Biology and host specificity of Mecinus Janthinus Germar (col.: Curculionidae), a candidate for the biological control of yellow and dalmatian toadflax,Linaria Vulgaris (l.) mill,and Linaria Dalmatica (l.) mill. (scrophulariaceae) in North America

The biology and host specificity of Mecinus janthinus Germar, an oligophagous, univoltine stem‐borer of Linaria spp. are discussed. The results of feeding and oviposition tests with 38 species in 13 families and of larval transfer tests with four plant species are presented. They show that M. janthinus is restricted to the genus Linaria and does not develop on snapdragon Antirrhinum majus, an important ornamental in North America. The weevil is widely distributed in Europe. It accepts and develops normally on plants from the target North American toadflax populations. Therefore, it should be relatively easy to establish M. janthinus where the control of L. dalmatica and L. vulgaris is required. The release of M. janthinus in Canada and the USA is recommended.     

Variability of nectar production and composition in Linaria vulgaris (L.) Mill. (Scrophulariaceae)

 We studied nectar characteristics during the long flowering period (late June to end of November) in two populations of Linaria vulgaris (L.) Mill. spontaneously growing in the Botanical Gardens of Siena University (Tuscany, central Italy). The two populations were close to each other but they differed in blooming period. Plants of population 1 sprouted in May and flowered from the end of June to the end of September. Population 2 sprouted at the end of August and flowered from September to the end of November. Differences in nectar production and composition were found between and within populations. Flowers of population 1 produced a very small amount of nectar (not collectable) that remained on the nectary surface. The quantity of nectar increased in late September, when each flower produced 2–3 μl of nectar that flowed into the spur. Total sugar concentration was 175.8 mg/ml in young flowers. Flowers of population 2 produced 5–8 μl of nectar with a total sugar concentration of 200.9 mg/ml in the young stage. In bagged senescent flowers nectar volume decreased in both populations and nectar sugar concentration decreased down to 11.6 mg/ml in population 2 and increased up to 289.6 mg/ml in population 1. For both populations, the decrease in nectar volume in bagged flowers may have been due to water loss by evaporation. In population 2, the decrease in sugar concentration may have been due to nectar reabsorption that was never observed in population 1. Nectar variability is discussed in relation to insect visits and seed set. Received August 14, 2002; accepted December 17, 2002 Published online: June 2, 2003     

Interactions between two biological control agents and their target weed: a beetle,a bug and a cactus weed

ABSTRACT

Pereskia aculeata Miller (Cactaceae) is an invasive alien shrub introduced into South Africa from Brazil. The leaf-feeding beetle, Phenrica guerini Bechyne (Chrysomelidae), was released as a biological control agent in South Africa in 1991 followed by the stem-wilting bug, Catorhintha schaffneri Brailovsky & Garcia (Coreidae), in 2014. This study investigated the interactions between the two agents under laboratory conditions. Potted plants were exposed to one of four treatments: control (no agents), P. guerini only, C. schaffneri only and both species together. Four densities, ranging from 2 to 12 insects per plant were used. Cathorhitha schaffneri alone at low to moderate densities resulted in the same reduction in number of leaves and shoot length as when combine with P. guerini. At the highest density, C. schaffneri reduced the number of leaves significantly more than any treatment. Mortality of P. guerini was significantly higher than C. schaffneri at the highest density when in combination. The antagonistic interaction between P. guerini and C. schaffneri suggests that these agents should not be released together because this would impact negatively on the overall biocontrol programme against P. aculeata. It is recommended that C. schaffneri should be released at sites where P. guerini is not present. Extrapolation of laboratory-based studies into the field is often challenging, so mass-rearing and releases of P. guerini should continue until there is convincing proof that C. schaffneri alone is more effective than P. guerini in the field.     

