Determination and rates of parasitization of Oomyzus spp. (Hymenoptera: Eulophidae) on Diorhabda spp. (Coleoptera: Chrysomelidae) eggs in choice and non-choice scenarios

Oomyzus spp. (Hymenoptera:Eulophidae) are chalcidoid wasps that parasitize elm leaf beetle (Xanthogaleruca=(Pyrrhalta) luteola (Müller)) (Coleoptera:Chrysomelidae) eggs. We wanted to determine if Oomyzus spp. would parasitize Diorhabda spp. (Coleoptera:Chrysomelidae), an important biological control agent for saltcedar (Tamarix spp.). When wasps were confined in small cup arenas, parasitization rates were 93.3% at densities of two Oomyzus spp. wasps per egg cluster and 87% at densities of one wasp per egg cluster. Parasitization of clusters resulted in 28.4 + 6.75 SEM wasps emerging per cup. When comparing the rates of parasitization separately, Oomyzus spp. parasitized only 33.3% of the X. luteola egg clusters whereas Oomyzus spp. parasitized 77% of Diorhabda spp. egg clusters. A choice test study between X. luteola and Diorhabda spp. had a mean of 31 + 2.26 SEM wasps hatching from Diorhabda spp. eggs compared to a mean of 2.5 + 0.98 SEM wasps emerging from X. luteola eggs. In a sleeve cage test on a branch of saltcedar, Oomyzus spp. parasitized 60% of Diorhabda spp. egg clusters with an average of 3.27 + 1.82 SEM wasps per egg cluster. While laboratory studies demonstrate that Oomyzus spp. will parasitize Diorhabda spp. eggs, field tests are needed to confirm our results.