Our beautiful plum tree was 2014 übersäät with aphids. According to research on the net I found out that lacewing larvae should be quite helpful. So we ordered these larvae (via another provider). In addition, we have attached a red Florfliegenkasten in the tree. The larvae are very small and hard to see (in the supply already ... I mean of course if they are then examined in the tree).
After a few days you could see the result ... the lice are gone. This year (2015) I found no lice in the tree, but as a precaution will again acquire larvae and expose them in the plum tree and at our berry bushes in the garden.
Give it a try ... soooo expensive the investment is not, and you can pinch then still take other action.
