**3.** *Xylella fastidiosa:* **A threat for olive trees**

the emergency is going to be converted into a normal trend, as a consequence of the perma‐

On the basis of novel knowledge, some new approaches are emerging, changing the aspect of insect control. Integrated pest management is an important approach, developed in the last years to control disease vectors and limit economic agricultural damages, improving crop yield with minimum cost. Main goals are (a) to increase basic knowledge of biology of the insect pest and its relationship with other organisms sharing the same ecological niche [15]; (b) to reduce pesticide application and quantity developing biological controls, farming practices, farmers collaboration, and mechanical and physical controls; and (c) to build new models of integrated managements on the basis of laboratory and field experiments, including the research of new active compounds. Novel pesticides to be suitable must be low cost, ecofriendly, from renewable raw material, nontoxic to nontarget organisms, of rapid degradation,

However, resistance is only the last consequence of a series of events. Most of this paper will be dedicated to the deep knowledge of this sequence, being considered the key to struggle resistance. Insect-borne diseases are the result of complex multiorganism interactions. The network of several different collaborating organisms is on the basis of diffusion, effectiveness, and metabolism of insect vectors, including the resistance phenomenon. The integrated network acts like a "superorganism," integrating functions of all the different types of involved organisms. Disease is the result of a brave and useful collaboration between organisms totally different, from bacteria to insect, giving rise to an integrated system that is the key to survive and proliferate. It is the example that we must learn, asking for several levels of eco-friendly interactions. The consequences that we consider as negative are only the collateral effects of

In these years, the Mediterranean Sea was an incubation sap of several massive migrations of organisms, mainly due to climate changes and commercial routes, which radically modified previous equilibrium. Migrations start from distant sites but are able to spread in a large area

Therefore, insects, like microorganisms, are particularly able to change their genome. It is a problem of survival. In some cases, the change generates an organism more aggressive and virulent. Previous treatments are usually not useful, in particular when they are the cause of

In Italy, at least three cases are focusing on scientific, social, and policy attention, causing strong alert for the consequences of their anomalous increasing speed of spreading. The first one concerned *Aedes albopictus* (Skuse), commonly known as the Asian tiger mosquito [16–18]. This species is currently retained the most invasive mosquito species in the world since it is able to rapidly adapt to different anthropogenic environments, thanks to its ecological and physio‐ logical plasticity [19]. Recently, the Asian tiger mosquito has invaded many countries, spreading rapidly to Europe, North and South America, the Caribbean, Africa, and the Middle East [20,21]. *A. albopictus* is both a nuisance and a disease vector. Its medical importance is

until they find the right conditions to set up and rapidly become dominant.

the genetic change, like the exaggerated use of pesticides and/or climate changes.

nence of several factors, including in first place the climate changes [14].

and no accumulation in the environment.

the competitive struggle.

222 Insecticides Resistance

In 2013, one of the most beautiful part of South Italia, the Salento Peninsula, well known for the production of the olive oil and wines, was alerted by a dramatic phenomenon, never reported since human memory. The centenary olive trees that are the hearth of the monumental natural architecture of the region started to die, as Golias killed by invisible Davids. The sentence was that the responsible bacterium, *X. fastidiosa*, causes so-called Pierce's disease. So far, Pierce's disease (PD) was mainly known as a deadly disease of grapevines [22]. It is caused by the bacterium *X. fastidiosa*, which is spread by xylem feeding leafhoppers, known as sharpshooters. PD is known to be prevalent within the US from Florida to California and outside the US in Central and South America (Table 1).

