Anti-Predatory defences in the shieldbug Graphosoma lineatum (Heteroptera: Pentatomidae) differ between life stages and colour forms: an experiment with hand reared great tits (Parus major) as predators
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Crypsis and aposematism are strategies used to avoid predation. Cryptic coloration helps prey to avoid detection and aposematic coloration signals unpalatability to the predator. In the Swedish populations of striated shieldbug Graphosoma lineatum there is a change in coloration and presumably protective strategy that coincides with a change of season and the natural background in the environment. We have compared effectiveness of warning function of colour patterns and chemical defence of three consecutive instars of G. lineatum: the cryptic fifth-instar larvae, the cryptic pale brown and black pre-hibernation adults and the aposematic red and black post-hibernation adults. In experiments with hand reared great tits (Parus major) we investigated the birds’ initial response, avoidance learning and generalisation between forms. We also noted if bugs used their scent glands on attack and if they survived attacks or not. Birds attacked the larvae faster and to a higher extent than the adults, both in naïve birds and after experience, but we found no difference between the adult colour forms in this regard. However, birds generalised asymmetrically between adults and larvae. Previous experience of adults benefited the larvae, but previous experience with larvae increased attack risk on adults and significantly more on the pale than the red adults. Spraying the defensive secretion increased the survival of adults but not the larvae. We conclude that the life stages of G. lineatum differ in defensive strategy against bird predators so that larvae rely on crypsis and the red adults rely mainly on aposematism, whereas the pale adult form seems to do both.
Behavioral Sciences Biology
Research subject Ethology
IdentifiersURN: urn:nbn:se:su:diva-62461OAI: oai:DiVA.org:su-62461DiVA: diva2:442011
ProjectsSeasonal change in defensive coloration in a shieldbug