Host gall size and oviposition success by the parasitoid Eurytoma gigantea

Abstract. 1. Eurytoma gigantea Walsh is a specialist parasitoid of the tephritid gallmaker Eurosta solidaginis (Fitch).
2. In the natural environment the incidence of parasitism by Eurytoma is greater in small galls than in large ones.
3. Laboratory experiments demonstrated that small galls are not more frequently discovered; however, oviposition attempts on small galls were more likely to be successful.
4. Eurytoma spends much time probing galls too big to penetrate; this leads to a decrease in foraging efficiency when many large galls are present.
5. The chance of successfully penetrating a gall depends on the thickness of the gall wall and the length of the parasitoid's ovipositor.
6. A simulation model was constructed which shows that a gallmak-er's chance of being parasitized depends on gall size, the number of parasitoids that discover the gall, and their ovipositor lengths.     

Multiple forms of amylase in leaf extracts: electrophoretic transfer of the enzyme forms into amylose-containing polyacrylamide gels

A method for the analysis of multiple forms of glucan-degrading enzymes is described. The procedure consists of the separation of the proteins by electrophoresis or isoelectric focusing in glucan-free polyacrylamide gels followed by the nondenaturing electrophoretic transfer into a second polyacrylamide layer which contains immobilized glucans. The method combines the resolving power of electrophoretic separations in glucan-free media with the sensitivity of amylase activity detection in amylose-containing polyacrylamide gels. The procedure is especially useful when samples containing low amylase activity, but a large number of multiple enzyme forms, are to be analyzed.     

The Relationship between the Traits of the Two-Row Spike,the High Number of Thillers,and the High Regeneration Capacity in in vitro Culture in Barley

In barley (Hordeum vulgare L.), the traits of the two-row spike, the high rate of plant tillering, and the high capacity for multiple plant regeneration (MPR) in a callus culture of immature embryos were shown to correlate. When a dihaploid line (DH) obtained from cv. Golden Promise (two-row spike, high number of thillers) was crossed to a DH line from cv. Bruce (six-row spike, low number of thillers), the two-row trait dominated the F₁ generation, whereas, in F₂, the segregation ratio was 3 : 1. From F₃ progeny, we isolated the families comprising two-row homo- and heterozygotes and six-row homozygotes. In an F₃ hybrid population, the two-row plants manifested higher tillering and MPR rates as compared to the six-row plants. The correlation between the traits of the two-row spike, the high tillering, and the high MPR capacity may depend on the pleiotropic V gene, which controls the general mechanisms of meristem functioning essential for the development of these three traits.     

Adaptation to salinity at the plant cell level

Summary Various mechanisms of adaptation of plant cells to salinity are reviewed: (1) protection of enzymes and maintenance of turgor by organic solutes; (2) prevention of ion toxicity by compartmentation; and (3) energization of solute transport by the proton pump. All these mechanisms seem to play a role in adaptation. The particular advantages of using salt-adapted cells in suspension culture to identify mechanisms of adaptation are pointed out.     

Understanding plant reproductive diversity

Flowering plants display spectacular floral diversity and a bewildering array of reproductive adaptations that promote mating, particularly outbreeding. A striking feature of this diversity is that related species often differ in pollination and mating systems, and intraspecific variation in sexual traits is not unusual, especially among herbaceous plants. This variation provides opportunities for evolutionary biologists to link micro-evolutionary processes to the macro-evolutionary patterns that are evident within lineages. Here, I provide some personal reflections on recent progress in our understanding of the ecology and evolution of plant reproductive diversity. I begin with a brief historical sketch of the major developments in this field and then focus on three of the most significant evolutionary transitions in the reproductive biology of flowering plants: the pathway from outcrossing to predominant self-fertilization, the origin of separate sexes (females and males) from hermaphroditism and the shift from animal pollination to wind pollination. For each evolutionary transition, I consider what we have discovered and some of the problems that still remain unsolved. I conclude by discussing how new approaches might influence future research in plant reproductive biology.     

Plant Sources of Chinese Herbal Remedies: Effects on Pratylenchus vulnus and Meloidogyne javanica

More than 500 plant species, used alone or in combination, are documented in Chinese traditional medicine to have activity against helminth and micro-invertebrate pests of humans. We subjected 153 candidate medicines or their plant sources to multilevel screening for effectiveness against plant-parasitic nematodes. For extracts effective in preliminary screens, we determined time-course and concentration-response relationships. Seventy-three of the aqueous extracts of medicines or their plant sources killed either Meloidogyne javanica juveniles or Pratylenchus vulnus (mixed stages), or both, within a 24-hour exposure period. Of 64 remedies reported as antihelminthics, 36 were effective; of 21 classi- fied as purgatives, 13 killed the nematodes; of 29 indicated as generally effective against pests, 13 killed the nematodes. Sources of extracts effective against one or both species of plant-parasitic nematodes are either the whole plant or vegetative, storage or reproductive components of the plants. Effective plants include both annuals and perennials, range from grasses and herbs to woody trees, and represent 46 plant families.     

