The Varroa Mite
Varroa destructor is an external parasitic mite that attacks honey bees Apis cerana and Apis mellifera. It was until recently mislabeled as Varroa jacobsoni. Varroa mites have been found on flower feeding insects such as the bumblebee Bombus pennsylvanicus, the scarab beetle Phanaeus vindex and the flower-fly Palpada vinetorum (Kevan et al. 1990). Although the Varroa mite cannot reproduce on other insects, its presence on them may be a means by which it spreads short distances (phoresy). Varroa can only replicate in a honey bee colony. It attaches at the body of the bee and weakens the bee by sucking haemolymph. In this process the mite spreads RNA viruses like Deformed Wing Virus to the bee. A significant mite infestation will lead to the death of a honey bee colony, usually in the late fall through early spring. The Varroa mite has been the parasite with the most pronounced economic impact on the beekeeping industry. It may be a contributing factor to Colony Collapse Disorder which is threatening hives throughout North America.
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 which hatch into females and finally one male. The young mites 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.
The adults suck the "blood" of adult honey bees for sustenance, leaving open wounds. The compromised adult bees are more prone to infections. With the exception of some resistance in the Russian Honey Bee, 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 [1].) Apis cerana has developed grooming procedures that remove these parasites so they are not a threat to these hives.
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 fall can cause a crisis when drone rearing ceases and the mites switch to worker larvae, causing a quick population crash and often hive death.
Description: Reddish-brown in color; 1.00-1.77 mm long and 1.50-1.99 mm wide; Flat, button shape; Eight legs
Introduction around the world
• Early 1960s Japan, USSR
• 1960s-1970s Eastern Europe
• 1971 Brazil
• Late 1970s South America
• 1982 France
• 1984 Switzerland, Spain, Italy
• 1987 USA
• 1989 Canada
• 1992 England
• 2000 New Zealand (North Island)
• 2006 New Zealand (South Island) [2]
Identification
Varroa destructor was, until recently, thought to be a closely related mite species called Varroa jacobsoni[3] [4] [5]. Both species parasitize the Asian honey bee, Apis cerana. However, the species originally described as V. jacobsoni by Oudemans in 1904 is not the same species that also attacks Apis mellifera. The jump to mellifera probably first took place in the Philippines in the early 1960’s where imported Apis mellifera came into close contact with infected Apis cerana. Up until 2000, scientists had not identified Varroa destructor as a separate species. This late identification in 2000 by Anderson and Trueman corrected some previous confusion and mislabeling in the scientific literature. As of 2005, the only Varroa mites that can reproduce in colonies of Apis mellifera (Western honeybee) are the Korea and Japan/Thailand genotypes of Varroa destructor.