Temporal dynamics of leafy spurge (Euphorbia esula) and two species of flea beetles (Aphthona spp.) used as biological control agents

The goal of this study was to evaluate the biological control program of leafy spurge (Euphorbia esula) in a large natural area, Theodore Roosevelt National Park, western North Dakota, USA. Aphthona lacertosa and Aphthona nigriscutis have been released at more than 1800 points in the 18,600-ha South Unit of the park beginning in 1989; most releases have occurred since 1994. We established permanent vegetation plots throughout the infested area of the park and determined stem counts and biomass of leafy spurge and abundance of the two flea beetle species at these plots each year from 1999 to 2001. Both biomass and stem counts declined over the 3 years of the study. Both species of flea beetle are well established within the park and have expanded into areas where they were not released. A. nigriscutis was more abundant than A. lacertosa in the grassland areas we surveyed, but in all other habitats abundances were similar. Using structural equation models, only A. lacertosa could be shown to have a significant effect on counts of mature stems of leafy spurge. A. nigriscutis numbers were positively correlated with stem counts of mature stems. Previous year’s stem counts had the greatest influence on change in stem counts over each 2-year time step examined with structural equation models.     

Energy potential of leafy spurge (Euphorbia esula)

Leafy spurge (Euphorbia esula) is a noxious, perennial weed that infests pastures, rangeland and waste areas in the northern Great Plains. The objective of this study was to determine the productive potential of this species when grown under optimum agronomic conditions. Plants were fertilized and irrigated. Oil, hydrocarbon, total protein, and dry-weight production were measured on 3 harvest dates. Calorimetric analyses were performed to determine the potential of leafy spurge as a fuel crop. The hydrocarbon content of 12 strains of leafy spurge was determined to measure genetic variability for this trait. The addition of fertilizer doubled dryweight production but did not affect percent oil or hydrocarbon content. Oil and hydrocarbon production averaged 6.8 and 0.6% on a plant dry-weight basis. Maximum production of plant biomass, protein, and hydrocarbon was obtained from a mid-July harvest. Oil content increased later in the growing season. The total protein content of leafy spurge averaged 12%. Whole-plant biomass had a caloric value of 4,407 cal/g while the oils contained 10,019 cal/g. Leafy spurge hay can produce 4 times more energy per year than wheat straw; therefore, the immediate potential of leafy spurge whole-plant biomass as a locally grown fuel crop for home-heating purposes is suggested.     

Organogenesis in leafy spurge (Euphorbia esula L.)

Summary All parts of leafy spurge seedlings can be regenerated when isolated and placed onto B5 medium. One-centimeter isolated hypocotyl segments were tested successfully for their usefulness as a bioassay system by comparing the response of auxins, herbicides, and cytokinins. Indole-3-acetic acid (IAA) was the most effective auxin to stimulate root formation. IAA was effective whether the hypocotyl segments remained on the same medium up to 60 days, or the segments were transferred to basal media after 2 or 5 days (pulse treatment). Pulse treatments with the other auxins resulted in stimulation of root formation; continuous or 5-day pulses of higher concentrations of indole-3-butyric acid,α-naphthaleneacetic acid and especially 2,4-dichlorophenoxyacetic acid and picloram formed excessive callus instead of roots. Picloram did not stimulate root formation, whether the treatment was continuous or pulse-treated. No roots formed with continuous picloram at 0.1 mg/liter or greater, but transfer to basal media did result in root and shoot formation at about 50% of the number formed on the controls. Lesser picloram concentrations had no effect. Shoots formed readily on untreated (control) segments, but continuous treatment with all three cytokinins, kinetin, zeatin, and zeatin riboside, increased the numbers of shoots about equally. Root formation was inhibited by the cytokinins at the higher concentrations (0.1 to 0.2 mg/liter). With the exception of a 5-day pulse of 0.04 mg/liter IAA, the auxins did not stimulate shoot formation, but generally inhibited shoot formation, even in pulse-treated cultures.     

Analytical pyrolysis-pattern recognition for the characterisation of leafy spurge (Euphorbia esula L.) biotypes

Curie-point pyrolysis-gas chromatography-pattern recognition was used to elucidate chemical variations within leafy spurge (Euphorbia spp.). Hierarchical cluster analysis (HCA) readily identified two major clusters corresponding to E. esula and E. cyparissias. The E. esula cluster further separated into three distinct subclusters. Results from principal components analysis (PCA) and fuzzy c-varieties (FCVPC) pattern recognition were similar, verifying the presence of three biotypes among the E. esula samples studied. It is suggested that analytical pyrolysis in combination with pattern recognition may predict the behaviour of biocontrol agents introduced into fields to control leafy spurge.     

