Pathogenicity tests with entomopathogenic nematodes isolated from chestnut groves on Cydia and Curculio larvae

The Italian chestnut-growing, particularly in rural areas, continues to represent an ecological niche and a reservoir of cultural and historical significance, as well as an important economic source for farmers. Chestnut cultivation is threatened by phytophagous insects that cause early drops of fruits and considerable losses of harvested product. Tortrix moths [Cydia fagiglandana (Zeller), C. splendana (Hübner), Pammene fasciana (L.)] and chestnut weevils (Curculio elephas Gyllenhaal, C. propinquus Desbrochers des Loges) are considered among the most economically damaging native species. The study of entomopathogenic nematode (EPN) communities in these cultivated areas aims to enhance the knowledge useful for the development of low-impact control strategies, in order to promote the proliferation and conservation of these natural biological control agents for the control of harmful insects. Monitorings were carried out in autumn and spring period, in two different types of chestnut groves in Northern Italy: pure and mixed with other tree species. A clear predominance of EPNs was recorded in mixed chestnut groves, where the genus Steinernema was the most frequent. In particular S. feltiae was the most abundant species (31.3% of positive samples), however it was exclusively isolated in mixed chestnut groves. Moreover, two new Steinernema species were isolated in the spring period sampling, one only in mixed and the other in both types of chestnut grove. These species are under description. Laboratory tests were carried out to assess the pathogenicity of S. feltiae and S. carpocapsae strains isolated from chestnut groves against Cydia and Curculio larvae. The results obtained indicate that both EPN species are excellent biocontrol agents. In particular, S. carpocapsae gave the best results against both pests, killing 100% of Cydia and Curculio larvae.