**4. The climate hypothesis**

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

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

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

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

act. Also, in this case, the total control is quite impossible.

cost, and eco-friendly antibiotic to be inserted inside the plant.

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

plant.

226 Insecticides Resistance

There have been several marked changes in climatic conditions in Europe during the last century. In the 20th century two main periods of warming have occurred in Europe (Fig. 2). The second was the warmest decade (the 1976–2000) on record, and it is still in act. The evidence was an increasing of approximately 1.2°C over the past 100 years, which means twice the average global rate. Turnover of hot and glacial periods is a normal trend for our planet, mainly due to the CO2 the quantity of this gas in the atmosphere. We are now in a warming period, and the trend is accelerated by the emission due to human activities [30–34]. Warning conse‐ quences are higher nighttime temperature, with limited difference between day and night, and few frost days in winter, associated with milder temperature in all winter period, longer dry periods, and peaks of temperature. In particular, temperature increases were most marked in both Central Europe (Italy, Corsica, and Balearic Islands) and Eastern Europe (western Bulgaria, northern Greek, Albania, Macedonia, Bosnia, Montenegro, and Croatia). On the contrary, central Iberia and the region around the border between Morocco and Algeria have cooled. Simplifying the model tendency, Europe is getting warm and North Africa is cooling. This resulted in changes in precipitation dividing Europe in two parts: the number of wet days have increased in the North Europe and decreased on the South, increasing the already presence tendency to desertification of several regions. North Europe, including the UK, northern Iberia, and Scandinavia, is becoming wetter, whereas southern Iberia, France, Germany, and Italy are becoming drier.

Vector-borne pathogens are particularly sensitive to climate, a fact that has led to widespread and continued speculations that anthropogenic climate change will increase the incidence and intensity of their transmission. Other nonclimatic abiotic and biotic factors can also affect disease distribution. Diffusion can be very rapid and effective. Adult insects are usually not strong fliers, but they can be passively dispersed by the wind, possibly up to several kilometers in a single night, especially over the sea. Thus, natural barriers cannot be considered an efficient control of the diffusion. Otherwise, they can travel utilizing ancient transportations, like other animals (street ruminants), or new unexpected ones, i.e., inside old tires as happened for *A. albopictus*.

There is an urgent need for ecologically sound, equitable, and ethical pest management, based on control agents that are pest-specific, nontoxic to humans and other biota, biodegradable, less prone to pest resistance and resurgence, and relatively less expensive. The last aspect is fundamental for a large-scale use in emerging countries.
