Effects of nitrogen supply on interactions between Gala apple trees and Dysaphis plantaginea (Hemiptera: Aphididae)

The rosy apple aphid (Dysaphis plantaginea) is a major pest of apple orchards in Europe and northern Africa, where its preference for colonising annual terminal shoots leads to considerable reductions in shoot growth and commercial yield. This study investigated the effects of varying nitrogen (N) fertilisation levels (0, 25, 37.5, and 50 g tree^-1, corresponding to 0%, 50%, 75%, and 100%, respectively) on shoot development and aphid dynamics in 1-year-old 'Gala' apple trees under controlled conditions. Nitrogen supply had a pronounced impact on vegetative growth, with the 75% N treatment yielding the highest relative growth rate (17.8%). Aphid populations increased throughout the experiment, reaching peak abundances at 100% and 75% N levels (62.04 and 54.21 aphids per leaf, respectively). A significant relationship was found between aphid abundance and leaf number per shoot, particularly at the 75% N level. These results emphasise the need to optimise nitrogen fertilisation as part of integrated pest management strategies and improve understanding of the complex interplay between nutrient supply, vegetative growth, and aphid infestations in apple orchards.