White Admiral Butterfly Establishes
White admiral photographed at the Waikato site in late 2015.
One of the highlights of last year was releasing the Honshu white admiral butterfly (Limenitis glorifica) in November 2015 and observing that it had successfully reproduced at a location in the Waikato, with subsequent generations emerging in January and again in March 2016.
However, Quentin Paynter, who has been leading the project, noted that “we cannot be certain an agent has successfully established until it has successfully overwintered.” “We were concerned that conditions in New Zealand might not be ideal for hibernating larvae because winters here are generally much milder than in Japan,” he added. So, it was with a little trepidation that Quent returned to the Waikato release site this spring.
Japanese honeysuckle (Lonicera japonica) is now a widespread weed in both the North and South Islands and biological control is the only reasonable option left to reduce the prevalence of this vigorous vine. “We were limited to releasing newly emerged adult butterflies because of the difficulty we had rearing them in containment, where the conditions were not suitable for their courtship flight and mating,” said Quentin. “It was a bit of a long shot because we were relying on them finding a mate and producing offspring from relatively small numbers.”
Fortunately the larvae did successfully overwinter, as Quent saw several adult butterflies at the Waikato release site last November, despite relatively cool and windy conditions. “November is equivalent to May in Japan, which is when butterflies emerge in lowland sites there, so as it turns out, we released butterflies at just the right time.”
Quent and Hugh Gourlay visited the Waikato release site again in December finding eggs and 1st instar larvae. The eggs and larvae were not that hard to find, but they were not abundant enough to consider collecting and redistributing larvae to other sites yet. “They are probably diluted by the vast amount of honeysuckle present at the site,” said Quent. “The presence of eggs and larvae several hundred metres from the release site also shows that butterflies have clearly begun dispersing away from the original release site,” noted Hugh, adding that “dispersal could be rapid because the adults are strong fliers and there is a vast amount of honeysuckle in the nearby valley.” Quent confirmed this to be the case in late January, when he found adult butterflies about 1.3 km from the release site “as the butterfly flies”, which was as far as he had time to search. He noted that “they could have gone much further than this as there is suitable habitat for several more kilometres in all directions!” More recent sightings of the butterflies have been made 1.5 km in the opposite direction. “If the butterflies have dispersed about 1.5 km in all directions, then the population must occupy at least 7 square kilometres and we estimate there must already be several thousand of them. The females lay hundreds of eggs, so we are hopeful that there will be sufficient numbers to be able to begin safely harvesting from this site next spring,” said Quent.
The news from the second release site on Waiheke Island is less positive. “I didn’t find any signs of establishment last spring,” said Quent. “It was a much smaller release, compared to the Waikato one, so failure is not that unlikely, but I’m not giving up hope just yet and folk should still be on the lookout in case there are butterflies present,” he added.
Another key step in the Japanese honeysuckle project this year will be to progress work on the longhorn beetle (Oberea shirahatai), which attacks the stems. “We have been given approval from the Environmental Protection Authority (EPA) to release them but have not made any actual field releases as yet,” confirmed Hugh Gourlay. These beetles are also difficult to mass rear and our best option is probably to take a similar approach to the white admiral and attempt to set up a field population that can eventually be harvested. “We have a small population of late instar larvae in containment presently and they are currently in their hibernation phase, which can last up to a period of 2 years,” said Hugh. It is expected that the beetles will emerge from diapause in April this year but we will need to wait until spring before we can release them in the field, rather than plunge them straight into another winter. Hugh will also be heading off to Japan in May to collect additional beetles to boost the population and allow for a larger field release.
This project was funded by the National Biocontrol Collective.