘Charlotte’ ‘Bintje,’ and ‘Nicola’ were tested. Using a flying tunnel, we observed that females reared on tomato preferred flying toward tomato and, to a lesser extent, potato cv. ‘Charlotte.’ These preferences might be explained by the high release of terpenes by these two plants. When conducting oviposition choice assays, we found no preference between tomato and potato in the number of eggs laid by females that had been previously reared on either host plant. This study indicates that the host finding behavior of T. absoluta is mediated by solanaceous volatiles, while oviposition behavior appears to depend on additional stimuli. These results provide baseline information for use in the development of new control strategies against T. absoluta using semiochemicals and plant breeding.     

Host specificity of Metriona elatior, a potential biological control agent of tropical soda apple, Solanum viarum, in the USA

The leaf beetle Metriona elatior from Brazil-Argentina was screened in the Florida (USA)State quarantine facility as a potential biological control agent of tropical soda apple, Solanum viarum, a recently arrived weed species. Multiple-choice host-specificity tests were conducted in small cages (60 cm × 60 cm × 60 cm) using 95 plant species in 29 families. Adults fed heavily on the main target weed (S. viarum), and on turkey berry,Solanum torvum (noxious weed of Asiatic origin); fed moderately on red soda apple, Solanum capsicoides (weed of South American origin), and eggplant, Solanum melongena (economic crop); and fed lightly on aquatic soda apple, Solanum tampicense (weed of Mexican-Caribbean-Central American origin), and onsilverleaf nightshade, Solanum elaeagnifolium(native weed widely distributed). M.elatior adults laid 84 to 97% of their egg masses onS. viarum, and 3 to 16% on S. melongena. Non-choice host-specificity tests were also conducted in quarantine in which M. elatior adults and neonate larvae were exposed to 17 and 19 plant species, respectively. Tests with the neonates indicate that this insect was able to complete its development on S. viarum, S. torvum, S. melongena, and S. capsicoides. Although some adult feeding and oviposition occurred on S.melongena in quarantine on potted plants in small cages, no feeding or oviposition by M. elatiorwas observed in field experiments conducted in Brazil. Surveys in unsprayed S. melongena fields in Argentina and Brazil indicated that M. elatioris not a pest of S. melongena in South America. The evidence obtained from the South-American field surveys, Brazil open-field experiments, and Florida quarantine host specificity tests indicate that M. elatior causes significant feeding damage toS. viarum, and does not represent a threat to S. melongena crops in the USA. Therefore an application for permission to releaseM. elatior against S. viarum in the USA was submitted in October 1998. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gratiana boliviana, a potential biocontrol agent of Solanum viarum: Quarantine host-specificity testing in Florida and field surveys in South America

Host-specificity tests andfield surveys were conducted to determine thesuitability of the tortoise beetleGratiana boliviana Spaeth (Coleoptera:Chrysomelidae) from Argentina for classicalbiological control of Solanum viarumDunal (Solanaceae) in the USA. Thehost-specificity tests were conducted at theFlorida Department of Agriculture and ConsumerServices-Division of Plant Industry quarantinefacility in Gainesville, Florida (USA). Multiple-choice host-specificity tests wereconducted in small cages using 123 plantspecies in 35 families. Adults fedsignificantly (>41% of the leaf area offeredwas damaged) on the target weed(S. viarum), and fed lightly (<20%) onSolanum torvum Sw. (noxious weed native towest-Africa). Adults did some exploratoryfeeding (<5%) on eggplant, Solanummelongena L. (economic crop), Solanumelaeagnifolium Cav. (major agricultural weedin the western US), and on Solanumtampicense Dunal (weed of Central Americanorigin). No feeding was observed on any of theother 118 plant species that were testedincluding another 21 Solanum species.G. boliviana adults laid an average of 68eggs per female on S. viarum, 5 eggs perfemale on S. torvum, and an average of0.2 eggs on eggplant. No-choicehost-specificity tests were also conducted inwhich G. boliviana adults and neonatelarvae were exposed to 19 and 22 plant speciesrespectively. Tests with the neonatesindicated this insect was able to complete itsdevelopment only on S. viarum (67%reached the pupae stage). The no-choice testswith adults indicated that this insect fed,laid eggs, and completed development only onS. viarum. The unsprayed eggplant fieldsthat were surveyed in its natural range inArgentina, Brazil, Paraguay, and Uruguay fromJune 1997 to March 2000 indicated thatG. boliviana is not a pest of eggplants in SouthAmerica. Therefore, a petition for fieldrelease of G. boliviana for classicalbiological control of S. viarum in theUSA was submitted in April 2000.     

Impact of the belowground herbivore and potential biological control agent, Ceutorhynchus scrobicollis, on Alliaria petiolata performance

We studied the influence of the root-crown weevil Ceutorhynchus scrobicollis on its host plant Alliaria petiolata, a European biennial herb that is currently invading much of temperate North America. Varying timing of attack and herbivore densities in a common garden allowed to assess seasonality of plant response, density-dependence of impact, and the effect of intraspecific competition on C. scrobicollis recruitment (number of F₁ generation adults emerged). Data collected in the common garden were compared with data collected at field sites. C. scrobicollis is a common weevil in Europe, frequently attaining high attack levels on its host plant. In the common garden, weevil attack decreased plant survival by up to 43%, reduced plant height by 54%, increased the number of shoots by up to four–fold and delayed seed ripening, but had no significant negative effect on seed production. Plants infested in spring allocated less biomass to aboveground plant parts, and remained smaller than plants attacked in autumn, indicating that the latter were able to partly compensate for weevil attack. Increasing weevil density rarely had an effect on A. petiolata performance, and did not increase F₁ recruitment, suggesting strong intraspecific competition. At field sites, C. scrobicollis attack is spread over a long time period, which probably alleviates intraspecific competition. In summary, attack by the root-crown feeding weevil, C. scrobicollis, can substantially reduce growth and survival of A. petiolata. If introduced as a biological control agent into North America, C. scrobicollis is likely to decrease the fitness and competitive superiority of A. petiolata.