Interaction of rhizobacteria with leafy spurge (Euphorbia esula L.) callus tissue cells

The interaction of two rhizobacterial isolates,Pseudomonas fluorescens isolate LS 102 andFlavobacterium balustinum isolate LS 105, with leafy spurge cells at the cellular level was studied using scanning and electron microscopy. Leafy spurge callus tissue inoculated with either isolate showed considerable changes compared to non-inoculated tissue. The attachment of rhizobacteria to cell surfaces was associated with the elaboration of fibrillar material which may anchor bacteria to surfaces and contribute to mediation of the phytotoxic effect caused by rhizobacteria. At the ultracellular level, inoculated callus tissue showed numerous cell alterations including esiculation and convolution of the plasmalemma, cell wall degradation and disorganization of the cytoplasm, similar to those detected in the whole plant. It is concluded that callus tissue may provide an excellent working model to investigate the mode and/or mechanism of action of potential biocontrol agents on their host plants.     

Effect of drying on yield and calorific values of extractables from leafy spurge (Euphorbia esula)

The effect of dehydration on yield and calorific values has been investigated for oils, hydrocarbons, and polyphenols extracted from leaves of Euphorbia esula/ (leafy spurge). Methods of dehydration employed were with a warm oven (50 degrees C), a hot oven (105 degrees C), at room temperature (25 degrees C), and with freeze drying. Generally, dehydration resulted in a loss of yield for all extractives. Noteworthy exceptions were oil yields from the warm-oven- or air-dried biomass which did not differ significantly from fresh tissue. Significant differences in calorific values (range 4643-5192 cal/g) were observed for each category of whole leafy biomass dehydrated as indicated above. Dehydration reduced the calorific value of oils (range 9483-10,095 cal/g) but tended to increase the calorific values of polyphenols (range 4178-6033 cal/g). NMR spectroscopy of the oil fraction suggested that dehydration did not grossly alter the composition of oils, despite differences in yield and calorific values.     

The influence of matrix habitat on Aphthona flea beetle immigration to leafy spurge patches

Variation in movement ability by insects among different non-habitat (matrix) types may have important implications for both metapopulation dynamics and weed biocontrol practices. We used a mark-recapture experiment to explore the effects of two different matrix habitats (grass vs shrub) on the ability of two species of Aphthona (Chrysomelidae: Coleoptera) flea beetle to immigrate to patches of the invasive weed, leafy spurge. Using generalized linear models, we compared effects of the matrix habitat types, species and sex on observed immigration probabilities. Our analyses demonstrated that one species (A. nigriscutis) had a much higher immigration probability when moving through a grass-dominated matrix than a shrub-dominated matrix whereas immigration probabilities for the second species (A. lacertosa) were similar in both matrix habitats but significantly lower overall than for A. nigriscutis. Furthermore, A. nigriscutis females were more likely to immigrate to spurge patches embedded in a grass matrix than in shrub, whereas the opposite occurred for males. Our results suggest that metapopulation dynamics may be strongly affected by the type(s) of matrix habitat present on a landscape. These effects also suggest that release strategies for weed biocontrol should be tailored according to the structure of the landscape into which releases are planned. In addition, even closely related species can have significantly different movement abilities which will also affect release strategies.     

Carbon and nitrogen reserves of leafy spurge (Euphorbia esula) roots as related to overwintering strategy

Leafy spurge ( Euphorbia esula L.), a serious perennial weed of temperature range and pasture lands, has continued to colonize despite various control strategies. The persistence of this species can be attributed in part to the presence of an extensive root system containing abundant organic reserves. These components, established towards the end of the growing season, are remobilized to support early spring growth. Carbohydrates comprise the bulk of reserve material with late fall incrents in free sugars being associated with reductions in starch content. Nitrogenous components undergo significant seasonal fluxes, with free amino acids and soluble proteins reaching maxima during late fall. Asparagine, glutamic acid, serine, ornithine, proline, arginine and aspartic acid all contribute significantly to the storage of nitrogen. Changes in nitrate content are associated with the overwintering process. These observations are indicative of the role that nitrogen plays in the overwintering strategy and regenerative capacity of leafy spurge roots.     

