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Author

Davide Bellone

Bio: Davide Bellone is an academic researcher. The author has contributed to research in topics: Sawfly & Neodiprion sertifer. The author has an hindex of 1, co-authored 1 publications receiving 2 citations.

Papers
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Dissertation
01 Jan 2018
TL;DR: In this article, the European pine sawfly (Neodiprion sertifer) was used as a model organism to investigate how heterogeneity affects the bottom-up and top-down mechanisms influencing pest insect population dynamics.
Abstract: Mixed forests are proposed as a management strategy that enables high levels of wood production while also supporting ecological and social benefits that are weakened by traditional monoculture strategies. An ecological benefit of mixed forestry is that it is expected to reduce plant damage caused by specialist insect pests because theory suggests that heterogeneous habitats such as mixed forests should limit fluctuations in pest insect population dynamics. Two main hypotheses have been proposed to explain this reduction in plant damage. The first is based on a bottom-up effect whereby plants grown in a diverse habitat have more effective defences against herbivores. The second is based on a top-down effect whereby plant species diversity creates habitat diversity that supports a higher abundance of pests’ natural enemies. However, the mechanisms underlying these bottom-up and top-down effects are not fully understood. To fill this gap, I investigated how heterogeneity affects the bottom-up and top-down mechanisms influencing pest insect population dynamics. As a model organism, I used the European pine sawfly (Neodiprion sertifer), an herbivorous insect that frequently reaches outbreak densities and whose larvae cause severe damage when feeding on pine needles. Sawfly performance is known to be affected by pine needle chemistry – particularly the concentration of di-terpenes, which affect larval survival, and nitrogen levels, which affect cocoon weight and thus adult fecundity. Generalist and specialist natural enemies have been showed to cause significant mortality in sawfly larvae and cocoons. Despite their importance, the effects of plant chemistry and natural enemies on insect herbivores have not been studied in the context of forest heterogeneity. I found that the variation in cocoon weight within groups of sawfly larvae feeding on Scots pine needles increased with the needles’ contents of di-terpenes, and that this trend was stronger in mixed forests than monocultures. Additionally, the rate of generalist predation on sawfly larvae was higher in more densely planted spots within forest stands. Predation on sawfly cocoons was favoured by tree diversity, but the presence of dead wood mitigated the negative effect of low tree diversity. In addition, forest heterogeneity had no discernible effect on specialist enemies, which were able to locate their hosts equally well in simple and complex habitats. This thesis shows that bottom-up effects on sawfly larvae cannot explain the observed reduction in tree damage in heterogeneous habitats. It may be that the higher variation in cocoon weight observed in mixed stands increases the average fecundity of adult sawflies, resulting in higher likelihood of outbreaks. Conversely, heterogeneity promoted top-down effects because it favoured generalist predators without negatively affecting specialists. These results will be useful to forest managers seeking to understand how mixed forestry can be used to mitigate anticipated increases in insect pest damage due to future climate change.

2 citations


Cited by
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01 Jan 2014
TL;DR: In this paper, the authors reported results from laboratory and field-enclosure experiments estimating rates of pupal predation by bank voles (Myodes glareolus) on an outbreak insect, the European pine sawfly (Neodiprion sertifer), at different temperatures (15 and 20 A degrees C), in different micro-habitats (sheltered and non-Sheltered), and with or without access to alternative food (sunflower seeds).
Abstract: Population densities of forest defoliating insects may be regulated by small mammal predation on the pupae. When outbreaks do occur, they often coincide with warm, dry weather and at barren forest sites. A proposed reason for this is that weather and habitat affect small mammal population density (numerical response) and hence pupal predation. We propose an alternative explanation: weather and habitat affect small mammal feeding behaviour (functional response) and hence the outbreak risks of forest pest insects. We report results from laboratory and field-enclosure experiments estimating rates of pupal predation by bank voles (Myodes glareolus) on an outbreak insect, the European pine sawfly (Neodiprion sertifer), at different temperatures (15 and 20 A degrees C), in different microhabitats (sheltered and non-sheltered), and with or without access to alternative food (sunflower seeds). We found that the probability of a single pupa being eaten at 20 A degrees C was lower than at 15 A degrees C (0.49 and 0.72, respectively). Pupal predation was higher in the sheltered microhabitat than in the open one, and the behaviour of the voles differed between microhabitats. More pupae were eaten in situ in the sheltered microhabitat whereas in the open area more pupae were removed and eaten elsewhere. Access to alternative food did not affect pupal predation. The results suggest that predation rates on pine sawfly pupae by voles are influenced by temperature- and habitat-induced variation in the physiology and behaviour of the predator, and not necessarily solely through effects on predator densities as previously proposed.

4 citations