Theoretically, if you don't want the bees involved, you would be best to bag the flower truss so that it can self pollinate and keep the fruit true to type. I'm not sure at what point you can be certain that the bees are not involved though so you'd have to do this pretty quickly in the open before the bees get to them. Even in the hothouse the air gets filled with clouds of pollen ( according to my allergic husband) and the mix is going to be there even without bees. I plan on bagging next year because there are a few varieties that are worth saving. Other more experienced growers than me might have better advice - I'm a play it by ear type of gardener ;-) I draw the bees attention by planting borage and lambs ears which they love. Some of those bumble bees are big enough to saddle and ride aren't they? I believe there is a move to export them to the north island because they are such good pollinators. There's a lot of debate about the merits and commercial tomato growers seem to be in the thick of it.
Cheers
Linda

Here is a link that might be useful: Debate about Bumble Bees.

The last thing we need is another introduced species. There are plenty of bee species already in Australia and many are good pollinators. We have two species of native bee here and both love tomato flowers. European honey bees don't seem to care for them, though if they get hungry, they'll certainly have a go at them.
Well, stepping off the soap box, bagging is the only way to be sure of getting pure seed. Choose a truss with some unopened flowers and remove any that have already opened. Bag this truss. You may have to trim some foliage and you will need to check it every now and then to adjust the bag as the truss grows. The bag can be removed once you have fruit set - little baby tommies instead of flowers. When you remove the bag, remove any newly developing flowers. Tie a bright ribbon (yellow is a good colour) around the truss base so that identification is easy. And make sure you tell the family what the bright ribbons mean. Bags around 6cm x 12cm are good. I've used those cheap 'organza' gift bags they sell in places like Kmart or BigW. Failing that, Green Harvest have a new range of fruit fly exclusion bags that would be perfect I think. They are big enough to do a branch. They're called Bug Off Bag and are 30cm x 30cm. I'm getting a few to try. They should be good for caps and chillies as well.

Hey - don't shoot the messenger!

Cheers
L

My apologies Linda. It wasn't meant as an attack. Just me mouthing off. Sorry if I worded it badly. Forgiven?

no worries mate - I meant it as a joke - I agree with you entirely, they are here though and they do pollinate well and seem to be placid critters. First time I saw one I thought it was the invasion of the body snatchers!

Linda