Real harmfulness of insects in agroecosystems, with particular reference to the olive moth Prays oleae Bernard Lesne Donnosita reale degli insetti negli ecosistemi agrari, con particolare riferimento alla Tignola dellolivo Prays oleae Bernard Lesne
Solinas, M.; Vannicola, P.
Atti della Accademia Nazionale Italiana di Entomologia Rendiconti 50: 117-130
Agricultural Entomologists are well convinced that insect blind chemical control was a negative custom in the past which nobody could nowadays suggest in the view of IPM, well concerned as it is with safeguarding of the environment. Nevertheless, it still does happen that chemical treatments against well known pest insects are applied without having well ascertained first its actual harmfulness nor the intervention decision has been made on the base of a reliable economic threshold. Here is reported, as an example, the case of Prays oleae (the Olive moth), a notoriously important pest insect of the olive tree but whose economic harmfulness (including carpophagous generation) is still doubtful in the opinion of many Entomologists. Aiming at verifying the Olive moth real harmfulness in Umbria, as well as the opportunity of chemical control of the pest, investigations on Prays population dynamics with particular reference to correlation between adult population levels, percentage of young olive fruit infestation in July and loss of production (immature olive dropping off the trees). Eventually, to contribute for a possible identification of a reliable economic threshold to control the Prays carpophagous generation. Results of the first three year investigations, although preliminary due to reduced limits of space and time, already they may represent a virtual confirmation of Prays epidemiology as it is known for the Mediterranean Region, i.e.: - moths are always present at high population levels in all of its three generations; - the said condition does not mean that a heavy larval infestation from the following generation is going to occur; - the heavier the larval infestation in July, the heavier (proportionally) the immature olive dropping off the trees in September-October; - 33% of young olive infestation in July (that happened only once in the triennium) seem to be just sufficient to cause a notable loss of production so as to justify chemical control. Finally, the olive dropping off the trees is caused by an interaction between the plant and the insect, not by mechanical damage from the latter.