Morphological variation of Varroa destructor (Parasitiformes, Varroidae) in different seasons

Abstract

Varroosis is one of the most dangerous and common diseases of honey bees (Apis mellifera Linnaeus, 1758) worldwide, caused by gamasid mites of the species Varroa destructor Anderson and Trueman, 2000. This external parasite is widespread and adapted to the climate conditions of most countries of the world, and it can infect bees at any life stage. It parasites on worker bees, male and queen bees, larvae and pupae, feeding on their hemolymph and fat bodies, causing lower survival rates and lower density of bee colonies, decreasing the bees’ life span. Here, we studied the specifics of the seasonal variation of female V. destructor mites, obtained from honey bees, by the morphological characters of mites belonging to the summer and winter generations, and their differences were established. Using the methods of multivariate statistics, we found significant differences between the summer (June–July) and winter (October–November) morphotypes of V. destructor mites. There are differences between the seasonal samples by 12 morphological characters of the parasite, namely the width of dorsal shield, width of dorsoventral shield, number of pores on sternal shield, length of tarsus and macrochaeta IV, and distances between setae of gnathosoma. Processing the seasonal samples of mites with discriminant analysis resulted in differences by 11 morphological characters including the length of dorsal shield, number of lancet setae, length and width of genitoventral shield, width of anal shield, number of setae and pores on sternal shield and distance between setae of gnathosoma. In general, the summer females are smaller and elongated compared to winter females, with larger genitoventral shield and shorter legs. The mites of summer and winter generations are adapted to different seasons: the summer mites to the reproductive period, the winter generation to overwintering on bees. The ratio of morphotypes in female V. destructor mites is observed to change during the year, from 20.2% winter morphotype in summer generation to 20.7% summer morphotype in winter mites. Studying the influence of acaricides on the distinguished morphotypes is a promising approach to improve pest control measures against varroosis of honey bees.

Varroa destructor from the Laboratory to the Field: Control, Biocontrol and IPM Perspectives—A Review

“…Females are smaller with larger shields and shorter legs in summer. The ratio of morphotypes is dynamic and goes from 20% of winter morphotype in summer to 20% of summer morphotype in winter [ 173 , 174 ]. Viruses loads add a third dimension where the mite can be free of viruses, positive with replication of the virus or positive without replication of the virus (asymptomatic).…”

“…In the same way, the heterogeneity of the V. destructor population intra hive, between hives and locations has to be taken into account. The numerous sources of physiological, pathological, environmental, behavioural and genetic variations can interfere with the treatment against the mite and determine the success of the method (Figure 2) [172,174,258]. Several works took this aspect into account while testing different molecules or agents against the acari and showed a customised response per location [29,222,259].…”

“…Genetics through several traits can influence the phenotype [ 168 ]. Mites differ from winter to summer with a dynamic morphotype ratio going from 20% of winter morphotype in summer to 20% of summer morphotype in winter [ 173 , 174 ]. In addition, V. destructor can be divided in four different states: dispersal ecto-parasite attached to honeybee’s body, comb mite freely moving inside the hive, reproductive acari confined in brood cell and non-reproductive mite confined in brood cell [ 30 , 172 ].…”

State epizootic monitoring of contagious diseases of bees in the territory of the Volyn region

“…These changes indicate the development of adaptive mechanisms in the mite for parasitizing bees at different times of the year. In particular, in winter -in sealed brood and in summer on bee adults (Yevstafieva et al, 2020). In addition, because of the toxic parasitic action of this mite, the resistance of the bee decreases, which in turn provokes the activation of other bacteria (activation of the opportunistic microflora of the hive and insects); in addition, the bee body becomes susceptible to damage by other pathologies (bacterial diseases, viral infections, diseases, caused by protozoa, etc.)…”

Standard Methods for Dissection of Varroa destructor Females

“…Varroa destructor is a 1.7 mm large, 1.1 mm long brown mite (Mesostigmata, Acari) [26,29,30]. Its flattened body is covered by articulate sclerotized plates, one large dorsal shield, and seven smaller ventral plates, which have to be removed to have access to the internal organs.…”