How should living entomological samples be stored?

Abstract

Sampling and storing insect evidence alive are important tasks in forensic entomology as it can impact survival and growth rates. To investigate the effect of cooling and storing of insect evidence before its arrival in the laboratory, samples of all three larval stages of the blow fly species Lucilia sericata and Calliphora vicina were analyzed. A first group was stored at room temperature and a second one in a refrigerator (~ 5 °C) for 16 h, all without air, supply of food, and sawdust. Afterwards, they were kept at 6–8 °C in a Styrofoam box for 8 h, simulating a transport situation. Mortality rate (MR) was calculated and 25% of the surviving larvae were killed and measured to check for interim growth. The remaining alive specimens were reared at 25 °C until adult’s eclosion for estimating a possible storage impact on survival during later development. The results were then compared with a control which was not temporarily stored and chilled but left feeding in boxes with an air-permeable lid on food substrate at 25 °C. A 24-h temporary storage stopped the larval growth in comparison with the control especially in early larval stages in both species. A high MR of up to 100% for third instar (L3) larvae stored both at room temperature and in a cold environment without air supply was found. Oxygen supply can reduce significantly the MR at least for L3 larvae of L. sericata. Findings provide scientific evidence for the recommendation to store larval samples at cold temperatures with both oxygen and food supply. The high MR for samples of the last larval stage clearly shows the need for a fast delivery after sampling and a more sophisticated storage procedure like, e.g., providing air supply. Storing live samples at room temperature without air access should be avoided.