総合的害虫管理学の確立に向けて

Since the 1940's, we have had a powerful tool to combat crop pests, i.e. synthetic pesticides. The application of pesticides has undoubtedly contributed to a remarkable increase and stability in crop production. The heavy use of unsuitable pesticides, however, has brought about various undesirable effects on the agroecosystem and environment. Frequent applications of these pesticides have led to the development of resistance in key pests, and induced a resurgence of primary pests or an upsurge in secondary pests. In order to cope with the issue brought about by almost singular dependence on insecticidal control, the Food and Agriculture Organization’s (FAO) panel of experts proposed a new concept for future pest control, in 1965 as follows: “a pest management system that in the context of the associated environment and the population dynamics of the pest species, utilizes all suitable techniques and methods in a manner as compatible as possible and maintains pest population at levels below those causing economic injury”. The proposal has been called Integrated Pest Management (IPM) since the late 1970s. The proposal includes three key concepts, namely (1) integration of plural control measures, (2) economic injury level (EIL), and (3) population management system. Basecally, IPM integrates fundamental tactics, mainly natural control agents and subsidiary tactics, e.g. agricultural chemicals and physical methods. It is primarily significant in IPM that when both set of tactics are integrated, the latter tactics should not suppress the action of the former. Therefore any agricultural chemicals including pesticides must be highly selective against targeted pests, taking into account the crops, natural enemies and the environment. The concept of EIL suggests that the pest population is not necessarily suppressed completely in IPM and control should be implemented with due consideration to a balance of cost and benefit. The population management system is used for monitoring pest population dynamics to forecast whether or not the pest density will overshoot an EIL. It is also used for assessing the efficacy of control tactics.

最近農業現場で IPM という英略語の知名度が高まっている．総合的害虫管理，または総合的病害虫・雑草管理（integrated pest management，以下 IPM と言う）のことであり，私がライフワークとしてきた分野である．岡山大学農学部または他大学での集中講義で，私の「総合的害虫管理学」の授業を受けて卒業し，国や県の農業職に就いた学生諸君と顔を合わせた時，在学中は良く理解出来なかったが，農業現場に来て IPM の重要性を認識出来たと言われることがしばしばある．農業現場では，IPM は持続的農業環境保全型農業における植物保護技術の切り札のように言われているが，果たしてそうであろうか．ここでは，IPM がどのような考え方に基づいているのかについて解説する（中筋房夫（1997）「総合的害虫管理学」養賢堂に詳しい)．