Host‐plant use in the range expansion of the pine processionary moth, Thaumetopoea pityocampa

Abstract

1. During range expansions of phytophagous insects, secondary or novel hosts may allow colonisation of areas without primary hosts. Because plant species often differ in their relative attractiveness and suitability for insects, insect preference for, and performance on, these hosts can determine recruitment potential in the current and future expansion areas.2. This study explores the relative roles of female preference and larval performance in an important pine defoliator, Thaumetopoea pityocampa (Denis & Schiffermüller) (Lepidoptera, Notodontidae), which colonises three Pinus species at its current range margin in the Italian Alps: P. nigra (primary host), P. sylvestris (secondary host), and P. mugo (novel host).3. Host use patterns in multiple insect populations were studied through choice and no-choice oviposition experiments in cages, field surveys of mixed stands, and laboratory and field monitoring of larval growth and mortality. It was predicted that a specific lifehistory trait -time limitation of short-lived females to lay a single batch of eggs -would act as a component of female performance, and lead to similar rates of host acceptance in no-choice settings.4. In the choice experiment, P. nigra was accepted the most frequently while P. sylvestris was accepted the least frequently, confirming nest density patterns in the field. Contrary to prediction, females remained discriminating in no-choice settings in spite of time limitation. In contrast, relative growth rate (RGR) and mortality of larvae did not differ significantly among the three hosts, highlighting a discrepancy between female preference and larval performance.5. Recruitment potential of T. pityocampa in future expansion into stands of P. sylvestris and P. mugo is evaluated by combining host quality, conservatism in oviposition behaviour, habitat suitability, and the opportunity for local adaptation. Entomology, 31, 481-490 * Number of larvae found in each of the remaining colonies included in parentheses. † Mean ± SE of relative growth rate (mg mg −1 day −1 ). 488 Michael Stastny et al.

Genetic diversity of Thaumetopoea pityocampa in Greece: the role of Quaternary changes in Aegean Sea

“…A case study in the Spanish Sierra Nevada shows an increased attack on relict Pinus sylvestris stands that had formerly been out of reach for the pine processionary moth because of their high growing altitude and low winter temperature [45]. However, laboratory tests show that the caterpillar can thrive on this pine species [45] despite being considered a secondary host [47]. Since Thaumetopoea pityocampa females commonly only live one night, migrating individuals are very likely to adjust their preferences in oviposition and therefore may accept secondary or novel hosts, depending on regional characteristics [47].…”

“…However, laboratory tests show that the caterpillar can thrive on this pine species [45] despite being considered a secondary host [47]. Since Thaumetopoea pityocampa females commonly only live one night, migrating individuals are very likely to adjust their preferences in oviposition and therefore may accept secondary or novel hosts, depending on regional characteristics [47].…”

Performances of an expanding insect under elevated CO2 and snow cover in the Alps

“…Moreover, the same quantity of fae ces produced in the two treatments does not support the hypothesis of compensatory feeding, that has been associated with in crease of C/N ratio and lower tissue quality (Williams et al 1994), although some recent studies have suggested that a differential post-ingestive adsorption may compensate for diminished food quality (Barbehenn et al 2004). In the study of Stastny et al (2006), the performance of the processionary moth larvae did not differ between three host-plant species with different nitrogen content, showing a high plasticity. This may display such a post-ingestive compensatory beha viour.…”

Monitoring a genetically modified Pseudomonas sp. released on pine leaves reveals concerted successional patterns of the bacterial phyllospheric community

“…We decided to use P. mugo, instead of the original host of isolation of the bacterium (P. nigra), for multiple reasons: (A) The target insect pest attacks both pine species with equal success. The pine needles of the two species have similar traits and nutritional value for the test insect (Stastny et al 2006). (B) P. mugo offers the possibility of having multiple branches of the same type on a potted tree, which enables to carry out many parallel replicates.…”