Defesas quimicas em larvas de Plagiometriona flavescens e Stolas aerolota (Coleoptera: Chrysomelidae: Cassidinae)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

Chrysomelidae beetles have a great diversity of natural enemies .and also present many different defensive strategies. In this work we have studied two Cassidinae species (a Chrysomelidae .subfamily), P/agiometriona flavescens and StoIas areolata, with the main objective to understand if these species can protect themselves against predators using their fecal shields or chemical substances.. We have carried. out short-term experiments in the field and in the laboratory to test shield protection by comparing the mortality of larvae of both species with their fecal shield maintained,. removed or substituted by an artificial shield, without unpalatable chemical substances. Field experiment revealed that larvae of both species experimented with their natural shield survived more. frequently than larvae without shield or with artificial shield, thus suggesting the chemical nature of the defense. In .laboratory experiments we have offered larvae to ants. Camponoms crassus and to chicks, Gallus gallus. We have obtained for P. flavescens similar patterns of those obtained in the field, but with non-significant differences. We have confirmed the chemical protection provided by its shield because of the high rejection rates of baits treated with shield extract both in the fie1d and laboratory bioassays. Both predators preyed upon few S. areolata larvae, independently or the treatment they were submitted. In long-term experiments in the field and in the laboratory using P. flavescens larvae, we have observed that the maintenance of the shields did not represent any cost in the performance and survivorship of the larvae. Therefore, shields represent a defense for being unpalatable and cheap for larvae. Long-term experiments in the laboratory, using S. areo/ata larvae, showed the presence of the shield increases larval mortality, although no difference in the performance of larvae with and without shield was detected. In a similar experiment conducted in the field we did not detect any significant difference in the mortality of larvae with or without shields. In this case, we concluded that this structure may have a different function than protecting larvae against predators. In the second chapter, We have tested the efficiency of other strategies or chemical defense: We have observed that. P. flavescens larvae protect themselves against chemically oriented predators by the chemical camouflage. Cuticular hydrocarbons of larvae are 78% similar to the hydrocarbons of its host plant; thus C. crassus ants were not able to find P. flavescens. Larvae of S. areolata protect themselves by apoIar compounds, which are present in their body. We have observed in laboratory bioassays that baits treated with the apolar extract of larvae are rejected by G. gallus. We did no! observe the same type of predator behavior in a field experiment. However, it is possible that such apolar substances could -be potentially defensive to S. areo/ata larvae. Finally, this work shows that two different species belonging to the same sub-family can protect themselves-against predators-somfferently

ASSUNTO(S)

animais - defesas larva ecologia predação (biologia)

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