Effect of Prey Sex, Density, and Age on Oviposition of Cybocephalus sp. nr. nipponicus (Coleoptera: Cybocephalidae), a Natural Enemy of Euonymus Scale (Homoptera: Diaspididae)

Abstract

Cybocephalus sp. nr. nipponicus Endrody-Younga (Coleoptera: Cybocephalidae) females lay their eggs individually under the cover of scale insects, similar to some hymenopteran parasitoids. Because this beetle's oviposition occurs in close association with individual scale insects, qualities of individual scale insects or patches of scale insects are factors that can potentially be used by beetles to select oviposition sites. The effect of two such factors (scale sex and density) on the oviposition of C. sp. nr. nipponicus were evaluated in the laboratory using the euonymus scale Unaspis euonymi (Comstock) as the ovipositional prey. For comparison, the effect of scale sex, density, and age on beetle oviposition also was investigated for a second oviposition prey, San José scale (Quadraspidiotus perniciosus (Comstock)). Oviposition rates for C. sp. nr. nipponicus were strongly affected by prey sex when ovipositing on euonymus scale, with 97% of all eggs being placed under covers of male scales. In contrast, beetles placed eggs in equal proportions under covers of mature (>29 days) female and the empty scales of emerged male San José scales. Oviposition rates were affected by San José scale density. There were significantly more beetle eggs laid in patches with more than 70 scales than in those with fewer scales. Increasing scale age positively affected beetle oviposition on San José scale. Fifty-five percent of all eggs were laid in the oldest group of scales (age 53-58 days), whereas no eggs were laid in the youngest group of scales (age 9-14 days).