Biosecurity NZ officers are on high alert for fruit flies, such as the Queensland fruit fly that was found in Grey Lynn in 2015.

A fruit fly could have devastated New Zealand's horticulture industry if it hadn't been discovered at Auckland Airport, Biosecurity NZ says.

The fruit fly came in on undeclared food from Malaysia last month, Biosecurity NZ passenger manager Craig Hughes said on Thursday.

The fly was found in chillies after an X-ray screening of a tour leader's baggage.

A caterpillar was also found in garlic bulbs.

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"Many horticulture crops are susceptible to attack by fruit fly," Hughes said.

"Affected fruit and vegetables could be inedible or subject to trade restrictions if the pest became established in New Zealand."

Hughes said the fly was believed to be a Malaysian fruit fly, which had invaded the Pacific Islands.

It had attacked more than 60 types of fruit and vegetables, he said.

SUPPLIED The fruit fly was found with undeclared food from Malaysia.

More than 10 fruit flies have been found at the border by Biosecurity officers this year and they are on high-alert following outbreaks in Tasmania and Adelaide, Hughes said.

"This is about protecting New Zealand from an invasive pest that could seriously harm an industry worth $5 billion in domestic sales and exports."

The tour leader was fined $400 for failing to declare the food.

The Auckland central suburb of Grey Lynn was put under a fruit and vegetable lockdown in 2015 after a Queensland fruit fly was found.

It was the fourth time the pest had been found in northern New Zealand since 2012.