Low Residual Effect Research Articles

Expression of mosquito active toxin genes by a Colombian native strain of the gram-negative bacterium Asticcacaulis excentricus.

Mosquito control with biological insecticides, such as Bacillus sp. toxins, has been used widely in many countries. However, rapid sedimentation away from the mosquito larvae feeding zone causes a low residual effect. In order to overcome this problem, it has been proposed to clone the Bacillus toxin genes in aquatic bacteria which are able to live in the upper part of the water column. Two strains of Asticcacaulis excentricus were chosen to introduce the B. sphaericus binary toxin gene and B. thuringiensis subsp. medellin cry11Bb gene cloned in suitable vectors. In feeding experiments with these aquatic bacteria, it was shown that Culex quinquefasciatus, Aedes aegypti, and Anopheles albimanus larvae were able to survive on a diet based on this wild bacterium. A. excentricus recombinant strains were able to express both genes, but the recombinant strain expressing the B. sphaericus binary toxin was toxic to mosquito larvae. Crude protease A. excentricus extracts did not degrade the Cry11Bb toxin. The flotability studies indicated that the recombinant A. excentricus strains remained in the upper part of the water column longer than the wild type Bacillus strains.

The effects of refuge size and number on acarine predator–prey dynamics in a pesticide‐disturbed apple orchard

1. In apple orchards, the use of pesticides such as pyrethroids for the control of lepi dopteran and dipteran pests can severely disturb natural equilibria by killing or repelling acarine predators. After spraying, phytophagous mite populations will often subsequently increase to densities which are above economic thresholds. To conserve predator populations we manipulated the size and number of predator refuges. Refuges were made with various sizes of polyethylene sheeting placed over 0, 10, 30, 60 or 100% of the leaves on trees before spraying with the pyrethroid permethrin. 2. At the time of spraying the phytoseiid predator Typhlodromus caudiglans and the stigmaeid predator Zetzellia mali were present in similar densities. The main phytophagous mites present were the tetranychid mites Panonychus ulmi and Tetranychus urticae. After spraying, Typhlodromus caudiglans was virtually eliminated from sprayed leaves, but not from refuge leaves. Recolonization of sprayed leaves by T. caudiglans was slow, probably due to toxic or repellent effects of the pyrethroid residue. Densities of Z. mali were only slightly affected by the pyrethroid, but this species was unable to control tetranychid densities on sprayed leaves in the absence of T. caudiglans. After spraying, P. ulmi and Tetranychus urticae increased on sprayed leaves to densities well in excess of crop economic thresholds, while densities remained low on refuge leaves. 3. The major effect of refuge size was a high positive correlation between entire‐tree densities of T. caudiglans and refuge size, and a high negative correlation with P. ulmi densities. The refuge size necessary to control P. ulmi to below economically damaging densities was predicted to be in excess of 60% of each tree. Thus, only 40% of each tree would receive a pyrethroid spray. This is not practical for management purposes as the reduced spray coverage is unlikely to control target lepidopteran and dipteran pests. No significant effects of refuge number were observed. 4. The application of a pyrethroid spray resulted in a major disturbance to natural acarine population dynamics in this orchard for up to 11 weeks after spraying. While refuges were useful in conserving a population of the predator Typhlodromus caudiglans and reducing entire‐tree densities of phytophagous mites, the use of refuges may be more valuable when using pesticides with a lower residual effect.

Comparative Evaluation of Five Surgical Hand Scrub Preparations: New data on the efficacy of hand scrub preparations

Abstract Surgical hand scrubs should remove microorganisms from health care professionals' hands and forearms and maintain the lowest possible microbial counts during surgical procedures. This study evaluated the immediate, persistent, and residual efficacy of five surgical hand scrub products. The two chlorhexidine gluconate CHG) products achieved significant immediate reduction in the microorganism count and demonstrated persistent and residual efficacy. The iodophor product exhibited effective immediate and persistent antimicrobial properties but failed to show significant residual effects. The parachlorometaxylenol products demonstrated low levels of immediate and persistent effects and no residual antimicrobial effects. The alcohol product demonstrated low immediate, persistent, and residual effects. The investigator concludes that CHG products are the most favorable surgical hand scrub preparations. AORN J 60 (August 1994) 246-256.

