Experts in Italy Offer Advice for Olive Growers Combating the Fruit Fly

Careful monitoring of traps and applying treatments at the right times are among the keys to preventing extensive damage from the olive tree pest, experts say.

Bactrocera dorsalis
Nov. 12, 2020
By Ylenia Granitto
Bactrocera dorsalis

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The Tuscan Regional Phytosanitary Service has released tech­ni­cal guide­lines for mon­i­tor­ing and con­trol­ling the olive fruit fly pop­u­la­tion by grow­ers and tech­ni­cians work­ing on organic and inte­grated farms.

Considered one of the most harm­ful olive tree pests due to the dam­age they cause to both the quan­tity and qual­ity of the fruit, this dipter­ous insect is found in the Mediterranean basin, South Africa, Central and South America, China, Australia and the U.S.

Prevention should be the main focus of an effec­tive and sus­tain­able approach.- Massimo Ricciolini, Tuscan Regional Phytosanitary Service

The instruc­tions, pro­vided by the experts focused on the sit­u­a­tion in Tuscany can be adapted by farm­ers accord­ing to the devel­op­ment cycle of the fly, which can vary depend­ing on the soil and weather con­di­tions of the olive grow­ing area.

In European coun­tries, the chal­lenge aris­ing from the ban on Dimethoate requires a new approach in the con­trol of the olive fly,” said Massimo Ricciolini of the Tuscan Regional Phytosanitary Service. Yet, con­sid­er­ing the wide­spread need of sus­tain­abil­ity, we believe that not only phy­ti­atric reli­a­bil­ity but also tox­i­co­log­i­cal and envi­ron­men­tal safety should be at the base of any effi­cient strat­egy against this pest.”

See Also: Farmers Warn Pesticide Ban Jeopardizes Italy’s Olive Oil Production

The mar­ket with­drawal of the sys­temic organophos­phate insec­ti­cide Dimethoate, which was used against the lar­vae of the fly, has led experts to con­sider the adult stage of the insect as the main goal of the fight.

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Prevention should be the main focus of an effec­tive and sus­tain­able approach,” Ricciolini said. There is no alter­na­tive in organic farm­ing at this time, so while we wait for the research results on new valid cura­tive treat­ments (i.e. against eggs and lar­vae), it is nec­es­sary to imple­ment tech­niques to kill or repel the adults.”

It is impor­tant to note that in our region the fly com­pletes its first annual gen­er­a­tion in spring,” he added. The insect uses the olives that remain on the plants, due to incom­plete har­vest­ing or aban­doned olive groves, as a repro­duc­tive sub­strate and food source. Hence, between the end of June and early July, usu­ally, the sec­ond flight of the year, which is larger than the first one, occurs.”

The females deposit their eggs in the olives of the cur­rent year, which are already recep­tive and usu­ally at the begin­ning of the stone lig­ni­fi­ca­tion process.

From these eggs, the sec­ond gen­er­a­tion of the year, which is the first of the sum­mer, emerges,” Ricciolini said. The green, grow­ing fruits are then dam­aged by the activ­ity of the lar­vae which, pass­ing through three stages, develop at the expense of the pulp, dig­ging a tun­nel in the meso­carp that is at first super­fi­cial and thread­like, then deep and with a larger sec­tion, and, finally, sur­fac­ing at the ellip­ti­cal section.” 

According to the sea­son, the mature lar­vae drop to the ground to pupate or, when the pupal stage is com­pleted, the adults eclose [emerge from the pupal case],” he added.

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During the warmer months, peri­ods of high tem­per­a­tures (above 30 to 33 °C — 86 to 91.4 °F) and low lev­els of rel­a­tive humid­ity (below 60 per­cent) can cause the death of sub­stan­tial parts of eggs and young lar­vae pop­u­la­tion, with con­se­quent poten­tial harm reduction.

The fly pop­u­la­tions gen­er­ally increase con­sid­er­ably in September and October, caus­ing a risk of pro­gres­sive dam­age until the har­vest, due to both fruit drop and oxida­tive processes affect­ing the holed olives. In order to pre­vent ovipo­si­tion and lar­val devel­op­ment, grow­ers should carry out an early har­vest, which is effec­tive espe­cially in years of high infestation.

In Tuscany, with all due excep­tions, the risk of attacks is usu­ally greater along the coast, and tends to decrease toward the inland areas, high hills, and the Apennines,” Ricciolini said. In the last 15 years, increased knowl­edge about olive fly biol­ogy and the set­ting up of an exten­sive agrom­e­te­o­ro­log­i­cal and demo­graphic data­base have made it pos­si­ble to define a cli­mate-based infes­ta­tion risk fore­cast model.”

