The Relationship Between Surface Area and Volume of Common Blow Fly (Diptera: Calliphoridae) Oviposition Sites and Carrion Body Mass.

Female blow flies (Diptera: Calliphoridae) demonstrate site preferences when ovipositing on carrion. Preference for oviposition sites is believed to reflect the suitability of the site such that the most preferred locations provide offspring with the greatest chance of survival. A number of factors might influence female choice, including area available for oviposition. For species known to aggregate during oviposition, the surface area of oviposition sites may be a key factor in the decision-making process. Using ImageJ, the surface area or volume of eight common oviposition sites on 13 fetal pig (Sus scrofa domesticus L.) carcasses was measured. Regression analysis was used to determine if body mass could predict the area or volume available for oviposition. We observed significant positive relationships between size of oviposition sites and body mass for all eight oviposition sites. The strongest relationships were observed for the face (R2 = 0.86) and legs (R2 = 0.84). To test the predictive capacity of this relationship, a blind validation study was performed. Five pigs of various body masses were randomly selected, and the available space of the eight sites was estimated using the regression equations. The validation study confirmed that the regression equations for most oviposition sites demonstrated their predictive capacity based on 95% prediction intervals. This research provides a tool that can be used to correct for differences in oviposition site area or volume between carcasses of varying mass so that researchers may gain a greater understanding of the oviposition preferences and aggregation behaviors in future studies.

Estimating the Number of Eggs in Blow Fly (Diptera: Calliphoridae) Egg Masses Using Photographic Analysis.

Little work has been done to quantify the number of eggs oviposited by blow flies (Diptera: Calliphoridae) in studies examining colonization behavior. Egg counting methods currently available are time-consuming and destructive. This study used ImageJ software and analysis of covariance to relate the volume of egg masses to the number of eggs laid by three different blow fly species: Lucilia sericata (Meigen), Phormia regina (Meigen), and Chrysomya rufifacies (Macquart). Egg mass volume, species, and the interaction of species and egg mass volume all affected the number of blow fly eggs deposited in egg masses. Both species identity and egg mass volume are important when predicting egg number, as such a single regression equation cannot be used to estimate egg number for these three species. Therefore, simple linear regression equations were determined for each species. The volume of individual eggs was incorporated into the model, yet differences between species were observed, suggesting that the orientation of the eggs oviposited by multiple conspecific females within egg masses influences egg estimates. Based on our results, we expect that imaging software can be used for other blow fly species, as well as other insect species; however, equations specific to each species must be developed. This study describes an important tool for quantifying egg deposition in a nondestructive manner, which is important in studying the colonization behavior and life history of insects of ecological and forensic importance.