Axillary bud proliferation and organogenesis of <Emphasis Type="Italic">Euphorbia pulchurrima</Emphasis> winter rose

Summary Protocols for both axillary bud proliferation and shoot organogenesis of Euphorbia pulchurrima Winter Rose^TM were developed using terminal buds and leaf tissues. Greenhouse-grown terminal buds were placed on Murashige-Skoog (MS) basal medium supplemented with various concentrations of either benzlyaminopurine (BA) or thidiazuron (TDZ). Explants produced the greatest number of axillary buds on media containing between 2.2 and 8.8 μM BA. The number of explants that produced axillary buds increased with increasing BA concentration. TDZ at concentrations between 2.3 and 23.0 μM caused hyperhydricity of shoots and were not effective in promoting shoot proliferation. The most calluses and shoots were produced from leaf midvein sections from in vitro grown plants placed on the medium containing 8.8–13.3 μM BA and 17.1 μM indole-3-acetic acid (IAA) for 1 mo. before transferring to the medium containing only BA. Adventitious buds were produced only from red-pigmented callus, and explants that produced callus continued to produce adventitious shoots in the presence of IAA. Five-mo.-old shoots derived from shoot culture or organogenesis rooted readily in artificial soil with or without treatment with indolebutyric acid, and were acclimatized in the greenhouse.     

First interception of Bemisia tabaci Mediterranean (Q biotype) in Serbia

The whitefly Bemisia tabaci (Gennadius) is a cosmopolitan insect pest and causes great damage to many agricultural crops by direct feeding, and transmitting many plant viruses causing disastrous effects. The global distribution of B. tabaci was previously investigated, but so far, it has not been confirmed in Serbia. Sampling conducted on plants at three localities in Serbia revealed the presence of three whitefly species, one is B. tabaci Mediterranean (MED) species, a quarantine pest. Additionally, Trialeurodes vaporariorum Westwood and an Aleurodes sp. that was not identified to the species level were also confirmed. The last two are common and widespread species in Serbia. Whitefly collections were made from cabbage, kale and oilseed rape plants (Brassica oleracea, B. oleracea var. sabauda, B. napus, respectively) grown in the field, on sunflower (Helianthus annuus) grown in the greenhouse and on potted hibiscus (Hibiscus sp.) and poinsettia (Euphorbia pulcherrima) plants grown indoors. DNA sequence analysis from a portion of the Cytochrome Oxidase I gene (COI) revealed the presence of B. tabaci MED species, which is considered to be a very important pest worldwide and has been reported from neighbouring countries, however, not yet from Serbia. Bemisia tabaci MED is recorded here for the first time in Serbia. This first interception suggests its introduction with ornamentals grown indoors, with no outdoor reports and that it is not yet spread. This report is an important alert for local authorities to take the necessary steps in monitoring and preventing its possible expansion.     

Effect of imidacloprid on the sivlerleaf whitefly, Bemisia argentifolii Bellows and Perrring (Homoptera: Aleyrodidae), and whitefly parasitism

Bioassays were conducted under greenhouse conditions to determine the effect of imidacloprid on adult and nymphal stages of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, and parasitism by Encarsia formosa (Gahan). A flowable formulation (24Oglitre^-1) of imidacloprid at six rates (0.09, 0.04 and 0.02 g a.i. litre^-1 pot volume for experiments 1 and 2; 0.009, 0.004, and 0.002 g a.i. litre^-1 pot volume for experiment 3) was evaluated. After a 48 h exposure to treated plants, high mortality of adult whitefly (>94%) was observed. Adults exposed to poinsettias treated 150 days earlier also had significantly greater mortality (>79%) than the adults on control plants. When exposed to treated plants for only 6 h, >65% of adults were killed. All three rates of imidacloprid caused >97% mortality of immature whiteflies by day 19. When treated plants were continually exposed to adult whiteflies, immature mortality was 100% for the three higher rates of imidacloprid up to and including 88 days after treatment. During the same time, emerging adults were reduced significantly. Immatures reinfested on plants treated 161 days earlier, incurred 80% mortality at the higher rate 0.09 g a.i. litre^-1 pot volume and 38% mortality at 0.02 g a.i. litre^-1 pot volume. At lower treatment rates, results varied. At 0.009 g a.i. litre^-1 of pot volume, mean percentage whitefly mortality (65%) 25 days after treatment was significantly higher than the controls; however, whitefly mortality at 0.004 and 0.002 g a.i. litre^-1 pot volume was not significantly different from controls or plants treated with the higher rate. Parasitoids could develop to the adult stage on whiteflies infesting imidacloprid treated plants. Parasitism occurred at low levels (< 10%), doe to high levels of whitefly mortality on treated plants. No phytotoxicity was observed for any treatment throughout the length of the trials that lasted through flowering.     

