Toxicity of chitosan derivatives to Varroa destructor (Anderson and Trueman) and their effects on immune gene expression in honey bees

Abstract

Varroasisis caused by Varroa destrucor (Anderson and Trueman) is considered the most dangerous honey bee disease. V. destructor mites parasitize both brood and adults, causing considerable losses to the colony population. The control of Varroa mites is highly dependent on the application of synthetic acaricides, however, acaricide resistance can develop. To eliminate the risk of Varroa mite resistance and to reduce residues in hive products, organic-based substances for Varroa mite control are being applied. In the present study, the acaricidal activity of N-alkyl and O-acyl chitosan derivatives against Varroa mites and their side effects on honey bees have been evaluated. Chitosan has been extracted from the corpses of honey bees. The yield, degree of deacetylation, and molecular weight of chitosan from the chitin of honey bee corpses were determined as 89%, 90%, and 20 kDa, respectively. Varroa mite mortalities were observed between 6.28-84.38% and 0.00-90.47% by N-alkyl and O-acyl chitosan derivatives, respectively. The best derivatives against Varroa mite were N-(3-phenylbutyl)chitosan (NAC-5) and O-(heptanoyl)chitosan (OAC-4). The results showed that different lethal concentrations of NAC-5 and OAC-4 had side effects against honey bees less than 26%. No significant difference was found between honey bee mortalities at 24, 48, and 72 hours post-treatment, while mortalities significantly differed between 4, and 24 h post-treatment. Immune gene expression in honey bees exposed to a lethal concentration of NAC-5and OAC-4 showed that the expressions of AmHym, AmBask, and AmSpz were significantly lower compared with those of control honey bees.