Insecticide metabolism by multiple glutathione S-transferases in two strains of the house fly,Musca domestica (L)

Glutathione S-transferases from two strains of house fly have been prepared in a high degree of homogeneity by a procedure involving affinity chromatography and isoelectrofocusing. They fall into two groups in each strain. One group, of isoelectric point greater than pH 6.5, catalyzes the glutathione-dependent degradation of lindane, diazinon and methyl parathion. The other group, of low isoelectric point, has conjugating activity with the model substrate CDNB, but very little activity with the insecticide substrates. In the Cornell R strain the three isoenzyme forms in the high pI group appear to be almost identical in their substrate specificities. In the A strain, it is apparent that the enzyme forms falling into this group vary markedly in substrate specificity. The dehydrochlorination of DDT paralleled very closely the conjugation of the other insecticides catalyzed by the three high pI enzymes in the Cornell R strain. In the A strain, DDT dehydrochlorinase was most strongly associated with a glutathione S-transferase isoelectric at pH 7.1. It is tentatively concluded that multiple genes are involved in the production of the glutathione S-transferases involved in pesticide metabolism in the house fly and that DDT dehydrochlorinase may be derived from some, but not all, of these same genes.     

Temperature and diet modulate cytochrome P-450 activities in southern armyworm,Spodoptera eridania (Cramer), caterpillars

Larvae of the southern armyworm, Spodoptera eridania (Cramer), grew well in the 15–30°C temperature range. Pupae survived poorly at 15°C but moths emerged from 85% of the pupae at 30°C. The time for development was prolonged at 15°C and larvae grew significantly bigger than at 30°C. Cytochrome P-450 content, cytochrome P-450 reductase, p-chloro N-methylaniline N-demethylation, methoxyresorufin 0-demethylation, and aldrin epoxidation activities were higher at 15°C than at 30°C. All cytochrome P-450 activities were more inducible by dietary pentamethylbenzene at 30°C than at 15°C. High cytochrome P-450-catalyzed activities were associated with increases in microsomal protein rather than with changes in membrane lipid or phospholipid content. Phosphatidylcholine was the major midgut membrane phospholipid. There was only a tendency towards increased unsaturation of the phospholipid fatty acyl moieties and lowered membrane phase transition temperature in cold-adapted larvae. Acute oral carbaryl toxicity was generally inversely correlated with cytochrome P-450 catalyzed activities. Carbaryl toxicity was decreased about 10-fold by pentamethylbenzene induction and about 3-fold by the lower acclimatization temperature.     

Binding of ioxynil to photosynthetic membranes

Two binding affinities for ioxynil to isolated thylakoids of the alga Bumilleriopsis filiformis are observed. Higher concentrations needed for the “low-affinity” binding site inhibit electron transport, while low ioxynil concentrations saturating the “high-affinity” binding site do not affect electron transport. For higher plant thylakoids (Chenopodium, Spinacia) the high-affinity binding site apparently is also the site to inhibit electron flow. The time dependence known for electron-transport inhibition is also apparent for the binding of phenol-type inhibitors to thylakoids of higher plants. Long incubation times (40 min) with the herbicide are necessary to equilibrate the binding site. Time dependence can be abolished by decreased pH, short trypsin or lysyl-endoprotease digestion of the isolated membranes. These treatments only increase the accessibility of the binding site, but the amount of bound herbicide after equilibration does not change. As a second effect the number of binding sites is reduced by prolonged trypsin digestion. This is not observed by treatment with a lysyl-specific protease. In contrast to herbicides like atrazine or diuron, short trypsin treatment alters the accessibility only (presumably provided by a shielding protein) but not the properties of the binding site of phenol-type herbicides. In contrast, thylakoids from the alga Bumilleriopsis, either from wild-type or a diuron resistant mutant, do not exhibit a time-dependent binding.     

