Investigating the importance of altitude and weather conditions for the production of toxic honey in New Zealand

Toxic honey is produced in New Zealand when honey bees (Apis mellifera) forage on honeydew containing the phytotoxin tutin that is produced by the passion vine hopper (Scolypopa australis) when feeding on the poisonous plant tutu (Coriaria arborea). Observational studies suggest that there are a set of conditions required for the production of toxic honey, but these factors have not been well studied. This research aims to investigate the importance of altitude and weather conditions for the production of toxic honey in New Zealand and makes some recommendations for a review of the New Zealand Food Safety Authority (NZFSA) Food (tutin in honey) Standard 2008 that was introduced after a toxic honey outbreak in 2008. Transects were established in parts of the North Island during the summer of 2009 and were visited weekly for 6 consecutive weeks. Variables recorded were elevation, S. australis density, honeydew abundance, honey bee and wasp (Vespula spp.) presence and temperature and rainfall data. Weather conditions present during the 2008 outbreak were compared with those from 1999 to 2009. S. australis were not present at altitudes of 375 m and above; with more research, some higher areas of New Zealand may be able to be reclassified as 'low risk'. Honeydew was available in a wide range of temperature and rainfall conditions. Rainfall appeared to wash honeydew from tutu bushes; however, it quickly reappeared in densely populated sites. Honey bee and wasp presence was positively affected by the presence of honeydew, nevertheless 30-50% of the time they were observed foraging in the absence of honeydew, indicating they may feed on small amounts of dew. As the absence of honeydew is an option given by the NZFSA to demonstrate honey safety, this requires investigation. Weather conditions leading up to the 2008 toxic honey outbreak were warm and dry but were not significantly different from other years. Therefore, inadequate management practices, rather than more favourable environmental conditions were probably responsible for the 2008 toxic honey outbreak. Future research should focus on determining the conditions required for toxic levels of honeydew to be incorporated into hives, and regions that have not produced toxic honey historically should be closely studied to determine whether any fit the low-risk criteria.