Diplolepis rosae (l.) (hymenoptera: Cynipidae): Development, ecology and galls in the brno region

Abstract

The paper results from two years of studying development and formation of the galls of Diplolepis rosae (L.) on Rosa canina (L.) in the Brno region (Czech Republic). Following the extremely warm and dry growing season of 2015, 70 % of prepupae and 30 % of grown-up 2nd instar larvae hibernated. After the climatically milder growing period of 2016, only 47 % of prepupae and 53 % of grown-up larvae hibernated. Pupae were recorded from mid-March to mid-July and imagoes occurred from April to July. The average percentage of males in the populations was 4.5 %. Eggs were found in the galls from May to July. Larvae of the 1st and 2nd instars were found in the galls from June to August and from July to October (or to next March), respectively. Average cranium width in the 1st instar larvae increased during the growth of larvae from 0.25 to 0.35 mm, i.e. by 38 %. Average cranium width in the 2nd instar larvae was 0.55 mm and practically did not change during the growth of the larvae. 85.1 % of galls were formed on budding leaves, 14.9 % on flowers and fruits. The galls were growing most rapidly in June and July, and their growth ended in October when they reached average height and width of 40 mm and 47 mm, respectively. They consisted of 1 to 20 (on average 7) +- intergrown parts with 1 to 225 (on average 54) cells. 63.5 % of them were localized along the sides of shoots and 36.5 % were found on the shoot tips. The largest cells (3.9 x 3.1 mm) were those with the completed development of gall wasp larvae. Cells inhabited by parasitoids were by 15.0 % smaller and by 24.5 % smaller were cells with dead gallwasp larvae due to natural reasons. As compared with the cells with the completed development of gall wasp, cells with the larvae of inquiline Periclistus brandtii (Ratz.) were by 43.6 % shorter and by 50.6 % narrower. The inquiline was found in 10 % of galls and in 3.6 % of cells. In 2015, parasitoids inhabited on average 15.0 % (in 2016 22.1 %) of cells. Approximately 50 % of the population of D. rosae died in the galls during the preimaginal development.