Prevention of Toxoplasma gondii abortion in goats by vaccination with oocysts of Hammondia hammondi

Nineteen does (female goats) were dosed with 500,000 oocytes of Hammondia hammondi prior to breeding. At about 90 days of gestation these, and 18 uninoculated does were challenged with 25,000 Toxoplasma gondii oocysts. The 19 H. hammondi--inoculated does produced 26 live and one dead kid (newborn goat). The 18 does not given H. hammondi produced 12 live and 19 dead kids. However, examination of all of the kids by isolation of T. gondii in mice, serology and histology revealed that they were all infected with T. gondii. Thus, while H. hammondi "vaccination" is protective against the deleterious effects of T. gondii on pregnant does, perhaps by reducing the severity of placental lesions, it does not prevent foetal infection.     

Potassium leaching from cut grassland and from urine patches

In grassland farming, especially on coarse‐textured soils, K can be a critical element. On these soils, the actual K management as well as fertilizer history to a large extent determine the leaching of K. The effects of four fertilizer regimes on the nutrient balances and leaching of K from grassland grown on a sandy soil were investigated. The swards differed in the source and level of N input and K fertilizer: no fertilizer N + 166 kg K ha^?1 year^?1 (Control), 320 kg inorganic N ha^?1 + 300 kg K ha^?1 year^?1 (MIN 320), 320 kg N + 425 kg K ha^?1 year^?1 in form of cattle slurry (SLR 320) and a grass–clover sward + 166 kg K ha^?1 year^?1 (WCL 0) without any inorganic N input. In a second experimental phase, cores from these swards were used in a mini‐lysimeter study on the fate of K from urine patches. On cut grassland after 6 years K input minus removal in herbage resulted in average K surpluses per year of 47, 39, 56 and 159 kg K ha^?1 for the Control, MIN 320, WCL 0 and SLR 320, respectively. Related leaching losses per year averaged 7.5, 5, 15 and 25 kg K ha^?1. Losses of urinary‐K through leaching were 2.2–4.5 and 5.7–8.4% of the K supplied in summer and autumn applications, respectively. Plant and soil were the major sinks for K from fertilizer or urine. High levels of exchangeable K in the soil and/or large and late fertilizer or urine applications stimulated leaching of K.     

Comparative analysis of neonicotinoid binding to insect membranes: I. A structure-activity study of the mode of [3H]imidacloprid displacement in Myzus persicae and Aphis craccivora

Neonicotinoids bind selectively to insect nicotinic acetylcholine receptors with nanomolar affinity to act as potent insecticides. While the members of the neonicotinoid class have many structural features in common, it is not known whether they also share the same mode of binding to the target receptor. Previous competition studies with [3H]imidacloprid, the first commercialised neonicotinoid, indicated that thiamethoxam, representing a novel structural sub-class, may bind in a different way from that of other neonicotinoids. In the present work we analysed the mode of [3H]imidacloprid displacement by established neonicotinoids and newly synthesized analogues in the aphids Myzus persicae Sulzer and Aphis craccivora Koch. We found two classes of neonicotinoids with distinct modes of interference with [3H]imidacloprid, described as direct competitive inhibition and non-competitive inhibition, respectively. Competitive neonicotinoids were acetamiprid, nitenpyram, thiacloprid, clothianidin and nithiazine, whereas thiamethoxam and the N-methyl analogues of imidacloprid and clothianidin showed non-competitive inhibition. The chloropyridine or chlorothiazole heterocycles, the polar pharmacophore parts, such as nitroimino, cyanoimino and nitromethylene, and the cyclic or acyclic structure of the pharmacophore were not relevant for the mode of inhibition. Consensus structural features of the neonicotinoids were defined for the two mechanisms of interaction with [3H]imidacloprid binding. Furthermore, two sub-classes of non-competitive inhibitors can be discriminated on the basis of their Hill coefficients for imidacloprid displacement. We conclude from the present data that the direct competitors share the binding site with imidacloprid, whereas non-competitive compounds, like thiamethoxam, bind to a different site or in a different mode.     

Comparative analysis of neonicotinoid binding to insect membranes: II. An unusual high affinity site for [3H]thiamethoxam in Myzus persicae and Aphis craccivora

