International Congress BIOLOGICAL PRODUCTS - Gruppo di ...

ose, bramble, dogrose
birch
hazelnut
apple tree
vine
Picea sp.
March April May June
Figure 3 – Phenology of Anagrus atomus, adults and eggs , and of Empoasca vitis, adults and
eggs , on different host plants (from Cerutti et al., 1989, modified).
The species stays here until summer when, from the beginning of August, the hibernating females which leave the
vineyards start to appear. The first step has been to identify the key antagonist, identified as Anagrus atomus Haliday,
an Hymenoptera Mymaridae, oophagous parasitoid that controlled “naturally” in some vineyards this leafhopper, being
able to hit a part between 20 and 82% of the germs (Arzone et al., 1988; Vidano et al., 1988; Cerutti et al., 1990). Later
on Cerutti et al. (1989) studied the cycles of E. vitis and of A. atomus highlighting the fundamental importance of the
maintenance of plants on which the parasitoid spends the last stages of the season and passes the winter and above all,
on which it starts again its activity in April just before the sprouting of the grapevine (figure 3). Therefore it is the adults
of the first generation of the year that migrate on the culture starting from the end of May. The success of the
colonisation of the vineyard by the parasite therefore depends on the presence of suitable host plants. They include
different Rosaceae (Rubus spp., Rosa spp., the apple tree), Lonicera sp., Corylus avellana and also Betula pendula. In
such structured areas the action of A. atomus on the leafhopper is decisive. Very similar results had been obtained in
North America too, where the species involved were Anagrus epos Gir. and Erythroneura elegantula Osb.. In this
way in numerous cases the permanent control of these harmful leafhopper in different European countries and in North
America has been obtained. At present, though, the diffusion of these strategies is obstructed by too low threshold
levels which over-estimate the symptoms, such as the leaf reddening, which probably are of little importance. As a
matter of fact the threshold level is 2 or even 1 specimen per leaf while it has been noted that there are no effective
damages even if there are more than 3 specimens per leaf (Lozzia and Rigamonti, 1994). Also considering the different
sensitivity of the cultivars it would be a good idea to increase these threshold levels in order to avoid that useless
treatments reduce parasitoid populations, obviously where the environmental conditions described above exist or where
it is thought they will start. In this general framework Jacobiasca lybica (Bergevin & Zanon) is not included. In Italy it
is mainly to be found in Sardinia, it is harmful at lower densities than with respect to the preceeding species and does
not seem, at present as far as is known, to be sufficiently controlled by natural antagonists.
In the last years a programme of inoculative releases has been started in many regions, whose aim is to rebuild the
balance between an exotic phytophagous insect, the Rhynchota Flatidae Metcalfa pruinosa (Say) and one of its
parasitoids, the Hymenoptera Dryinidae Neodryinus typhlocybae (Ashmead). In this case, too, the introduction of the
auxiliary in the environment is the final result of a long research process. The leafhopper arrived in Italy from Northern
America at the end of the 70’s (Zangheri and Donadini, 1980) and since then it has spread in different European
countries. Thanks to the fact that it is polyphagous it has colonised the most diverse environments, including many
cultures to which it is harmful, especially due to its abundant production of honeydew and to the problems linked to
this. In the first years after its arrival, the research for its natural enemies in the area of origin was carried out and the
key antagonist N. typhlocybae was identified. After this a breeding on a small scale of this Dryinidae was started in
order to evaluate its capabilities in the laboratory and with the specimens obtained the first experimental tests were
carried out in the field. After having obtained a mass production, the launch on a large scale was started at the end of the
90’s (Girolami et al., 1996). The technique is the classic one adopted in these cases. Taking advantage of the polyphagy
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