Soybean production ranks among the largest agricultural cash crops in the U.S., second only to corn. U.S. soybean production topped 3 billion bushels in 2005 with sales of $17 billion. Approximately 58% of U.S. soybeans are grown in Iowa, Illinois, Minnesota, Indiana, and Nebraska. A small percentage of the U.S. soybean crop, 2%, goes to human consumption in the form of whole beans, soybean oil, and soybean meal products. A third of the crop, 1 billion bushels per year is exported annually to China, EU, Mexico, Japan, and Taiwan, and other countries. Most of the crop, 2 billion bushels, goes to the U.S. livestock industry to feed poultry, hogs, and cattle. Variations in the supply of soybeans thus directly impact livestock production. In recent years, soybean prices have exceeded the $5 per bushel U.S. loan rate fluctuating from $5 to over $7 per bushel. Continued success of this crop is threatened by the introduction of two new invasive species, soybean rust and soybean aphid. Soybean aphid (Aphis glycines), an insect pest, thrives on plants in the North and Midwest. Soybean aphids were first detected in Wisconsin in 1995, but confirmation of the pest did not occur until five years later in 2000. The delay in confirmation may have enabled the pest's dissemination. Spreading at the rate of 600 miles per year, by 2003 soybean aphid's had infested crops in 21 states (North Central Soybean Research Program, 2004). Because the soybean aphid's wintering host (buckton) is not found outside the Midwest and Northern plains, the extent of aphid damage may be limited to these regions. Furthermore, studies have shown the insect to be intolerant to temperatures above 95F further precluding widespread infestation in the South. Soybean rust (Phakopsora pachyrhizi), is an established disease in Australia, Africa, Asia, India, and South America. First detected in Louisiana in 2004, soybean rust rapidly spread through the South. By 2005, soybean rust had spread to crops in Alabama, Florida, Georgia, Mississippi, and South Carolina (Bissonnette, 2005). The fungus is most damaging to cultivated soybean, but documentation shows it can reproduce on 95 other plant species including peas, beans, and kudzu, a widespread, invasive plant. Soybean rust spores are disseminated naturally by wind. Constructed windbreaks can provide a first level of defense against spore deposition. Complete protection, however, is impossible. This paper offers projections of national damages from two recently introduced agricultural pests. To allow for multiple heterogeneous producing regions, variable price, domestic demand inelasticity, and export demand, a market equilibrium approach was used. Within the model, the reduction in soybean output due to crop damages from two pests contribute to a rise in soybean market prices tempering overall producer loss. The rise in domestic price in turn causes export quantities to fall, thereby stabilizing domestic consumption quantities and buffering consumer losses. The dynamic elements of the model simulate the spatial spread of the introduced pests over time and the extent of future damages. Findings show the magnitude of the damages and further reveal the importance of modeling the impacts of the two pests concurrently. Examining the pests separately may underestimate the long term fate of the industry. Considering the impacts of both pests independently and summing the impact may result in underestimating the rise in price, underestimating production in the intermediate term, overestimating production in the long term, overestimating welfare loss in the middle term, and underestimating welfare loss in the long term.

大豆是美国最大的经济作物之一，仅次于玉米。2005年，美国大豆产量超过30亿蒲式耳，销售额达到170亿美元。大约58%的美国大豆生长在爱荷华州、伊利诺伊州、明尼苏达州、印第安纳州和内布拉斯加州。美国大豆作物的一小部分(2%)以全豆、大豆油和豆粕制品的形式被人类消费。每年有三分之一，即10亿蒲式耳的玉米出口到中国、欧盟、墨西哥、日本、台湾和其他国家。其中20亿蒲式耳的大部分都流入了美国畜牧业，用于饲养家禽、猪和牛。大豆供应的变化因此直接影响牲畜生产。近年来，大豆价格已经超过了5美元/蒲式耳的美国贷款利率，从5美元/蒲式耳波动到7美元/蒲式耳。大豆锈病和大豆蚜虫这两种新的入侵物种的引入，威胁着该作物的持续成功。大豆蚜虫(大豆蚜虫)是一种害虫，在美国北部和中西部的植物上茁壮成长。1995年，威斯康辛州首次发现了大豆蚜虫，但直到5年后的2000年才证实这种害虫的存在。确认的延迟可能导致了这种害虫的传播。到2003年，大豆蚜虫以每年600英里的速度蔓延，已经侵袭了21个州的农作物(中北部大豆研究计划，2004)。由于大豆蚜虫的越冬寄主(buckton)在美国中西部和北部平原以外没有发现，因此对大豆蚜虫的危害程度可能仅限于这些地区。此外，研究表明，这种昆虫无法忍受95华氏度以上的温度，这进一步阻止了南方大面积的虫害。大豆锈病(Phakopsora pachyrhizi)是一种已在澳大利亚、非洲、亚洲、印度和南美建立的疾病。2004年，在路易斯安那州首次发现了大豆锈病，随后大豆锈病迅速蔓延到整个南部地区。到2005年，大豆锈病已经蔓延到阿拉巴马州、佛罗里达州、乔治亚州、密西西比州和南卡罗来纳州的农作物上(Bissonnette, 2005)。这种真菌对大豆的危害最大，但文件显示，它可以在95种其他植物上繁殖，包括豌豆、豆类和葛根(一种广泛的入侵植物)。大豆锈病孢子通过风自然传播。建造的防风林可以提供对孢子沉积的第一级防御。然而，完全的保护是不可能的。本文对最近引入的两种农业害虫对全国的危害进行了预测。考虑到多个异质生产地区、可变价格、内需无弹性和出口需求，采用市场均衡方法。在该模型中，由于两种害虫对作物造成损害而导致大豆产量下降，导致大豆市场价格上涨，从而缓和了生产者的整体损失。国内价格的上涨反过来导致出口数量下降，从而稳定国内消费数量，缓冲消费者损失。模型的动态要素模拟了引入的害虫随时间的空间分布和未来危害的程度。研究结果显示了这两种害虫的危害程度，进一步揭示了同时模拟这两种害虫影响的重要性。单独研究害虫可能会低估该行业的长期命运。考虑独立害虫和加法的影响可能会导致低估价格上涨的影响,低估了生产从中期来看,长期高估生产,中间高估福利损失项,低估了长期的福利损失。