DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 9-10/2017 str. 44 <-- 44 --> PDF |
2000; Mutun, 2003; Forster et al., 2005; Dioli et al., 2007; Mutun et al., 2009; Dobreva et al., 2013). It has occasionally been found on Rubus ulmifolius Schott, but fewer eggs are deposited on this host compared to Quercus spp. R. ulmifolius is used by C. arcuata as an overwintering site (Bernardinelli, 2006). In Croatia, besides the predominantly affected leaves of pedunculate oak, damage and tingid developmental stages were also found on European crab apple (Malus sylvestris /L./), Rubus spp. and, for the first time, the field elm (Ulmus minor Mill.) (Hrašovec et al., 2013). In the northeastern states of the USA, where it is native, C. arcuata is known to complete two generations a year and have a partial third generation, with some adults from the second generation and those from the third overwintering (Connell and Beacher, 1947). In the warmer climate of Italy, it can complete three generations a year and have a partial fourth (Bernardinelli, 2000). C. arcuata feeds directly on leaves, sucking fluid from the cells between the upper and lower epidermis of the leaves and causing discoloration of the upper leaf surface. This results in a reduction in photosynthesis and may cause premature leaf fall in heavy infestations. The pest may also increase the susceptibility of its host to other insects and diseases (Connell and Beacher, 1947). Materials and methods Materijali i metode Information on the discovery of oak lace bug in the park at Lužnica Castle near Zaprešić, Croatia, 6 kilometers from Slovenian border, was provided by prof. Boris Hrašovec from the Faculty of Forestry, University of Zagreb, Croatia in autumn 2016. On 17 November 2016 we performed a search for the pest on still attached and fallen leaves of Q. robur at the following locations in southeastern Slovenia: Mokrice Castle (5 trees of Q. robur), the village of Obrežje (2 trees), the village of Rigonce (1 tree), Dobova (3 trees), Mostec (3 trees), Zakot (oak forest), and Bukošek (oak forest). Partially green leaves attached to the branches and fallen leaves of Quercus robur were carefully inspected for signs of oak lace bug and suspected samples were placed in plastic bags and brought to the laboratory for further study. In early July 2017 we visited a wider area of western Slovenia and searched for the symptoms and the presence of C. arcuata. Morphological identification was performed on samples of egg clusters on the underside of leaves and larval molts (exuviae) that were present on the fallen leaves of Q. robur. The number of eggs in 9 clusters of eggs was counted and length and width of 30 eggs were measured. Photographs were taken and measurements performed using an Olympus SZX16 binoculars equipped with an Olympus UC90 digital camera and the cellSens program Standard and with Nikon D200 camera (AF-S MICRO NIKKOR 105mm 1:2.8G). Results and discussion Rezultati i rasprava In autumn 2016 the pest was found only at Zakot, a village near the town of Brežice, in a mature oak forest stand measuring 4,427 m2 (coordinates of the find: 15°36’47“ E, 45°54’48“ N), which is 14 km from the find in Croatia at the Lužnica Castle. Egg clusters and numerous larval exuviae were found on fallen leaves and not on those still attached to branches. The egg clusters contained from 12 to 61 empty eggs. Egg shells were spindle shaped and black with an apical opercular area with a rim. They were 560 μm long (475 – 596 μm) and 196 μm (183 – 196 μm) wide and generally corresponded to the measurements reported by Baker and Brown (1994), which were on average 583 μm long and 206 μm wide. |