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La Dinamica di popolazione di Lymantria dispar L. in Sardegna: 1.: indicatori della gradazione ricavati dalle ovideposizioni

Luciano, Pietro and Prota, Romolo (1979) La Dinamica di popolazione di Lymantria dispar L. in Sardegna: 1.: indicatori della gradazione ricavati dalle ovideposizioni. Studi sassaresi: organo ufficiale della Società sassarese di Scienze mediche e naturali. Sez. 3: Annali della Facoltà di Agraria dell'Università di Sassari, Vol. 27 , p. 137-160. ISSN 0562-2662. Article.

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Abstract

The present work, dealing with the egg stage of Lymantria dispar L., forms part of a 9-year (1972-1980) research program on the population dynamics of the insect in a N. E. Sardinian cork-growing region. Egg-cluster counts (per hectare of forest surface) showed that total defoliation is to be expected every 7-9 years, that population density increase is not necessarily concomitant, and that different population densities may occur even in adjacent biotopes. The average egg count per cluster was low .(329 to 353) in peak population years and in the first year of retrogradation (288 to 339), but appreciably higher in years of latency and progradation (674 to 726). Egg sterility showed lower (from 1.7% to 6.0%) in latency years than in years of progradation, peak and retrogradation (from 7.6% to 18.4 %). The height above ground of ovideposition on the cork-oak trunks also varied. In latency years, more than 75% of the c1usters were laid below 2 metres: in progradation years, from 40% to 60% at above 2 m. In peak years, more than 75% were laid above 6 m, and in retrogradation years 40% to 60% between 2 m and 6 m. Information gathered on parasites (Ooencyrtus kuwanai (How.) and Anastatus disparis Ruschka) and predators (Dermestes lardarius L. and Haplocnemus jejunus Kinsenw.), which, at most, reached 27.9% in 1978 - a latency year for L. dispar -, would suggest that these are not of prime significance in controlling the defoliating populations. Statistic correlations are shown between egg-cluster dimensions and egg count per cluster, in particular the linear regression between the length of the egg-cluster major axis and total eggs in the cluster (y = – 11.86 + 11.26 x), in order to enable estimates of population levels to be made more rapidly. If correctly used on a large scale, the indicators analysed taken as a whole should enable sufficiently reliable forecasts to be made of L. dispar population levels and gradation phases, forming the basis of commen· surate programming for the protection of Quercus suber forests from defoliation.

Item Type:Article
ID Code:2131
Status:Published
Refereed:Yes
Uncontrolled Keywords:Lymantria dispar, Quercus suber, Sardinian cork forests, parasities, insects
Subjects:Area 07 - Scienze agrarie e veterinarie > AGR/11 Entomologia generale e applicata
Divisions:001 Università di Sassari > 01 Dipartimenti > Protezione delle piante
Publisher:Università degli studi di Sassari, Facoltà di Agraria - Gallizzi
ISSN:0562-2662
Publisher Policy:Depositato per gentile concessione dell'Editore Gallizzi
Deposited On:18 Aug 2009 10:07

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