Olive seed wasps (Hymenoptera: Chalcidoidea), potentially important pests of olive crops in the Western Cape of South Africa

Abstract

Most phytophagous insects on cultivated olives, Olea europaea L. subsp. europaea var. europaea, in South Africa are native and come from the local wild olive tree, Olea europaea subsp. cuspidata. This paper presents the first qualitative and comparative data regarding the phytophagous seed wasps on cultivated and wild olives. From 2009 to 2012, 62 random fruit samples were collected from untreated cultivated olive trees and 53 random fruit samples from wild olives at 13 different localities in the Western Cape. During spring 2013 and summer 2014, olives collected from the trees were dissected with a scalpel (when the pit was still soft) in search of seed wasp eggs and young larvae or cut with a pipe cutter (when the pit was hard) in search of mature larvae and pupae. Collected young and mature larvae were sequenced for the barcoding COI region (650 bp), and compared with adult seed wasp reference sequences. Seed wasp infestation was clearly higher in cultivated olives than Bactrocera oleae infestation (14% vs. 8%), reaching a peak of 66% in cultivar Koroneiki. Our results, including field data obtained from cultivated olives for the first time, demonstrate that Eupelmus spermophilus is phytophagous and in the Western Cape is virtually the only seed wasp in cultivated olives (99% in cultivated olives, 81% in wild ones). A precise assessment of the economic impact of seed wasps is being done by calculating the induced fruit drop, studying the susceptibility of olive cultivars and the influence of wild olives near olive crops.