Bionomics and harmfulness of Tetraneura ulmi (L.) (Aphidinea, Pemphigidae) in elms

The paper deals with the bionomics and harmfulness of a common cecidogenous aphid Tetraneura ulmi L. (Pemphigidae) which showed outbreak in elms in Moravia in 2002. The majority of examinations was conducted in Ulmus minor in a riparian and accompanying stand of the Svitava river, Bílovice nad Svitavou near Brno. The aphid was most abundant in U. minor, much less in U. glabra and never occurred in U. laevis. In one leaf, about 2.5 (max. 16) galls were found there (at Čejkovice near Znojmo, as much as 21 galls). Fundatrices hatched from 15 April to 7 May. Through the areal sucking on the abaxial face of leaves, they damaged on average 1.4 cm2 (about 6%) of the leaf blade, in leaves with 10 and more galls often the whole blade. Within 3-4 weeks from hatching (from mid-May), fundatrices matured and during 1-3 weeks they produced on average 35.2 fundatrigeniae. At the beginning of June, galls reached 10.8 mm in length and 6.2 mm in width. Fundatrigeniae developed about 18 days and from 10 to 30 June they formed migrantes alatae. Aphids left 73.3% galls. In 10.4% galls, fundatrices were killed by insect and other predators in the 1st instar (in the initial stage of the gall formation). In 7.0% galls, immature fundatrices died in later stages of development due to the effect of a protective activity of plant tissues. The mortality of fundatrigeniae including migrantes alatae was caused to a very small extent only by e.g. Anthocoris confusus Reut., larvae of Syrphidae, caterpillars of Pyralidae and birds. Effects of mortality factors on the shape and size differentiation of galls are documented in the paper.