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Efficiency of biological control of Gonipterus platensis (Coleoptera: Curculionidae) by Anaphes nitens (Hymenoptera: Mymaridae) in cold areas of the Iberian Peninsula: implications for defoliation and wood production in Eucalyptus globulus
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Orientador(es)
Resumo(s)
Sustainable management of forest plantations and cost-effective control strategies depend on previous
estimations of the economic level of damage caused by the pests. The eucalyptus weevil, a key pest of
Eucalyptus plantations worldwide, is mainly controlled using classical biological control, using the mymarid
egg-parasitoid Anaphes nitens (Girault). Nevertheless, in several temperate regions, the parasitoid
fails to reduce the weevil populations to economically sustainable levels. This study attempts to (i) relate
the efficiency of the parasitoid with climate variables, (ii) relate the level of damage caused by the weevil
with the rate of parasitism, (iii) estimate the implications of weevil damage on wood production. Weevil
density, damage caused by defoliation on the upper crown and parasitism rates were monitored in 2007,
in 34 Eucalyptus globulus stands. Elevation, temperature and precipitation were assessed by using the
Worldclim database. Using historic inventory data, wood production was projected to an age of 10 years,
prior to the arrival of the weevil, and compared with current data for the same stands.
Parasitism rate by A. nitens was a key element explaining weevil density and tree defoliation, r2 = 0.37
and 0.41 (p < 0.001), respectively. Significant relationships between parasitism rates and maximum temperature
of the winter months (MaxTw), r2 = 0.55 and elevation r2 = 0.59 (p < 0.001) were found. Other
climatic variables, such as temperatures of the warmest months and precipitation, were not significantly
related to parasitism rates. An upper threshold limit for the efficiency of the parasitoid appears for
MaxTw of 10–11 C. The mean percentage of parasitism was low 10.1% (±4.9) for MaxTw below 10 C,
increasing to 70.9% (±3.8) above 11.5 C. A reduction of the efficiency of A. nitens due to differences in
the climatic niches of both the host and the parasitoid is hypothesised. The lower temperature threshold
in particular, is of paramount importance for this host-parasitoid system. In consequence, in colder areas
MaxTw < 10 C, a defoliation of 74.1% was attained. Wood volume (projected to the age of 10 years) was
estimated to decrease to 51% in the affected areas in 2004–2006, compared to the previous period of
1995–1998. Estimated loss in wood volume increased exponentially reaching 43% and 86%, for 75%
and 100% of tree defoliation, respectively. Therefore, considering the increase in the economic costs
calculated for these regions, due to the high defoliation caused by the weevil, research into alternative
control strategies is urgently needed.
Descrição
Available at SciVerse ScienceDirect
Palavras-chave
economic impact biological control climate niche defoliation wood loss Eucalyptus weevil
Contexto Educativo
Citação
"Forest Ecology and Management". ISSN 0378-1127. 270 (2012) 216-222