Measuring difference in prey detectability for predator molecular gut content analysis using half-life detectability

PCR-based molecular gut content analyses of arthropod predators have allowed researchers to better estimate occurrence of actual predation events in the field, where observation can be difficult and previously direct relationships were often inferred. Where understanding the relative strength of a trophic interaction is desired, one important variable that must be considered is the different digestion rates among predators, and the potential for differences in digestion rates between prey species, or targeted sequences within species. In the current study, I investigated the rates at which three exotic insect species, the imported classical biological control agent Diorhabda carinata (Coleoptera: Chrysomelidae) and two adventive species Opsius stactogalus (Hemiptera: Cicadellidae) and Coniatus splendidulus (Coleoptera: Curculioniae), are being utilized on invasive tamarisk by the commonly sampled tamarisk visitor Zelus tetracanthus (Hemiptera: Reduviidae), a generalist predator. To create prey-specific sequence half-life detectability times, I starved lab-reared Z. tetracanthus adults, before feeding each one unit of one of the three prey items. Groups of 20 adults per prey item were then killed immediately in pre-chilled ethanol at regular intervals (0, 12, 24, 36, 48, and 60 hrs. post-feeding) and stored for gut-content analysis.  Detectability was assessed by presence/absence of a visual band under UV fluorescence, and probit analysis was used for each prey item to determine the time at which a single predator fed that species had a 50% chance of producing a detectable band. These results will allow incidence of the three prey found in gut contents of field collected Z. tetracanthus to be corrected for variable digestion rates.