Population genetic structure of the newly invasive Q biotype of Bemisia tabaci in Taiwan

The sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is among the top 100 invasive pests in the world, and it causes serious agricultural damage and economic losses in many countries. More than 24 biotypes of the sweetpotato whitefly have been detected worldwide, of which the Q biotype has recently been reported to be a new invasive pest spreading throughout the world via trade in poinsettias, Euphorbia pulcherrima Willd. ex Klotzsch (Euphorbiaceae). In 2006, the Q biotype was first recorded in Taiwan in greenhouses, but not in the field, suggesting that the invasion of this biotype might be at an early stage in that country. The mitochondrial cytochrome oxidase I (COI) gene and 12 microsatellite loci were used to investigate the genetic structure of multiple B. tabaci Q biotype populations. The presence of only a few COI haplotypes and a low number of nucleotide differences suggest high genetic similarity among these populations. Microsatellite analyses also revealed low genetic differentiation and frequent gene flow among greenhouses. The molecular evidence supports the occurrence of a recent genetic bottleneck in the B. tabaci Q biotype. Bayesian cluster analyses indicated that at least two invasion events have occurred in Taiwan. Phylogenetic analyses of microsatellites support Q biotype migration among greenhouses, which was likely facilitated by the frequent movement of poinsettias between greenhouses. Future management strategies should focus on developing plantlet trade regulations to avoid further anthropogenic dispersal of the B. tabaci Q biotype among greenhouses in Taiwan.     

Are red leaves photosynthetically active?

At irradiances close to those representing a sunny day, red and green leaves of poinsettia (Euphorbia pulcherrima) showed only minor differences in their photosynthetic capacities despite the strong differences in their pigment composition. However, contrarily to green leaves, red leaves did not show inhibition of photosynthesis at high irradiances, because anthocyanins protected chloroplasts from photoinhibition.     

The identification of poinsettia cultivars by HPLC analysis of their flavonol content

The flavonols from each of 38 poinsettia cultivars were quantitatively resolved by HPLC. Careful selection of samples revealed significant quantitative differences in flavonol content. While all cultivars of seedling origin could be differentiated on the basis of their flavonols, several families of sports could not. Most new commercial poinsettia cultivars have been selected from among somatic mutants exhibiting different bract color. Such changes in color were usually the results of change in anthocyanin content rather than flavonol content. The flavonol content increased in color sports with less anthocyanin. Three of the flavonols were absent from a few of the cultivars but most differences between cultivars were only quantitative. Genetic data suggested independent assortment of control of quercetin 3-rhamnoside and quercetin 3-galactoside synthesis but linkage of quercetin 3-rhamnoside and kaempferol 3-rhamnoside synthesis.     

Evolution des flavonoides au cours de la croissance des bractees de Poinsettia

The changes in flavonoids were studies during the growth of Poinsettia bracts. Pelargonidin glycosides appeared after cyanidin glycosides; the 3-rutinoside after the 3-monoglucoside. The 3-mono-glucosides were predominant at all times. The bracts contained kaempferol and quercetin, both as aglycones and glycosides. There was no direct relationship between the pathways of flavonol and anthocyanin biosynthesis, but two separate pathways corresponding to the 4′-monohydroxylated- and 3′,4′-dihydroxylated-, flavonoids. Flavanonols and isoflavones were detected but not characterized.     