Seasonal activity,habitat preferences and larval mortality of the leaf-mining fly Calycomyza eupatorivora (Agromyzidae), a biological control agent established on Chromolaena odorata (Asteraceae) in South Africa

The leaf-mining fly Calycomyza eupatorivora Spencer (Diptera: Agromyzidae) has become widely established in the eastern regions of South Africa, following its release for the biological control of the invasive shrub Chromolaena odorata (L.) King and Robinson. This study was conducted to gain some insight into the impact of C. eupatorivora populations, by assessing their seasonal activity, habitat preferences, levels of leaf exploitation and extent of larval mortality in the field over a 1-year period. Leaf mining intensity was poorly synchronised with leaf availability, with leaf exploitation peaking at the end of the growing season of C. odorata. Although significantly more mines were recovered on plants growing in shaded situations, the percentage of available leaves that were exploited for mining was not significantly different between plants growing in shaded versus open situations. Overall, the levels of leaf damage were trivial with mines recovered from <5% of available leaves that were sampled during the study. Besides leaf-quality requirements, these low levels of leaf exploitation may have been influenced by high larval mortality which varied between 60 and 83%, depending on whether lower or higher estimates were used. These evaluations have verified the results of earlier laboratory studies which suggested that the impact of C. eupatorivora on mature populations of C. odorata in South Africa will be negligible.     

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.     

Interspecific interactions between the gall-fly Urophora affinis Frfld. (Diptera: Tephritidae) and the weevil Larinus minutus Gyll. (Coleoptera: Curculionidae), two biological control agents released against spotted knapweed, Centaurea stobe L. ssp. micranthos

Interspecific competition has been suggested as an explanation for the failure of some insects as biological control agents for weeds. Enclosure and exclusion cages were used, in southern British Columbia, Canada to evaluate the importance of interspecific competition between a seedhead weevil, Larinus minutus, and a gall-inducing fly, Urophora affinis, two biocontrol agents released against spotted knapweed in North America. At the seedhead scale, U. affinis, which is an inferior biological control agent based on knapweed seed mortality, was the superior competitor. Larinus minutus attack rates were significantly lower in the presence of U. affinis compared to release treatments where L. minutus was attacking alone. Reduced L. minutus attack rates were apparent in seed heads expected to contain both species, assuming insect distributions were random, but instead only contained U. affinis. L. minutus did not significantly affect U. affinis density. Although overall attack rates on knapweed seedheads were higher when both species were together at a site, the consequence of the antagonistic interaction is that overall seed destruction was not as high as it could have been if the weevil were attacking on its own. These results support minimizing the number of biocontrol agents released that use similar resources on the target weed, to avoid negative interactions between control agents and potential reductions in biocontrol efficacy resulting from competitive exclusion.     

Studies on the rustMaravalia cryptostegiae,a potential biological control agent of rubber-vine weed (Cryptostegia grandiflora,Asclepiadaceae: Periplocoideae) in Australia,I: Life-cycle

Three spore types are described forMaravalia cryptostegiae: hemileioid urediniospores; thin-walled, hyaline, ellipsoidal, non-resting teliospores and ovoid to lacrimoid basidiospores. Field surveys in the Madagascan native range of rubber-vine failed to confirm the existence of spermogonia and morphologically distinct aecia within the life-cycle. Greenhouse inoculations with basidiospores were unsuccessful. Cytological studies revealed that rubber-vine rust has a similar nuclear cycle to that reported for coffee leaf rust,Hemileia vastatrix. The working hypothesis is proposed thatMaravalia cryptostegiae is a primitive, autoecious tropical forest rust with only a short or partially expanded life-cycle represented by two teliospore forms. The predominant, functional form is uredinioid with a novel nuclear cycle, in which there is a delayed meiotic division (the Kamat phenomenon). The non-dispersed form appears to be vestigial or non-functional since it germinates to produce a metabasidium with genetically variable and unstable basidiospores. The relationships and evolutionary significance of the generaMaravalia andHemileia are discussed.     

