External mites, should be visible without a microscope. For internal mites, such as tracheal mites, a dissecting microscope (x6?) should be sufficient to see them. Are your samples queens, workers or males? The nematode Sphaerularia bombi is found in queens emerging from hibernation. Alcohol is likely to degrade your samples. 'Parasites in Social Insects' by Paul Schmid-Hempel and/or Chap 5 'Natural Enemies' by Dave Goulson and Mark J. F. Brown in Bumblebees by Dave Goulson should help you identify what you might find.

Hi Catherine!

Thanks for your reply :)

We have workers. I will look for the references :)

Hi Alexandre:

In addition to Catherine answer, you can also find conopid flies larvae with a dissecting microscope x2 to x6. You can contact me for further information if you want.

Cheers,

Mario

Hi Alexandre-

Most arthropod macroparasites are pretty obvious when dissecting bees under a dissecting scope (6-50X), and they seem to preserve well in alcohol. Identifying some of the smaller Dipteran larvae (e.g. Tachninids, Phorids) can be rough, and it might be best to enlist the help of a specialist to identify those. Conopids are larger, and at least in the US, rather easy to identify to genus (see Townsend, 1935 ref below), but you may have to dig a bit to see what to expect in your area. I haven't encountered any of the Hymenopteran larvae before, but I expect that their identification may be a little rough too. Tracheal mites are easy to spot, and I think that they should all be Locustacarus buchneri in Bombus. External mites are probably the most common, but many are phoretic, but so the life histories of most are really understudied. There's a website with a lot of information on bee mites in North America here: http://insects.ummz.lsa.umich.edu/beemites/. Their ID might be a bit difficult too, but the website has a key. Table one in the Schmid-Hempel ref below has a nice, concise list of what to expect to find in Bombus. Lastly, Most of the bees that I dissect have no macroparasites at all. Parasitism rates can be very low, and there's definitely a seasonal aspect to their prevalence.

I wish you the best of luck!

Amber

Townsend, L. H. 1935. The mature larave and puparium of Physocephala sagittaria (Say) (Diptera, Conopidae). Psyche 42: 142-148.

Schmid-Hempel, P. 2001. On the evolutionary ecology of host–parasite interactions: addressing the question with regard to bumblebees and their parasites. Naturwissenschaften 88(4): 147-158.

Thank you guys! :)