Modelling optimal timing and frequency of insecticide sprays for knockdown in preparation for other control measures

A modelling investigation was conducted into optimizing the number of sprays and inter-spray interval to reduce an insect population to a low level, for example, prior to pheromone trapping or the release of sterile males. The model population was age-structured and density-dependent. If spray mortality is 100% for each spray, then the ideal spraying schedule is easily determined from the durations of the various life stages. For spray mortality of less than 100%, a simulation was used to determine optimal spraying schedules. Relative length of the larval period, fertility rate and age to first oviposition were found to be the most important biotic parameters for this determination. Their importance is magnified as spray mortality decreases. The stage targeted by sprays and the percent mortality caused by each spray are also important in determining the required number of sprays. Using medfly (Ceratitis capitata Wiedmann) biotic parameters as an example when the spray targets adults, it appeared that neither the stage at which density-dependent mortality takes effect, nor the form of the adult survivorship curve are important in determining the optimal spray schedule.     

Threats to at-risk salmonids of the Canadian Rocky Mountain region

Trout and charr, members of the salmonid family, have high conservation value but are also susceptible to anthropogenic threats in part due to the specificity of their habitat requirements. Understanding historical and future threats facing these species is necessary to promote their recovery. Of freshwater trout and charr in the Canadian Rocky Mountain region, westslope cutthroat trout (Oncorhynchus clarkii lewisi), bull trout (Salvelinus confluentus; a charr species) and Athabasca rainbow trout (Oncorhynchus mykiss) are of conservation concern. And indeed, range contractions and declining populations are evident throughout much of their ranges. Range contraction was most evident in the southern Alberta designatable unit (DU) of westslope cutthroat trout. Diminished populations were also evident in the downstream watersheds of the Alberta bull trout range, and throughout the Athabasca rainbow trout range. We assessed historical and future threats to evaluate the relative importance of individual threats to each DU and compare their impact among species. Individual threats fall into the broad categories of angling, non-native species and genes, habitat loss and alteration, and climate change. Severity of each threat varies by DU and reflects the interaction between species’ biology and the location of the DU. Severity of threats facing each DU has changed over time, reflecting extirpation of native populations, changes in management and industry best practices, expansion of non-native species and progressing climate change. The overall threat impact for each DU indicates a high probability of substantial and continuing declines and calls for immediate action.     

Control of insect pests using trunk injection in a newly established apple orchard

We evaluated the potential for using preplant trunk injections of emamectin benzoate in nonbearing apple trees. Trees were evaluated for pest injury and emamectin residues throughout the planting season and into the following year. Injections into the trunk best delivered emamectin benzoate to the canopy compared with injections into the taproot, and the higher rate reduced insect pests more than the lower rate. In the following year, differences in insect control between trunk and root injections were less pronounced, but the higher rate of emamectin benzoate persisted longer and better reduced pests relative to the other treatments.     

How has the state-of-the-art for quantification of landscape pattern advanced in the twenty-first century?

Landscape Ecology - Landscape ecology was founded on the idea that there is a reciprocal relationship between spatial pattern and ecological processes. I provide a retrospective look at how the...     

Random-effects linear model application to herd-level assessment of bovine hepatic trace mineral concentrations

To evaluate the utility of random-effects linear modeling for herd-level evaluation of trace mineral status, we performed a retrospective analysis of the results for trace mineral testing of bovine liver samples submitted to the Michigan State University Veterinary Diagnostic Laboratory between 2011 and 2017. Our aim was to examine random-effects models for their potential utility in improving interpretation with minimal sample numbers. The database consisted of 1,658 animals distributed among 121 herds. Minerals were assayed by inductively coupled plasma–mass spectroscopy, and included cobalt, copper, iron, molybdenum, manganese, selenium, and zinc. Intraclass correlation coefficients for each mineral were significantly different (p < 0.001) from zero and ranged from 0.38 for manganese to 0.82 for selenium, indicating that the strength of herd effects, which are presumably related to diet, vary greatly by mineral. Analysis of the distribution and standard errors of best linear unbiased predictor (BLUP) values suggested that testing 5–10 animals per herd could place herds within 10 percentile units across the population of herds with 70–95% confidence, the confidence level varying among minerals. Herd means were generally similar to BLUPs, suggesting that means could be reasonably compared to BLUPs with respect to the distributions reported here. However, caution in interpreting means relative to BLUPs should be exercised when animal numbers are small, the standard errors of the means are large, and/or the values are near the extremes of the distribution.     

