Delayed density-dependent parasitism of eggs and pupae as a contributor to the cyclic
population dynamics of the autumnal moth
Tero Klemola*, Tommi Andersson and Kai Ruohomäki
*Corresponding author: Section of Ecology, Department of Biology, University of Turku, FI-20014 Turku,
Finland; tero.klemola@utu.fi; telephone: +358-2-3335769
Online Resource 4
Parasitoids and predators of the pupae and eggs of autumnal and winter moths
Predators and parasitoids of the pupae
All pupal parasitoids from field exposures were solitary endoparasitoids belonging to the
family Ichneumonidae. They have a univoltine life-cycle and winter dormancy occurs inside
the host pupae. Two common genera, with approximately equal shares, were found from both
moth species: Cratichneumon Thomson (subfamily Ichneumoninae) and Pimpla Fabricius
(Pimplinae). At species level, C. viator (Scopoli), C. rutifrons (Gravenhorst) and P. flavicoxis
Thomson were identified by ichneumonid specialists Reijo Jussila and Ilari E. Sääksjärvi at
Zoological Museum of the University of Turku.
Invertebrate predation on pupae was identified due to feeding marks on the pupa. Often
these were clear holes, which were assumed to be caused by coleopterans. For instance,
ground beetles (Carabidae) were commonly seen in the study area. However, no attempts
were made to clarify invertebrate abundance or the identity of invertebrate species or groups
that killed moth pupae.
Grey red-backed voles, Myodes rufocanus Sundevall, northern red-backed voles, M.
rutilus Pallas and Norway lemmings, Lemmus lemmus Linnaeus, were occasionally seen in
the area. During peaks of their population cycles, these primarily herbivorous rodents were
very abundant. Among insectivorous mammals, shrews, Sorex spp., are potential predators of
moth pupae. However, abundances or diets of small mammals were not examined.
Predators and parasitoids of the eggs
Due to northern location of the study area, potential egg predators are scarce, especially so
during winters. Some non-migrant passerines (e.g. tits) stay in low numbers in the area,
whereas most generalist invertebrate predators should be inactive, at least during most of the
egg-stage period of the moths. No further attempts were made to clarify egg predators, which,
however, seemed to be involved and even in an informed way, because both eggs of an egg
stick disappeared more than twice as likely as only one of them (Figs 8c, 8d in the main text),
implying an “area-restricted search” by a predator (Kareiva and Odell 1987).
The observed egg parasitoid Telenomus cf. laeviceps Förster was identified by Finnish
hymenopterist Veli Vikberg for both moth species. This species apparently has a univoltine
life-cycle. It flies in autumn (eggs exposed only in spring were not parasitized; data not
shown) and hibernates as an immature form inside a host egg. Species of Telenomus have
been able to regulate some geometrid and notodontid populations elsewhere (Anderson and
Kaya 1977; Hébert et al. 2001).
1
References
Anderson JF, Kaya HK (1977) Egg parasitism in Symmerista canicosta populations in
Connecticut. Environ Entomol 6:796–798
Hébert C, Berthiaume R, Dupont A, Auger M (2001) Population collapses in a forecasted
outbreak of Lambdina fiscellaria (Lepidoptera: Geometridae) caused by spring egg
parasitism by Telenomus spp. (Hymenoptera: Scelionidae). Environ Entomol 30:37–43.
doi: 10.1603/0046-225X-30.1.37
Kareiva P, Odell G (1987) Swarms of predators exhibit “preytaxis” if individual predators use
area-restricted search. Am Nat 130:233–270
2