Hymenopterous Parasites of Willow Insects

1. Eight Ichneumonoidea, fourteen Chalcidoidea and six Proctotrupoidea are recorded as parasites of willow insects. 2. The majority of records are of parasites bred from insects inhabiting the wood of the cricket bat willow, Salix alba var. caerulea, Smith, the more important being Torymus pulchellus, Thoms., Tridymus salicis, Nees, Eupelmus urozonus, Dalm., Microterys clavellatus, Dalm., Tetrastichus roesellae, DeG., Tetrastichus inunctus, Nees, Tetrastichus flavovarius, Nees, Tetrastichus ? acuminatus, Ratz., and Platygaster sp. 3. Microterys clavellatus is recorded for the first time as a parasite of Cecidomyiidae. 4. Evidence is given for the separation of the gall-midges, Rhabdophaga sp. and R. saliciperda, Duf., as distinct species based both on structural differences and on a study of their parasites, for the three parasites found most commonly attacking Rhabdophaga sp. were never bred from R. saliciperda, and the most common species parasitizing R. saliciperda was never obtained from Rhabdophaga sp. 5. It is confirmed that Eurytoma salicis, Thoms., supplements its animal diet with vegetable food. 6. The rate of parasitism of Euura atra, Jur., by Eurytoma salicis is given as 19·8 per cent., and that of Rhabdophaga sp. by Platygaster sp. as 40·5 per cent. 7. Histograms are given of Rhabdophaga sp. and its parasites, Torymus pulchellus, Thoms., Tetrastichus roesellae, DeG., and Platygaster sp., the emergence of Platygaster sp. coinciding approximately with that of its host.