Economic impacts
Honeydew
Honeybees
Vespula wasps are a major pest of the beekeeping industry in New Zealand. They cause direct financial loss by robbing beehives of honey and by killing bees. They also require beekeepers to expend time and money in control procedures (Clapperton et al. 1989).
A nationwide survey of beekeepers in the 1974/1975 season by Walton and Reid (1976) found that 88% of beekeepers thought wasps were a nuisance. At this time they were considered to be a beekeepers’ single most important pest.
A survey by Clapperton et al. (1989b) during 1985/1986 and 1986/1987 seasons also showed that >80% of respondents considered wasps a nuisance. The damage caused by wasps translated to an economic loss of $650,000 just for the replacement cost of beehives in 1986/1987 (Clapperton et al. 1989b).
Wasps destroy or seriously damage 8-9% of honeybee hives in New Zealand
However, wasps also cause lost honey production and out-compete honeybees for honeydew resources. Both of these will also add up to very large economic costs, although such data has not yet been estimated.
Horticulture
Economic losses to orchards and vineyards in New Zealand are probably low, mostly because many crops are already harvested when wasp numbers peak (Thomas 1960). Although costs from wasp damage appear to be relatively insignificant compared with other horticultural pests and diseases, even very small losses from individual growers add up across the entire horticultural sector. The biggest problems will be likely in orchards that have crops that i) are high in sugar (attract wasps), ii) need harvesting during the peak wasp period in February–May, iii) are hand-picked, and iv) have under low or poor management.
Agriculture
Mastitis is an inflammation of the udder tissue in dairy cows, and is a very common and costly disease worldwide. It is a serious problem in New Zealand, with estimates of its cost put at $180 million per annum (Malcolm 2006). Yeruham et al. (2002) found that German wasps inflicted injuries to the udder to ~40% of a milking herd in Israel; injuries that led to clinical and subclinical mastitis, and subsequently to large losses in milk production. Whether wasps cause lesions (and mastitis) in dairy cows in New Zealand is unknown.
However, wasps are a direct danger to stock, as they commonly nest in paddocks with grazing animals. There are antedoctal reports in New Zealand of stock dying (deer, sheep) after being stung on the tongue and being asphyxiated. Wasps are also a danger to farm workers cutting hay etc.