International Congress BIOLOGICAL PRODUCTS - Gruppo di ...

RELIABILITY AND PROSPECTIVES FOR THE BIOLOGICAL CONTROL OF PHYTOPHAGOUS
INSECTS
Giuseppe Carlo Lozzia, Ivo E. Rigamonti
Istituto di Entomologia agraria, Università degli Studi di Milano
In the last years there has been an explosion in the widespread of foodstuffs and other “biological” products that are
associated with an image of naturalness and hygienic safety by the public, even if these concepts are wrongly thought to
be closely linked. In reality, notwithstanding the great emphasis on the use of “natural” techniques and of the exclusion
of artificial products, biological agriculture is not so different from the most modern “conventional” strategies, and is
largely based on the use of active ingredients, which are natural but still toxic, that have all the problems of “pesticides”
(residues on foodstuffs, side effects on non-target organisms, etcetera) but on a different scale. This situation, both for
biological and traditional agriculture, is not due to a “strategic” trust in pesticides but to a lack of total efficacy in low
impact management techniques, and in particular to biological control.
Up to now, as a matter of fact, there is no culture of a certain importance for which the pest management can be given
solely to, or even mainly to, biological control. The situation is decidedly better if we only refer to animal organisms. In
this case there are consolidated strategies, at least theoretically; which refer to the reconstitution of balances and to the
improvement of the action against natural enemies, which are carried out in practice through the use of four
“techniques”: the diffusion of antagonists, the elimination of worrying sources and the adoption of environmental and
cultural management measures. Furthermore, the use of pheromones and other “modern” methods gives the possibility
to enlarge the possibilities of success. Modern strategies are based on this framework especially with the understanding
that a culture is a real ecosystem where limiting natural factors have a considerably important role. The most recent
research is analysing the influence of different cultural practices on the coenosys settled in the agro-ecosystem. The aim
of all this is, on the one hand to favour the diffusion of techniques with beneficial effects, and on the other to limit the
repercussions of harmful interventions which cannot be eliminated, as some phytosanitary treatments (Bassino, 1987).
One of the areas where the use of biological control practices is widely used, is in glasshouses cultures. The quick
succession of cultures one different from the other, with brief periods when there are no cultures, create a very
particular environment where techniques of permanent biological control of phytophagous insects have no possibility of
success. For this reason, there are usually routine “inundative” releases of antagonists in glasshouses and in tunnels.
Using this strategy the biological tool is almost like a chemical treatment. Large quantities of predators or parasitoids
are introduced into the structure in order to quickly bring down the population of the target pest and to keep it thereafter
under the damage level until the end of the cultivation cycle. Often the release has to be repeated over and over again
and more than one species of antagonists are introduced. In these environments phytophagous insects with determinate
characteristics tend to become affirmed (polyphagous, high number of generations, very prolific) which are able to
damage the cultures that follow, that, as already mentioned, can be very different one from another, and in any case the
species always tend to be the same ones. Numerous Rhynchota are particularly abundant (whiteflies, aphids, scale
insects), but Agromyzidae Diptera can also be easily found, as well as some Thysanoptera (Frankliniella occidentalis
(Pergande), Heliothrips haemorrhoidalis (Bouché), Thrips tabaci Lindemann) and spider mites. The low number of pest
species makes it possible for key antagonists to be restricted to a few units. All this has led to the birth and the diffusion
of structures, the commercial insectary, that have become similar in organisation to an industry, whereby the most
important natural enemies of every phytophagous insect is bred in large quantities and after put on sale on a large scale.
The breeding of auxiliaries is very complex (figure 1) requiring the development of refined and very reliable
techniques.
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