Introduction Varroosisis an ectoparasitosis of adult bees and bee larvae. The pathogen responsible isVarroa destructor, this parasite hasa sexual dimorphism. The female of the parasite is larger than the male andtheir morphology is perfectly adapted to their host (Rosenkranz et. al 2010).
Their life cycle is missing a free-living stage and can be divided into two main phases. First one is the phoreticstage, located on the adult bees, this stage is used by the female of theparasite in order to infestate otherlarva cells or other colonies of bees, atthis stage the adult bee is used as a carrier and as food source (Rosenkranz et. al 2010, Piou et. al. 2016). After a certain amount of time (that may vary between one and ten days)the female mite switches to the reproduction phase leaving the adult bee andentering a cell with brood larva (Piou et. al. 2016).
According to Rosenkranz et. al 2010 and Kuenen and Calderone, 2000 the miteprefers the brood larva in detriment of worker larva because the brood larvahas a longer period of incubation and that gives the mite more time to reproduce (Rosenkranz et. al 2010; Kuenen andCalderone, 2000; Martin and Cook, 1996). The reproductivecycle of the parasite is perfectly adapted toits host, the female mite chose’s and infestate a brood cell, a few hoursbefore the cell is closed by the nurse bees. A few hours after the cell issealed the Varroa female feeds of the brood larva hemolymph.
This step isnecessary to activate its ovary system, in less than three days after the cellis closed appears the first egg (which is always a haploid male mite), afterthat she lays up to 5 eggs at regular intervals of approximately 30h each (themite prefers drones because they require 24 days to hatch, which means moretime to reproduce). The mother and her offspring continue to feed with thehemolymph of the bee larva and the male mite will mate with his sisters, exceptthe case in which two adult female mites infest the same cell (Frey et. al.2013; Andino et. al., 2016).
Theoriginal host of the parasite is Apiscerana and until the mite infestation started to produce economical damageto the beekeepers at the end of the 20th century, the parasite had littleattention. At first, the mite responsible for the damage of the colonies wasconsidered V. jacopsoni, and onlyafter further studies was revealed the existence of more families of Varroa andhas been concluded that the mite responsible for the damage is V. destructor (Anderson and Trueman,2000).Types of geneticresistance When V. destructor started to produceeconomic damage (both in the production of the colony and the colony numbers)the beekeepers called the chemical option. They started using various chemicalsubstances in order to fight this parasite.
But this has brought new problems.In time the mites started to gain resistance to the treatments leaving thebeekeepers with a limited number of options. The chemical substances can alsoharm the bees not just the parasite and their residue can be found in the beeproducts. Also buying each year substances to treat the bees is prettyexpensive. So the researchers have reached the conclusion the obtaining beesresistant to Varroa destructor is theonly long term viable solution (Tsuruda et. al.
, 2012). Untilnow the researchers have identified and studied several resistance mechanismsthat allow bees to counteract the effects of infestation. 1.Theentombing of drone brood- Until now this behavior has been observed only on theoriginal host of the parasite A.
cerana,this behavior seams to manifest more when a brood cell is infested with 2 or 3mites. In this case the drone brood seems to remain without sufficient energyto be able to hatch and die in the cell, as a result the parasites also remainblocked with the dead brood. Also A. ceranaworkers seem to delay the dead brood removal (Rath, 1999; Boecking and Spivak,1999). 2.Effective grooming and hygienic behavior 3.
Noreproduction in worker brood at all