Výskyt, vývoj a hálkový polymorfismus Harmandiola cavernosa (Rübs.) (Diptera, Cecidomyiidae)

Abstract

A gall midge Harmandiola cavernosa (Rübs.) is the second most frequent Cecidomyiidae species on Po­pu­lus tremula in the CR. In 2007 and 2008, it occurred very abundantly in Forest District Bílovice nad Svitavou, Training Forest Enterprise Masaryk Forest in Křtiny (former Brno-venkov District). Imagoes occurred there at the end of April and at the beginning of May. Galls grew up as early as at the end the first week in May. The formation of galls is mainly indicated by larvae of the first instar and partly larvae of the second instar. Larvae of the third instar did not participate in the creation of galls. Mature galls were on average 5.4 mm long, 4.8 mm wide and 4.7 mm high showing an inner chamber of an ave­ra­ge length 2.4 mm and width 1.4 mm. Larvae abandoned galls from the end of May until mid-July. On average, 44% larvae completed successfully their development in galls. About 26% larvae were killed by insect parasitoids (mainly Torymus quercinus Boh.) and then same proportion of larvae died without any apparent exogenous causes). Insect predators and birds killed 4% larvae on average. It has been found that mortality factors markedly participated in the size, morphological, anatomical and physiognomic differentiation of galls. Gall polymorphism was analysed in detail in the paper. Galls significantly unfavourably affected the size of leaves and thus also photosynthesis.1