Augusto Henrique Arantes PORTUGAL & José Roberto TRIGO*
Lacoratório de Ecologia Química, Departamento de Zoologia, Instituto de Biologia,
UNICAMP, Caixa Postal 6109, Campinas, SP, 13083970, Brazil.
Immature stages of butterflies show high mortality rates due to predation and parasitism-1. While adults of Ithomiinae butterflies are known to become chemically defended against predators by the acquisition of pyrrolizidine alkaloids (PAs) from plants on which they feed-2, little is knowrn about the chemical ecology of immatures of the same butterflies. Most of these feed on Solanaceae plants, without PAs, but with known toxic compounds (e.g. steroidal glycoalkaloids, saponins, solamides and phenolics)-3.
To verify if the immatures of Mechanitis polymnia are chemically defended by compounds acquired from their host plants (Solanum spp - Solanaceae), we tested the palatability of eggs, larvae, pupae and ffactions of the larvae and of the hostplant on which the juveniles were reared (Solanum asperolanatum) to a generalist predator Camponotus crassus (Hymenoptera: Formicidae). Ants are considered to be important predators of butterfly immatures and particularly this ant species is frequently seen foraging and tending homopterans on the host-plants (Solanum asperolanatum, S. mauntianum and S. concinnum) of M. polymnia in the field.
In a disturbed secondary forest we verified that the cumulative survival rate from egg to adult of M. polymnia was 1.8%, while it was 16.7% in an urban area. The higher mortality in the former appears to be caused mainly by the high levels of predators (ants, wasps and reduviid bugs) and parasitoids (scelionid wasps and tachinid flies).
Laboratory tests showed that eggs (n=25) larvae (n=95) and pupae (n=6) are unpalatable to the ants (only two first instar larvae were eaten) Dead larvae were also rejected by them. After extraction of juveniles with MeOH and acid-base fractionation, each fraction was tested 6 times with different ant colonies. Larval fractions showed highest activity in deterring ants (6% of total visits to the alkaloidal fraction and 16% to the acid fraction) The alkaloidal, neutral and acid fractions of the plant extracts (S asperolanatum) had respectively 45 29 and 20% of the total visits in this test.
Although neither freshly emerged adults of M. polymnia nor palatable butterflies painted with extracts from its larval host-plants are protected against spider predators (e.g. Nephila spp )-2 the larvae of this butterfly seem to be protected against some invertebrate predators perhaps hy sequestering compounds from larvai host plants (FAPESP CNPq).