Seasonal variation in nitrogen storage reserves in the roots of leafy spurge (Euphorbia esula) and responses to decapitation and defoliation

Seasonal fluctuations of carbohydrates and nitrogenous components in the roots of the noxious perennial leafy spurge ( Euphorbia esula L.) are strongly associated with overwintering strategy, Amino acids and distinct soluble proteins accumulate during fall and remain at elevated levels throughout winter. The formation of carbohydrate reserves in roots was not significantly affected by decapitation or selective defoliation; however, maximum amino acid and soluble protein contents were markedly reduced. In particular, the accumulation pattern of a 26 kDa protein was altered. This protein may play a role in plant conditioning and regenerative potential.     

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.     

Post hoc assessment of an operational biocontrol program: efficacy of the flea beetle Aphthona lacertosa Rosenhauer (Chrysomelidae: Coleoptera), an introduced biocontrol agent for leafy spurge

Mixed populations of Aphthona lacertosa and Aphthona czwalinae were released at more than 50 locations in Alberta in 1997. Two and 3 years post-release, beetle populations were primarily A. lacertosa, with A. czwalinae forming less than 0.5% of the sampled populations. Beetle densities were moderate (10–70 beetles per m²) or high (>70 beetles per m²) at 14% and more than 60% of the sampled sites in 1999 and 2000, respectively. Larger beetles had greater instantaneous egg loads (r²=0.424,P=0.003). In 2000, the largest beetles were found at moderate density sites and there was a significant negative relationship between beetle size and the time taken to accumulate a degree day threshold of 1230 (for females: r²=0.678,P=0.001). Sites with the most rapid accumulation of degree days have the greatest potential for beetle population growth based on potential fecundity. Changes in leafy spurge percent cover, stem density, and canopy height from 1997 to 2000 were assessed across sites with low (<10 beetles per m²), moderate, and high beetle densities in 2000. Sites with high beetle densities had significantly greater reductions of leafy spurge within 5 m of the release point than sites with low beetle densities (P<0.017). Damage caused by the beetles at high-density sites was often visible as a halo-shaped patch of dead leafy spurge stems. The significant overall reduction of leafy spurge within release patches makes A. lacertosa a promising biocontrol agent for leafy spurge in Alberta.     

Effect of Leafy Spurge (Euphorbia esula) Genotype on Feeding Damage and Reproduction of Aphthona spp.: Implications for Biological Weed Control

North American leafy spurge (Euphorbia esula L.) is genetically diverse and composed of multiple genotypes introduced from several areas of Europe and Asia. Five species of leafy spurge flea beetle (Aphthona spp.) have been introduced as biological control agents for leafy spurge, but were collected in a relatively small region of Europe. Greenhouse and field experiments were conducted to determine if observed variation in feeding preference and reproduction of Aphthona spp. on North American leafy spurge may be due in part to leafy spurge genotype. Leafy spurge genotypes were collected from Austria; Manitoba in Canada; and the states of Montana, Nebraska, North Dakota, South Dakota, and Wyoming in the United States. Leafy spurge genotype affected feeding but not egg laying by Aphthona spp. adults. Aphthona czwalinae/lacertosa fed slightly less in a free-choice test on a genotype from Manitoba (7%) compared to genotypes from Nebraska and North Dakota (14%). Aphthona flava tended to feed less on the Nebraska genotype than any other genotype evaluated. Reproduction of Aphthona spp. was greatly affected by leafy spurge genotype. For instance, A. czwalinae/lacertosa produced 72 adults per plant from a Nebraska genotype compared to 11 to 32 adults per plant from all other genotypes evaluated. Thus, some observed variation in establishment and reproduction of Aphthona spp. can be attributed to leafy spurge genotype.     

Attack behavior and host utilization ofAphthona chinchihi (Col.: Chrysomelidae), a potential biological control agent ofEuphorbia esula (Euphorbiaceae, leafy spurge) in North America

Aphthona chinchihi Chen was collected in China feeding on leafy spurge (Euphorbia esula L.). Studies were conducted on its host specificity in the laboratory, using field collected adults and their progeny.Aphthona chinchihi can effectively complement the impact of the other natural enemies of leafy spurge established from Europe in the U.S.A. and Canada. The adults feed on leaves and shoots and the larvae, which cause the main damage to the plant, feed on the hypogeous portion of the plant, seriously stressing the plant and preventing its vegetative spread. The host range ofA. chinchihi was studied with tests on adult feeding and oviposition, larval survival and host suitability, using 40 plant species or varieties distributed in 12 families. The experiments demonstrated that it has a high level of specificity. This flea beetle completed its life cycle only on leafy spurge. Also, because of its ecological valence,A. chinchihi has a very good potential as a biocontrol agent in North America.     

