Damage caused by the small red-belted clearwing borer (Synanthedon myopaeformis Borkhausen) in cultivars grafted on different types of rootstocks

Considerable damage caused by the red-belted clearwing was observed in the biologically controlled apple orchard. In all cases, the larvae were found in the tumourlike tissue proliferations developing at the grafting point of the rootstock (M9) and scion, while no larva was found in crowns and cut surfaces. Samplings involving different cultivars were implemented in two apple orchards; in Bősárkány, where trees are grafted on M9 rootstocks and tumours were found at grafting points, and in Mosonmagyaróvár, where trees are grafted on M26 rootstocks and no proliferations were found at graft unions. During the aforementioned samplings, the numbers of larvae living in the tissue proliferations were counted, the sizes of tumours were measured, and the flight dynamic of adult clearwings was investigated. Research results reveal that damage caused by the clearwing larvae was only observed in trunks with tumour-like disorders (Bősárkány), where feeding larvae were found in 15.3% of the examined trunks in cultivar Royal Gala, 4.6% in Idared, 2.6% in Jonagold, and 1.3% in Florina. We investigated whether there is a correlation between the size of tumours and the degree of damage. The highest rate of proliferations was found on cultivar Florina, where only a minimum degree of damage was experienced. The lowest rate of proliferations was observed on cultivar Gala, which suffered the highest degree of damage done by clearwing larvae.

According to sex-pheromone trap catches, the flight period of male clearwings occurred simultaneously in both studied orchards from mid-May to mid-August. On the basis of scent trap catch results, however, it has to be highlighted that females were only present at the Bősárkány research site.

It is assumed that the absence of females in the Mosonmagyaróvár orchard can be attributed to the fact that they did not find such suitable oviposition sites as tissue proliferations. Hence, egg-laying and damage caused by the larvae did not happen there either.