Kate M. Barnes

The effect of bacterially-dense environments on the development and immune defences of the blowfly Lucilia sericata

Competitive interactions between insects and microbes and the associated cost of development in bacterially‐dense environments are investigated using the blowfly Lucilia sericata (Meigen) (Diptera: Calliphoridae) as a model. The effects of developing in a bacterially‐dense environment are measured by assessing the fitness consequences of competition using the pathogen Staphylococcus aureus. Fitness is quantified in terms of larval survival, puparial development and adult emergence.The influence of bacteria on larval immune defences is investigated using optical density to assess whether antibacterial potency of the larval excretion/secretion changes in response to the degree of contamination of the larval environment. The results obtained demonstrate that bacterial presence has no detrimental effect on survival of L. sericata from egg to adult eclosion, or on puparial size. Additionally, the level of microbial contamination of larvae has no effect on the antibacterial potency of the larval excretion/secretion. These findings confirm that larval antibacterial activity is not induced by the presence of environmental bacteria but is produced constitutively.

The antibacterial potency of the medicinal maggot, Lucilia sericata (Meigen): variation in laboratory evaluation

Research to quantify the potency of larval excretion/secretion from Lucilia sericata using liquid culture assays has produced contradictory results. In this study, viable counting was used to investigate the effectiveness of excretion/secretion against three marker bacterial species (Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli) and the effects of varying growing conditions in assays. Results demonstrate that factors such as number of larvae, species of bacteria and addition of nutrient influence its antibacterial potency. Therefore a standardised method should be employed for liquid culture assays when investigating the antibacterial activity of larval excretion/secretion from L. sericata.

Nocturnal Oviposition Behavior of Forensically Important Diptera in Central England.

Timing of oviposition on a corpse is a key factor in entomologically based minimum postmortem interval (mPMI) calculations. However, there is considerable variation in nocturnal oviposition behavior of blow flies reported in the research literature. This study investigated nocturnal oviposition in central England for the first time, over 25 trials from 2011 to 2013. Liver‐baited traps were placed in an urban location during control (diurnal), and nocturnal periods and environmental conditions were recorded during each 5‐h trial. No nocturnal activity or oviposition was observed during the course of the study indicating that nocturnal oviposition is highly unlikely in central England.

Microbial effects on the development of forensically important blow fly species.

Colonisation times and development rates of specific blow fly species are used to estimate the minimum Post Mortem Interval (mPMI). The presence or absence of bacteria on a corpse can potentially affect the development and survival of blow fly larvae. Therefore an understanding of microbial-insect interactions is important for improving the interpretation of mPMI estimations. In this study, the effect of two bacteria (Escherichia coli and Staphylococcus aureus) on the growth rate and survival of three forensically important blow fly species (Lucilia sericata, Calliphora vicina and Calliphora vomitoria) was investigated. Sterile larvae were raised in a controlled environment (16:8h day: night light cycle, 23:21°C day: night temperature cycle and a constant 35% relative humidity) on four artificial diets prepared with 100μl of 10(5) CFU bacterial solutions as follows: (1) E. coli, (2) S. aureus, (3) a 50:50 E. coli:S. aureus mix and (4) a sterile bacteria-free control diet. Daily measurements (length, width and weight) were taken from first instar larvae through to the emergence of adult flies. Survival rates were also determined at pupation and adult emergence. Results indicate that bacteria were not essential for the development of any of the blow fly species. However, larval growth rates were affected by bacterial diet, with effects differing between blow fly species. Peak larval weights also varied according to species-diet combination; C. vomitoria had the largest weight on E. coli and mixed diets, C. vicina had the largest weight on S. aureus diets, and treatment had no significant effect on the peak larval weight of L. sericata. These results indicate the potential for the bacteria that larvae are exposed to during development on a corpse to alter both developmental rates and larval weight in some blow fly species.

Effects of environmental temperature on oviposition behavior in three blow fly species of forensic importance

A number of factors are known to affect blow fly behavior with respect to oviposition. Current research indicates that temperature is the most significant factor. However temperature thresholds for oviposition in forensically important blow flies have not been well studied. Here, the oviposition behavior of three species of forensically important blow fly species (Calliphora vicina, Calliphora vomitoria and Lucilia sericata,) was studied under controlled laboratory conditions over a range of temperatures (10-40°C). Lower temperature thresholds for oviposition of 16°C and 17.5°C were established for C. vomitoria and L. sericata respectively, whilst C. vicina continued to lay eggs at 10°C. C. vomitoria and L. sericata both continued to lay eggs at 40°C, whilst the highest temperature at which oviposition occurred in C. vicina was 35°C. Within these thresholds there was considerable variation in the number of surviving pupae, with a general pattern of a single peak within the range of temperatures at which eggs were laid, but with the pattern being much less distinct for L. sericata.