On the gall midges injurious to the cultivation of willows II The so-called shot hole gall midges - Rhabdophaga spp

Summary. 1 The species of gall midges whose larvae live in the stems of willows have been briefly reviewed. 2 It is pointed out that, in the past, the so-called ?shot hole? midge damage on willow stems and branches has been frequently ascribed to R. saliciperda Dufour without considering either the insect itself or the species of willow. 3 This study has shown that several species of gall midges are responsible for this type of damage and that, so far as can be ascertained from an examination of cultivated species of willows, with S. fragilis in addition, each species of midge is restricted to one (in one case three) species of willow. 4 The adults, pupae and larvae of R. saliciperda Dufour, R. triandraperda sp.n., R. purpureaperda sp.n. and R. justini sp.n. have been described. 5 The bionomics of these species have been worked out. It has been found that, while all multiply by means of unisexual families, the first three species are single brooded but that R. justini sp.n. has two broods a year. R. saliciperda Dufour lives on S. caerulea, S. fragilis and S. alba (Cecconi), R. triandraperda sp.n. will only attack S. triandra, while R. purpureaperda sp.n. and R. justini sp.n. are restricted to S. purpurea. 6 The nature of the damage caused by the larvae of these midges has been described and control measures have been discussed. Tarring the stubs has been mentioned. It is suggested that cutting down the new growth in May, where practicable, would reduce the midge infestation. This latter treatment has the additional advantage of getting rid of initial caterpillar and frost damage which result in dead terminals and so produce side-branching close to the stubs. Wild Crack willow (S. fragilis) should be destroyed as it can act as a reservoir for R. saliciperda Dufour. 7 Keys have been drawn up for the identification of the midges using host plants, larval, pupal and adult female characters. 8 The following parasites are recorded?Torymidae: Torymu ssp., near auratus Fonsc; Eurytomidae: Eurytoma aciculata Ratz., E. saliciperdae. Mayr.: Pteromalidae: Tridymus salicis Nees; Eulophidae: Pleurotropis? caenus Walk., Tetrastichus flavovarius Nees, T. roesellae De Geer; Platygasteridae: Platygaster cecidomyiae Ratz., P. sp. (?philinna Walk.).