Varroa destructor

Varroa destructor
Varroa destructor, Photo by Scott Bauer
Varroa destructor, Photo by Scott Bauer
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Arachnida
Order: Acari
Family: Parasitidae
Genus: Varroa
Species: V. destructor
Binomial name
Varroa destructor
Anderson & Trueman, 2000
Low Temperature Scanning Electron Microscope (LTSEM) image of Varroa destructor on a honey bee host
Varroa mites on pupa
Varroa mites on pupae
Varroa destructor on bee larva.

Varroa destructor is an external parasitic mite that attacks honey bees Apis cerana and Apis mellifera. The disease caused by the mites is called varroatosis.

Varroa destructor can only replicate in a honey bee colony. It attaches at the body of the bee and weakens the bee by sucking hemolymph. 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 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 (CCD) which is threatening hives throughout North America.

Contents

Physical description

The adult mite is reddish-brown in color; has a flat, button shape; is 1-1.8 mm long and 1.5-2 mm wide; and has 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 which hatch into several females and typically 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 strains, 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]). Eastern Apis cerana honey bee 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.

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 these insects, its presence on them may be a means by which it spreads short distances (phoresy).

Introduction around the world

Identification

Varroa destructor was, until recently, thought to be a closely related mite species called Varroa jacobsoni[2][3][4]. 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 1960s 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.

Control or preventive measures and treatment

Chemical measures

Varroa mites can be treated with commercially-available miticides. Miticides must be applied carefully to minimize the contamination of honey that might be consumed by humans. Proper use of miticides also slows the development of resistance of the mites.

Synthetic chemicals

Natural occurring chemicals

Physical or mechanical methods

Varroa mites can also be controlled through non-chemical means. Most of these controls are intended to reduce the mite population to a manageable level, not to eliminate the mites completely.

Behavioral methods

Varroatosis

The infection and subsequent parasitic disease caused by varroa mites is called varroatosis. Its treatment has been of limited success. First the bees were medicated with fluvalinate which had about 95% mite falls. However the last five percent became resistant to it and later, almost immune. Fluvalinate was followed by coumaphos.

References

  1. ^  Anderson, D & Trueman, J. W. H. (2000). "Varroa jacobsoni (Acari: Varroidae) is more than one species." Experimental & Applied Acarology, 24, 165-189.
  2. ^ ZHANG, ZHI-QIANG Notes on Varroa destructor (Acari: Varroidae) parasitic on honeybees in New Zealand Systematic & Applied Acarology Special Publications (2000) 5, 9-14
  3. ^  Delaplane, Keith S. Varroa destructor: Revolution in the Making University of Georgia; Bee World; 2001; 82(4): 157-159

Notes

  1. ↑ Varroa Mite | MAF Biosecurity New Zealand
  2. ↑ Images in the news - chicagotribune.com
  3. ↑ starbulletin.com | Business | /2007/04/25/
  4. ↑ "A Sustainable Approach to Controlling Honey Bee Diseases and Varroa Mites". SARE. Retrieved on 2008-11-18.

External links

The Swiss Bee Research Centre scientifically investigated the life cycle of the varroa in the capped cell and described it in a paper (A Look under the cap).