Introduction of Samurai Wasp Proving Effective Against Stink Bugs in Italy

Samurai wasps parasitized 38 percent of the brown marmorated stink bug eggs in one area. Some see the wasp’s introduction as key to curtailing the stink bug.
Photograph by Elijah J. Talamas, ARS USDA
By Paolo DeAndreis
Feb. 15, 2022 08:28 UTC

Scores of so-called samu­rai wasps will soon be released for the sec­ond year in a row in the heart of north­ern Italy’s Po Valley, as part of a project to limit the spread of the brown mar­morated stink bug.

The tiny Trissolcus japon­i­cus wasp repro­duces by par­a­sitiz­ing stink bugs’ eggs, reduc­ing their abil­ity to repro­duce.

What we are see­ing is the very first evi­dence that the samu­rai wasp might be cur­tail­ing the mar­morated stink bug pop­u­la­tion.- Massimo Bariselli, ento­mol­o­gist, Emilia-Romagna regional phy­tosan­i­tary ser­vice

Both insects are native to Asia, but the stink bug has spread widely in sev­eral European coun­tries and some areas of the United States.

With this year’s samu­rai wasp releases, we will be tar­get­ing the areas where stink bug colonies will most likely be found,” Massimo Bariselli, a phy­topathol­o­gist and ento­mol­o­gist at the Emilia-Romagna regional phy­tosan­i­tary ser­vice, told Olive Oil Times.

See Also:Plant-Derived Treatment Against Asian Bug Shows Promise for Olive Growers

The good news is that the Japanese wasps we had pre­vi­ously released have shown to repro­duce and install them­selves in areas quite far from the areas of release, sug­gest­ing good poten­tial for spread­ing in the ter­ri­tory,” he added.

Fruit grow­ers in north­ern Italian regions, such as Emilia-Romagna, Lombardy and Veneto, have been severely hit by the spread of the stink bug, which dam­ages a wide vari­ety of crops, includ­ing tree fruits and soy­beans.

Since pre­lim­i­nary research has shown a pos­si­ble asso­ci­a­tion between stink bug out­breaks and the olive green drop” dis­ease, olive farm­ers have been espe­cially wor­ried about the spread of the pest.

In the Emilia-Romagna region alone, between 2020 and 2022, local author­i­ties have dis­trib­uted €63 mil­lion in com­pen­sa­tion to farm­ers affected by the insect, while local author­i­ties in Lombardy esti­mate that the stink bug causes €15 mil­lion worth of dam­ages annu­ally to regional agri­cul­ture.

At the moment, we have about 30,000 stink bugs gath­ered by the tech­ni­cians and farm­ers who bring them to the lab­o­ra­to­ries, which are then used to grow the samu­rai wasp,” Bariselli said. When the time comes, the tubes with the wasps are assigned to the dif­fer­ent farm­ing areas and released.”

Last year in Italy, the samu­rai wasp was released in more than 600 loca­tions, with more than 300 in Emilia-Romagna.

The first evi­dence of a pos­si­ble pos­i­tive impact of the samu­rai wasp’s intro­duc­tion comes from researchers sur­veilling stink bugs’ eggs. According to the data released by the project, the wasps col­o­nized 38 per­cent of the sam­ples.


Brown marmorated stink bug

While these find­ings con­firm the wasps’ abil­ity to tar­get the stink bug, experts in the field warn that the true impact of the bio­log­i­cal war against the insect is extremely dif­fi­cult to mea­sure.

Monitoring the bug pop­u­la­tion is dif­fi­cult since it under­goes sig­nif­i­cant changes each year. The stink bugs thrive at tem­per­a­tures between 30 ºC and 32 ºC and suf­fer from a high mor­tal­ity rate dur­ing the win­ter.

In a sea­son like the last one, where the fruit pro­duc­tion was more than halved by the freez­ing tem­per­a­tures, where there was no rain­fall in sum­mer and hedges are dry, all stink bugs would have been forced to attack the fruits,” Bariselli said. That cre­ates the incor­rect per­cep­tion that there was a large inva­sion in a sea­son in which the stink bugs could not repro­duce well.”

In other regions, such as Piedmont, the stink bug has been tar­geted by other preda­tors, includ­ing a sep­a­rate species of wasp that also par­a­sitizes the bugs’ eggs – the European Anastatus bifas­cia­tus. These tri­als are tak­ing place on organic farms.

According to Bariselli, Anastatus bifas­cia­tus also effec­tively tar­gets the stink bug. However, unlike the samu­rai wasp, they prey on other insects, so their effi­ciency in cur­tail­ing the stink bug’s spread might be lim­ited.


Looking at what hap­pens in Italy and what hap­pens in Asia, it seems that Anastatus bifas­cia­tus can affect between 10 and 15 per­cent of the stink bug pop­u­la­tion,” he said.

Chemical treat­ments cur­rently used on the stink bugs have not yielded promis­ing results. They are quite expen­sive and are not envi­ron­men­tally friendly. They also make it more dif­fi­cult for the stink bugs’ preda­tors to sur­vive.

Chemical war­fare against the stink bug tends to be highly inef­fi­cient,” Bariselli said. This is because the bug rarely lives in the trees and tar­gets a lot of dif­fer­ent plants.”

He added that the stink bugs also tend to sting the fruits and quickly leave, mean­ing they are not exposed to pes­ti­cides for long peri­ods.

Even if chem­i­cals do not work against the stink bug, heavy dam­age caused by the bug could push some farm­ers to invest heav­ily in that kind of treat­ment to get rid of the insect,” Bariselli added. That will not work.”

According to the data released dur­ing a recent sum­mit on the stink bug and reported by Agronotizie, 24 per­cent of the 47,000 stink bug eggs ana­lyzed in 2021 had been par­a­sitized.

Thirty-eight per­cent of them had been tar­geted by the samu­rai wasp, 31 per­cent by the related Trissolcus mit­sukurii and 22 per­cent by the Anastatus bifas­cia­tus.

What we are see­ing is the very first evi­dence that the samu­rai wasp might be cur­tail­ing the mar­morated stink bug pop­u­la­tion,” Bariselli said. But that mostly hap­pens in wild areas, where the wasps were released, areas where there are no chem­i­cal treat­ments on the veg­e­ta­tion.”

The bug is there, but not only there,” he added. We now need to under­stand how much the fruit crops [con­ven­tion­ally treated] can hin­der the spread of the stink bug’s nat­ural preda­tors.”

The cur­rent samu­rai wasp release project in the region will end in 2023.

During the sum­mit, Alessio Mammi, Emilia-Romagna’s regional sec­re­tary of agri­cul­ture, empha­sized how the goal of the first year of the project was to make the samu­rai wasp set­tle in the ter­ri­tory, and that is a tar­get we have acquired.”

In 2022, we must now step up the release activ­i­ties and spread­ing within and around the most rel­e­vant regional fruit-pro­duc­ing areas,” he added.

Bariselli said he is opti­mistic that a com­bi­na­tion of intro­duc­ing the stink bugs’ preda­tors and other con­tain­ment strate­gies would lead to an improved sit­u­a­tion in the com­ing years.

Within one or two years, we expect that the pres­sure of the stink bug will be slow­ing down a bit,” he said. It will stay, and it will con­tinue to be a dam­ag­ing pres­ence for farm­ers, but it will have found a new bal­ance within that envi­ron­ment just like other insects already have.”


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