Zespri’s global trials and data insights manager Dr Sonia Whiteman presented an update on Italian-based trials on stink bugs at an industry biosecurity update.
Based on four blocks of two green and two SunGold orchards in north eastern Italy, the scientists studied the bugs’ effects at different life-stages and times of year. Fruit was bagged and had stink bugs placed with it over a 40-50 day period to study its effects upon the fruit.
One of the key lessons for the Italian researchers was how the bug’s population tends to explode over autumn.
“This is brought on by BMSB’s ability to produce two generations a season, one in early summer and one in mid-summer, resulting in exponentially increasing the numbers into autumn,” Whiteman said.
In the SunGold orchards, the bugs were still present even after the fruit had been harvested later in autumn.
Researchers found there were slightly lower numbers of bug populations in orchards that had other desirable host plants in them, including cherries and apricots.
“And the concept of planting trap crops has been explored,” she said.
Damage to fruit fell over different months, with green fruit experiencing the most in June and SunGold in July, the equivalent of December and January for Kiwi orchardists.
“And the damage was high, up to 90% with no insecticide used,” she said.
Whiteman says in general, Italian kiwifruit orchardists are learning to live with the bug’s presence.
However, other horticulture crops are struggling and the bug has all but wiped out large tracts of Italy’s pear growing region in the north east, with apples also under growing threat.
The type of impact upon the kiwifruit also differed depending upon variety.
Green kiwifruit tended to hold to the vine but wither from within, while SunGold dropped to the ground. There was initially concern the infected green fruit can be mistakenly picked and packed, only to rot and potentially affect the quality of unaffected fruit while in storage, however this has not been the experience in Italian post-harvest.
High temperatures combined with high humidity, not unusual in NZ, were also regarded as favourable to the bug’s establishment.
Whiteman says researchers were not sure if NZ would be afflicted by the “two generations one season” breeding cycle.
“This is the Italian experience, the message is to be prepared and keep this bug out,” she said.
She says the major drop in people travelling into NZ due to the covid pandemic has had a silver lining in lowering the risk of stink bug incursion, just as its southern hemisphere breeding cycle is about to kick off.
Data confirms there were 57 interceptions of live brown marmorated stink bugs last season, a reduction of 73% from the previous season.
They were first noticed in 2012 when they started coming in with United States’ sourced machinery parts and vehicles.
The brown marmorated stink bug is regarded as the country’s greatest biosecurity threat, and if established could slice almost $4 billion from the economy over 20 years.
The bug has proven relatively challenging to manage using pesticides, particularly because it is often found in large numbers. In a world-first move, the horticultural sector sought and gained approval from the Environmental Protection Agency (EPA) to use the parasitoidal samurai wasp as a biological control, should the breeding population of stink bugs become established here.
Normally permission would be only granted for a bio-control once a pest is established here.
