> Bayer claim that 185 ppb is the LD50 level, according to the article > Brian Ames posted earlier. Actually, Bayer claim that is the acute toxicity level (the lethal dose for 50% of the bees in 24 hours. There is also the LD50 for 48 hours, which is lower, and the LD50 for ten days (a more chronic exposure) which is lower still. Perhaps a better measure is the NOLEC (no observed lethal effects concentration). This is the highest level at which chronic lethal effects are not observed. From a discussion on this last year here is what I posted (taken from a paper by Richard Schmuck, Bayer's main "imidacloprid and bees" researcher: > http://bee-quick.com/reprints/imd/Schmuck_2004.pdf >It certainly seems from this paper that Suchail et al's figures are out of line with other results. However, to summarize the survey of investigators that Schmuck lists, the NOLEC (no observed lethal effects concentrations) from different investigations using lab feeding are (each number=one paper): 4 ppb, 24 ppb, 48 ppb, 10 ppb, 10 ppb, 0.1 ppb from chronic dietary toxicity studies. From tunnel and field feeding studies (chronic): 100 ppb, 20 ppb, and >20 ppb. So, while 20 ppb (seems roughly a middle figure) is well below the 140 ppb for acute LD (or 192 if we take your average) it shows that the chronic toxicity is much lower (one order of magnitude) than the acute. end of quote So, if the citrus plantations are having high residual levels of imidacloprid in the soil for years, then all the things growing in that soil are potentially toxic, and the exposure of bees is certainly chronic, beyond even just the flowering of the oranges. Then of course, there are the sub lethal effects..... Stan *********************************************** The BEE-L mailing list is powered by L-Soft's renowned LISTSERV(R) list management software. For more information, go to: http://www.lsoft.com/LISTSERV-powered.html