Acute oral toxicity of zinc phosphide: an assessment for wild house mice (Mus musculus)

Irregular plagues of house mice, Mus musculus, incur major economic impacts on agricultural production in Australia. The efficacy of zinc phosphide (ZnP), the only registered broadacre control agent for mice, is reported as increasingly variable. Have mice become less sensitive over time or are they taking a sub-lethal dose and developing aversion? In this laboratory study, the sensitivity of mice (wild caught; outbred laboratory strain) was assessed using oral gavage of a range of ZnP concentrations. The estimated LD₅₀ values (72–79 mg ZnP/kg body weight) were similar for each mouse group but are significantly higher than previously reported. The willingness of mice to consume ZnP-coated grains was determined. ZnP-coated grains (50 g ZnP/kg grain) presented in the absence of alternative food were consumed and 94% of wild mice died. Mice provided with alternative food and ZnP-coated wheat grains (either 25 or 50 g ZnP/kg grain) consumed toxic and non-toxic grains, and mortality was lower (33–55%). If a sublethal amount of ZnP-coated grain was consumed, aversion occurred, mostly when alternative food was present. The sensitivity of wild house mice to ZnP in Australia is significantly lower than previously assumed. Under laboratory conditions, ZnP-coated grains coated with a new higher dose (50 g ZnP/kg grain) were readily consumed. Consumption of toxic grain occurred when alternative food was available but was decreased. Our unambiguous findings for house mice indicate a re-assessment of the ZnP loading for baits used for control of many rodents around the world may be warranted.     

Determinants of income-earning strategies and adoption of conservation practices in hillside communities in rural Honduras

Based on the results of participatory diagnostic surveys conducted in 95 rural communities in the hillsides of Honduras, we determine income earning strategies at the community level; identify their main determinants; and analyze the adoption of of conservation practices. Eight income-earning strategies were distinguished that reflect differences in comparative advantage between communities. We explain the choice of income earning strategy using a multinomial logit model that includes biophysical, economic, social and institutional variables. We use a probit model to show that adoption of conservation practices is determined by the type of income earning strategy, population density, market access, and organizational variables.     

Inverse Modeling to Quantify Irrigation System Characteristics and Operational Management

Remotely sensed (RS) data is a major source to obtain spatialdata required for hydrological models. The challenge for thefuture is to obtain besides the more direct observable data(landcover, leaf area index, digital elevation model andevapotranspiration), non-visible data such as soilcharacteristics, groundwater depth and irrigation practices.In this study we have explore the option of using inversemodeling to obtain these non-RS-visible data. For a commandarea in Haryana, India, we applied for the 2000–2001 rabiseason a RS-GIS-combined inverse modeling approach to derivenon-RS-visible data required in the regional application ofhydrological models. A Genetic Algorithm loaded stochasticphysically based soil-water-atmosphere-plant model (SWAP) wasdeveloped for the inverse problem and used in the study. Theresults showed good agreement with the inventoried data suchas soil hydraulic properties, sowing dates, groundwaterdepths, irrigation practices and water quality. The deriveddata could be used to predict the state of the system at anytime in the cropping season, which can be used to evaluateoperational management strategies.     

Concentration-Dependent Mobility of Chlorfenvinphos in Isolated Plant Cuticles

The mobility of chlorfenvinphos in isolated pear (Pyrus communis cv. Bartlett) leaf cuticular membranes (CM) was studied as a function of concentration of chlorfenvinphos sorbed in the cuticle. Mobilities of chlorfenvinphos increased approximately 9-fold when the amount sorbed increased from 1 to 100 μg cm⁻² pear leaf cuticle. From the amounts per area, average volume fractions of chlorfenvinphos in the cuticle were calculated ranging from 2×10⁻³ to 5·1×10⁻². The increase in mobilities was steepest at the lower and levelled off at higher volume fractions. This correlation could be described for the whole range of volume fractions investigated by an equation which assumes homogeneously dispersed chlorfenvinphos. Temperature dependence of mobilities was studied at 17, 25 and 35°C and chlorfenvinphos volume fractions of 5·5×10⁻³ and 0·12, respectively. Arrhenius graphs were linear for both volume fractions, showing that cuticles did not undergo a phase transition due to the high amount of sorbed chlorfenvinphos. However, at a volume fraction of 0·12, the activation energy of diffusion, E_D, was significantly lower (83·6 kJ mol⁻¹) than at 5·5×10⁻³ (135 kJ mol⁻¹). We interpret these findings as evidence for a plasticising effect on cuticular waxes by chlorfenvinphos. So far, such an effect had been demonstrated only for certain adjuvants (ethoxylated alcohols) but not for active ingredients. Chlorfenvinphos not only increased its own mobility in pear leaf cuticles, but also that of 2,4-D in Citrus leaf cuticles. This would be expected if plasticising of waxes was the sole mechanism responsible for increased mobilities. From these data we predict that permeabilities of cuticles to chlorfenvinphos are not constant. Depending on temperature as well as types and amounts of adjuvants, rates of foliar penetration of chlorfenvinphos can be higher if its concentration in the spray liquid is increased.     

Quinone Binding Sites of Membrane Proteins as Targets for Inhibitors

Quinones are a central component of most photosynthetic and respiratory electron transfer chains. The proteins that reduce and oxidise these quinones have quinone binding sites—Q sites—that are good targets for pesticides. This paper reviews the diversity of these sites, their possible structure, and the types of compounds that act upon them.     

The Validation of Pesticide Leaching Models

The validation of pesticide leaching models presents particular problems where the number of model predictions is far in excess of the observed data. Normally, however, there are more frequent field observations for other parameters (notably the site hydrology) than for pesticide concentrations in either water or soil. A five-stage validation procedure which takes advantage of the most frequently available observations and which tests each of the components of the model in a cumulative way, is thus advocated: Stage 1: Parameterisation of the model using only independently measured parameters. Stage 2: Hydrological validation: the validation of the predictions of water movement and water content of the soil. Stage 3: Solute movement validation: where field data are available for solutes other than pesticide, the model should first be validated for them, especially if they are more abundant than the pesticide observations. Conserved solutes such as chloride or bromide are preferred, although nitrate may be used for short periods. Stage 4: Pesticide fate in the soil: models should use parameters of pesticide fate derived from independent studies. Stage 5: Pesticide leaching: only in the last stage are the relatively small number of pesticide observations compared with the model predictions with respect to patterns and orders of magnitude of occurrence. With this scheme, the results of each stage are carried forward to the next, and confidence in the model is built with each stage. This is illustrated using the CRACK-P model and hydrological, nitrate and pesticide data from the Brimstone Farm Experiment Oxfordshire, UK.