Host plant utilization has been advocated as a major factor in the diversification of herbivorous insects through host shifts. Although most phytophagous insects graze on a few species of host plants, many defoliating Lepidoptera are polyphagous i.e., they feed on species from different genera. This constitutes a challenging situation, as more distantly related plants will most likely produce different primary and secondary metabolites and present different architecture and phenology, all affecting insects survival, life-history and population dynamics. Still, being able to cope with such a diverse host pool might be the first step leading to host-race formation and species differentiation.
The browntail moth Euproctis chrysorrhoea, presents a remarkable polyphagy feeding on 26 genera belonging to 13 different families, from oak trees to wild roses, and it is distributed throughout Europe. In 1897 E. chrysorrhoea was accidently introduced in the USA from Europe and by 1913, it had spread to New England, New Brunswick and Nova Scotia. Since then, populations of this pest slowly decreased inland due to natural parasites and cold temperatures, being currently restricted to a few areas along the coast of Maine, mainly Cape Cod and Casco Bay. Given its polyphagy, eruptive dynamics and invasive potential, E. chrysorrhoea is an economically important defoliator. In addition, its larvae may also be responsible for sanitary problems as a result of their urticating hairs. Most people that come into direct or indirect contact with these hairs develop a skin rash, which lasts from a few hours to a few days. Respiratory distress from inhaling the hairs can be very serious and has also been reported (11% of the population in one health survey in the USA) (Maine Forest Service - Forest Health and Monitoring Division, 2008).
E. chrysorrhoea is also characterized by a peculiar life-history, spending most of the year (10 months) in the larval stage and overwintering as young larvae, inside communal nests. However, when feeding on the evergreen woody shrub Arbutus unedo, E. chrysorrhoea demonstrates a shifted phenology (Frago et al., 2010): young larvae emerging in the summer feed communally and enter diapause in autumn inside winter nests. Two months later, larvae resume communal feeding. In early spring they abandon A. unedo and feed individually on small shrubby plants. Pupation occurs in late spring, and imagos appear about 1 month later; they do not feed and have a short lifespan. Hence, leaf persistence in A. unedo is associated to a shifted phenology in E. chrysorrhoea suggesting the existence of host-races in this species.
The present project aims, therefore, to investigate if populations of browntail moth feeding on evergreen and deciduous hosts, on several areas of Europe and the USA, are genetically differentiated and if adaptation to specific host plants has affected the chemical communication between males and females, giving insight into the process of host race formation in this species. Ultimately, results will allow monitoring and controlling outbreaks of the species by possibly using its sex pheromone. DNA sequences coding for different genes (including the barcoding COI sequence) will be analysed for individuals collected in several European countries (e.g. France, Italy, Romania, Spain, UK) and in the USA, including areas where individuals feeding on evergreen and deciduous hosts exist in sympatry. This information will be used to evaluate population genetic differences and to infer the relatedness between populations feeding on different hosts and/or inhabiting different geographic areas. Differences in sexual communication (i.e. pheromones) will be evaluated through gas chromatography-mass spectrometry (GC-MS), electrophysiological antennal recordings (EAG) as well as behavioural experiments. The compounds found in the browntail moth female sex pheromone glands from different populations will be compared and tested in the field for their effectiveness in prompting behavioural responses in males.
Frago, E., Guara, M., Pujade-Villar, J. and Selfa, J. 2010. Winter feeding leads to a shifted phenology in the browntail moth Euproctis chrysorrhoea on the evergreen strawberry tree Arbutus unedo. Agricultural and Forest Entomology 12:381-388.
Maine Forest Service - Forest Health and Monitoring Division. 2008. Browntail Moth precautions.
Enrico Frago, UK.
Jean-Marc Lassance, USA
Eduardo Prez-Laorga Arias, Spain
Leonardo Marianellii, Italy
Markus Franzén, Germany
George Boettner & Joe Elkinton, USA
Ashot Khrimian, USA
The Carl Trygger Foundation