Varroa destructor (Varroa mite) is an external parasitic mite that attacks the honey bees Apis cerana and Apis mellifera. The disease caused by the mites is called varroosis.
Varroa mites can only reproduce in a honey bee colony. It attaches to the body of the bee and weakens the bee by sucking hemolymph. In this process, RNA viruses such as the deformed wing virus (DWV) spread to bees. A significant mite infestation will lead to the death of a honey bee colony, usually in the late autumn through early spring. The Varroa mite is the parasite with the most pronounced economic impact on the beekeeping industry. It may be a contributing factor to colony collapse disorder, as research shows it is the main factor for collapsed colonies in Ontario, Canada[1] and the United States.
Physical description[]
The adult female mite is reddish-brown in color, while the male is white. Varroa mites are flat, having a button shape; are 1–1.8 mm long and 1.5–2 mm wide; and have eight legs.
Reproduction, infection and hive mortality[]
Mites reproduce on a 10-day cycle. The female mite enters a honey bee brood cell. As soon as the cell is capped, the Varroa mite lays eggs on the larva. The young mites, typically several females and one male, hatch in about the same time as the young bee develops and leave the cell with the host. When the young bee emerges from the cell after pupation, the Varroa mites also leave and spread to other bees and larvae. The mite preferentially infests drone cells, allowing the mite to reproduce one more time with the extra three days it takes a drone to emerge vs a worker bee.
The adults suck the "blood" (hemolymph) of adult honey bees for sustenance, leaving open wounds and transmitting diseases and viruses. The compromised adult bees are more prone to infections. With the exception of some resistance in the Russian strains and bees that have Varroa sensitive hygiene (about 10% of colonies naturally have it), the European Apis mellifera bees are almost completely defenseless against these parasites (Russian honey bees are one-third to one-half less susceptible to mite reproduction).[3]
The model for the population dynamics is exponential growth when bee brood are available and exponential decline when no brood is available. In 12 weeks, the number of mites in a western honey bee hive can multiply by (roughly) 12. High mite populations in the autumn can cause a crisis when drone rearing ceases and the mites switch to worker larvae, causing a quick population crash and often hive death.
Varroa mites have been found on Tricia larvae of some wasp species, such as Vespula vulgaris, and flower-feeding insects such as the bumblebee, Bombus pennsylvanicus, the scarab beetle, Phanaeus vindex and the flower-fly, Palpada vinetorum.[4] It parasitizes on the young larvae and feeds on the internal organs of the hosts. Although the Varroa mite cannot reproduce on these insects, its presence on them may be a means by which it spreads short distances (phoresy).
Introduction around the world[]
- Early 1960s Japan, USSR
- 1960s-1970s Eastern Europe
- 1971 Brazil[verification needed]
- Late 1970s South America
- 1980 Poland
- 1982 France
- 1984 Switzerland, Spain, Italy
- 1987 Portugal
- 1987 United States
- 1989 Canada
- 1992 United Kingdom[5]
- 2000 New Zealand (North Island)
- 2006 New Zealand (South Island)[6]
- 2007 Hawaii (Oahu, Hawaii Island)[7][8]
- 2008 Hawaii (Big Island)
As of mid-2012, Australia is thought to be free of the mite.[9][10] In early 2010, an isolated subspecies of bee was discovered in Kufra (southeastern Libya) that appears to be free of the mite.[11] The Hawaiian islands of Maui, Kauai, Molokai, and Lanai are all free of the mite.