A framework for examining inter-regional aerial transport of fungal spores

Aerial transport of fungal spores has no doubt been responsible for occasionally spreading plant diseases over distances of 500 km or more. With currently available methods, however, there is little basis for estimating the likelihood of such occurrences. Models capable of estimating the relative probability of infection of a crop from known sizes of local or distant sources of pathogenic spores could help farmers with decisions about fungicide use, local sanitation and quarantine. A logical framework for estimating long-distance transport of viable spores is presented which encompasses: production of spores at the source region, escape of spores into the air above the diseased crops, transport and dilution of spores in the atmosphere, survival of airborne spores and deposition of spores onto a distant crop. Hypothetical examples of spore transport over 700 km are calculated to illustrate the relative magnitudes of the five parts of the spore transport process. Although the combined uncertainties in spore transport are estimated to be a factor of 10⁴–10⁶, this should be compared to the expected factor of 10¹³ dilution of spore concentration experienced by a cloud of spores after having been transported through the atmosphere for 700 km. The largest uncertainties lie in our ability to estimate daily spore production in a geographic region, survival of spores while airborne and deposition of spores during rainfall. Survival of spores and deposition of spores during rainfall are difficult to predict because of temporal and spatial variations in weather. To account for this, it will be necessary in the future to combine the physical model of spore transport described here with weather records and air parcel trajectory calculations to develop a “climatology” of danger of disease transmission between geographic regions.     

The effects of population density and intercropping with cowpea on the water use and growth of sorghum in semi-arid conditions in Botswana

Soil moisture was measured below sorghum crops of differing density in rainfed trials in increasingly droughty conditions from 1981/2 to 1983/4. Additional measurements were made in sorghum/cowpea intercrops and cowpea monocrops during the drought seasons of 1982/3 and 1983/4.Increasing crop density, by addition of either sorghum or cowpea, resulted in increased effective root activity, which was accompanied by small increases in actual/potential evapotranspiration (E_a/E_p) early in each season. These small increases were followed by small decreases later in the season, but these effects were rarely statistically significant. Both sorghum density and intercropping had little effect on total seasonal water use.Dry matter production increased linearly with increasing seasonal water use. Water use efficiencies of dry weight production were increased by increasing sorghum density. Intercropping in dry conditions did not have significant effects on water use efficiencies. Estimates of soil evaporation suggested that the effects of density on water use efficiency could be attributed to reductions in soil evaporation.The effects of density on reproductive yields were governed by two opposing processes: increasing crop density increased water use efficiencies of dry weight production, but decreased the proportions of dry weight allocated to grain.     

Population trends and feeding preferences of flea beetles (Phyllotreta cruciferae Goeze) in collard-wild mustard mixtures

Population densities of flea beetles (Phyllotreta cruciferae Goeze) were lower per unit collard plant in polycultures composed either of non-host plants (field bean, vetch and barley) or of additional host plants (wild mustard) than in collard monocultures. Flea beetles exhibited decreased movement patterns in the non-host polycultures, but similar movement activity in the monoculture and collard-wild mustard polyculture. Differences in flea beetle abundance between collard monoculture and collard-wild mustard polycultures disappeared when flowers were artificially removed from wild mustard. Significantly fewer flea beetles occurred in collard rows immediately adjacent to wild mustard borders, but their numbers tended to increase further away from the border. Collard plants sprayed with wild mustard extracts, and especially with allylisothiocyanate emulsions, proved to be more attractive to flea beetles than collard plants sprayed with water. Flower extracts seemed to exert greater attraction than leaf extracts. Understanding of these spatial and temporal interactions (apparently chemically mediated) could lead to development of effective trap cropping systems for flea beetle control in crucifer crops.     

A statistical study of seven curves for describing the sorption of phosphate by soil

Seven mathematical models, which have been advanced for describing phosphate sorption by soils, are studied here with respect to their statistical behaviour in estimation. These seven non-linear regression models include the Langmuir equation and two extensions of it, the Freundlich equation and two extensions of it, and Gunary's equation. Measures of non-linear behaviour, such as the Bates & Watts (1980) curvature measure of intrinsic non-linearity and the Lowry & Morton (1983) asymmetry measure of non-linearity, were calculated for each model in combination with each of six data sets. It was found that the Freundlich equation and the extension of it proposed by Sibbesen behaved best, with Gunary's equation also having acceptable statistical properties, whereas the Langmuir equation and its extensions behaved worse, exhibiting properties which indicate that the estimators of their parameters would be severely biased and non-normal in distribution. It is believed that similar conclusions may apply to other processes involving surface adsorption.