Garrell E. Long

Optimal Control of Vector-Virus-Plant Interactions: The Case of Potato Leafroll Virus Net Necrosis

This paper introduces a new specification to the economic pest management literature designed to optimally manage vector-virus-plant interactions for a single crop. The viral, insect-vector, and plant-host stocks are treated as renewable resources and conjunctively controlled in a discrete-time control framework subject to crop quality standards established in marketing contracts. The result is a conceptual integrated pest management model providing optimal insecticide scheduling and dynamic decision-making thresholds in a novel economic pest management context. Model results are compared qualitatively with those from previous specifications. The model is applied empirically to control potato leafroll virus net necrosis in commercial potato production.

Some alterations in hemolymph proteins of Hemigrapsus nudus associated with temperature acclimation

Abstract 1. 1. The purple shore crab, Hemigrapsus nudus, was exposed to environmental temperatures 10 and 20°C, and the time course of changes in hemolymph proteins and clotting time was recorded. 2. 2. Results indicate that this animal exhibits responses to abrupt changes in environmental temperature characteristic of acclimation. Initial shifts of total hemocyanin concentrations of up to 54 per cent of initial value were followed by a return to within 2 per cent. 3. 3. Total hemolymph protein and hemolymph clotting time exhibited similar responses, with a correlation between these two variables of −095313814.

GPA-Phenodynamics, a simulation model for the population dynamics and phenology of green peach aphid in potato: formulation, validation, and analysis

A model, GPA-Phenodynamics, was developed for the population dynamics and phenology of green peach aphid, Myzus persicae (Sulzer), in potato during the summer: the model describes the interaction among the green peach aphid population, its predators, and abiotic factors (e.g. temperature). The model includes functions for population growth of the aphid and its predator complex. Developmental degree days were used for the time dimension. Model agreement with field data was good. The model precisely predicted (within 2 days) when the aphid reached its highest density. A regression analysis between observed and predicted population density showed a slope of 0.952 with a coefficient of determination equal to 0.976. Model output was sensitive to the intrinsic rates of increase for green peach aphid and its predator complex. Degree days required for the aphid and its predator complex to appear in potato were described as uniform random distributions with different means and deviations. Using 10 different sets of generated weather data, the model successfully simulated phenologies and dynamics of the aphid population. GPA-Phenodynamics can be used as a decision-making tool in integrated pest management program for green peach aphid in potato fields during the summer season.

The Larch Casebearer in the Intermountain Northwest

The larch casebearer, Coleophora laricella Hubner (Lepidoptera: Coleophoridae), is a small silver-gray moth whose larvae mine needles of larches, Larix spp. Apparently of European origin, this defoliator was first recorded in North America near Northampton, Massachussetts, in 1886.3 It had spread westward to Minneapolis by 195012 and, in the spring of 1957, was collected just south of St. Manes, Idaho. A survey of larch forests in the intermountain region that year indicated that about 44,000 ha (170 sq mi) were infested.1 The population spread rapidly and uniformly until, in 1970, it occupied virtually all larch stands in the intermountain regions of eastern Washington, Oregon, and northern Idaho (Fig. 1).

Population Dynamics Pattern of Green Peach Aphid (Homoptera: Aphididae) and Its Predator Complex in a Potato System

Green peach aphid, Myzus persicae (Sulzer) (Homoptera: Aphididae), interacts with many predatory insects in potato fields during the summer. The concept of the predator complex associated with green peach aphids was applied to explain the interactions between the aphid and its predators. The predator power of the predator complex was determined by two factors: the number of predators and the relative feeding capacity. The dynamics of the green peach aphid population was expressed by the number of individuals while the predator power was used to characterize the predator complex. Cumulative degree‐days for green peach aphids were used as a time scale to analyze phenology and dynamics patterns of the aphid and its predator complex. The patterns of population changes in aphids were similar during the period of study (1993–1995) although the highest density of aphids fluctuated significantly from year to year. However, the predator power appeared more stable than the green peach aphid population over the thre...

Surface approximation: A deterministic approach to modelling spatially variable systems

Abstract The Fourier series in two independent variables represents an approximate solution to the two-dimensional diffusion equation and can be used to describe the spatial pattern resulting from dispersal of some organisms. For regularly spaced sample points, the mathematical properties of Fourier series and procedures for finding the series which best fits a particular set of data can significantly decrease the number of variables that must be retained during computer simulation of interacting, mobile populations.

Model stability, resilience, and management of an aquatic community

SummaryA community model may be considered stable when, in the absence of exogenous variation, all population trajectories encircle or asymptotically approach equilibrium. In this paper, community models in which, in the absence of analytical indications of stability, all populations either 1.exhibit trajectories toward equilibrium or2.possess properties such that departures from equilibrium are inhibited will be defined as resilient. The necessary properties include appropriate sensitivity (i.e., the total derivative, dfi/dVj, of the ith species function, fi=dNi/dt, with respect to the jth variable) to exogenous variables. A real, though simplified, ecological system consisting of Daphnia galeata and its algal food source in an oligotrophic lake appears to be generally resilient in that changes in the exogenous factors nitrate concentration and temperature of the lake water consistently restrain the departure of predicted population densities from equilibrium.Each population in the community is represented by the Verhulst-Pearl logistic model of population growth augmented to include environmental effects on rate of increase, r; carrying capacity, K; and the effects of predation on population density, N; and therefore the population rate of change, dN/dt.It is suggested that such community submodels and sensitivity analysis represent logical and appropriate amplifications in the use of mathematical models in the management of populations.

An application of the logistic equation to the population dynamics of salt-marsh gastropods

The logistic equation for population growth N = K(1 + be−rt) with modifications for environmentally influenced changes in habitat carrying capacity K, and species intrinsic growth rate r, can satisfactorily simulate density levels of real populations of herbivores. The model assumes that carrying capacity is a function of incident solar energy while intrinsic growth rate is a function of temperature and salinity. Test animals were Cerithidea and Assiminea from Mission Bay, San Diego, California.