Revised methods for the mass-rearing of the spotted knapweed biological control agent,Cyphocleonus achates (Coleoptera: Curculionidae), in field corrals

Cyphocleonus achates (Fahraeus), a root-feeding weevil introduced from Eurasia, is an effective biological control agent against spotted knapweed, Centaurea stoebe L. ssp. micranthos. Because C. achates is univoltine and does not fly, distribution of the weevil has been slow. To hasten the weevil's distribution, a rearing effort using field corrals was initiated at a facility in Corvallis, Montana. Procedures for mass-rearing the weevil in field corrals are described, with an emphasis on improvements over earlier methods. The described field-corral approach is effective and appropriate for producing C. achates for distribution in the western United States.     

Evidence for multiple introductions of Centaurea stoebe micranthos (spotted knapweed,Asteraceae) to North America

Invasive species’ success may depend strongly on the genetic resources they maintain through the invasion process. We ask how many introductions have occurred in the North American weed Centaurea stoebe micranthos (Asteraceae), and explore whether genetic diversity and population structure have changed as a result of introduction. We surveyed individuals from 15 European native range sites and 11 North American introduced range sites at six polymorphic microsatellite loci. No significant difference existed in the total number of alleles or in the number of private alleles found in each range. Shannon–Weaver diversity of phenotype frequencies was also not significantly different between the ranges, while expected heterozygosity was significantly higher in the invasive range. Population structure was similar between the native range and the invasive range, and isolation by distance was not significant in either range. Traditional assignment methods did not allocate any North American individuals to the sampled European populations, while Bayesian assignment methods grouped individuals into nine genetic clusters, with three of them shared between North America and Europe. Invasive individuals tended to have genetically admixed profiles, while natives tended to assign more strongly to a single cluster. Many North American individuals share assignment with Romania and Bulgaria, suggesting two separate invasions that have undergone gene flow in North America. Samples from three other invasive range sites were genetically distinct, possibly representing three other unique introductions. Multiple introductions and the maintenance of high genetic diversity through the introduction process may be partially responsible for the invasive success of C. stoebe micranthos.     

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.     

Interactions and effects of multiple biological control insects on diffuse and spotted knapweed in the Front Range of Colorado

Abundances and interactions among biological control insects and their effects on target invasive plants were monitored within the flower heads and roots of diffuse knapweed, Centaurea diffusa, and in spotted knapweed, Centaurea stoebe, along the Colorado Front Range. Flower weevils, (Larinus species) and root-feeders (Cyphocleonus achates and Sphenoptera jugoslavica) were released on knapweed that already supported biological control gall flies (Urophora species). At a single monitoring site, seed production by C. diffusa declined from 4400 seeds m⁻² in 1997 to zero seeds m⁻² on the monitoring sites in 2006, while the flowering stem density of C. diffusa declined from a peak of almost 30 stems m⁻² in 2000 to zero stems m⁻² in 2006. The average abundance of Urophora and Larinus in flower heads fluctuated independently during the 2001–2006 interval, while the relative abundance of C. achates and S. jugoslavica in roots exhibited a weak inverse relationship that appeared driven by climate effects. The relative abundance of insects on a population of C. stoebe was monitored for five years as Larinus species and C. achates became established on spotted knapweed that already supported Urophora species. Spotted knapweed seed production on our monitoring site declined from 4600 seeds m⁻² in 2003 to zero seeds m⁻² in 2006. Unlike C. diffusa, substantial numbers of rosettes of C. stoebe remained present. Larinus consumed almost all Urophora encountered in C. diffusa, and consumed about 40% of the Urophora in co-infested flower heads of C. stoebe (ca. 10–15% of the total Urophora population). No negative correlations between the relative densities of flower head and root-feeding insects were observed. The effects of these insects on target plants have produced results consistent with the ‘cumulative stress hypothesis’ for biological control of Centaurea species.     

Intergenerational above- and belowground responses of spring wheat (Triticum aestivum L.) to elevated CO2