<H1>*Xylella fastidiosa:* **a threat for olive trees**

Two recent exceptional cases of overflowing insect-borne diseases not directly involving human

health are reported to evidence of the difficulties of fighting new insect emergencies. Both

emergencies are the results of a complex multiorganism interaction. The network of several

different organisms is on the basis of the mechanism of survival and diffusion, conditioning

effectiveness and metabolism of insect vectors, including the resistance phenomenon. The network

acts like a "superorganism," integrating functions of all the different types of involved organisms,

asking for several levels of eco-friendly actions. Integrated methods are urgently needed for control

of these pests. On the basis of novel knowledge, some new approaches are emerging, changing the

Both cases present several, not casual, similarities and therefore can be considered as paradigms of

next future or actual situations. The first case is the expanding relevance of bluetongue disease,

vectored by *Culicoides* sp., so far concerning Southern Europe (Sardinia in particular) and going to

be present in other countries. The second case is the alarm concerning the olive trees epidemic

disease, probably due to *Xylella fastidiosa*, which may lead to the disappearance of extensive areas

cultivated with olive trees in Southern Italy. Actually, no useful control tools have been reported.

Fig. 1. The effect of *Xylella fastidiosa* on olive trees in Apulia (Photo: Marcello Nicoletti, October 2014). **Figure 1.** The effect of *Xylella fastidiosa* on olive trees in Apulia (Photo: Marcello Nicoletti, October 2014).

Table 1. Chronology of *Xylella fastidiosa* outbreaks 1870 Reports in California of grape wine "mysterious disease"

1890 The disease practically disappeared

1892 Newton B. Pierce reports on the disease on grapes in California.

1870 Reports in California of grape wine "mysterious disease" 1920 New epidemic diseases in California, apparently not linked to the previous episode

aspect of insect control.

1890 The disease practically disappeared 1920 Alfa-alfa disease (AD), no other cases reported

1892 Newton B. Pierce reports on the disease on grapes in California. 1930 Hewitt names the rediscovered grape wine disease as Pierce disaster (PD)

1930 Reports on peach disease

1920 New epidemic diseases in California, apparently not linked to the previous episode 1933 PD spreads in South US

1920 Alfa-alfa disease (AD), no other cases reported 1940 Major epidemic disaster; vectors come from alpha-alpha (AD) through the some "virus"; they are xylem sapfeeders and disease is xylem-limited

1930 Hewitt names the rediscovered grape wine disease as Pierce disaster (PD) 1970 Almonds and oaks also affected; symptomless plant host discovered

2011 First cases of dehydrated olive trees near Lecce town in Puglia

2012–2014 Most of the peninsula of Puglia region, named Salento, evidences the presence of *Xylella* in the centenary olive trees.

2014 The disease spreads interesting more than 9000 hectares.

2015 The eradication campaign, in accordance with the EU protocols, starts with the destruction of dozens of trees, against the population concern. The regional court accepts the considerations against the eradication, but the campaign goes on.

**Table 1.** Chronology of *Xylella fastidiosa* outbreaks

*X. fastidiosa* works blocking the xylem, which conducts the water around the plant. Symptoms include chlorosis and scorching of leaves, and entire vines will die after 1–5 years. Pierce's disease is less prevalent where winter temperatures are cold, that is, at high altitudes and in inland northern areas [23–26]. The anomalous recent diffusion of the bacterium *X. fastidiosa* is causing a great alert and enormous damage. The disease risks to menace the surviving of olive trees, at least in Southern Italy. Starting from a little area in Gallipoli, near the town Lecce, most of the olive trees of a great part of Apulia region in the South of Italy were totally destroyed during the last 2 years. Therefore, the diffusion was very rapid, epidemic, and devastating. However, the disease is known by long time and so far considered mainly affecting grape wine and sporadically other plants, like oleander, almond, cherry tree, *Polygala myrtiflora*, and *Spartium junceum*. Concerning olive trees, so far it was considered one of the hundred diseases affecting the species, without any report of epidemic virulence.