Mechanisms behind soil N dynamics following cover restoration in degraded land in subtropical China

Purpose

Nitrogen (N) is an important nutrient for re-vegetation during ecosystem restoration, but the effects of cover restoration on soil N transformations are not fully understood. This study was conducted to investigate N transformations in soils with different cover restoration ages in Eastern China.

Materials and methods

Soil samples were collected from four degraded and subsequently restored lands with restoration ages of 7, 17, 23, and 35 years along with an adjacent control of degraded land. A ¹⁵N tracing technique was used to quantify gross N transformation rates.

Results and discussion

Compared with degraded land, soil organic carbon (SOC) and total N (TN) increased by 1.60–3.97 and 2.49–5.36 times in restoration land. Cover restoration increased ammonium and nitrate immobilization, and dissimilatory nitrate reduction to ammonium (DNRA) by 0.56–0.96, 0.34–2.10, and 0.79–3.45 times, respectively, indicating that restoration was beneficial for N retention. There were positive correlations between SOC content and ammonium and nitrate immobilization and DNRA, indicating that the increase in soil N retention capacity may be ascribed to increasing SOC concentrations. The stimulating effect of SOC on ammonium immobilization was greater than its effect on organic N mineralization, so while SOC and TN increased, inorganic N supply did not increase. Autotrophic and heterotrophic nitrification increased with increasing SOC and TN concentrations. Notably, heterotrophic nitrification was an important source of NO₃^??N production, accounting for 47–67% of NO₃^??N production among all restoration ages.

Conclusions

The capacity of N retention was improved by cover restoration, leading to an increase in soil organic carbon and total N over time, but inorganic N supply capacity did not change with cover restoration age.

     

Field scale row unit vibration affecting planting quality

Precision Agriculture - With recent developments allowing increased planter speeds, improving spatial uniformity of crop emergence will continue to be an important focus of research. Vertical...     

Variation in juvenile steelhead (Oncorhynchus mykiss) dispersal in relation to age and growth performance

Volitional dispersal is a ubiquitous strategy characteristic of species across major faunal groups. Dispersal during the juvenile life stage is of interest because early performance can be critical for determining future success (survival/reproduction). For salmonids, dispersal can influence local density, competition, individual growth and survival, though drivers of dispersal at meso-scales are rarely quantified. Here, we evaluate dispersal of tagged juvenile steelhead (Oncorhynchus mykiss) through habitat units in extended stream reaches (500 m) at sites across a watershed from July to October 2017. Our aim was to quantify the frequency and spatial extent of dispersal, identify links to biotic and abiotic factors, evaluate the implications for individual growth and test for associations between dispersal and migration initiation. Dispersal rates varied between sites, but were consistently higher for age 1+ than for age 0 steelhead (avg. 21% vs. 6% respectively). Age 1+ dispersal probability was positively correlated with time between recapture events and body mass, and negatively correlated with growth rate, maximum temperature experienced and age 1+ density. At sites where there appeared to be growth benefits to remaining sedentary compared to moving, proportionally fewer fish performed dispersal. We found no links between dispersal and timing or probability of migration initiation the following spring. Our results support the hypothesis that although dispersal over intermediate scales (10–1,000 m) might be rare, it could be an important strategy that permits fish to seek out better opportunities (foraging, shelter or otherwise) in underutilised areas.