How many Cook Islands News readers have noticed an abundance of one particular butterfly recently - one they may not have seen in previous years.
Staff at Te Ipukarea Society have noticed many of these new butterflies around their office, homes, and also up in the Takitumu Conservation Area (TCA) where they have been helping TCA chairman Ian Karika with some work.
A little research led us to identify this new butterfly as Heliconius erato cyrbia, commonly known as the red postman. We also learned that the butterfly is here to do a very important job, as a biological control, or biocontrol agent. It was introduced to control the invasive red passionfruit vine Passiflora rubra.
The red passionfruit is an invasive vine throughout much of the southern group of the Cook Islands. It out-competes native plants, and can kill old trees by smothering them. It is one of 12 weeds that are “dominant invaders” in the Cook Islands and is one of a number of invasive weeds that has been blamed for the recent extinction of the native shrub Acalypha wilder, which was endemic to Rarotonga.
The importation of this butterfly was enabled under a joint project by Landcare Research in New Zealand and the Cook Islands Ministry of Agriculture.
The chief scientists on this project were Dr Maja Poeschko from the Ministry of Agriculture and Dr Quentin Paynter from Landcare Research. Dr Paynter came to Rarotonga in the first half of 2016 with about 80 of these butterflies, which were then bred at the Ministry of Agriculture to increase their numbers. Shortly after the butterflies were released into the wild (see CI News August 5, 2016). Extensive testing was done before releasing the butterflies to make sure they didn’t pose a threat to edible varieties of passionfruit.
Biocontrol agents are usually a much more effective way of controlling pests than mechanical removal (weeding and cutting) and much safer than using chemical poisons, which are often toxic to useful plants, as well as to humans.
These days a very detailed and thorough environmental impact assessment (EIA) must be done before introducing any biocontrol agent.
The EIA for this project was conducted in late 2015. A good example of a biocontrol project that had no EIA, and possibly the first biocontrol agent introduced to the Cook Islands, was the mynah bird (manu kavamani), possibly to control coconut stick insects (‘e’e) and paper wasps (rango patia), in 1906. Most people in the Cook Islands, and especially fruit growers, would agree that the introduction of mynah birds was a biocontrol project that was not good for the country, validating the need of a thorough EIA process!
In an article just after the original release, Dr Paynter said there were plans to eventually release the butterfly on other islands, in particular Atiu, which has a globally recognised remnant of makatea forests that is threatened by invading red passionfruit vines, which could overtake the native forest. Mangaia is another southern group island suffering badly from the invasive vine.
In a return visit to the Cook Islands last month to follow up on other biocontrol agents that are being trialled here, Dr Paynter said he was amazed to see how common the butterfly has become in the 16 months or so since it was first released.
Landcare Research’s weed biocontrol work in the Cook Islands is funded by New Zealand’s Ministry of Foreign Affairs. Te Ipukarea Society hopes to be more involved in this biocontrol work in the future.