Analysing the diets of invertebrate predators using terminal restriction fragments

Analysing food webs in agricultural habitats is essential for the development of natural control strategies. Several molecular tools to investigate trophic interactions on a species-specific level have been developed in recent years and their advantages and limitations have been discussed. With this study we introduce another tool, terminal restriction fragment length polymorphism (tRFLP). Generalist predators found in Australian brassica crops, their prey and abundant parasitoids were chosen as a model system to adapt and evaluate the tRFLP approach. Using general primers and selecting six restriction enzymes, we obtained species-specific tRF patterns for 21 of the most abundant arthropods in brassica crops. We detected up to three prey species in the gut contents of laboratory-fed predators. Detection rates differed among predators, ranging between 28 and 100%. The identification of a species-specific tRF pattern was strongly affected by the presence and concentrations of DNA from other species. In a preliminary field study, prey could be identified from 20% of the collected brown lacewings. The advantage of the tRFLP method is the possibility of identifying multiple species at once. This advantage is counterbalanced by methodological limitations, among which the most critical one is the fact that it will be difficult to maintain specificity in highly diverse ecosystems. However, if species diversity is limited and the target sequence and the primers are chosen to increase detection success, the tRFLP method can be used to study trophic interactions in the field.