L'AZIONE SVOLTA CONTRO IL DACUS OLEAE GMEL. DALL'OPIUS CONCOLOR SZEPL. (HYM. - BRACONIDAE), DISTRIBUITO IN PUGLIA IN OLIVETI DEL GARGANO, E DAI PARASSITI INDIGENI NELLO STESSO AMBIENTE

Abstract

A Mattinata (Foggia), sul versante meridionale del Gargano, nel 1968 l'Istituto di Entomologia Agraria di Palermo in collaborazione con l'Osservatorio Fitopatologico di Bari e nel 1969 l'Osservatorio Fitopatologico di Bari, hanno condotto prove di lotta biologica contro il Dacus oleae Gmel. mediante allevamento in laboratorio e distribuzione negli oliveti dell'Opius concolor Szep. - La zona comprende 120.000 piante su una superficie di 1.100 Ha circa; gli Opius distribuiti sono stati 11.056.000 nel 1968 e 10.030.000 nel 1969.

Nel corso di tali prove di lotta l'Autore ha rilevato:
-- che l'apporto benefico del Braconide è stato modesto e che, comunque, il parassita non è in grado di controllare lo sviluppo del Dacus specialmente quando gli attacchi di questo hanno un decorso rapido e intenso per il veri- ficarsi di favorevoli condizioni climatiche;

- che i parassiti ectofagi, specialmente nel periodo estivo, sono molto attivi, eliminando anche il 90-95% delle larve e pupe di Dacus: tale azione, diretta sul fitofago, indirettamente coinvolge anche l'Opius che allo stato di uovo, larva o pupa viene eliminato insieme alla vittima dai Calcididi quando questi ne attaccano le larve o, come l'Eupelmus, in gran numero i pupari. Questo fatto, accertato mediante osservazione esterna e dissezione delle larve e delle pupe di Dacus, trova conferma nella constatazione che fra i parassiti ectofagi sfarfallati da olive infestate predomina l'Eupelmus, il quale è l'unico fra i parassiti indigeni del Dacus che si sviluppa anche sul contenuto dei pupari, Opius compreso;

- l'Imenottero Formicide Crematogaster scutellaris 01. principalmente in agosto e settembre distrugge un gran numero di uova e di pupari del Dacus.

Vengono inoltre riportate osservazioni comprovanti un'azione negativa eser- citata sull'Opius dai trattamenti antidacici mediante Dimetoato.

Nell'autunno 1969 è stata accertata la presenza dell'Opius concolor in grande quantità in zone della Puglia ove non era stato mai segnalato, essendo difl:uso in modo continuo a partire dall'area di distribuzione fino ad una di- stanza di 200 km circa.

The author reports own observations on Dacus oleae Gmel. parasites (indigenous: Eupelmus urozonus Dalm., Eurytoma martellii Dom., Pnigalio mediterraneus Ferr. e Del., Cyrtoptyx dacicida (Masi), and the imported: Opius concolor Szep)) executed near Mattinata (Foggia, Apulia) in 1968-1969 during tests of biological control against D. oleae carried out on 120.000 olive trees of the same cultivar, on an area abaut 4.250 sq. mi. which have a amphitheatre shope (exposed to South-East and open toward the sea). The level part of thes is during summer partially irrigated and so constitutes a very particular biotope.

From July to October 1968 11.056.000 Opius were rebeased. In the same period, Dacus infestation was: in the irrigated olive groves: 51% on the 27th July, 80-95% during August, and 96% on 21st October; in the other part of the observation area (not irrigated): about 2% on the 19th August, but then gra- dually increasing unti! 85% on 21st October. In an olive grove reserved as control (it is 3-4 sta. mi. far) for the unirrigated area Dacus infestation had a trend like (a little higher) those percentages above reported, and on 21st October it was 91%.

The parasitism everage during 27th July - 21th October was: in the irrigated groves 57,4% (33,3 Calcididae and 24,1 Opius); in dry groves: 71% (33,4 Calcididae and 10 Opius). In all tbree observation areas tbe tops of parasitism (80-100%) bave been found in August and . Tbe of every single parasite species emerged trom tbe mtested ohve frmts was: Eupelmus Sl,S%; Eurytoma 19,6%; Pnigalio 27,6%; Cyrtoptyx 1,2%. .

In summer (mainly August-September) many Dacus eggs and pupana (also witb parasites) were destroied in olive fruits by adults of Crematogaster scuteliaris Ol. Tbe everage of destroied eggs by Crematogaster was m l%8: 5,1%, 34,3%, and 48% respectivly in tbe three observation areas (irrigated, unirrigated, control), while destroied Dacus puparia were 8,8%, 7,5%, 39,1%.

In 1969 10.030.000 Opius bave been released: Dacus infestation in tbe irrigated groves began early in July and it was 45-55% in August-September and 75% on tbe 10th November. In tbe unirrigated groves tbe infestation began late in July and it was 17-20% in August-September, and in two groves 40% on 10th November; while in the other two contro! groves it was 100% since the 19th of October.

The parasitism undergone by the Dacus (it is ascertained by means of direct observations and larvae and pupae dissection) was 30-60% for the Calcididae and 20-40% for tbe Opius.

However this has been eliminated (directly or indirectly) by the Calcididae especially in summer, often in the measure of 20-40% and until 84%. During July-October Crematogaster scutellaris destroied Dacus eggs on everage 2%, 8,7% and 7,4% in the observation areas (irrigated, unirrigated, control) respectively; while Dacus puparia destroied by Crematogaster were 29,6%, 60,7% and 53,2% respectively.

Dimetoato treatments against the Dacus kill eggs and larvae of the Opius into tbe Dacus larvae, but they are inoffensive for Opius larvae and pupae that are already in the puparia of the Dacus on the moment of the chemical applichation.

The Calcididae emerged from infested olive fruits in 1969 were: 61,2% Eupelmus; 33,6% Eurytoma; 4,6% Pnigalio; 0,6% Cyrtoptyx.

The ratio between females and males of the Opius emerged from infested drupae was 1/1,32.

In November Dacus larvae parasitised by Opius have been found up to abaut 130 st. mi. far from the experiment area. Altogether, in the experimental conditions above mentioned Opius has chown itself to be of little utility. because sudden, it is not able to control the Dacus when the attacks of this are intense and also because it is parasitised in a remarkable measure by the Calcididae. especially during summer.