Two recent exceptional cases of overflowing insect-borne diseases not directly involving human

health are reported to evidence of the difficulties of fighting new insect emergencies. Both

emergencies are the results of a complex multiorganism interaction. The network of several

different organisms is on the basis of the mechanism of survival and diffusion, conditioning

effectiveness and metabolism of insect vectors, including the resistance phenomenon. The network

acts like a "superorganism," integrating functions of all the different types of involved organisms,

asking for several levels of eco-friendly actions. Integrated methods are urgently needed for control

of these pests. On the basis of novel knowledge, some new approaches are emerging, changing the

Both cases present several, not casual, similarities and therefore can be considered as paradigms of

next future or actual situations. The first case is the expanding relevance of bluetongue disease,

vectored by *Culicoides* sp., so far concerning Southern Europe (Sardinia in particular) and going to

be present in other countries. The second case is the alarm concerning the olive trees epidemic

disease, probably due to *Xylella fastidiosa*, which may lead to the disappearance of extensive areas

cultivated with olive trees in Southern Italy. Actually, no useful control tools have been reported.

aspect of insect control.

<H1>*Xylella fastidiosa:* **a threat for olive trees**

**Figure 1.** The effect of *Xylella fastidiosa* on olive trees in Apulia (Photo: Marcello Nicoletti, October 2014).

1870 Reports in California of grape wine "mysterious disease"

1892 Newton B. Pierce reports on the disease on grapes in California.

1920 New epidemic diseases in California, apparently not linked to the previous episode

1930 Hewitt names the rediscovered grape wine disease as Pierce disaster (PD)

1970 Almonds and oaks also affected; symptomless plant host discovered 2011 First cases of dehydrated olive trees near Lecce town in Puglia

2014 The disease spreads interesting more than 9000 hectares.

**Table 1.** Chronology of *Xylella fastidiosa* outbreaks

1890 The disease practically disappeared

1930 Reports on peach disease 1933 PD spreads in South US

224 Insecticides Resistance

olive trees.

goes on.

feeders and disease is xylem-limited

1920 Alfa-alfa disease (AD), no other cases reported

1890 The disease practically disappeared

1940 Major epidemic disaster; vectors come from alpha-alpha (AD) through the some "virus"; they are xylem sap-

2012–2014 Most of the peninsula of Puglia region, named Salento, evidences the presence of *Xylella* in the centenary

2015 The eradication campaign, in accordance with the EU protocols, starts with the destruction of dozens of trees, against the population concern. The regional court accepts the considerations against the eradication, but the campaign

*X. fastidiosa* works blocking the xylem, which conducts the water around the plant. Symptoms include chlorosis and scorching of leaves, and entire vines will die after 1–5 years. Pierce's disease is less prevalent where winter temperatures are cold, that is, at high altitudes and in

Table 1. Chronology of *Xylella fastidiosa* outbreaks

1920 Alfa-alfa disease (AD), no other cases reported

1870 Reports in California of grape wine "mysterious disease"

1892 Newton B. Pierce reports on the disease on grapes in California.

1930 Hewitt names the rediscovered grape wine disease as Pierce disaster (PD)

Fig. 1. The effect of *Xylella fastidiosa* on olive trees in Apulia (Photo: Marcello Nicoletti, October 2014). 1920 New epidemic diseases in California, apparently not linked to the previous episode In October 2013, the bacterium was found to be infecting olive trees in the region of Apulia in southern Italy. The disease was causing a rapid decline in olive plantations, and by April 2015, it was affecting the whole Province of Lecce and other zones of Apulia, focused in the Salento Peninsula. Almond and oleander plants in the region have also tested positive for the pathogen. The disease has been called Olive Quick Decline Syndrome (OQDS). The disease causes withering and desiccation of terminal shoots, distributed randomly at first but which then expands to the rest of the canopy. This results in the collapse and death of the trees (Fig. 1). In the affected groves, all of the plants show symptoms. By the beginning of 2015, it had infected up to a million trees in the southern region of Apulia [25–30]. The epidemic damage affected thousands of centenary olive trees, completely dehydrated by the disease. After the eradica‐ tion, the treated areas appeared totally desertified. Beside the great economic damage, loss of the olive trees means a tremendous cultural and environmental impact for a territory, where they are the symbol of region's identity. Centenary olive trees are the living monuments of the Apulia. Furthermore, there are convincing hypotheses that the epidemic infection will propagate rapidly to the neighboring regions and later in several parts of the Mediterranean area. Therefore, interested countries, like France and Greece, are asking for a rapid control of the disease before further pandemic diffusion.