We quantified intergenerational above- and belowground responses of two genotypes of semi-dwarf, hard red, spring wheats (Triticum aestivum L.) to elevated (700 μmol mol⁻¹) CO₂. These plants were progeny of seeds produced from previous generation plants grown at elevated CO₂ under well-watered and high nutrient conditions. Because neither genotype in the first generation exhibited enhanced performance with CO₂ enrichment, our objective in this investigation was to assess if exposure to CO₂ enrichment in subsequent generations resulted in temporal changes in the relative enhancement (elevated/ambient) of above- and belowground plant growth. Relative enhancement occurred in both the second and third generations for both above- and belowground variables. Above- and belowground variables were enhanced by similar relative amounts at elevated CO₂ within a generation at each harvest date. Relative enhancement of measured variables was generally greater in the third than second generation when plants were in the seedling or vegetative stage, but not when plants were reproductive. Additional research is needed to investigate physiological or other limitations of translating above- and belowground responses to CO₂ in vegetative growth stages to reproductive performance. Intergenerational above- and belowground responses of this C₃ annual plant to CO₂ enrichment are not driven by genetic change (selection) that occurred between generations, but rather CO₂-induced changes in seeds that affected seedling responses to CO₂ enrichment. Wir quantifizierten die intergenerationelle ober- und unterirdische Reaktionen von zwei Genotypen mittellangen, hartroten Winterweizen (Triticum aestivum L.) auf erhöhtes CO₂ (700 μmol mol⁻¹). Diese Pflanzen waren Abkömmlinge von Samen, die von Pflanzen der vorherigen Generation produziert wurden, welche ihrerseits bei erhöhtem CO₂ und bei ausreichender Wasserversorgung sowie guten Nährstoffbedingungen kultiviert wurden. Weil keiner der beiden Genotypen in der ersten Generation eine verbesserte Leistung bei CO₂-Anreicherung zeigte, war unser Ziel, in der Untersuchung abzuschätzen, ob die Exposition einer CO₂-Anreicherung in den nachfolgenden Generationen zu temporären Veränderungen in der relativen Förderung (erhöht/umgebend) des ober- und unterirdischen Wachstums führte. Eine relative Steigerung fand in der zweiten und in der dritten Generation sowohl bei den ober- als auch unterirdischen Variablen statt. Bei jedem Erntetermin waren die ober- und unterirdischen Variablen innerhalb einer Generation bei erhöhtem CO₂ mit ähnlichen relativen Anteilen positiv beeinflusst. Die relative Steigerung der gemessenen Variablen war im Allgemeinen bei Pflanzen im Keimlings- oder vegetativen Stadium in der dritten Generation größer als in der zweiten, jedoch nicht bei reproduktiven Pflanzen. Zusätzliche Forschung ist notwendig, um physiologische oder andere Limitierungen zu untersuchen, die ober- und unterirdische Reaktionen von vegetativen Wachstumsstadien auf CO₂ in die reproduktiven Leistung übersetzen. Intergenerationelle, ober- und unterirdische Reaktionen dieser C₃-Pflanze auf CO₂-Anreicherung werden nicht durch genetische Veränderungen (Selektion) im Laufe der Generationen gesteuert, sondern eher durch CO₂-induzierte Veränderungen in den Samen, welche die Reaktion der Keimlinge auf eine CO₂-Anreicherung beeinflussen.     

Using simulated herbivory to predict the efficacy of a biocontrol agent: the effect of manual defoliation and Macaria pallidata Warren (Lepidoptera: Geometridae) herbivory on Mimosa pigra seedlings

Abstract  The effect of manual defoliation, and real and simulated herbivory by the leaf-feeding moth Macaria pallidata on the growth and biomass of Mimosa pigra seedlings was assessed to determine the likely success of defoliating herbivores as biocontrol agents against the weed. Manual removal of at least half of all leaf material, maintained over a 6-week period, significantly suppressed plant growth, as did a single week of herbivory by M. pallidata larvae. This suggests that M. pallidata and other defoliators have the potential to be highly successful agents in the biological control program for M. pigra.     

Suitability of Bemisia tabaci (Hemiptera: Aleyrodidae) instars for the parasitization by Encarsia bimaculata and Eretmocerus sp. nr. furuhashii (Hymenoptera: Aphelinidae) on glabrous and hirsute host plants

The host instar preferences of Encarsia bimaculata and Eretmocerus sp. nr. furuhashii parasitizing Bemisia tabaci and their development on four host plants, collard, eggplant, cucumber and tomato, were studied in the laboratory. Both of the parasitoids accepted all nymphal stages of B. tabaci, but E. bimaculata preferred third and fourth instars while Er. sp. nr. furuhashii preferred second and third instars under both choice and no choice conditions. Regardless of host stage parasitized, adults of parasitoids emerged only from fourth instars. When given the simultaneous choice of all instars, E. bimaculata reduced parasitization of first and second instars (3.73 and 4.76%, respectively) while increasing parasitization of third and fourth instars (5.44 and 6.93%, respectively), in contrast Er. sp. nr. furuhashii increased its parasitization of second and third instar nymphs (1.27 and 3.17%, respectively) and decreased that of first and fourth instars (7.0 and 3.06%, respectively). Host plants did not significantly influence instar preference for either parasitoid. Developmental periods of both the parasitoids from egg to adult emergence were longest when first instars were parasitized and shortest when fourth instars were selected. Parasitoid developmental time was generally shorter on glabrous plants than on hirsute plants.     

