Behavioral chemoattractants for the shrimp, Palaemonetes pugio: identification of active components in food extracts and evidence of synergistic mixture interactions

We are studying chemoattractants for the shrimp, Palaemonetes pugio, to identify the active components of stimulatory food extracts, and to determine whether the mixtures of substances occurring in extracts express themselves in an additive or an interactive manner. The results of quantitative analyses of the specific amino acids, quaternary ammonium compounds, organic acids, nucleotides and related substances in extracts of four organisms (crab, shrimp, oyster, mullet) were used to formulate artificial mixtures based on the composition of each organism. Quantitative behavioral bioassays with P. pugio showed that the artificial mixtures based on the composition of the crab and shrimp extracts were virtually as effective as the respective natural extracts, whereas artificial mixtures based on the composition of the oyster and mullet extracts were far less effective. Since the same types of substances were included in all of the mixtures, it is apparent that the substances serving as chemoattractants in different extracts are not constant but can vary depending upon the source of the extract. To examine for interactions among the components of the four artificial mixtures, responses to the mixtures and to their individual components were analyzed using the additive methods of stimulus summation and response summation. Synergistic interactions were evident since each mixture was markedly more effective than predicted on the basis of these additive models. The degree of synergism varied with the composition of the mixture.