Yeast. Coloured scanning electron micrograph (SEM) of a variety of yeast species growing in a larval tunnel (gallery) of the codling moth (Cydia pomonella) in a mature apple. The larvae, known as apple worms, are an agricultural pest. They can cause serious damage to apple crops as well as pears, walnuts, and various other tree fruits. Magnification: x1000 when printed 10 centimetres wide.