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Use of molecular techniques to assess dispersal abilities of oak pest insects: applications for the biological control of acorn borer weevils in dehesas and montados

AuthorsBonal, Raúl ; Ortego, Joaquín ; Aparicio, José Miguel ; Muñoz, Alberto ; Hernández, Marisa; Canelo, Tara; Espelta, Josep Maria
Issue Date2016
Abstract[Background]: Recent findings on the negative effects of ungulate intra-guild predation on oak pest insects have encouraged the development of livestock management strategies aimed at pest control in agroforestry systems. A grazing scheme that concentrated large herbivores on different sectors of the farms when insects are more vulnerable to predation could serve to reduce acorn predation rates by Curculio weevils. However, even if the controlled spatial concentration of livestock reduces pest insect populations, insect dispersal estimations are needed to assess pest recolonization risk. In this sense, the knowledge gaps on the dispersal abilities of forest insects cast doubts on the effectiveness of a livestock-driven pest control. [Purpose]: In the context of a project aimed at the control of oak pest damages through livestock management in Iberian dehesas, our purpose was to assess the dispersal abilities of the main acorn borer insect Curculio elephas combining field monitoring and applied molecular techniques. [Methods]: We performed a six-year long monitoring of weevil population dynamics in 24 Holm oaks Quercus ilex. Dispersal abilities were estimated indirectly by recording at each tree weevil population size and acorn infestation rates. In addition, we assessed C. elephas spatial genetic structure at a landscape scale and calculated gene-flow between weevil populations inhabiting different trees. We used highly variable molecular markers such as DNA microsatellites and cutting-edge new techniques like Single Nucleotide Polimorphisms (SNPs). [Results]: Both approaches evidenced the reduced dispersal abilities of C. elephas. During the whole study period, acorn infestation rates recorded at each tree depended on the number of weevils emerging from their underground refuges below the canopy, suggesting a lesser importance of immigration from neighbor oaks. Moreover, weevil population genetic structure and measurements of gene-flow showed between-population isolation at distances of just 200 metres. [Discussion]: Our results highlight the utility of molecular techniques to assess insect dispersal in agroforestry systems. Their usefulness increases in the case of insects like acorn weevils, in which their small size complicates the performance of capture-recapture samplings. The low dispersal abilities of this insects mean that local reduction of acorn weevil numbers by means of livestock predation could be effective. Once local weevil populations decrease in certain areas, further recolonization likelihood is reduced. We think that this strategy of biological pest control should be implemented and favoured in agroforestry systems with high environmental value like Iberian dehesas and montados.
DescriptionTrabajo presentado al World Congress Silvo-Pastoral Systems celebrado en Évora (Portugal) del 27 al 30 de septiembre de 2016.
Appears in Collections:(IREC) Comunicaciones congresos
(EBD) Comunicaciones congresos
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