Competition of insect decomposers over large vertebrate carrion: Necrodes beetles (Silphidae) vs blow flies (Calliphoridae)

Large carrion is inhabited by highly variable and interactive communities of insects. Positive interactions in carrion insect communities have been recently the focus in carrion ecology. By contrast, competition between carrion insects is rather undervalued. Here we provide evidence that blow flies (Calliphoridae) and Necrodes beetles (Silphidae), dominant decomposers of large carcasses in terrestrial habitats, compete over carrion. By reanalysing the results from 90 pig carcasses we demonstrated that the contribution of the flies and the beetles to the decay was negatively related. The greater part of the large carrion pool was monopolised by blow flies, whereas Necrodes beetles abundantly colonized carcasses, on which blow flies were less effective as decomposers. In behavioural assays, we found that adult beetles killed four times more frequently feeding than postfeeding third instar larvae of the flies, with the large decrease in the killing frequency after the larvae reached the age of early third instar. Therefore, adult Necrodes beetles preferentially killed the larvae that were before or in their peak feeding. The study provides evidence that the interaction between blow flies and Necrodes beetles is a combination of indirect exploitative effects of the flies and direct interference effects of the beetles (the mixed competition).

Isolation of Multi-Drug Resistant Potential Pathogenic Bacteria From Blow Fly Collected From Different Areas of Dhaka City

The research work was conducted for isolation and identification of potential pathogenic bacteria from blow fly (Calliphora spp.) and to investigate their antibiotic susceptibility. For this purpose, 20 blow flies were collected from 4 selected areas (Curzon Hall, Dhaka Medical College Hospital, Fruit Store and Fish Market) of Dhaka city. A total of 40 samples (20 from external surface and 20 from alimentary gut homogenates) were prepared from the blow flies. Among the total 20 flies, 3(15%) were collected from Curzon Hall and 5(12.5%) isolates were obtained from them; 6(30%) flies were collected from DMCH which had 11(27.5%) isolates; 5(25%) flies were collected from fruit stores and 10(25%) isolates were collected from there; 6(30%) flies were collected from fish market and 14(35%) isolates were collected from there. The isolated bacteria were presumptively identified as Escherichia coli, 12 (30%); Salmonella spp., 8 (20%); Shigella spp., 4(10%); Enterobacter spp., 3 (7.5%); Klebsiella spp., 2 (5%); Bacillus spp., 7 (17.5%) and Staphylococcus spp., 4 (10%) in number which were based on morphology as observed under microscope as well as cultural and biochemical properties. All of these isolates were resistant to various antibiotics. Bacterial susceptibility showed that E. coli isolates were highly resistant (66.6%) to Penicillin, Salmonella spp. mostly resistant (62.5%) to Penicillin and Tetracycline. Klebsiella spp. Isolates were 100% resistant to Penicillin and 100% sensitive to Ciprofloxacin, Imipenem and Tetracycline. In case of Shigella spp. and Enterobacter spp., 75% and 100% isolates were resistant to Penicillin respectively. Among the Staphylococcus spp. isolates, 75% were resistant to Ampicillin and Penicillin. In case of Bacillus spp. isolates, 57.2% were resistant to Penicillin and 100% sensitive to Imipenem. Antibiotic resistance of these species affect our human health also. This study demonstrated the potential of blow flies as a vector of various pathogenic microorganisms and a mode of transmission of antibiotic resistance. Bangladesh J. Zool. 49 (2): 205-214, 2021

Chronobiological Effect on the Reproductive Behavior of Chrysomya megacephala (Diptera: Calliphoridae)

The most widely used entomological method of determining the time since death (minimum postmortem interval, mPMI) has been calculating the developmental time of blow flies (Diptera: Calliphoridae) on the deceased body. However, because blow flies are known to be diurnal, nocturnal oviposition has been excluded from standard mPMI calculations. This has been challenged by recent studies demonstrating nocturnal oviposition due to an unknown reason. Therefore, this study investigated the role of chronobiology. We recorded the locomotion amount and pattern of Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae) under different chronobiological conditions and examined whether Ch. megacephala can oviposit under nighttime conditions in field and laboratory settings. Subjects were found to have a daily activity pattern under normal darkness conditions (12:12 L:D) and under continuous darkness (DD), but they exhibited no pattern under continuous light (LL). Free-running period was approximately 1,341 min/d (22.35 h/d). In the field, no flies were observed during nighttime. Oviposition occurred in the laboratory setting during daytime with no lights and during nighttime with artificial lights. Free-running subjects oviposited in both active and resting periods, with more eggs laid during active than resting periods. The result of this study indicates it is possible to induce oviposition behavior during evening hours on Ch. megacephala. However, this was only observed in the laboratory setting and could only happen during the flies’ subjective day.

Initial Work on Sex-Specific Growth Curve Guidelines for Forensically Important Blow Flies Using Chrysomya megacephala (Diptera: Calliphoridae) Entire Age Cohorts

Sex is a factor influencing development in many insect species, but is not widely studied in forensically important blow flies. If sex influences blow fly development, knowing the sex of a larva from a corpse can increase precision in estimates of that larva’s age. The improved prediction of larval age will make estimates of time since death using entomological evidence better. Larvae lack sexually dimorphic morphological characteristics, so sex is not immediately known visually. To generate sexually dimorphic reference growth curves, a subsample must be large enough to ensure enough males and females are present for comparison. Using two entire age Chrysomya megacephala (Fabricius) cohorts, we evaluated the minimum sample number needed to have enough individuals of both sexes for comparison using 95% prediction intervals. Through a simulation of three trials of 1000 random replicates, we determined that a sample size of 19 would prevent any instance of a comparison not occurring because of insufficient sampling from one sex. As the current method for molecular sex determination can be expensive, we also compared how the results of various subsampling percentages compare those of the entire age cohorts. We found that subsampling at least 50% of an entire cohort leads to almost identical results in comparison to the entire age cohort. Together, these findings will help establish guidelines for generating sex-specific reference growth curves. A uniform approach to generating these sex-specific growth curves will lead to more consistency in age estimates made from them.

Assemblages of Necrophagous Blow Flies (Diptera: Calliphoridae) in Four Contrasting Ecoregions of Los Angeles County, California, United States

An ecological study to evaluate necrophagous species richness, abundance, and diversity was conducted in four contrasting ecoregions of Los Angeles County, California, United States: a highly anthropized area, two moderately populated areas, and a sparsely populated area. Our hypothesis states that there will be higher abundance of exotic species in greatly anthropized ecoregions and higher diversity of native calliphorid flies in sparsely populated sites. A total of 2,883 blow flies belonging to 12 species were captured from the four ecoregions. The exotic Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae) was the most abundant species, representing 72.84% of all Calliphoridae collected. The highest abundance was in the highly anthropized ecoregion. Differences of the blow fly assemblages across environmentally and anthropically different ecoregions were found, and that the relative abundance of the exotic species increased with anthropization. Our results suggest that both anthropization and elevation alter the structure of blow fly assemblages, modifying the abundance and species richness of Calliphoridae. The results of this study support the hypothesis of biotic homogenization, since we found a higher proportional abundance of exotic species and lower diversity of native blow flies in ecoregions heavily modified by human action. Additionally, the hypothesis of intermediate disturbance was supported as the highest diversity was found in the ecoregion with moderate anthropization mixed with natural elements. This is the first study to conduct an intensive survey of the Calliphoridae assemblages in Los Angeles County, which can be potentially used as a tool in human and veterinary health and forensic sciences.