Phenology of first and peak emergence of Aphthona lacertosa and A. nigriscutis: Two flea beetles introduced for biological control of leafy spurge, Euphorbia esula L.

Nonlinear models were used to estimate first emergence and peak abundance dates for Aphthona lacertosa Rosenhauer and A. nigriscutis Foudras, two flea beetles introduced to control leafy spurge, Euphorbia esula L., in North America. For model development, 26 field sites were sampled for flea beetle abundance at weekly intervals for eight weeks in three western Minnesota counties in 2000, 2001, and 2002. A three-parameter Weibull function, fit to observed cumulative probability distributions, were used to predict accumulated degree-days (ADD) to first emergence. Bias testing indicated the Weibull function provided a useful estimate of first emergence for A. lacertosa (304 ADD, lower developmental threshold 7.5 °C), but failed to produce a useful estimate for A. nigriscutis. A third-order polynomial was used to approximate seasonal abundance and predict peak abundance for each species. Estimated ADD to peak abundance of A. lacertosa was 594 ± 24 (DD > 7.5 °C) and 670 ± 15 (DD > 9.3 °C) for A. nigriscutis. Models were validated with additional data sets from Minnesota, Montana, and North Dakota. Estimated date of peak emergence provided useful predictions of peak emergence for Minnesota and North Dakota, but failed to predict peak emergence in Montana. We speculate that variation in climate and environmental conditions between Midwestern states and Montana were responsible for differing emergence patterns. We conclude that phenology models should be developed regionally to provide useful predictions of peak emergence for land managers. Maps were developed for Minnesota to spatially display predicted dates of peak abundance for A. lacertosa and A. nigriscutis.     

Laticifers and the classification of Euphorbia: the chemotaxonomy of Euphorbia esula L.

Laticifers and the classification of Euphorbia: the chemotaxonomy of Euphorbia esula L. Articulated and non-articulated laticifer cells represent distinctive cell types of relatively recent origin and occur in only a few families. Both types are of separate phylogenetic origin, reflecting independent evolutionary trends in the Euphorbiaceae. Supra-generic groupings of this family can be segregated into three taxonomic units using the laticifer character; with either articulated laticifers, non-articulated laticifers, or no laticifers. Such units may reflect more natural assemblages than now represented in the classification of this family. Laticifers possess chemical and morphological features of potential application as taxonomic characters to aid in delimiting species and interpreting evolutionary trends. The triterpenoid profile from latex of Euphorbia species has been shown to be diagnostic for a taxon. The qualitative and quantitative composition show a high level of stability under diverse environmental and physiological conditions indicating a genetic basis for triterpenoid synthesis. Triterpenoid profiles of known accessions of European E. esula L. and related presumptive taxa from North America readily separated them into distinctive chemotaxa that include one for E. esula L., whereas morphological features were found inadequate for separating accessions to presumptive taxa. Identification of adventive spurges in North America requires diagnostic analyses of Eurasian leafy spurges for comparison. Laticifer characters used in conjunction with relevant morphological features will provide a broadened insight into phylogenetic relationships with the Euphorbiaceae.     

Phylogenetics and taxonomy of the New World leafy spurges,Euphorbia section Tithymalus (Euphorbiaceae)

The 480 species of leafy spurges, Euphorbia subgenus Esula, represent the main temperate radiation in the large genus Euphorbia. This group is distributed primarily in temperate Eurasia, but with smaller, disjunct centres of diversity in the mountains of the Old World tropics, in temperate southern Africa and in the New World. The majority of New World diversity (32 species) occurs in a single section, section Tithymalus. We analysed sequences of the nrITS and plastid ndhF, trnH‐psbA, trnS‐trnG and trnD‐trnT regions to reconstruct the phylogeny of section Tithymalus and to examine the origins and diversification of the species native to the New World. Our results indicate that the New World species of section Tithymalus form a clade that is sister to the widespread, weedy E. peplus. The New World species fall into two primary groups: a ‘northern annual clade’ from eastern North America and a diverse clade of both annual and perennial species that is divided into three subgroups. Within the second group, there is a small ‘southern annual clade’ from Texas and northern Mexico, a perennial ‘Brachycera clade’ from the western United States and northern Mexico, and a perennial ‘Esuliformis clade’ from montane areas of Mexico, Guatemala, Honduras and the Caribbean island of Hispaniola. Ancestral state reconstructions indicate that the annual habit probably evolved in the ancestor of E. peplus and the New World clade, with a subsequent reversal to the perennial habit. In conjunction with this phylogenetic framework, the New World species of section Tithymalus are comprehensively reviewed. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 191–228.