There is a widespread use of agricultural insecticides in the
developing countries, including Thailand, an agricultural
country. Organophosphate pesticides (OPs) are triesters of
phosphoric acid. OPs became widely used as the environmentally
persistent organochlorine pesticides were banned
in the 1970s. OPs gained popularity in the early 1980s
because they were relatively inexpensive, readily available,
less persistent in the environment, and less susceptible to
pest resistance (Wessels et al. 2003).