Contribution to the knowledge of incidence, development and galls of the bisexual generation of Biorhiza pallida (Hymenoptera: Cynipidae)

Abstract

The research study deals with the occurrence, cecidogenesis and development of the bisexual generation of Biorhiza pallida in the Brno region. Galls were found most frequently on Quercus petraea and on Q. robur. At the end of the winter season, females deposited 2 - 290 (on average 83.6) eggs, mainly into the above average sized buds on last-year's shoots. Larvae came to age in May in the 3rd instar, in the extremely warm and dry growing period of 2015 already in the 2nd instar. Adult individuals were leaving galls from the end of May to the end of July. Females were 3 - 4.5 - times superior to males in numbers. Females, males and individuals of both sexes emerged from 64.3%, 21.4% and 14.3% of galls, respectively. Galls were created from the beginning of April. In the second half of April (or at the beginning of May) they were 3 - 35 (on average 15.2) mm high and 3 - 45 (on average 20.2) mm wide. The percentage of buds infestation, average number of deposited eggs and average size of galls were increasing with the increasing mean diameter of shoots. Parasitoids (incl. parasitoid inquilines) killed 30 - 100 (on average 65) percent of gall wasp population. We found as many as 40% and 10% of galls with the developing Curculio villosus (Curculionidae) and Synergus spp. (Cynipidae), respectively. In the spring of 2016, nearly the whole gall wasp population in Brno-Komín was killed by late frosts. The pest infests mid-aged woody plants, sporadically also young growths and epicormic shoots of old oak trees.