The identification of poinsettia cultivars by HPLC analysis of their anthocyanin content

The anthocyanins of 28 cultivars of poinsettia were resolved by HPLC. The amount of each of the 5 anthocyanins was calculated, both by integration of the under their HPLC profile peaks and by second derivatives of the peaks. Comparisons of the two methods showed a correlation of 0.986. The amount and proportion oft he anthocyanins were affected by maturity, season of flowering, quality of irradiance and the specific area of the bract sampled. With careful selection of samples from plants grown under uniform conditions, there wre significant differences amongall 28 cultivars in the amount and proportion of the 5 anthocyanins.     

Editorial note

Generalist herbivores can face many challenges when choosing their host plant. This can be particularly difficult if their choice and performance are affected by host experience. Greenhouse whitefly, Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae), is an invasive generalist herbivore, which has established in year‐round greenhouses at northern latitudes where it cannot overwinter outdoors. It mainly uses crops such as cucumber (Cucumis sativus L.), tomato (Solanum lycopersicum L.), and ornamentals as host plants. However, every summer the insect escapes greenhouses and is exposed to natural vegetation. We evaluated the performance of T. vaporariorum on diverse vegetation outside greenhouses after prolonged experience of greenhouse crops. First, we surveyed the vegetation near infested greenhouses. Development success of the insect differed among wild hosts. We identified five new hosts among 12 plant species that bore pupae and were thus considered suitable as the insect's host plants. Members of the Urticaceae and Onagraceae were the most preferred and frequently inhabited by all insect life stages. The highest abundance of insects occurred in plots with low plant species richness, independent of plant family in these habitats. We then studied experimentally the impact of 1 year of preconditioning to one of three common greenhouse crops, cucumber, tomato, or poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch), on the performance of the preconditioned adults and their progeny on four wild plants. Adults from tomato and poinsettia preferred the novel host species over the species to which they were preconditioned. The whitefly population preconditioned to cucumber was the most fecund on all offered hosts. We conclude that generalist herbivores can have large variation in performance, despite polyphagy, on novel hosts as shown by the variable abundance of T. vaporariorum pupae among outdoor hosts. Furthermore, performance of whiteflies on natural vegetation was affected by experience on greenhouse crops. Based on our observations, we provide insights and recommendations for pest management.     

Interspecific Interactions among Natural Enemies ofBemisiain an Inundative Biological Control Program

Interspecific interactions among insect natural enemies have seldom been investigated experimentally within the context of biological control. Research in this area is needed due to the often contradictory predictions provided by the many theoretical models, the increasing dependence on biological control, and the concern that biological control agents may adversely affect some nontarget organisms. We describe a study whereby the occurrence and dynamics of interspecific interactions among three natural enemies (two parasitoids:Encarsia formosaandEncarsia pergandiella;and one predatorDelphastus pusillus) of the whitefly,Bemisia argentifolii(previously referred to asBemisia tabacistrain “B”), were evaluated in greenhouse cage experiments. Eight populations consisting of all possible combinations of the three natural enemies and one population of whitefly alone were established to test the following hypotheses: (1) Natural enemy introductions are capable of suppressingB. argentifoliipopulations; (2) all interspecific interactions are detrimental to achieving biological control; (3) the likelihood of achieving biological control decreases as the potential number of interspecific interactions increases; and (4) the species composition of biological control agents is of greater consequence than the number of natural enemy species released. In addition, we tested the hypothesis (5) that the frequency of interspecific interactions increases with a decrease in host or prey availability. Our results demonstrate that all combinations of natural enemies provided significant levels of whitefly suppression. While the intensities of interspecific interactions among natural enemy species were frequently positively and significantly correlated with the densities of parasitized whitefly, interspecific interactions among natural enemies were not detrimental to achieving higher levels of biological control. The composition of species released, rather than the number of species released, was of greater importance to accomplishing biological control. Releases ofD. pusillusin combination with one or both of the parasitoids provided the greatest levels of whitefly suppression. These results suggest that the types of interspecific interactions rather than the numbers of interspecific interactions among natural enemies may be important to the outcome of inundative biological control programs.