Does anyone know why…

Hi,

Three plants have totally evaded pests this year. They are – Roma tomatoes (grown from seed in a greenhouse), strawberry plants (grown outdoors from runners of existing plants), and avocado (grown from seed from a consumed avocado, grown in a greenhouse). All three have, at one point, been extremely close to my other pest-infested plants for extended periods of time. In particular, it’s the greenfly that have been a real issue this year. There is not a single one on any of the three named plants.

Does anyone know why?

Edit: I should add that the things that have suffered badly this year from pests are chili plants, bell pepper plants, coriander and parsley. They have grown in close proximity to the aforementioned three plants.