International Congress BIOLOGICAL PRODUCTS - Gruppo di ...

important alternative foodstuff for the Phytoseiids (Wiedmer and Boller, 1990; Remund and Boller, 1992; Engel and
Ohnesorge,1994) that are able to colonise even the grass flora, in particular many dicotyledons that then become
another reservoir of useful species available for the grapevine (Lozzia and Rigamonti, 1998).
Biological control, as can be seen from the above examples and from numerous other cases, has often been an
efficacious and reliable instrument for a permanent solution linked to infestations of single phytophagous insects.
However, it still cannot be considered suitable for the management of pests on the whole, not even limiting itself to
animal organisms. Also in the case of the wine grapevine, which is perhaps the culture that today has the best situation,
there have been problems following the expansion of flavescence dorée, a phytoplasma disease carried by Scaphoideus
titanus Ball, whose control requires the carrying out of treatments against the vector, interventions that risk to frustrate
also the results obtained with biological control against other phytophagous insects of the grapevine. This situation can
be generalised and applied to all viral, bacterial or phytoplasma diseases transmitted by vector organisms, whether they
be insects, mites or nematodes. In these cases, in fact, it is necessary to maintain the populations of the parasite at
extremely low density levels that cannot be obtained through the action of natural antagonists which for their own
existence, need the presence of a suitable quantity of victims. Only the availability of resistant plants will make
treatments against vectors superfluous in the future.
The management of vector species, the one of key phytophagous insects of the various cultures for which usually
“natural” control is not sufficient, the side effects of fungicide treatments are at present and in the near future the main
obstacles to the creation of a phytosanitary defence against phytophagous insects only using biological control
strategies. Another factor that must be considered and that today limits the reliability of biological control is the
dynamic nature of agroecosystems. The appearance of new phytophagous insects, the pullulations of secondary or
occasional species, the expansion of the area of numerous pests and so on, are highly probable events but they cannot be
forecasted, and this makes it necessary to have continuous adjustments to the methods adopted even if they are widely
experimented and to study new strategies. The same variability that exists between different areas whereby a culture is
diffused implies the need not to generalise solutions but to find those more suitable to the single realities through a
continuous process of experimentation. To sum up, we can say that biological control is without a doubt the main
weapon on hand in modern agriculture for the management of phytophagous insects but it still requires many studies
before all its potential can be used to the full and for a certain period of time it will be necessary to use more invasive
techniques.
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