Hello Louie:
I can offer up some insight into your question on insecticide use around 1980. At that time, many of the organochlorines (e.g., DDT, etc.) had been restricted, and organophosphorous (e.g., diazinon, etc.) and carbamate (e.g., carbofuran, etc.) insecticides dominated. Another group that had been in development from the 1960s was the synthetic pyrethroids. These were derived from pyrethrum, a compound with known insecticidal properties found in East African chrysanthemums. The 1st generation synthetic pyrethroids had low mammalian toxicity but were very sensitive to light, so they had very short persistence in daylight. By the mid-1970s, chemists had come up with 2nd generation synthetic pyrethroids (e.g., permethrin, cypermethrin, deltamethrin, etc.). These 2nd generation compounds were much more resistant to degradation by light and air, thus making them more suitable for agriculture. However, by tweaking their chemistry in this way, they substantially increased their mammalian toxicity. So, by 1980, the 2nd generation synthetic pyrethroids began making their way in number to the agricultural insecticide markets. So, this may help explain the decline in Mexican bean beetles you mentioned in your email - or at least it could be one factor in their decline. One other thing to consider about synthetic pyrethroids on the market - they usually have a compound called piperonyl butoxide (PB) added to them, which is a synergist. This causes the pesticide to be more effective because the PB inhibits the detoxifying enzymes of organisms which would be used by the organisms to deal with the synthetic pyrethroid insecticide. You mentioned mode of action - synthetic pyrethroids act by keeping Na+ channels open in neurons, so organisms become paralyzed (muscles all fatigue) and eventually die. This is pretty much the same mode of action seen with the organochlorine insecticides in wide use prior to 1973. Hope this helps! Regards, Steve Steve Sheffield, Ph.D. Department of Natural Sciences Bowie State University Bowie, MD 20715 and College of Natural Resources and Environment Virginia Tech National Capital Region - Northern Virginia Center Falls Church, VA 22043 [email protected] ----- Original Message ----- From: "Louis Nottingham" <[email protected]> To: [email protected] Sent: Sunday, March 3, 2013 1:04:47 PM Subject: [ECOLOG-L] Question about insecticides I am interested to know if there were any significant changes and/or advancements in insecticide use that began around 1980 (new chemical, shift to a different mode of action, etc.). I am trying to formulate a hypothesis regarding what caused a sharp decline in Mexican bean beetle in soy and snap beans that occurred around 1980 (an observation that has been corroborated by numerous extension agents). It is possible that the decline involved climate change, but according to surveys i've conducted, it still is a pretty severe issue in the organic farming community. So I am guessing that we must have developed some sort of chemical, chemical treatment method, or something along those lines that was very successful for controlling the beetle in a conventional setting. Any thoughts? Good references? (I do not know much about insecticide use, so feel free to provide obvious information!) Louie Nottingham Virginia Tech Masters Candidate 216(A) Price Hall (0319) Virginia Tech Blacksburg VA, 24061
