Pulvinaria hydrangeae Steinweden (Homoptera, Coccidae) - a new soft scale species in Slovenia

The cottony hydrangea scale (Pulvinaria hydrangeae Steinweden; Homoptera, Coccidae), with certainty identified in the area of Nova Gorica only in 1998, is a new scale species in Slovenia. Its origin is in all probability East Asia. In Europe it is known since the mid sixties and at the present it is diffused in some countries of Southern Europe (France, Italy, Slovenia) and West Europe (Belgium, the Netherlands, Switzerland). The Slovene population originates without any doubt from Italy. Based on a systematical monitoring of the species in the last two years it can be stated that the species is already quite diffused in the Valley of Vipava as well as in the Slovene Istria. The most frequent hosts are the Hydrangea macrophylla, Tilia platyphyllos, Tilia cordata and the Acer spp. The species is univoltine and it overwinters in the 3rd nymphal stadium, the mature female appears at the end of April up to the beginning of June, forming in this period an oblong and very visible ovisac. The culmination of the larva hatching is in the second half of June. The cottony hydrangea scale is without doubt harmful for the hydrangea. The severely attacked bushes weaken gradually. Single shoots or even whole bushes can then die away. For other host plants the damages caused by this species are less important. At present there are very few natural enemies which would restrain the population. A common predator is the species Coccophagus lycimnia (Walk.) (Hymenoptera, Aphelinidae), which however, couldn't be found as predator of the said species in the monitored area. But also some other predators of the scale like the Exochomus quadripustulatus L. and some species of the genus Scymnus (Coleoptera, Coccinellidae) were found. The most appropriate time for the control with insecticides is at the end of June when the majority of larvae hatch or with oil insecticides in late autumn. In the present paper the morphology and the taxonomy of the species Pulvinaria hydrangeae will be described in comparison with other species of the genus Pulvinaria known up to the present in the territory of Slovenia.