Seed-eating insects of wild and cultivated olive trees exclusive to South Africa, harmfulness and identification also from early instar larvae

Some insects exclusive to South Africa and Eritrea collected on the sub-Saharan and Asian wild olive tree Olea europaea subsp. cuspidata develop on seeds: olive seed wasps and a seed olive weevil. Silvestri (1915) saw six Chalcidoidea wasps emerging from the wild olive kernel, attributing the role of seed eater to Eurytoma oleae, considering the other five as its parasitoids. In the absence of adequate studies, until a few years ago, E. oleae was still considered the only olive seed wasp, while in our recent studies in the Western Cape, Eupelmus spermophilus was found to be a spermophagous, the first truly phytophagous Eupelmus, and the most frequent seed wasp on both cultivated (99%) and wild olive trees (81%). Its oviposition occurs when the olive stone is still soft; the average infestation recorded on wild olive trees was 18%, while on cultivated olive ones it was 14%, reaching a maximum of 66% on Koroneiki cultivar, which has not a very thick pulp. In a subsequent three years study conducted on cultivated olives, the early fruit drop due to E. spermophilus ranged from 0% to 14% (average 4.9%) of the entire production, concluding that in the Western Cape economically significant yield losses occurred sporadically. DNA-based identification of larvae collected inside the olive kernel confirmed that E. spermophilus is the most abundant seed wasp, E. oleae is a seed wasp rarely present in cultivated olive trees, while Sycophila aethiopica and Eurytoma varicolor are parasitoids of E. spermophilus. The African olive seed weevil Anchonocranus oleae, was recently found in several sites of the Western Cape also on cultivated olive fruit, even where wild olive trees were far from olive crops, suggesting a low but stable presence in cultivated olives in those sites. However, A. oleae does not yet represent a problem of significant economic importance.