Intraspecies transmission and effects of an unidentified microsporidium on the convergent lady beetle, Hippodamia convergens Guérin-Méneville (Coleoptera:Coccinellidae), used for biological control

Abstract

Convergent lady beetles, Hippodamia convergens Guérin-Méneville, are often used for aphid control in agriculture and in home gardens. Beetles are collected from overwintering sites in California and are customarily released in large quantities. Although H. convergens are known to host the microsporidium Nosema hippodamiae, there are currently no screening procedures in place to ensure beetle health or quality. The purpose of this study was to examine the effects of an unidentified microsporidium found in commercially-available H. convergens on its life history characteristics and to examine vertical and intraspecies horizontal transmission routes. Microsporidia-infected H. convergens larvae took significantly longer to develop than did their uninfected cohorts. There was no significant difference in mean egg hatch and larval mortality. Cumulative mean egg production and mean adult survival for microsporidia-infected females was significantly lower than that of uninfected females. Vertical transmission was 100% efficient and horizontal transmission occurred through ingestion of spores. Microspondian spores in this study measured 3.6 × 2.4 μm, which is within the range reported for N. hippodamiae measure.