THE DIFFICULTY OF REDUCING INTRODUCED WASP (VESPULA-VULGARIS) POPULATIONS FOR CONSERVATION GAINS

Introduced common wasps (Vespula vulgaris) are widespread, abundant pe sts in New Zealand. They compete for food with native birds and feed o n native invertebrates. We poisoned wasps annually over 4 years to see if it was possible to reduce their abundance in two 30-ha beech fores t sites. Two different poisons (sodium monofluoroacetate and sulfluram id) were used, mixed with sardine catfood. There was no evidence that one poison was more effective than the other. Between 82 and 100% of t he colonies were killed in the poisoned sites, but reinvasion by forag ing workers meant that cumulative wasp biomass (measured using Malaise traps) was reduced by only 55-70%. Individual wasps were about 16% he avier in the poisoned sites at the peak of the wasp season (March) tha n in the non-poisoned sites, although this had a minimal effect on cum ulative biomass over the entire season. Conservation gains need to be quantified in order to assess whether the expense of such poisoning op erations is warranted.