1. Outbreaking vs stable population dynamics in insects: the key is in the oviposition behaviour? Juhan Javoiš, University of Tartu

2. “Outbreaking” insects Periodical drastic increases in abundance Defoliation of hostplants (often pests)

3. Epirrita autumnata

4. Polyphagous geometrid moth Periodical pest of birch forests in northernmost Europe Eggs are laid in autumn on branches of trees. Hatching in spring.

5. Epirrita autumnata No supression of oviposition in response to low host quality host leave injuries conspecific eggs or sex pheromone

6. Scotopteryx chenopodiata

7. Oligophagous geometrid moth Although abundant and wide-spread, abundancy is stable (no outbreaks) Lays eggs directly on hostplants

8. Scotopteryx chenopodiata Strong selectivity towards host-species (ranking of hosts) In response to low-quality host supression of egg-production (weak) low oviposition rate after initiating (weak) longer latency period (strong) similar pattern in two other geometrid species with stable population dynamics

9. “Stable” geometrids (or other insects) Able to discriminate between hosts In response to low host availability postpone oviposition and spend time searching around (dispersing) Spread their offspring evenly, according to host availability No outbreaks!

10. In contrast: “outbreakers” Unable to detect quality of hosts for larvae Lay eggs in vicinity of their hatching place Egg abundancy does not accord to host availability Dispersal ability of larvae is weak, so Outbreaks!

11. Why “outbreak-strategy”? Does not seem adaptive (long-time damage to the host, lots of supressed or dead larvae) Phylogenetic constraints Selection in favour of large body

12. Thanks!