267, if you have a new colony consisting of only a few thousand BSF grubs I wouldn't expect them to be able to repel houseflies yet, especially if you have a lot of food scraps in your unit. A BioPod can house 10's of thousands of grubs at full capacity. For the repellent effect you need to have waste that is dominated by the BSF.

EDIT: Your BSF unit doesn't need to be at the maximum capacity to repel other fly species. I believe it has more to do with the ratio of food scraps to BSF. There is a limit to how much waste I could add to my present colony and still have the pest fly repellent action. For example if I added 30 lbs of raw fish instead of a few pounds I would expect house flies or blow flies to invade the colony. Also, if I added stinky decomposed fish I would also expect pest flies. In fact I did once add rotten fish to my colony and it was overwhelmed by blow flies. I wrote a blog post about it here. Successfully operating a BSF colony is about balancing a few basic factors. What makes it relatively simple is that once you've established a colony, imbalances can be corrected in a matter of days.

If you have a wild population of BSF laying eggs in your BioPod you can achieve a full colony in a matter of weeks. Have you confirmed that you have BSF laying eggs in your unit? If you could upload a few photos I could give you better advice.

Yesterday I took a series of photos of my colony processing some fish scraps. Our temps are in the mid 90's and I had very few houseflies in my unit, even with raw fish present. My colony is probably at full capacity at the moment and you could certainly say they are dominating any scraps that I add.

Here's the colony in the morning (click to enlarge):


Here I added 2.5 lbs of raw fish (whole and scraps):


A few hours later:
(Notice there are 3 BSF females laying eggs and 1 housefly wishing it could get at those fish)


A few more hours:


When I checked on the colony through the day I would usually see some houseflies on the outside of the BioPod, and maybe a few inside, but I haven't seen housefly larvae in the colony or in the collection bucket for months. I doubt that houseflies would lay eggs in my BioPod now.

My experience is only one source and I'm not doubting what you say. There are exceptions to every rule and I'm still learning a lot about BSF.