LEAF DAMAGE OF THE BLACK CHERRY, PRUNUS SEROTINA EHRH., BY THE LEAF BEETLE, GONIOCTENA QUINQUEPUNCTATA FABR.: AN ACCIDENTAL FORAGING ON A NEOPHYTIC HOST, OR AN ESTABLISHED TROPHIC LINK?

The Black Cherry (Prunus serotina Ehrh.), a North American forest tree, had been extensively planted for timber production in order to improve soil quality in pine plantations in European forests during the first half of the 20th century. Unfortunately, it failed to meet the foresters' expectations. It has instead spread rapidly in silvicultures becoming a notorious weed species, difficult to control. Although it still has alien plant status, it seems that 150 years of its presence on the European continent might suffice for this neophyte to become adopted as a host plant by the native fauna of insect herbivores. The observations of Prunus serotina were conducted in 2009-2010 in the Rudno Forest District, Lower Silesia, Poland, on Prunus serotina plants growing as a thick understorey shrub layer in fresh mixed deciduous forest. The analyses, performed in 7-10 day intervals from April until the end of July each year, aimed at monitoring the population dynamics of Gonioctena quinquepunctata on P. serotina plants, and the dynamics of leaf perforation caused by this herbivore, in order to determine the relation between these two species. The insects were observed on 100 shoots on 10 plants on each observation date, and were recorded in situ. Based on the estimates of the leaf damage, the mean perforation index (P sub(I)) (%) was calculated on each date for each plant shoot, expressed as the mean percentage of the perforated leaf blade area. P sub(I) (%) was subsequently correlated with the beetle and larvae density on the plants. It has been demonstrated that the feeding of G. quinquepunctata on Black Cherry plants is more closely associated with the presence of its larvae, than with that of the beetles. Although the mean P sub(I) value on each observation date was never higher than 12%, the maximum perforation of individual leaf blades occasionally exceeded 50%, whereas the maximum mean P sub(I) calculated for individual shoots on each observation date reached as much as 47%. The authors suggest that feeding of G. quinquepunctata on P. serotina may represent an example of a well established trophic link between a native herbivore and a plant species still considered a neophyte.