Abstract
The insect parasites bred out of Psyllid hosts, in the course of studying their biology in Scotland, belong to four families of Hymenoptera and one of Diptera, the total number of species encountered being seven. Of these one and possibly two more of the hymenopterous species are hyperparasites. The hosts involved include four species, of which only one, Psyllia mali race peregrina, may be said to have been fairly heavily parasitised. As observed by Ferrière (1926), species of Psyllidae, in spite of their nymphs leading a comparatively sedentary life, are less susceptible to attack by parasites than are the other Homoptera. As a rule the hymenopterous parasites attack them in the nymphal stage, while the dipterous species parasites the adults as well.

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