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Influence of adult and egg predation on reproductive success of Epirrita autumnata (Lepidoptera: Geometridae)


  • Miia Tanhuanpää,

  • Kai Ruohomäki,

  • Pekka Kaitaniemi

M. Tanhuanpää, K. Ruohomäki and P. Kaitaniemi, Section of Ecology, Dept of Biology, and Kevo Subarctic Res. Inst., Univ. of Turku, FIN-20014 Turku, Finland ( Present address for PK: Hyytiälä Forestry Field Station, Univ. of Helsinki, Hyytiäläntie 124, FIN-35500 Korkeakoski, Finland.


We studied the effects of predation and oviposition activity on reproductive success of a late-season moth, Epirrita autumnata by exposing adult females and eggs to predation in their natural habitat in two successive years. Daily survival rates of adult females ranged from 0.4 to 0.8, average being 0.7. Most predation occurred during nights and was caused by harvestmen and other invertebrate predators. Avian predation did not have an effect on adult survival rates, most likely because of the lateness of E. autumnata flight season. Eggs were also preyed upon by invertebrate predators, although a notable proportion of egg mortality was attributable to causes other than predation. Daily survival rates of eggs were more than 0.99. Using modeling based on empirical data on eclosion of female adults, their oviposition behavior and survival rates of adults and eggs, the daily survival rates were translated into population level consequences. Adult predation was estimated to decrease reproductive success of non-outbreaking E. autumnata by 60–85 percent and egg mortality by 20–40 percent. Predation on adult lepidopterans is a mortality factor potentially as relevant as predation in any other life history stage and thus, should not be ignored in studies of population regulation.