> In conclusion, there are two main hypotheses about future scenarios: (a) a natural stressinduced dieback: this is consistent with widespread groves of various ages all suffering to different degrees and slowly declining rather than a virulent point infection that can be seen to spread. In other words, the disease is due to a "normal" increasing of virulence coupled with the "stress effect," derived from climate change and agricultural loss, that will affect mainly the old trees, causing a turnover in favor of the new stronger generations; (b) a modified, more virulent pathogen appeared, and plants defenses will be not able to face the new challenge, with devastating consequences.

> So far, the only real performed action was the application of the UE protocol consisting in the eradication of any olive tree and creating a defensive line of 2 km in extension in the northern part of Salento Peninsula, where any plant must be eradicated, in order to isolate the disease. This measure should stop the diffusion of *X. fastidiosa*? The bacterium relies to insect vectors. Known vectors of *X. fastidiosa* are xylem-sap feeder insects belonging to the families Cicadel‐ lidae, Aphrorophoridae, Cercopidae, and Cicadidae within the Cicadomorpha. Among them, the meadow spittlebug, *Philaenus spumarius*, is one of the most abundant field insect in that region, although other species are probably involved. The spittlebug xylem-sap feeding

possesses a piercing-sucking beak, named rostrum. Introducing the rostrum into the tree for feeding, the insect causes the infection and the bacterium propagation close the xylem vessels, causing the dehydration of the plant. It is very difficult that the EU protective approach will give significant effects. The vectors are not good flyers; they usually move by jumping, but they can be efficiently transported by the wind and human of animal occasional transportation, travelling for many kilometers in only one day. The block of plant import from America is in act. Also, in this case, the total control is quite impossible.

The bacterium cannot be controlled by the use of antibiotics, either because they are banned in agriculture in EU or because they are highly costly and complicated. The insect vector could be controlled by adequate insecticide. Insecticides usually select as target the adults, but the larval stage is the best situation to act on the insects, before they are able to move and fly away.

In any case, to obtain any real result, we must learn the Nature's lesson. Olive tree disease evidences three main actors: the bacterium, the vector and the plant, and probably a symbiotic fungus. They work together, acting like a "superorganism." It is a very complex system, but in some way also very efficient. The only way to face the *X. fastidiosa* challenge is an integrated pest management. It is necessary to operate considering together the several involved aspects: a treatment of soil to sustain the plant; an insecticidal agent to control the insect; a natural, low cost, and eco-friendly antibiotic to be inserted inside the plant.

A key step is the reply to the following question: How did *X. fastidiosa* become so dangerous in the last 2 years? We know the presence of bacterium in Italy from at least 30 years, and so far it was considered just one of the several diseases involving olive oil. Something happened during the last years changing completely the equilibrium between the microorganism and the host. There are several hypotheses about the causes of the change and a consequent relevant debate. The local official institutions have accepted the idea that some infected plants of oleander imported from Costa Rica were the epidemic start. Everything could be, but it is strange that only a single little point of Apulia was affected by the only infected imported plant.

**Figure 2.** Temperature changes over the last centuries.

The second hypothesis is that a change in the *X. fastidiosa* genoma occurred, giving rise to more aggressive and dangerous strains. In this case, there are two possibilities: the change is derived from some experiment or a biological cause. Due to climate change (Figure 2), some virulent strains from hotter countries could be able to survive and proliferate against local populations. Other causes, like the absence of the traditional treatment of the soil and the trees due the urbanization of the population, could have interfered. The phenomenon is quite well known and possible, as explained in the next part of this chapter.