Direct and Residual Effect of Different Organic Fertilizers on Potato and Cereals

AbstractField experiment with 8 different organic fertilizers (cattle dung with and without litter, pig slurry, peat compost formed from hen and pig slurry, sawdust‐duck manure, noncomposted peat and straw litter with pig slurry) was carried out on loamy brown podzoluvisol since 1985.The organic fertilizers were applied in the spring of 1985 on two backgrounds: with and without mineral fertilizers. The material is based on the data of four years (1985–1988). The arrangement of crops was the following: potato, spring wheat, barley and early barley.On both backgrounds cattle dung with litter turned out to be the best organic fertilizer, while noncomposted peat manure had a low direct and residual effect. However, before the application it must be composted with pig or hen slurry. The effect of peat composts was dependent on the background of mineral fertilizers. Pig slurry had a low residual effect and acted only as a liquid nitrogen fertilizer. The joint application of straw and pig slurry can be a suitable opportunity for diminishing their undesirable effects.

Polymers' Effects on Infiltration and Soil Erosion during Consecutive Simulated Sprinkler Irrigations

AbstractImpact energy of water drops from overhead sprinkler irrigation can cause seal formation, and an increase in runoff and in soil erosion. The effects of low concentrations (5, 10, and 20 g m−3) of two polymers, an anionic polyacrylamide (PAM) and a cationic polysaccharide (PSD), on soil permeability and erosion from a grumusol (Typic Chromoxerert) and a loess (Typic Haploxeralf), were studied during five consecutive irrigations of 60 mm each. The polymers were added to the irrigation water during the first three consecutive irrigations, and thereafter the soils were subjected to two additional irrigations of water only. During the first three irrigations, the final infiltration rates (FIR) of the soils were significantly higher than those of the untreated samples (control). In the subsequent two irrigations with water only, the FIR values of the treated samples decreased to values similar to those of the control. The low residual effect of the polymers was explained by erosion of the thin treated layer and an insufficient amount of the polymers. A lower concentration of PAM (10 g m−3) was needed for optimal effect on the FIR and cumulative infiltration, compared with PSD (20 g m−3). For the optimal treatments, infiltration parameters were generally higher in the PAM‐ than in the PSD‐treated soils. Soil losses in all the PAM treatments were significantly lower than those in the PSD treatments. Both polymers stabilized soil aggregates, but PAM also cemented aggregates together and increased their resistance to erosion.

Effects of soil and foliar applications of sodium borate to sugar beet

AbstractThe effects were examined of liquid and solid applications of sodium borates, used at the rate of 20 lb. borax equivalent/acre, to sugar beet at seeding, mid‐June and late August. The trials were conducted at twelve sites on light‐land farms in East Anglia, selected as far as possible as having a previous history of boron deficiency.Treatments were effective in controlling, but not always entirely eliminating, boron‐deficiency symptoms, and had no detrimental influence on germination, population or growth. Nevertheless yields of roots and sugar, and sugar content, were increased significantly only at severely deficient sites; juice purity was not improved nor was noxious nitrogen reduced even at such sites; and these trials lend no support to theories that boron addition has some specific value in increasing sugar content, even where soils have a normal supply of the element. Leaf weight was increased more consistently, even where boron had no effect on root yield and there were no noticeable deficiency symptoms. Climatic and soil influences were very marked, serious deficiency being more prevalent in drier years and on lighter soils, where temporary attacks in intermittent dry periods were also liable to occur. No consistent differences could be observed between liquid or solid applications whether to the seed bed or to the growing crop, but August treatment in neither case gave good results.Boron analyses were made on soils and leaves. Results suggest that soil analysis (either for total or available boron) is an unreliable means of diagnosing boron requirement, that roots neither reflect boron contents of soils or plants, nor the results of boron addition. The analysis of blades of older leaves in June when it is not too late to take the necessary corrective action, is the best procedure for sugar beet. The available boron content of soils and the total boron content of plants were highest in late summer, and even where boron had been added in August, residual effects were small and well below the safety margin for crops less tolerant than beet. In view of climatic hazards, the uncertainty of soil analysis as a means of diagnosis, the low residual effects of boron addition, and the damaging losses from serious deficiency, a routine application of borate to all sugar beet crops grown on lighter soils seems a wise precaution. These trials indicate that for this purpose a foliar spray applied in June, or after singling, is just as effective as a fertiliser applied to the seed bed.