Effect of Api-Bioxal® and ApiHerb® Treatments against Nosema ceranae Infection in Apis mellifera Investigated by Two qPCR Methods

Abstract

<i>Nosema ceranae</i> is a worldwide distributed midgut parasite of western honey bees, leading to dwindling colonies and their collapse. As a treatment, only fumagillin is available, causing issues like resistance and hampered bee physiology. This study aimed to evaluate ApiHerb^® and Api-Bioxal^® as treatments against <i>N. ceranae</i>. The efficacy was tested using two qPCR methods based on the <i>16S rRNA</i> and <i>Hsp70</i> genes. In addition, these methods were compared for their aptitude for the quantification of the infection. For this, 19 colonies were selected based on the presence of <i>N. ceranae</i> infections. The colonies were divided into three groups: treated with ApiHerb, Api-Bioxal with previous queen caging and an untreated control. All colonies were sampled pre- and post-treatment. The bees were analyzed individually and in duplicate with both qPCR methods. All bees in the pre-treatment tested positive for <i>N. ceranae</i>. Both treatments reduced the abundance of <i>N. ceranae</i>, but ApiHerb also decreased the prevalence of infected bees. Analysis with the <i>16S rRNA</i> method resulted in several orders of magnitude more copies than analysis with the <i>Hsp70</i> method. We conclude that both products are suitable candidates for <i>N. ceranae</i> treatment. From our analysis, the qPCR method based on the <i>Hsp70</i> gene results as more apt for the exact quantification of <i>N. ceranae</i> as is needed for the development of veterinary medicinal products.