Studies on the rust,Maravalia cryptostegiae,a potential biological control agent of rubber-vine weed,Cryptostegia grandiflora (Asclepiadaceae: Periplocoideae), in Australia,II: Infection

The parameters which govern infection of rubber-vine weed by the rustMaravalia cryptostegiae were investigated. The infection process, from appressorial formation to sporulation, is described and illustrated. Uredinioid teliospores have an optimum temperature range for germination at 22–27 °C, both in vitro and in vivo. However, germination on the rubber-vine leaf was more than double (81–92%) that in the absence of the host, and appressoria were formed only in vivo. An optimum temperature of 20–22°C and a dew period of 12 hours or more gave the highest level of infection as measured by sporulation density. The latent period from inoculation to pustule formation decreased with increasing temperature; the shortest period (8–11 days) being recorded at 25–27°C. At the lower temperatures (18°C), this was significantly extended (19–21 days). Four successive inoculations significantly reduced plant height and dry weight, although a compensatory growth flush occurred after the third inoculation. The addition of cryoprotectants had a negative affect on spore viability and subsequent infectivity. Cooling dry spores to –196°C at the rate of 10°C min^–1 gave the best results, with high germination (93–65%) up to 8 days after thawing.     

A molecular survey concerning the origin of Cyperus esculentus (Cyperaceae,Poales): two sides of the same coin (weed vs. crop)

Background and AimsCyperus esculentus is widespread in tropical and temperate zones and is also present in cooler regions. It is used as a crop plant, but it also occurs in the wild and as a weed. As a consequence of its ecological plasticity, C. esculentus has remarkable variability, with several morphotypes. Four wild-type varieties are presently recognized, in addition to the cultivated form. This study investigates the phylogenetic position and biogeography of C. esculentus with the objective of contributing new data to increase the understanding of its evolutionary history.Methods Genealogical relationships among genotypes were inferred by using plastid DNA haplotype and nuclear ribosomal (nr) DNA ribotype sequences for 70 specimens either collected in the field or obtained from herbaria. Statistical dispersal–vicariance (S-DIVA) and Bayesian binary method (BBM) analyses were used to reconstruct the possible ancestral ranges of C. esculentus. In order to determine the age of C. esculentus, a time-measured phylogenetic analysis was performed.Key Results Considerable variation between the chosen nuclear and plastid markers was detected (27 ribotypes vs. six haplotypes). No geographical structure was displayed among the haplotypes, but information on the dispersal pattern may be deduced. Two types of ribotypes were detected in nrDNA, with an evident geographical segregation into an Old World group and a polymorphic New World group. Both S-DIVA and BBM analyses suggested a biogeographical history in which dispersal from the African region has been crucial in shaping the current distribution pattern of C. esculentus. The most recent common ancestor between C. esculentus races has an age of 5.1 million years (95 % highest posterior density 2.5–10.2).Conclusions The molecular analysis provides novel insights into the evolutionary history of C. esculentus. The results have various taxonomic and phylogenetic implications, including a hypothesis on the origin and phylogeography of this species, which probably originated in the late Cenozoic in Africa, and reached the Americas repeatedly, independently of Columbian exchanges.     

The biology of two Eretmocerus spp. (Haldeman) and three Encarsia spp. Forster and their potential as biological control agents of Bemisia tabaci biotype B in Australia

The performance, as measured by daily rate of parasitism and total parasitism, of five aphelinid species found in Australia parasitising Bemisia tabaci were compared on cotton, hibiscus, rockmelon, soybean and tomato. Two Eretmocerusspp., both indigenous to Australia, gave the highest levels of parasitism on each of the plant host species tested. The tritrophic interactions between B. tabaci, host plant species and Eret. mundus(Australian parthenogenetic form) (APF) were also examined. In general, more whiteflies were parasitised when cotton was the source host or rockmelon the test host. Parasitism was always low when tomato was either the source or test host. When parasitoids were transferred from rockmelon to cotton, parasitism declined. In contrast, parasitism increased when parasitoids were transferred from cotton to rockmelon. Parasitism also increased when parasitoids were transferred from soybean to rockmelon, yet failed to do so when shifted from soybean to cotton despite cotton normally being a better host. However, when parasitoids were transferred from cotton to soybean there was a marked increase in parasitism. Possible causes are discussed. The field cage trial demonstrated that parasitism by both Eretmocerus spp. increased with increasing whitefly density. Further, the increase in parasitism was not due to the presence of more parasitoids as neither the parasitoid-whitefly ratio nor the total number of parasitoids present had a significant effect on parasitism. The combination of the two species, gave similar levels of parasitism to that achieved by Eret. mundus(APF) alone. Subsequent identification of the emerged individuals indicated that over 50% of the parasitism was due to this species suggesting that it out-competed Eret. queenslandensis. Despite this competition, there was no evidence that overall control was compromised.     

