Spatial patterns at host and forest stand scale and population regulation of the pine processionary mothThaumetopoea pityocampa

Abstract

1 Different spatial processes are likely to generate variability at different scales. Thus, the explanation of patterns may be facilitated by knowledge about the spatial scales where variation in patterns occurs. In the present study, the link between spatial patterns of the pine processionary moth Thaumetopoea pityocampa Den. & Schiff.(Lepidoptera, Notodontidae) at two different scales, as well as its population dynamics, was assessed. 2 First, the spatial patterns of T. pityocampa population were assessed at the forest stand scale by surveying the distribution of larval colonies within the pine forest, indicative of adult dispersion. Second, egg-laying patterns across individual host-plants, indicative of female oviposition choices, were assessed, as well as their impact on the survival of immature stages. 3 It was found that T. pityocampa presents a gregarious distribution in homogeneous pine forests, over distances of a few dozen metres. At the pine tree scale, females tend to aggregate their egg batches, whereas aggregation increases with population density. Natural enemies such as parasitoids do not appear to play an important role in regulating the population dynamics of the species. At the same time, aggregation in individual hosts leads to increased mortality in the period from hatching to the third instar, which is notable at high population densities. 4 A patchy distribution in the landscape over short distances has a potentially positive effect on population dynamics of the species, avoiding the Allee effect, and allowing for a rapid increase in population, even where initial numbers are low, leading to localized outbreaks. At the same time, increased mortality as a result of egg-batch clumping at high population densities is a potential density-dependent mechanism of population regulation.

Ecological characteristics of pine processionary moth Thaumetopoea pityocampa (Lepidoptera: Notodontidae) larval nests in pine and cedar forests of Algeria

“…can play a significant role in the natural regulation of T. pityocampa and contribute to maintain their populations at low abundance levels within its distribution range (Tarasco et al 2016;Zamoum et al 2017;Rahim and Chakali 2022;Sebti et al 2022;Hein et al 2023;Lagogiannis et al 2023). Pimentel et al (2017) showed that the population density of T. pityocampa decreases dramatically after a year of severe defoliation as a consequence of both activity of the natural enemies and change in food quality (Pimentel et al 2017;Rahim et al 2021;Sebti et al 2022).…”

From sympatry to parapatry: a rapid change in the spatial context of incipient allochronic speciation

“…However, this might not be the case in Portugal, where mild winters offer good climatic conditions for larval development. On the other hand, high nest density at the tree level tends to increase overall mortality of young larvae (Pimentel et al 2017). More, SP larvae are still in the very beginning of their development when WP females lay their eggs, but most SP larvae have reached L4 and L5 instars when WP individuals hatch.…”