Role of plant parasitic nematodes and abiotic soil factors in growth heterogeneity of sugarcane on a sandy soil in South Africa

A feature of many sugarcane fields is the patchy growth. This is often thought to be due to physical or chemical differences in the soil. In this paper we investigate the causes of growth heterogeneity of sugarcane on a sandy soil in KwaZulu-Natal, South Africa. To identify the factors that were associated with the good and poor areas, soil texture, pH, organic matter content and a number of soil chemical elements and nematode community data were subjected to principal component analysis (PCA). The numbers of each of the nematode species (Meloidogyne sp., Pratylenchus zeae, Helicotylenchus dihystera, Xiphinema elongatum and Paratrichodorus sp.) were first converted to relative proportions of ectoparasites and endoparasites. The data were collected from the 2nd ratoon crop of a nematicide trial, where half of the plots had been treated with aldicarb in the preceding two crops. Yields of control plots varied from 34.7 to 126.8 t cane ha^–1 and from 85.4 to 138.7 for the treated plots. The yield data were centred and normalised separately for the treated and control plots and the values projected on the trial map to study spatial distribution. Plots with above-average yields, whether treated or untreated, occurred in the lower part of the trial site. The PCA factorial values were also projected onto the map of the trial. According to the first factor of the analysis of the abiotic soil characteristics in the 0–20 cm surface layer, the trial site could be divided into two areas, one on the left and one on the right. PCA of the soil data from the 0–20 and 20–40 cm layers showed that there was little or no difference between the two that might explain the two growth areas. However, analysis of the nematode community distinguished two main areas that largely corresponded to the distribution of the plots of low and high yielding cane. Correlation analysis confirmed the relationship between nematodes and yield. H. dihystera was positively correlated with yield of cane whereas the reverse was true for the Meloidogyne species.     

Influence of Nutrient Availability on the Interaction Between Spotted Knapweed and Bluebunch Wheatgrass

Centaurea maculosa (Lam.) (spotted knapweed) reduces wildlife and livestock habitat biodiversity and increases erosion. Nutrient availability to plants may be used to accelerate succession away from spotted knapweed. Early‐successional plant communities often have high nutrient availability, whereas late‐successional communities are often found on lower nutrient soils. We hypothesized that removal of nutrients would change the competitive advantage from spotted knapweed to Pseudoroegneria spicatum (bluebunch wheatgrass) (late seral). In two addition series matrices, background densities of Secale cereale (annual rye) and Elymus elimoides (bottlebrush squirreltail) (3,000 seeds/m²) were used to remove nutrients from the soil. In another set of addition series matrices, nitrogen (33 kg/ha) or phosphorus (33 kg/ha) were added to the soil. Nutrient analysis of soil and vegetation indicated that annual rye and bottlebrush squirreltail reduced nutrient availability in soils. In another matrix, neither a background density nor nutrients were added. Data were fit into Watkinson's curvilinear model to determine the competitive relationship between bluebunch wheatgrass and spotted knapweed. This allowed comparison of the equivalence ratios (C) generated from each addition series. The C parameters are the per‐plant equivalent of bluebunch wheatgrass or spotted knapweed and can be interpreted as the ratio of intra‐to‐interspecific competition. The C parameters are also the equivalence ratio of the number of spotted knapweed it takes to have equivalent effect on bluebunch wheatgrass or the number of bluebunch wheatgrass having the equivalent effect on spotted knapweed. Without nutrient manipulation, spotted knapweed was more competitive than bluebunch wheatgrass. The C for bluebunch wheatgrass was 0.17, indicating that 0.17 knapweed plants were competitively equivalent to one wheatgrass. Annual rye changed the competitive balance in favor of bluebunch wheatgrass (C = 9.9). Addition of nitrogen, phosphorus, or the mid‐seral species did not change the competitive relationship between the two species. This preliminary study suggests that succession from spotted knapweed to late‐seral bluebunch wheatgrass community may be accelerated by altering resource availability.     

Pollen-based biome reconstruction for southern Europe and Africa 18,000 yr bp

Pollen data from 18,000 ¹⁴C yr bp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present‐day biomes are shown. Forest and xerophytic woods/scrub were replaced by steppe, both in the Mediterranean region and in southern Africa, except in south‐western Cape Province where fynbos (xerophytic scrub) persisted. Sites in the tropical highlands, characterized today by evergreen forest, were dominated by steppe and/or xerophytic vegetation (cf. today’s Ericaceous belt and Afroalpine grassland) at the last glacial maximum. Available data from the tropical lowlands are sparse but suggest that the modern tropical rain forest was largely replaced by tropical seasonal forest while the modern seasonal or dry forests were encroached on by savanna or steppe. Montane forest elements descended to lower elevations than today.     

An Evaluation of Revegetation Success on Bauxite Residue

The current study was undertaken to evaluate the success of a revegetation program on three sites within the Bauxite Residue Disposal Area at the Aughinish Alumina Ltd. refinery. This was achieved by determining botanical diversity, substrate conditions, and plant uptake. Two sites revegetated in 1999, with and without the use of gypsum, were assessed and compared to a site revegetated in 1997. Compared to an initial 6 species used in seeding, a total of 47 species were recorded growing on the three sites with greatest diversity on the 1997 site. There was limited variation in the residue properties of the three treatments indicating that diversity was most influenced by succession and not substrate conditions. Limited available manganese was found in all treatments and significantly lower exchangeable magnesium in the gypsum-amended treatment. Exchangeable sodium, aluminum, and pH in the substrate were not at levels of concern. Appreciable nitrogen, phosphorus, and potassium were found as a result of a fertilizing program. Dominant species in the 1999 treatments, Holcus lanatus and Trifolium pratense , were analyzed for elemental composition. Compared to previous studies, foliar nitrogen, phosphorus, potassium, and calcium were adequate and sodium levels were low. Manganese and magnesium levels were low, and availability should be assessed as part of the monitoring program. Furthermore, the effect of a fertilizing regime on plant uptake and substrate conditions needs to be assessed.