Potential economic impacts of the Varroa bee mite on the pollination of major crops in Papua New Guinea

• National Agricultural Research Institute, Papua New Guinea
• Rural Industries Research and Development Corporation, Australia

Honeybees (Apis mellifera) were introduced to Papua New Guinea (PNG) more than 50 years ago, where they have been managed for their honey and have spawned feral populations. Insect pollination increases the yield and the quality of many important crops, and bees are widely regarded as the most important pollinators. But in recent decades the most potent threat to bee pollination has come from a deadly parasitic mite of bees, Varroa destructor. So far Papua New Guinea and Australia have been free of this mite disease, but in other countries such as the USA and New Zealand it has caused significant economic impacts. In 2008 it was discovered that the endemic Varroa species in PNG (V. jacobsoni) has acquired traits that threaten to make it as deadly as V. destructor to the honeybees.
This project assessed how this significant development could affect crop production in PNG through the development of future scenarios for the impact of bee mites on pollination. Scientists estimated the potential economic losses and associated ranges for the crops of highest value within each scenario developed and identify knowledge gaps regarding management of this threat to PNG agriculture as a guide for future research. They developed a bioeconomic model for PNG based on one already used by CSIRO, designed to assess the possible economic impact should varroa mite invade Australia. The outcomes are designed to improve decisions for PNG on the strategies needed to control the newly identified V. jacobsoni. This will benefit Australia because PNG is one of the main potential pathways for entry of this disease.

The scientists conducted two workshops in PNG to collect and discuss information and formulate possible scenarios. This information was supplemented by the published scientific literature. They conducted economic modelling, using an existing model of varroa spread and impacts, but modified to the particular circumstances in PNG. They also made observations of insect visitors to flowering crops at lowland and highland locations to improve their knowledge regarding which bees are acting as potential pollinators.
The scientists concluded that in the most likely scenario the impacts of the new varroa would be limited to Apis mellifera and therefore geographically limited to the highlands. Losses to agricultural production are expected to be low because dependence on A. mellifera for crop pollination is low. This is because the managed honeybee population is small and rarely used for managed pollination. The feral honeybee population may be large, but nevertheless there are many other wild and feral bee species that are likely to provide a similar crop pollination service (most notably A. cerana) and therefore a decline in one species is unlikely to have significant repercussions. The impact on managed hives would cause damage to honey production and limit opportunities for future development of managed pollination.
This predicted impact was, however, contingent upon a number of assumptions made because of limited local information. Therefore the scientists also estimated the possible impact if honeybee decline were to lead to crop pollination decline (a 'worst case' scenario). They concluded that the largest economic risk was associated with the cash crop, highland coffee. Assuming that the new varroa actually emerged six years previously, and assuming only honeybees were effective pollinators of highland coffee, then the predicted mean annual losses would be PNG Kina 14.2 million over the next 24 years.
To provide greater certainty around the likely economic impacts of the new mite the scientists suggested the gathering of more data regarding the distribution and abundance of feral honeybees, and also the influence of variation in the pollinator community on fruit set by highland coffee in PNG. Further research on coffee pollination would also assist in coping with changes expected due to the mite, and could help coffee growers increase the fraction of their crop sold with a premium for large bean size.