American foulbrood
The most serious disease of honeybees in New Zealand is American foulbrood (AFB), which is caused by a bacterium. Extremely contagious and deadly, it affects only the larvae and has a characteristic smell. It was accidentally introduced with the first bee imports and by the 1880s was well established. Legislation in the early 20th century set up measures to control AFB and helped keep commercial beekeeping economically worthwhile.
Controlling disease
In 1991 the New Zealand government stopped funding the honeybee disease control programme, and the National Beekeepers Association began to contract agencies to control disease. They inspect about 10% of apiaries each year and are on standby for an outbreak of exotic bee disease. Using the Biosecurity Act 1993, the National Beekeepers Association created the Biosecurity (National American Foulbrood Pest Management Strategy) Order 1998, which aims to eliminate the disease from New Zealand. The Ministry for Agriculture and Forestry has a role in border protection and export certification.
Varroa mites
In 2000 the parasitic varroa bee mite (Varroa destructor) was found in New Zealand. It has become established in the North Island, and detected in some northern South Island hives. The mite appears as a red or brown spot on the bee’s thorax, or on a larva. It enters a hive on an adult bee, then crawls into a brood cell, where it lays its eggs. These hatch, and the mite goes through two juvenile stages before reaching adulthood. When the adult bee emerges from the cell it takes the mites, which are feeding on its body fluids. Mites may also carry a harmful virus.
Varroa mites are usually not a problem in a thriving hive, but in autumn and winter, when the bee population drops, the mites can overtake a hive and destroy it. Between 2000 and 2005, more than 25,000 hives were lost in the North Island. The spread and impact of the mite can be minimised by isolating affected hives.
Other diseases
Other exotic threats to the beekeeping industry are European foulbrood (Melissococcus pluton), Asian bee mite (Tropilaelaps clareae), bee louse (Braula coeca), and Africanised bees (Apis mellifera scutellata), which introduce aggressive behaviour. Wasps can be a problem in large numbers, as they can destroy hives.
In 2007 a new disease known as deformed wing virus was found in Northland. This was linked to the varroa mite and had the potential to seriously affect the bee industry.