Radiocarbon dating insect samples: new data and recommendations

Radiocarbon dating insects, whilst theoretically appealing when the environmental record is driven by changes seen in the insect record, is difficult because insects are small, fragile, and rarely found in quantities sufficient for dating. Interactions between the chitin that comprises the insect body and sources of carbon contamination are less well understood than for collagen and cellulose-based organic materials such as bone and plant remains. This means that there is as yet no single radiocarbon pretreatment that can be applied to reliably remove all contaminating carbon across all types of insect remains. In the absence of a standard pretreatment various studies have highlighted important information concerning the practicalities and applicability of different approaches to the problem of radiocarbon dating insect remains. However, this information is currently in a disparate range of sources and there are no papers that synthesise findings across different studies. Here, we present a review of previous work alongside new data to investigate different chemical approaches to sample processing and long-term storage and their impact on the chemistry of samples and contaminants. This confirms the difficulty of exhaustively removing contamination from older samples while balancing the need to retain sufficient pretreated material for subsequent measurement. It also shows that Fourier transform infrared (FTIR) spectroscopy does not always provide sufficient resolution to detect carbon contamination from non-insect sources with confidence. Thus, insect samples that have been in contact with paraffin or stored in ethanol for an extended period of time should not be selected for radiocarbon dating.