Zhang, W. 2007. Optimal pest management in the presence of natural pest control ecosystem services. Ph.D. Dissertation, Michigan State University, East Lansing, Michigan, USA.
By integrating natural pest control services into managerial decision-making, there are new opportunities for improving agricultural pest management in an economically appealing and socially desirable manner. This research develops dynamic and spatial bioeconomic models to investigate optimal economic management of an insect pest in the presence of natural enemies. Of central economic importance are the opportunity cost of natural enemy mortality due to broad-spectrum insecticides and the opportunity cost of setting aside land as non-crop habitats for the enhancement of natural enemy populations. The models are applied to a recent invasive pest of U.S. soybean, the soybean aphid, whose management is of both economic and environmental importance to the North Central region of the United States.
The thesis is divided into three essays. Essay 1 develops a dynamic bioeconomic The thesis is divided into three essays. Essay 1 develops a dynamic bioeconomic model for the insecticide-based management of soybean aphid that explicitly takes into account both the predation effect of natural enemies on pest density and the nontarget mortality effect of aphid insecticides on the level of natural predation supplied. The study develops a natural enemy-adjusted economic threshold that represents the pest population density at which pesticide control becomes optimal in spite of the opportunity cost of injury to natural enemies of the target pest.
Essay 2 applies the bioeconomic model developed in Essay 1 for a simulation experiment on the optimal control of soybean aphid. The study examines the difference in optimal control choices and associated economic gains with and without consideration of natural enemies. For instance, the presence of one ladybeetle would justify a change of optimal control choice from spray to no-spray when the pest density is 20 per plant. The results highlight the importance of assessing both pest and natural enemy populations in making insecticide application decisions and accounting for the opportunity cost of insecticide collateral damage to natural enemies.
The study also estimates the private economic value to farmers of the natural control services of ladybeetles in suppressing soybean aphid damage. The estimate constitutes a lower bound for the total economic value of this ecosystem service, because it omits such benefits as the avoidance of health and environmental risks from insecticide spraying.
Farmers desiring to rely on natural pest control in lieu of insecticide-based control can try to manage the habitat for natural enemies. Essay 3 develops a spatial optimization model to explore economically optimal habitat configurations for the natural enemies of crop pests. The model is applied to soybean aphid management in representative conventional and organic farming systems. Results indicate that non-crop habitat management can potentially be a promising pest management option for organic cropping systems. However, it tends to reduce farm net returns for conventional farms. Both area and shape of non-crop habitats affect economic performance, with the greatest value coming from small, scattered areas of habitat.
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