I keep seeing references to sterile or nearly-sterile cultivars of butterfly bush. Having worked on eradication projects I'm still leery. Nearly sterile doesn't work for me. It's like almost pregnant. Additionally, having seen historical industry sterility claims regarding sterility in plants not only later be found to be not sterile but also quite invasive, I have not made the jump to butterfly bush. So, regarding butterfly bush, is there actually such a beast?