Differential expression of antimicrobial peptide encoding genes of honey bee (Apis mellifera) after Varroa mite (Varroa destructor) infestation

Varroa destructor mite is a serious threat to the world apiculture industry, and severely hampered beekeeping practices. Innate immune systems are key defenses of animals and are particularly important in species that lack the sophisticated adaptive immune systems found in vertebrates. In honey bees, antimicrobial immune peptide genes play a significant immune response against pathogens. The present study analyzed the detrimental effects of Varroa infestation on Apis mellifera at all developmental stages in both Varroa challenged and controlled hives. Physical attributes were observed in Varroa hives at different time intervals (0, 30, and 45 days respectively). After 45 days of Varroa exposure, the samples were taken, and the AMPs immune response of bees parasitized by Varroa was detected by studying the expression levels of antibacterial peptides (defensin, apidaecin, abaecin, and hymenoptaecin). Significant alterations in the physical parameters viz. body length, body weight, wing shape, and mean numbers of brood cells were observed compared to the control. Colony density was also decreased with marked negative behavioural changes. Ct values of Real-Time PCR results showed that AMP-specific immune gene transcription level in Varroa-challenged bees was downregulated, except for abaecin and defensin (adult stage). There was a significant (p < 0.05) increase in abaecin gene transcription folds i.e., 1.064 larvae, 1.732 pupae, and 1.264 adults bees. As a whole, all these findings can be taken as critical biomarkers in the advancement of control techniques against Varroa and other pathogen infections as a part of wide-ranging programs of honey bee health and Varroa control.