BIOTECHNICAL ENGINEERING8 B iotechnical Engineering specializes in developing new chemicals for agricultural applications. The company is a pioneer in using the sterile-male procedure to control insect infestations. It operates several laboratories around the world that raise insects and expose them to extra-large doses of radiation, making them sterile. As an alternative to chlorinated hydrocarbon pesticides, such as DDT, the sterile-male procedure has been used frequently with a good track record of success, most notably with the Mediterranean fruit fly (or Medfly). That pest was controlled in California through the release of treated flies on the premise that the sterile male flies would compete with fertile wild males for mating opportunities. Any female that has mated with a sterile fly will lay eggs that do not hatch. The California Medfly campaigns required about five successive releases of sterile males—at intervals timed to coincide with the time for newly hatched flies to reach adulthood—before the Medfly was virtually eliminated. (Only sterile flies were subsequently caught in survey traps.) The effectiveness of the sterile-male procedure was enhanced by the release of malathion poisonous bait just a few days before each release, cutting down on the number of viable wild adults. More recently, Biotechnical Engineering has had particular success in using genetic engineering to duplicate various insect hormones and pheromones (scent attractants). Of particular interest is the application of such methods against the Gypsy Moth, a notorious pest that attacks trees. The company has developed synthetic versions of both hormones and pheromones for that moth. It has a synthetic sexual attractant that male moths can detect at great distances. Most promising is the synthetic juvenile hormone. The juvenile hormone controls moth metamorphosis, determining the timing for the transformation of a caterpillar into a chrysalis and then into an adult. Too much juvenile hormone wreaks havoc with this process, causing caterpillars to turn into freak adults that cannot reproduce. Biotechnical Engineering has received a government contract to test its new technology in an actual eradication campaign. The company will participate in a small-scale campaign against the Gypsy Moth in the state of Oregon. Because the pest is so damaging, Dr. June Scribner, the administrator in charge, is considering using DDT as an alternative procedure. Of course, that banned substance is only available for government emergency use because of the environmental damage it may cause. In addition to spraying with DDT, two other procedures may be employed: (1) using Biotechnical’s scent lure, followed by the release of sterile males, and (2) spraying with the company’s juvenile hormone to prevent larvae from developing into adults. Dr. Scribner wants to select the method that yields the best expected payoff, described below. Although both of the newer procedures are known to work under laboratory conditions, there is some uncertainty about successful propagation of the chemicals in the wild and about the efficacy of the sterile-male procedure with moths. If the scent-lure program is launched at a cost of $5 million, Biotechnical claims that it will have a fifty-fifty chance of leaving a low number of native males versus a high number. Once the results of that phase are known, a later choice must be made to spray with DDT or to release sterile males; the cost of the sterilization and delivery of the insects to the countryside is an additional $5 million. But if this twophase program is successful, the net present value of the worth of trees saved is $30 million, including the benefit of avoiding all other forms of environmental damage. The indigenous moth population would be destroyed, and a new infestation could occur only from migrants. Biotechnical’s experience with other eradication programs indicates that if the scent lure leaves a small native male population, there is a 90% chance for a successful eradication by using sterile males; otherwise, there is only a 10% chance for success by using sterile males. A failure results in no savings. The cost of synthesizing enough juvenile hormone is $3 million. Biotechnical maintains that the probability that the hormone can be effectively disseminated is only 0.20. If it works, the worth of the trees saved and environmental damage avoided will be $50 million. This greater level of savings is possible because of the permanent nature of the solution because a successful juvenile hormone can then be applied wherever the moths are known to exist, virtually eliminating the pest from the environment. But if the hormone does not work, the DDT must still be used to save the trees. DDT constitutes only a temporary solution, and the worth of its savings in trees is far less than the worth of either of the esoteric eradication procedures—if they prove successful. To compare alternatives, Dr. Scribner proposes using the net advantage (crop and environmental savings, minus cost) relative to where she would be were she to decide to use DDT at the outset or were she to be forced to spray with it later. (Regardless of the outcome, Biotechnical will be reimbursed for all expenditures. The decision is hers, not the company’s.) Questions 1. Under Biotechnical’s proposal, the selection of DDT without even trying the other procedures would lead to a neutral outcome for the government, having zero payoff. Discuss the benefits of Dr. Scribner’s proposed payoff measure. 2. Construct Dr. Scribner’s decision tree diagram, using the proposed payoff measure 3. What action will maximize Dr. Scribner’s expected payoff? 4. Dr. Scribner is concerned about the assumed fifty-fifty probability for the two levels of surviving native males following the scent-lure program. a. Redo the decision tree analysis to find what action will maximize Dr. Scribner’s expected payoff when the probability of low native males is, successively, (1) 0.40 or (2) 0.60 instead. b. How is the optimal action affected by the probability level assumed for the low native male outcome? 5. Dr. Scribner is concerned about the assumed 0.20 probability for the dissemination success of the juvenile hormone. a. Keeping all other probabilities and cash flows at their original levels, redo the decision tree analysis to find what action will maximize Dr. Scribner’s expected payoff when the probability of juvenile hormone success is, successively, (1) 0.15 or (2) 0.25 instead. b. How is the optimal action affected by the probability level assumed for the juvenile hormone’s success? 6. Dr. Scribner is concerned about the assumed probability levels for the success of the sterile male procedure. a. Keeping all other probabilities and cash flows at their original levels, redo the decision tree analysis to find what action will maximize Dr. Scribner’s expected payoff when the sterile male success probabilities are instead as follows: (1) 80% for a low number of native males and 5% for a high number of native males (2) 70% for a low number of native males and 15% for a high number of native males b. How is the optimal action affected by the probability level assumed for the success of the sterilemale procedure? 7. Dr. Scribner is concerned about the assumed levels for the net present value of the worth of trees saved and damage avoided. She believes these amounts are only accurate within a range of ±10%. a. Keeping all other probabilities and cash flows at their original levels, redo the decision tree analysis to find what action will maximize Dr. Scribner’s expected payoff when the two net present values are instead, successively, (1) 10% lower or (2) 10% higher than originally assumed. b. How is the optimal action affected by the level assumed for the NPVs of the savings from using one of the two esoteric Gypsy Moth eradication procedures?
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