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The current market for OPs and MCs of 19 % of worldwide insecticide sales is only half of that of 10years ago for several reasons : there have been no major new compounds for 30years ; resistance has eroded their effectiveness ; human toxicity problems are still encountered ; the patents have expired reducing the incentive to update registration packages ; alternative chemotypes or control methods have been developed .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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