It showed that, in our ter­ri­tory, low tem­per­a­tures in win­ter act as a lim­it­ing fac­tor for this insect and that the sur­vival rate of its pop­u­la­tions in win­ter influ­ences the pop­u­la­tions of the spring gen­er­a­tion,” he added.

The sug­ges­tion is to mon­i­tor both the adult pop­u­la­tion dynam­ics, start­ing from the first annual flight, and the olive infes­ta­tion trend, start­ing from the sec­ond flight of the year. 

The flight mon­i­tor­ing should be car­ried out, on a weekly basis, with chro­motropic or pheromone traps (one to three traps for a stan­dard one-hectare/2.5‑acre plot with 280 olive trees); the infes­ta­tion mon­i­tor­ing should be car­ried out, on a weekly basis, sam­pling of 100 olives per olive plot (con­sid­er­ing an aver­age one hectare/2.5 acre with 280 olive trees).

If the infes­ta­tion exceeds the thresh­old of five per­cent (given by liv­ing eggs, first and sec­ond age lar­vae) or 10 per­cent (given by liv­ing eggs and first age lar­vae), it is pos­si­ble to pro­ceed with the use of the allowed lar­vi­cide products.

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Olives damaged by the olive fly (Tuscan Regional Phytosanitary Service.)

Within this frame­work, based on the knowl­edge of the ter­ri­tory and the harm­ful­ness of attacks in terms of fre­quency and inten­sity, the experts stress the impor­tance to imple­ment a deter­rent and/or killing action against the first sum­mer adults.

We must con­sider that some devices and prod­ucts per­form best in vast orchards,” Ricciolini said. Others tend to be more effi­cient in small plots.”

Large olive groves (more than five hectares/12.4 acres) require devices or bait prod­ucts with an attract and kill’ action which aim to lure males and females adults to a food or pheromone source and then kill them by inges­tion (of the poi­soned bait) or by con­tact (with the active sur­face of the device).

Pheromone and insec­ti­cide traps avail­able on the mar­ket, as well as hand­made traps con­tain­ing pro­tein baits are exten­sively used and effec­tive; more­over, the nat­ural insec­ti­cide, Spinosad, is allowed in sev­eral countries.

In small plots it is rec­om­mended to use prod­ucts with repel­lent action against males and females and with anti-ovipo­si­tion effects against females, such as cop­per, kaolin, other min­er­als such as zeolith and ben­tonite, and a com­pound based on fun­gus, Beauveria bassiana. Research is ongo­ing on the lat­ter two treatments.

Growers in inte­grated farm­ing can use, where allowed, insec­ti­cides based on Phosmet (organophos­phate), Acetamiprid (neon­i­coti­noid) and Deltamethrin (in Italy, this pyrethroid ester can be used only in the traps).

In all cases, the aim is to pre­vent ovipo­si­tion,” Ricciolini said. In our region, this implies act­ing against the adults of the first sum­mer flight, that occurs in late June to early July. We should con­sider as crit­i­cal para­me­ters the first cap­tures of adults in the traps, the very first ovipo­si­tion holes and the pit hard­en­ing in the fruit.”

The Tuscan Regional Phytosanitary Service offered final gen­eral suggestions:

  • It is nec­es­sary to iden­tify the defense tech­nique (i.e. the type of prod­ucts) that one intends to use against the olive fly before the start of the olive cam­paign, in order to get an idea of the inter­ven­tion period, tak­ing into account the sea­sonal weather trend and the devel­op­ment and growth of the olives.
  • The choice of the tech­nique (i.e. the prod­uct) should be made tak­ing into account the risk of infes­ta­tion and loss of pro­duc­tion in the area where the olive grove is located. Usually, the risk is higher along the coast, and lower inland and at higher alti­tudes. Furthermore, it is impor­tant to con­sider the expected pro­duc­tion: the risk is higher in an off-year, lower in an on-year.
  • It is impor­tant to esti­mate, based on the pro­duc­tion and phy­tosan­i­tary char­ac­ter­is­tics of the year, the extent of the dam­age and loss of pro­duc­tion that one can handle.
  • If, dur­ing the cam­paign, the strat­egy adopted or the prod­uct used is not effec­tive, try to inte­grate the prod­ucts choos­ing those rec­om­mended and allowed in the region.

From the sec­ond sum­mer flight on, pre­ven­tive inter­ven­tions can be decided by tak­ing into account the dura­tion of action of the prod­uct used, the com­ple­tion of the pre­vi­ous preimag­i­nal (i.e. devel­op­ment stage that imme­di­ately pre­cedes the adult) stage of the insect, the first catches of adults of the pre­vi­ous gen­er­a­tion, and the very first ovipo­si­tion holes of the new gen­er­a­tion,” Ricciolini said.





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