On 21 October at 10:15 Sille Holm will defend her doctoral thesis „Comparative ecology of geometrid moths: in search of contrasts between a temperate and a tropical forest“
Research Juhan Javoiš, Research Fellow of Entomology
Research Erki Õunap, Research Fellow of Entomology
Professor Konrad Fiedler, University of Vienna, Austria
Insects are extremely diverse and we still know relatively little about them. The major aim of this thesis was to compare lives of moth species from the family Geometridae from a temperate and a tropical forest ecosystem. Worldwide there are approximately 24 000 described geometrid species, but we do not know much about the tropical species. For about 250 temperate and tropical region geometrid species, data on host-plant specificity, longevity and breeding strategy were collected. A phylogeny was derived for these species and the collected data compared in phylogenetically informed analyses. The suitability of 15 common tree species as food for freshly hatched caterpillars was tested in host-plant acceptance trials and the larval diet breadth of tropical and temperate species was compared. There were broadly polyphagous species in both regions. For temperate species it was shown that oviposition latency (i.e. pre-oviposition waiting time of a female) in captivity was longer for those geometrid species that have a narrower larval diet breadth. This result provided the possibility to use oviposition latency as an indirect measure of host specificity for the tropical region, where the host plants are not known. When oviposition latency was compared between temperate and tropical regions the waiting times were found to be similar. These results suggest that host-plant specificity is similar in both regions. Tropical species were found to be heavier than temperate ones; the difference is probably caused by the large wings and flying muscles of tropical species, which increase mobility in dense and diverse tropical vegetation. Compared to temperate females, tropical females lay smaller eggs. Therefore, it is also possible, that freshly hatched larvae are smaller in the tropical region. Adult lifespans of wild-caught individuals were found to be similar for both regions. Larger species were shown to have longer lifespans. Opposite to the predictions, the stable supply of adult food in the tropics (fruit and nectar) did not increase adult lifespans. Neither was income breeding strategy (i.e. breeding strategy depending on adult-derived resources) found to be more prevalent in the tropics than in temperate habitats. The results of this thesis suggest that host-plant specificity, longevity and breeding strategy are similar for the studied temperate and tropical moths. Quite opposite to expectations, the world the moths experience and the factors that shape their life histories may not be so different for the tropical and temperate zones after all.