Reports of sightings of the invasive harlequin ladybird in the North Waikato are not yet a cause for concern, according to Ministry of Primary Industries for the area.
MPI Recovery and Pest Management senior adviser Brad Chandler said reports had been sent in from Pokeno right down to Huntly.
It feeds on aphids, usually from willow, oak, maple and poplar trees. This has made it useful as a biological control of pests in some countries. Unfortunately, its huge appetite allows it to out-compete native ladybirds. It will also eat other ladybirds and beneficial insects if it runs out of aphids. It may also feed on pip fruit, causing blemishes on the fruit.
It has been known to cluster within bunches of grapes before harvest, resulting in the tainting of the juice and any wine made from the juice.
The species spreads very quickly, making it difficult to manage. It is native to Asia.
The harlequin ladybird is considered an invasive species in many countries. The ladybird can also become a general nuisance as it can build up in large numbers inside buildings and houses, seeking shelter during winter.
“Most of these reports have been in the last month, most likely because populations have built up through summer and the warm autumn,” Chandler said.
“MPI received a report from around this area soon after this insect was first detected in New Zealand in 2016, so the ladybird may have been present in these areas for some time.”
Chandler said the insect could pose a risk to the biodiversity of New Zealand’s ecosystem and potentially to horticulture.
They have the ability to out-compete native ladybirds for food, will also eat native ladybirds as well as other insect species, and they may feed on fruit, he said.
But at the moment, it’s not an issue.
“To date it does not appear to have been of major widespread significance, either for horticulture, biodiversity or households,” he said.
However because it is not feasible to attempt eradication of the insect, MPI is working on monitoring its geographical spread.
“It is also providing the horticultural industry in affected regions with information about the insect and its management. The focus has been to provide potentially-affected horticultural growers with management information to assist them in minimising any impacts of the insect,” he said.
“For this reason, it is useful that people report suspected sightings to MPI. The ministry will be able to help callers with identification of the insect and information.”
The harlequin is large by ladybird standards – 5–8 mm long and 4–6.5 mm wide.
• It is well known for its very variable colouration and patterning, which makes it difficult to distinguish from other ladybird species.
• It looks similar to the common spotted ladybird (Harmonia conformis). The harlequin ladybird usually has M-shaped makings on the pronotum (the area between the head and abdomen), although this pattern is not present with darker specimens. In contrast, the pronotum of the common spotted ladybird features a W-shaped black mark or two separate U-shaped patches.
• The harlequin also has small bumps on the rear of its back.
• Harlequin larvae and pupae have a spikier skin than the common spotted ladybird.