Aggregative oviposition varies with density in processionary moths-Implications for insect outbreak propensity

In gregarious insects, groups commonly originate from females laying eggs in masses and feeding groups are established as soon as larvae hatch. Some group-living insect species may aggregate beyond the individual parent level, such that offspring from two or more egg masses develop within a common resource. Here we show that aggregative oviposition can vary with population density at oviposition and possibly be an important factor in outbreak dynamics of phytophagous insects. We analysed density data with respect to egg mass aggregation for two species of pine processionary moths, Thaumetopoea pinivora (in Sweden 2005-2019) and T. pityocampa (in Spain 1973-1991). Both species lay their eggs in egg masses and feed in groups. During the study periods, insect population density for both species varied by at least an order of magnitude. The two species showed strikingly similar patterns of egg mass aggregation. Egg masses were overdispersed at high population density, with few trees showing a high load of egg masses. Our data suggest that aggregative oviposition can be important in explaining the previously documented higher propensity for outbreaks in insects laying eggs in clusters, compared with those laying individual eggs

Winter temperature predicts prolonged diapause in pine processionary moth species across their geographic range

Prolonged diapause occurs in a number of insects and is interpreted as a way to evade adverse conditions. The winter pine processionary moths (Thaumetopoea pityocampa and Th. wilkinsoni) are important pests of pines and cedars in the Mediterranean region. They are typically univoltine, with larvae feeding across the winter, pupating in spring in the soil and emerging as adults in summer. Pupae may, however, enter a prolonged diapause with adults emerging one or more years later. We tested the effect of variation in winter temperature on the incidence of prolonged diapause, using a total of 64 individual datasets related to insect cohorts over the period 1964-2015 for 36 sites in seven countries, covering most of the geographic range of both species. We found high variation in prolonged diapause incidence over their ranges. At both lower and upper ends of the thermal range in winter, prolonged diapause tended to be higher than at intermediate temperatures. Prolonged diapause may represent a risk-spreading strategy to mitigate climate uncertainty, although it may increase individual mortality because of a longer exposure to mortality factors such as predation, parasitism, diseases or energy depletion. Climate change, and in particular the increase of winter temperature, may reduce the incidence of prolonged diapause in colder regions whereas it may increase it in warmer ones, with consequences for population dynamics

Natural History of the Pine Processionary Moth,Thaumetopoea pityocampa

International audienc

Natural History of the Pine Processionary Moth,Thaumetopoea pityocampa

International audienc

Natural history of the Processionary Moths (Thaumetopoea spp.): New insights in relation to climate change

La partie est intégrée dans le Chapter 2: Natural history of the Processionary Moths (Thaumetopoea spp.): New insights in relation to climate changeInternational audienceIt is difficult to find a genus of Lepidoptera showing the high variability of life history traits observed in Thaumetopoea. There are typical summer feeding close to winter feeding species, and in one special case a recent switch has been detected even within one species, the pine processionary moth, indicating that the natural history traits are constantly evolving at a fast rate. There are species adapted to cold conditions of high mountains and high latitude close to truly Mediterranean and sub-desert region species. All species have gregarious behaviour as larva and are protected against vertebrate predators by urticating setae

Climate Warming and Past and Present Distribution of the Processionary Moths (Thaumetopoea spp.) in Europe, Asia Minor and North Africa

International audiencePine processionary moth, Thaumetopea pityocampa, is a model insect indicator of global warming, the northwards and upwards range expansion of this Mediterranean species being directly associated with the recent warming up. The knowledge about the drivers of moth expansion is synthesized. A first standardized mapping of the northern expansion edge, from Western Europe to Turkey, is presented, then detailed for 20 countries of Europe, Asia Minor and North Africa, including future trends. Additional data about the responses of the other Thaumetopoea species are given. Finally, the chapter points out the importance of the man-mediated introductions in the expansion process