Nut phenological development and feeding activity by true bugs as factors in the occurrence of main damage in two European hazelnut districts

Abstract

Hazelnut cultivation is continuously exposed to biotic adversities, with insect pests typically causing considerable production losses. Most of the damage is the result of feeding activity of ‘true bug’ species (Hemiptera: Heteroptera), which affects both nut quality and quantity. True bugs can cause the traumatic abortion of cotyledon tissues or other changes in the nut. The latter consists of necrosis of the kernel with the appearance of black or white spots and shrivelling. The type of damage is related to the timing of the feeding activity and the phenological stage of the nuts. This study aims to evaluate the relationship between the nut phenological stages and some of the most important true bug species in two different districts where European hazelnuts are produced. To pursue this aim, an experiment was conducted in the Tarragona hazelnut district (Spain) and in the Viterbo hazelnut district (Italy). Hazelnut plants were selected, and some branches were wrapped with net sleeves. In each net sleeve, Palomena prasina, Gonocerus acuteangulatus, and Nezara viridula adults were inserted when the nuts reached different stages of phenological development. As a result, two developmental stages of the kernel were identified during which the feeding activity of the true bugs causes traumatic abortion and ‘cimiciato’, respectively. According to the phenological scale developed by IRTA, these two stages are g2/G1 and G4/G5. These results are of great importance in the development of control strategies and the information provided will be helpful in reducing the number of treatments required to control true bugs.