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The molecular analysis of predation through specific DNA amplification has been utilized extensively over the last decade, and has been shown to be fast and effective. However, it is necessary to evaluate the prey detectability half-life if we are to correctly infer the relevance of particular predators to particular pests and to accurately model the effect of biocontrol. We present here the design and analysis of a set of primers to amplify olive fruit fly (Bactrocera oleae) DNA in predator gut contents, allowing fast evaluation of the digestion time. We modified the existing protocol by solubilizing the prey DNA directly from the gut, and we applied this modified protocol to demonstrate that Pterostichus melas, one of the most common carabids in olive groves in Italy, feeds on B. oleae pupae. After feeding carabids with a single pupa, traces of the pest were found to be detectable more than 20 h after ingestion. This method could also be applied to other predators to evaluate trophic interactions of the olive fruit fly. The relevance of generalist predation to the mortality of the pupal stage of B. oleae is of great economic interest since B. oleae causes serious damage during olive production, reducing the commercial value of olive oil and table olives. [ABSTRACT FROM AUTHOR]