Performance and impact of the biological control agent Xubida infusella (Lepidoptera; Pyralidae) on the target weed Eichhornia crassipes (waterhyacinth) and on a non-target plant, Pontederia cordata (pickerelweed) in two nutrient regimes

Xubida infusella (Walker) (Lepidoptera: Pyralidae) is potentially a useful biological control agent targeting Eichhornia crassipes (waterhyacinth) in the USA but many regions infested with waterhyacinth are also inhabited by an alternative native host, Pontederia cordata (pickerelweed). Experiments were conducted in Australia to assess the impact of X. infusella on pickerelweed compared to waterhyacinth where both these plants were available and X. infusella had already been released. Overall X. infusella had a greater impact on pickerelweed than on waterhyacinth. More than one larva per plant was required to reduce the total shoot dry weight of waterhyacinth but only one larva per plant reduced the total shoot dry weight of pickerelweed. Insect feeding caused the number of secondary shoots (daughter plants) of pickerelweed to double whereas the number of daughter plants produced by waterhyacinth remained unchanged. We suggest this indicates a considerable impact on pickerelweed rather than effective compensation for insect damage because the shoots produced were very small. Waterhyacinth produced a constant number of daughter plants when fed on by up to three larvae per plant. Higher nitrogen status of both species of host plant increased the rate of larval development and pupal weight of X. infusella. The weight and fecundity of X. infusella reared on pickerelweed were lower than those reared on waterhyacinth but large numbers of progeny were produced on both plant species. This experiment demonstrates a considerable impact of X. infusella on pickerelweed suggesting this plant is at risk from this agent if released in the USA where pickerelweed is present. The considerable impact on waterhyacinth demonstrates the potential for this insect to contribute to waterhyacinth control in countries where risk assessment favours release.     

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.     

Vegetation history and lake-level changes from the Younger Dryas to the present in Eastern Pyrenees (France): pollen, plant macrofossils and lithostratigraphy from Lake Racou (2000 m a.s.l.)

A multi-proxy palaeoecological investigation including pollen, plant macrofossil, radiocarbon and sedimentological analyses, was performed on a small mountain lake in the Eastern Pyrenees. This has allowed the reconstruction of: (1) the vegetation history of the area based on five pollen diagrams and eight AMS¹⁴C dates and (2) the past lake-level changes, based on plant macrofossil, lithological and pollen analysis of two stratigraphical transects correlated by pollen analysis. The palaeolake may have appeared before the Younger Dryas; the lake-level was low and the vegetation dominated by cold steppic grasslands. The lake-level rose to its highest level during the Holocene in the Middle Atlantic (at ca. 5060±45 b.p.). Postglacial forests (Quercetum mixtum and Abieto-Fagetum) developed progressively in the lower part of the valley, while dense Pinus uncinata forests rapidly invaded the surroundings of the mire and remained the dominant local vegetation until present. The observed lowering of the lake levels during the Late Atlantic and the Subboreal (from 5060 ± B.P. to 3590±40 b.p.) was related to the overgrowth of the mire. The first obvious indications of anthropogenic disturbances of the vegetation are recorded at the Atlantic/Subboreal boundary as a reduction in the forest component, which has accelerated during the last two millennia.     

