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24 Insects and Humans 1. Introduction This final chapter will focus on those insects that humans describe, in their economically minded way, as beneficial or harmful, though it should be appreciated from the outset that these constitute only a very small fraction of the total number of species. | 24 Insects and Humans 1. Introduction This final chapter will focus on those insects that humans describe in their economically minded way as beneficial or harmful though it should be appreciated from the outset that these constitute only a very small fraction of the total number of species. It must also be realized that the ecological principles governing the interactions between insects and humans are no different from those between insects and any other living species even though humans with their modern technology can modify considerably the nature of these interactions. Of an estimated 5-10 million species of insects probably not more than a fraction of 1 interact directly or indirectly with humans. Perhaps some 10 000 constitute pests that either alone or in conjunction with microorganisms cause significant damage or death to humans agricultural or forest products and manufactured goods. Worldwide food and fiber losses caused by pests principally insects plant pathogens weeds and birds are generally estimated at about 40 of which 12 are attributable to insects and mites. These figures do not include postharvest losses estimated to be about 20 and occur despite the application of about 3 million tonnes of pesticide worth more than US 31 billion including about US 9 billion of insecticide Pimentel 2002 . In the United States alone crop losses related to insect damage rose from 7 to 13 in the period 1945-1989 despite a tenfold increase in the amount of insecticide used 120 000 tonnes each year Pimentel et al. 1992 . On the other hand the value of benefits derived from insects is severalfold that of losses as a result of their pollinating activity their role in biological control and their importance as honey silk and wax producers. That insects do more good than harm probably would come as a surprise to laypersons whose familiarity with insects is normally limited to mosquitoes houseflies cockroaches various garden pests etc. and to farmers who must protect .