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The model developed by J. C. Headley to illustrate the entomologists' concept of the economic threshold is presented and criticized. A two-variable model directed at the problems of optimal timing and pesticide application as well as optimal pest population level is presented. and h= a parameter relating the inverse of population units to dollar units of control costs.in dollars to pest density and time. The economic threshold is that population level where the marginal benefit from damage prevented by the control program is equal to the marginal cost of realizing that population through a control program. The model has four basic elements: a pest population growth function (equation 1.1), a pest damage function (equation 1.2), a product yield function (equation 1.3), and a pest control cost function (equation 1.4). Each of these elements is presented below.where P t = pest population level at time period t, the harvest time; P t-n = pest population level n periods prior to t; r= net growth rate of the pest population per time period; D, = cumulative damage at time period t, given as a function of P t, where the pest population has grown from P t-n to P, with no external interruption; A = a constant related to the pest damage tolerance level based on the recuperating potential of the crop; b= a parameter relating units of pest population to units of crop damage; Y = realized product yield at harvest time (t) in dollars; N = potential yield at harvest time if no pest damage, expressed in dollars; e= a parameter relating damage units to dollars; K = total cost in dollars of reducing the pest population to Pc.; at time t-n;r, = P t-n (1 + r)n

"Water rates are designed to meet multiple objectives, typically resulting in trade-offs among the objectives of economic efficiency, revenue sufficiency, and related revenue stability. Standard theory of natural monopoly is extended here to explain why long-run marginal cost (LMC) can be greater than both average cost and short-run marginal cost (SMC) for municipal water utilities. The distinctions between "benign monopoly rates" and "marginal cost rate design" favor LMC over SMC as the basis for economically efficient rate design. Taking into account conservation investments by consumers, SMC rates are economically inefficient, except during temporary shortages. The City of Los Angeles adopted economically efficient, revenue sufficient, and revenue-stable water rates at the end of a prolonged drought. After the drought ended, Los Angeles (LA) modified the rate design, making the design politically feasible during normal rainfall years. Unique features in the LA rate design determine the allocation of consumer surplus among ratepayers, making the rate design politically feasible by sharing efficiency gains among customer classes. Revenue sufficiency and stability features in the rate design minimize adverse job effects on water utility management, reducing the frequency of rate hearings with an increasing block design." ("JEL" L51, L95, Q25, Q51) Copyright (c) 2009 Western Economic Association International.

An economic threshold of agricultural pest management is derived. Results provide a method for researchers to use in making improved pest control recommendations to farmers without farm level decisionmaking. An empirical illustration for lesion nematode management in irrigated corn is given and directions for further research are indicated.

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