Winter mortality of Aceria chondrillae, a biological control agent released to control rush skeletonweed (Chondrilla juncea) in the western United States

Abstract:  Classical biological control of weeds is based on the assumptions that: (1) plant species are in part invasive in their introduced range because of the absence of coevolved specialist herbivore arthropods and plant pathogens; and (2) that these specialist herbivores can regulate host-plant populations. Although the need for quantitative post-release monitoring studies testing these assumptions has been acknowledged repeatedly, the number of assessments is still remarkably small and usually restricted to systems with notable impact of an agent species. However, studying systems where biological control agents cause no observable target weed reductions may be important to identifying factors that limit the population size or impact of biological control agents. Three biological agents were released for the control of the herbaceous perennial rush skeletonweed, Chondrilla juncea in North America between 1975 and 1977. Although all three species are widely established, weed densities are increasing and there is little quantitative information on factors limiting biological control efficacy. We examined the winter biology and survivorship of the rush skeletonweed gall mite Aceria chondrillae at two rush skeletonweed field sites in south-western Idaho over 2 years. Gall mite winter mortality was high (>90%) in both years and for both sites. Gall mites were more abundant on plants that produced rosettes in fall and rush skeletonweed plants growing on southern aspect were 3.4 times more likely to produce rosettes than those growing on northern aspects. Our data suggest that A. chondrillae population densities are limited by its high winter mortality. The gall mites may require fall rosettes to successfully survive the winter, which are commonly absent on north-facing aspects, impairing the efficacy of A. chondrillae to control rush skeletonweed in the intermountain western United States.     

Field colonization, population growth, and dispersal of Boreioglycaspis melaleucae Moore, a biological control agent of the invasive tree Melaleuca quinquenervia (Cav.) Blake

Invasion of native plant communities by the Australian paperbark tree (“melaleuca”), Melaleuca quinquenervia, complicates restoration of the Florida Everglades. Biological control, within the context of a comprehensive management program, offers a means to suppress regeneration of melaleuca after removal of existing trees and a mechanism to forestall reinvasion. To meet this need, a biological control program commenced in 1997 upon the release of an Australian weevil (Oxyops vitiosa [Pascoe] [Coleoptera: Curculionidae]). Release of a second biological control agent, the melaleuca psyllid (Boreioglycaspis melaleucae Moore), followed in February 2002 at field sites containing mixed age-class melaleuca stands or coppicing stumps. Each site was inoculated with 7000–10,000 adult psyllids, with one exception where 2000 nymphs were released on seedlings the following December. Psyllid populations established everywhere irrespective of colony source, site conditions, or the quantity released, although numbers released and, to a lesser degree, colony age influenced the numbers of colonies produced. Quantity included in the release was the major determinant of the resultant number of colonies, although the duration of their tenure in quarantine culture may have also influenced this. One site, comprised mainly of coppicing stumps, contained 3.3 million psyllids per ha within 3 months after release. Less than 1% of the coppices at a similar site harbored psyllid colonies 2 months after release (May 2002), but this rose to 75% in October then to 100% by December. The census population exceeded 715,000 adults and nearly 11 million nymphs by late January 2003. Psyllid populations dispersed 2.2–10.0 km/year, with the slower rates in dense, continuous melaleuca stands and faster rates in fragmented stands. Over 1 million psyllids had been redistributed to 100 locations as of December 2005. This species now occurs throughout much of the range of melaleuca in south Florida due to natural range expansion as well as anthropogenic dissemination.     

Evaluation and host specificity of two seed flies Mesoclanis polana and M. magnipalpis (Diptera: Tephritidae): biological control agents for Chrysanthemoides monilifera (Asteraceae) in Australia

Larvae of the South African tephritid flies Mesoclanis polana Munro and M. magnipalpis Bezzi feed in the developing seeds of Chrysanthemoides monilifera. Host specificity evaluation using 109 plant species from 25 families indicated that complete development was restricted to their natural host C. monilifera. Minor feeding and limited development was detected on 18 species, but was of no ecological or economic significance. Mesoclanis polana and M. magnipalpis have been released in Australia and M. polana has established and dispersed widely. Mesoclanis magnipalpis has not yet become naturalized. Parasitism of M. polana in Australia by several species of Hymenoptera has been detected, but is not expected to limit the establishment and impact of these flies.