Image copyright Getty Images Image caption The red outer layer of pistacchio verde di Bronte covers a bright green interior

Police captain Nicolo Morandi says that he and his colleagues are already preparing for September.

At least six officers are going to patrol in the daytime, and up to 12 at night. And if need be, they will launch the police helicopter.

"We will operate a number of precautionary operations," he says.

Capt Morandi is speaking from the northern foothills of Mount Etna, on the Italian island of Sicily.

It may initially seem incongruous, but what he and his team have started planning for is this year's pistachio harvest.

Image copyright Carabinieri Image caption Italy's national police force - the Carabinieri - use helicopters to patrol the pistachio fields

Sicily is home to the world's most-prized variety of the seed - the pistacchio verde di Bronte, or green pistachio from Bronte.

Centred on the town of Bronte, the pistachio trees grow across some 3,000 hectares (7,400 acres) on the slopes of Etna, an active volcano.

Although Bronte pistachios account for just 1% of global production of the crop, they are easily the most expensive.

Often called "Sicily's green gold", one kilogram (2.2lb) of the seeds, unshelled, typically costs 15.50 euros ($17.40; £13.45). This is more than double the price of pistachios from the world's two giant producers - the US and Iran.

Enrico Cimbali, president of the local trade organization Consorzio di Tutela, says there are 230 authorised farmers within the defined Bronte area, which has denominazione di origine controllata (DOC, or controlled designation of origin) protection. Aficionados say they can charge such a premium because their seeds both taste better, and keep their bright green colour for longer.

However, given the lucrative nature of the crop, it attracts a continuing problem during harvesting time - thieves.

These criminals turn up in cars in the dead of night, and try to make off with as many pistachios as they can.

Image copyright Gaetano Guidotto Image caption All pistacchio verde di Bronte seeds are harvested one-by-one by hand

Pistachio trees only produce a crop every other year, which in Sicily is in odd years, such as 2019, with the seeds being picked in September.

Back in 2009 thieves stole 300kg of Bronte pistachios during harvest time (more than 4,600 euros worth at today's prices), which led to the mayor of Bronte asking the police to do more to protect the crop.

This resulted in the Carabinieri, Italy's national police force, introducing helicopter patrols from 2011, and putting more officers on the ground.

"Honest citizens welcome this service, because harvest time is a very delicate moment for our community," says pistachio farmer Mario Prestianni.

"One evening I was closing the gate of my property, and Carabinieri stopped me, asking loudly who I was, and what I was doing there. I felt relieved to have their presence."

With 2019's Bronte pistachio seeds now slowly forming after the trees flowered back in March, Mr Prestianni and everyone else is hoping for bigger crop than the 1,250 tonnes produced in 2017. Entirely dependent upon weather conditions, that was down from 1,400 tonnes in 2015.

Image copyright A Aidala Image caption Producers are eyeing additional overseas markets

The industry is also aiming to boost exports, which currently account for some 80% of production. The biggest buyers are France, Germany, Japan, Switzerland, and the USA.

"In our efforts to increase exports we do online marketing, and participate in a minimum of six exhibitions around the world every year," says Francesco Di Sano, a Bronte-based pistachio businessman. "These include tradeshows in Nuremberg and Dubai.

"[But] we need more support on the promotion side, because people from abroad don't know how to reach us properly.

"[And] a global partner would also help us understand different habits of consumption, so that we can supply more markets."

Global Trade

More from the BBC's series taking an international perspective on trade:

The town of Bronte estimates that the seed gives its economy an income of 20 million euros a year.

In addition to the celebrated pistacchio verde di Bronte, it has food companies that process Sicilian pistachios from outside the DOC area, and even those sourced from overseas.

Image copyright Luca Vitello Image caption Pistachios are a mainstay of Italian cooking

"Workers in Bronte are so long-term experienced, that a large quality of foreign pistachio is also processed here," says Vincenzo Capizzi, from the local Pro-Loco tourism group.

This processing work can range from simply shelling the pistachios, to turning them into flours or pastes for use as a cooking ingredient. The seeds feature in numerous Sicilian desserts, and savoury dishes such as spaghetti with pistachio pesto, not to forget Italy's ubiquitous pistachio gelato.

Bronte also holds an annual pistachio festival, which attracts visitors from across Europe.

Image caption Pistachio farmer Mario Prestianni says he is grateful for the police presence

Pistachio trees, which are native to the Middle East, were first introduced to Sicily's volcanic soil by the Moors, who ruled the Italian island during the 9th-11th Centuries.

Today the seeds are harvested in exactly the same way - laboriously, by hand, one-by-one. Farmers such as Mr Prestianni spend the entire harvest period living in huts next to their precious crop.

"After harvesting we shell the seeds and spread them out to let them dry, by exposing them to the Sicilian sun for three days," he says.

"After each sunset we must remove them to protect them from the humidity of the night. We also have to act quickly on site to safeguard them from daylight rain."

The seeds are then stocked in warehouses before going to the local factories to be processed.

Image caption The seeds are currently growing ahead of harvest time in September

As he prepares for this September's harvest, Mr Prestianni is happy that the police have also started their planning work.

"The [growing] area is far from the town centres," he says. "We are pleased to have police patrolling at night time in order to avoid armed thieves that might be coming using a van to steal the crop in one go."

Follow BBC Global Trade editor Will Smale on Twitter.