Synopsis of Biological Control for European Fruit Lecanium (Parthenolecanium corni) by Parasitoids in North America and Preliminary Findings in Hybrid Hazelnut Orchards

The European fruit lecanium, Parthenolecanium corni (Bouché) (Hemiptera: Coccidae) is a native insect to North America that causes significant damage to a large variety of fruit and ornamental trees worldwide. Here we provide a summary of the insect’s worldwide distribution and synopsis of all the Hymenopteran parasitoid wasps found to parasitize P. corni in North America from past literature. Additionally, a preliminary parasitoid survey of P. corni was carried out in two hybrid hazel (Corylus avellana × C. americana) plantings as hazelnuts represent a potential new crop for the region. Parthenolecanium corni, were collected over two sample days in July 2022 from two hybrid hazelnut plantings and their parasitoid fauna recorded. Parasitism rates of P. corni were estimated for hymenopterous parasitoids as well as the entomophagous fungus Ophiocordyceps clavulata (Ascomycota: Hypocreales: Ophiocordycipitaceae). Hymenopterous parasitoids were identified to the lowest taxonomic level possible. Relationships between parasitism rates (a binomial response) and P. corni density (the predictor variable) were analyzed using binomial generalized linear models. Parthenolecanium corni experienced high parasitism rates: 24.0% by Hymenopter-an parasitoids, and 63.4% by entomophagous fungi, giving a combined parasitism rate of 87.4%. Hymenopteran and fungal parasitism exhibited contrasting density-dependent relationships. Plants with higher densities of scales experienced lower parasitism rates from Hymenopteran parasitoids, but higher scale densities experienced higher parasitism rates from O. clavulata. Further research is needed over the whole adult female life stage of P. corni to learn more about these ecological relationships that could be of great benefit to hybrid hazelnut growers if P. corni becomes a significant pest.