Effect of temperature and humidity on insect DNA integrity evaluated by real-time PCR

Insects collected in dry traps can degrade rapidly, especially in warm, humid environments where many biodiversity and biosecurity surveillance activities are undertaken. Degradation can severely impact diagnostics, as trap catches can become difficult to identify to species level using morphological characters or, of increasing importance, molecular approaches. This is especially problematic for biosecurity surveillance of exotic tephritid fruit flies, where diagnostics are heavily reliant on morphological characters. We tested the effects of differing temperature and humidity conditions on mock samples of tephritid fruit flies in a controlled environment and compared our results to field trap catches. DNA degradation was quantified using real-time PCR assays, including one assay newly developed and tested here. We observed a correlation between increasing DNA degradation and increasing temperature and humidity. The greatest DNA degradation occurred under combined high humidity (90% relative humidity) and constant high temperature (35 °C). Unexpectedly, fluctuating temperature did not have a significant impact on DNA. Other factors, such as trap design, time in the field, and rainfall, did not significantly correlate with DNA quality across the field samples tested. When plotted against mock samples, field samples clustered together, with no clear pattern or predictability regarding the quantity of DNA preserved, indicating other untested environmental variables may be at play. Predictably, increased exposure time was found to have a detrimental effect on DNA quality for all treatments. These findings will improve the delivery of surveillance activities through the implementation of shorter trap clearance timeframes and improved trap designs and procedures.