Referee 2's review (Alexandra Klein):

In general I find this paper very important as many people are currently thinking that Bt crops are involved in CCB (colony colopse disorder). It is relatively obvious for many scientists that this is not the cause for CCB but many people are concerned about transgenic plants and it would be great to publish new results of a meta-analysis showing that honey bees are not negatively affected by foraging Bt pollen. I also think that this innovative topic fits well to Plos One. My only concern is that only few studies and all conducted in the lab and mainly only considering one crop species (corn) are included in the meta-analysis. I think the authors should discuss that more research should be done with other Bt crops and also under field conditions. I have a couple of more specific points listed below.

Specific comments:
I would change the title and give a direction to the results, eg. Something like this:
Transgenic-modified crops do not contribute to honey bee colopse disorder (or recent colopses of honey bee hives)

Summary:
Page 2-background (please provide line numbers, that makes it easier to provide comments for specific sentences): Honey bees are the most important pollinators of many agricultural crops. Use "many" as not all agricultural crops are pollinated by honey bees, some are also negatively affected by honey bees and only other bee species can provide pollination.
........and are a key test insects, not animals.........
I would name the current concern together with CCD here

Introduction:
Page 2, last sentence: Because of this specificity, most experts feel it is unlikely that these Bt crops would negatively impact honey bee populations. So, give a direction how Bt is expected to influence honey bees.

Next sentences: that nearly third of our diet is coming from honey bee pollination comes originally from Mc Gregor 1976 (the book is online available at http://gears.tucson.ars.a...). It is a very rough estimate and Morse and Calderone are listing in their original publication (not in the Bee Cult Paper, but in the original document: Morse, R., Calderone, D. W. 2000. The value of honey bees as pollinators of U.S. Crops in 2000. Cornell University, Ithaca, New York, USA. Online availabe at http://www.masterbeekeepe...) the US crops that seem to depend on honey bee pollination). It is hard to figure out from this source from where they get the data to come to this conclusion. Most of the data are out of the Mc Gregor book, so you should cite the original citation or you should update it with a recent global review, showing that 35% of crops used for human consumption are depending to some degree on insect pollinator (Klein et al. 2007 Proceedings of the Royal Society of London, Series B, Biological Sciences 274: 303-313.). A more recent estimate of the monetary value of honey bee pollination gives Losey &Vaughan 2006 BioScience 56: 311-323. A recent paper by Winfree and Kremen in Ecol Lett also shows that for Pennsylvania non-Apis bees are able to provide the crop pollination services, so not in all US areas agriculture depend on managed honey bees.

Page 3: .......Bt proteins produced in insect resistant crops might be contributing to recent colopses of honey bee hives not declines in abundance. You might consider to cite Stokstad, E. 2007 The case of the empty hives. Science 316: 970-972. Check Science and Nature for other articles to this topic.

Is no study available for Bt rape? A recent article published in Applied Microbiology and Biotechnology (Volume 75 (3), 1432-0614) found no sign of a horizontal gene transfer from rape Bt pollen in the guts of honey bees. They might also have data to honey bee colony growth or mortality when bees forage on BT rape compared to colonies forage on "normal" oilsee rape flowers. This study is conducted in the field and it would be good to mention that not only lab-studies found no effect of Bt crops on honey bee mortality.

Discussions:
It would be worth mentioning that only few studies on only two Bt crops and mainly for maize are only available today and it would be good to test this with other Bt crops and also to compare results from lab and field studies.

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N.B. These are the general comments made by the reviewer when reviewing this paper in light of which the manuscript was revised. Specific points addressed during revision of the paper are not shown.