两种蚜小蜂对烟粉虱寄主的产卵选择性(英文)

双斑恩蚜小蜂和桨角蚜小蜂是华南地区烟粉虱的两种优势种寄生蜂。本文研究了两种寄生蜂对不同龄期烟粉虱寄主的产卵选择特性。结果表明:两种寄生蜂均可寄生烟粉虱的1~4龄若虫。当只有1个龄期的烟粉虱若虫存在时,双斑恩蚜小蜂更多地寄生3龄和4龄若虫,较少寄生1龄和2龄若虫;而桨角蚜小蜂则更多地寄生3龄和2龄若虫,较少寄生1龄和4龄若虫。在4个龄期若虫同时存在时,双斑恩蚜小蜂会明显增加对3龄和4龄若虫的产卵寄生,降低对1龄和2龄若虫的寄生;而桨角蚜小蜂则增加对2龄和3龄若虫的寄生,减少对1龄和4龄若虫的寄生。寄主植物的差异不影响这二种蚜小蜂对各龄期烟粉虱若虫的产卵选择倾向。结果提示,烟粉虱若虫3龄和4龄是双斑恩蚜小蜂最适宜的寄主,而桨角蚜小蜂最适宜的寄主是烟粉虱2龄和3龄若虫。     

Olfactory response of Anagrus,nigriventrls (HYM.: Mymaridae): Effects of host plant chemical cues mediated by rearing and oviposition experience

The egg parasitoid Anagrus nigriventris Girault is an important natural enemy of the beet leafhopper, Circulifer tenellus (Baker) which has a broad host range that includes cultivated sugar beets and the weed, Russian thistle. When parasitoids were reared on leafhopper eggs deposited in sugar beets, females were attracted to sugar beet volatiles and preferred them over a blank control and over Russian thistle volatiles in Y- tube olfactometer tests. No preference was detected for either plant by female wasps that were reared on Russian thistle. Wasps reared on Russian thistle and allowed an oviposition experience on sugar beet showed a strong attraction to sugar beet volatiles; however, wasps reared on sugar beets and allowed oviposition experience on Russian thistle demonstrated no preference between the two plants. The implications of parasitoid response towards plant volatiles and their importance in biological control are discussed.     

Host specificity of the rubber vine moth, Euclasta whalleyi Popescu-Gorj and Constantinescu (Lepidoptera: Crambidae: Pyraustinae): field host-range compared to that predicted by laboratory tests

Abstract The moth Euclasta whalleyi was introduced into Australia in 1988 for the biocontrol of its host plant, rubber vine Cryptostegia grandiflora , despite test results predicting it might also attack the related native vine Gymnanthera oblonga . Ten years after release, the moth is widespread and damaging on rubber vine, but there is no attack on G. oblonga , except when it is growing in close association with rubber vine plants. The implications of 'false positives' in host-specificity testing are discussed.     

The importance of the ratio UV-B/photosynthetic active radiation (PAR) during leaf development as determining factor of plant sensitivity to increased UV-B irradiance: effects on growth, gas exchange and pigmentation of bean plants (Phaseolus vulgaris cv. Label)

To evaluate the effect of different naturally occurring irradiation conditions on the sensitivity of bean (Phaseolus vulgaris cv. Label) to increased UV-B levels, plants were grown under six different light treatments. In the control series (at ambient levels of UV-B), UV-B and visible light were decreased in parallel, resulting in three different total irradiation treatments with the same UV-B/PAR ratio. A second series with a 15% increase in UV-B irradiation at each PAR level was used to investigate the effect of UV-B under the varying total irradiance levels. The different total irradiance levels resulted in large differences in total dry weight, specific leaf weight, photosynthesis-light response and pigment concentrations. Nevertheless, the 15% increase in UV-B resulted in equal reductions in total dry weight (from 24.5 to 34.3%) and effective photosynthesis for all light levels. The accumulation of protective pigments in the primary bean leaves was strongly correlated to the total irradiance level (200% increase from the lowest to the highest light level), but was not influenced by increasing UV-B levels. As the UV-B/PAR ratio outside increases with decreasing total irradiance (when induced by cloud cover) this implies that low radiation levels are potentially dangerous to some plants, even though the UV-B levels may seem negligible.