We have large garden which is mainly flowers and ponds and i also run tow allotments. We always try to work together with our local insect population to create a good outcome for all. This year i was dismayed to find black aphids on my runner beans. I decided to ignore them and hope that we would live together. Like many in this area the bean flowers have not been setting so i began watering the blooms to see if this helped. After just few days watering i found that all of the blckfly had gone. I have never seen this before.
In our flower garden, my wife grows nasturtiums. white butterflies then lay eggs on these and torn the leave to fertilizer. An unusual systen but it works well for us. This year being so dry we have been watering the garden to keep things alive. we are seeing Large Whites lay, the eggs ahtching but the larvea die after few days.
could this be related to something in our tap water?
I don't think there will something in the tap water. I'm guessing you have used the tap water many times in other years without similar effects.
I think it an effect of the exceptionally hot and dry weather we have experienced recently. Here in this bit of south east England I know there has been rain on only two days since June 29th and I think some days before that were rainless too. This combined with daytime temperature that been at least 23C and often much higher has put a lot of stress on the natural world.
Good luck with your runner beans; we have given up on ours.