Factors affecting diurnal flight and oviposition periods of blow flies (Diptera: Calliphoridae) in Indiana

The diurnal behavior of calliphorids (blow flies) and environmental factors affecting that behavior are used with increasing frequency as forensic science evidence in criminal cases. This study was designed to determine when calliphorid flight activity began during the day, when oviposition started and reached its peak, and when these activities ceased in the evening. Lower temperature thresholds, as well as optimum ranges of temperature, influences of cloud cover on flight activity and oviposition, and effects of prior rainfall on abundance of the blow flies were also studied. Fresh beef liver was used as bait over six sampling intervals for each daily trial with bait placement beginning at 0500 hrs and sampling occurring at 0700 hrs, 0900 hrs, 1200 hrs, 1500 hrs, 1830 hrs, and 2000 hrs. Baits were replaced at the start of each sampling interval. The duration of the study was from July, 1990, until late November, 1991. Frequency of sampling was approximately 2 days per month for the duration of the study with no sampling during the colder months (December, January, February, and March). Days with clear, partly cloudy, or overcast skies were selected as trial days, and days with precipitation were excluded. Eleven species of calliphorids were collected during the 2 calendar years, with seven species caught in sufficient numbers for statistical analysis. The calliphorid species showed a tendency to become active during late morning, with activity peaking in the late afternoon, and numbers declining sharply by sunset. Oviposition was never observed until late morning, the peak occurring during the late afternoon, and declining before sunset. The lower temperature threshold established for all calliphorids was 12$\sp\circ$C. The green bottle flies required a higher minimum threshold temperature than the blue bottle flies. Temperature range for greatest activity for most of the green bottle flies was 24 to 34$\sp\circ$C, while the range for the blue bottle flies was 12 to 28$\sp\circ$C. Cloud cover had a statistically significant effect only on the presence of eggs and with respect to the abundance of one blue bottle species, Cynomyopsis cadaverina (Robineau-Desvoidy). The number of days with 0.13 cm or more rainfall over the previous 36 days was of little statistical importance. Although the total number of individuals may have been affected by limited precipitation, the species were found to occur regardless of the quantity of rainfall. Statistical linear models were described for each group (calliphorid egg presence and total calliphorid abundance) or species. These predictive models included season, time of day, temperature, cloud cover, and rainfall