Neonicotinoids represent a class of insect-selective ligands of nicotinic acetylcholine receptors. Imidacloprid, the first commercially used neonicotinoid insecticide, has been studied on neuronal preparations from many insects to date. Here we report first intrinsic binding data of thiamethoxam, using membranes from Myzus persicae Sulzer and Aphis craccivora Koch. In both aphids, specific binding of [3H]thiamethoxam was sensitive to temperature, while the absolute level of non-specific binding was not affected. In M persicae, binding capacity (Bmax) for [3H]thiamethoxam was ca 450 fmol mg(-1) of protein at 22 degrees C and ca 700 fmol mg(-1) of protein at 2 degrees C. The negative effect of increased temperature was reversible and hence not due to some destructive process. The affinity for [3H]thiamethoxam was less affected by temperature: Kd was ca 11 nM at 2 degrees C and ca 15 nM at 22 degrees C. The membranes also lost binding sites for [3H]thiamethoxam during prolonged storage at room temperature, and upon freezing and thawing. In A craccivora, [3H]thiamethoxam was bound with a capacity of ca 1000 fmol mg(-1) protein and an affinity of ca 90 nM, as measured at 2 degrees C. Overall, the in vitro temperature sensitivity of [3H]thiamethoxam binding was in obvious contrast to the behaviour of [3H]imidacloprid studied in parallel. Moreover, the binding of [3H]thiamethoxam was inhibited by imidacloprid in a non-competitive mode, as shown with M persicae. In our view, these differences demonstrate that thiamethoxam and imidacloprid, which represent different structural sub-classes of neonicotinoids, do not share the same binding site or mode. This holds also for other neonicotinoids, as we report in a companion article.     

Pymetrozine,a Fast-Acting and Selective Inhibitor of Aphid Feeding. In-situ Studies with Electronic Monitoring of Feeding Behaviour

Pymetrozine, a pyridine azomethine compound, represents a novel insecticide with a selective activity against homopteran insects. It acts in a unique way: aphids are not knocked down on contact but seem to die of starvation. This implies an effect of pymetrozine on feeding behaviour. The aim of the present work was to elucidate how and at which step pymetrozine interferes with the complex mechanisms underlying phloem feeding. The effect of pymetrozine, applied in various ways, on different phases of stylet penetration and feeding activity of individual aphids was studied using the Electrical Penetration Graph technique (EPG). Initial choice experiments indicated that pymetrozine does not have a deterrent or antifeedant action. Topical application (150 ng pymetrozine mg^-1 fresh weight) inhibited stylet insertion into the plant. When injected, less than 30 ng mg^-1 was sufficient to produce the same effect. When pymetrozine was systemically applied via plant spraying or root uptake, aphids started feeding normally. After some time, however, they withdrew their stylets from the phloem and walked around with unaffected locomotion. At low doses aphids eventually recovered and resumed feeding. High doses, however, irreversibly disrupted feeding and prevented stylet reinsertion. Aphid motility was not affected up to an estimated haemolymph concentration of 1 mM pymetrozine. Aphids which eventually stopped feeding on pymetrozine-treated plants showed EPGs with distorted salivation/ingestion patterns. It is concluded that pymetrozine does not have a general toxic effect on aphids but selectively interferes with the nervous regulation of feeding behaviour which consequently results in death due to starvation after a few days. © 1997 SCI.     

Evaluation of hemato-immunological parameters during the reproductive cycle of the scallop Nodipecten nodosus in association with a carotenoid-enriched diet

The cultivation of scallops Nodipecten nodosus is a promising activity emerging in Brazil. The purpose of this study was to characterize the immune system of N. nodosus and evaluate the modulation of some hemato-immunological parameters during the reproductive cycle, in association with an astaxanthin-enriched diet. It was hypothesized that a supplementation on astaxanthin could enhance scallop immune system and minimize stress of reproduction. Scallops were separated in different groups: juveniles (J), adults (A), sexually mature (M), and recently spawned (S) animals. The last two groups were fed standard (M and S) or astaxanthin-enriched (Ma and Sa) diets. Scallop hemolymph contained two hemocyte populations: hyaline (HH) and granular hemocytes (GH). Antimicrobial peptides, similar to mussel defensins and mytilins, were found by immunodetection within the GH granules, even though the scallop hemolymph did not exhibit significant antimicrobial activity against different bacteria, including marine vibrios. Scallop hemocytes were able to phagocytose zymosan and produce reactive oxygen intermediates (ROI–NBT reduction). The number of circulating hemocytes (Neubauer chamber) varied from 12 to 26.10⁶ cells mL^− 1, and the GH was always the predominant cell type (67–99%). The plasma of N. nodosus contained lectins, specific to galactose and sialoconjugates, and their agglutinating activity was partially calcium-dependent. A phenoloxidase (PO) activity (146–446 U min^− 1 mg^− 1) was observed in the scallop hemolymph. However, this activity was not induced by trypsin or components of microorganism surface, and was strongly enhanced by alkaline pH (≥ 8.5). The total protein concentration of the plasma varied from 240 to 660 μg mL^− 1. In general terms, all examined hemato-immunological parameters (hemograms, superoxide anion production, PO activity, lectin titers and total protein concentration) had a similar profile during all the scallop reproductive cycle. Their levels increased significantly from juveniles to adults (except PO activity), and declined markedly (immune depletion) in the sexually mature scallops. After spawning, the animals had a tendency to recover the standard levels of their immune parameters. Apparently, the astaxanthin-enriched diet had no effect on the tested immune parameters except for a slight influence on the scallop immune-oxidative reactions (ROI production). The results obtained in this study suggested the occurrence of a general immune depletion in the sexually mature scallops, confirming that the reproductive stage is a critical period in scallop life.