Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2010
Publication Date: 5/3/2010
Citation: Chaudhury, M.F., Skoda, S.R., Sagel, A., Welch, J.B. 2010. Volatiles emitted from eight wound-isolated bacteria differentially attract and stimulate gravid screwworm flies (Diptera: Calliphoridae) to oviposit. Journal of Medical Entomology. 47(3):349-354. Interpretive Summary: Screwworm is an economically important pest of cattle. Maggots of these flies feed as obligate parasites on living tissue of animals. Gravid flies are particularly attracted to screwworm-infested wounds and navels of newborns where the flies lay their eggs. Infested wounds produce odors that attract the egg-laying flies to the wounds for egg-laying. Production of these attractive odors appears to be due to some bacterial activity. In the present study, bovine blood inoculated with bacteria isolated from screwworm-infested animal wounds was tested against gravid screwworm flies under laboratory conditions. Blood inoculated and incubated with eight species of bacteria, either in single species or in combination, produced odorous volatiles which attracted gravid flies. In 15-minute duration tests, blood incubated with each of five species of bacteria attracted significantly more flies than the blood inoculated with each of the other three species. Blood incubated with all eight species of bacteria attracted significantly higher percentage of flies than those incubated with single species. In 1-hour duration tests, blood incubated with each of the same five species of bacteria attracted significantly more flies to lay eggs than those incubated with each of the other three species. In a similar 1-hour test, blood incubated with all eight species of bacteria attracted highest number of flies to oviposit compared to all other tests. The rate of attraction and oviposition also depended on the length of incubation period with 72-hour incubation resulting in the highest attraction. If the attractive factor is isolated and chemically identified, this may serve as bait in traps to attract gravid flies in the field, or may be used in rearing cages to increase egg-laying for mass rearing.
Technical Abstract: Bovine blood inoculated with bacteria isolated from screwworm-infested animal wounds was tested against gravid screwworm flies, Cochliomyia hominivorax (Coquerel) in the laboratory in a cage bioassay as an attractant for oviposition. Eight species of gram-negative coliform (Enterobacteriaceae) bacteria inoculated in blood and incubated in single species or with all species combined, attracted gravid flies. In 15-min duration tests, volatiles of five species (Klebsiella oxytoca, Proteus mirabilis, P. vulgaris, Providencia rettgeri and P. stuartii) of the bacteria attracted significantly more females than the other three species (Enterobacter cloacae, E. sakazakii and Serratia liquefaciens). In 1-h duration oviposition tests, volatiles from the substrate using the same five species of bacteria attracted significantly more females to oviposit than the other three species. Volatiles from 24 h incubation period elicited least attraction and oviposition whereas volatiles from the 48 and 72 h incubation period resulted in significantly more attraction and oviposition. Attraction and oviposition decreased significantly when the substrates were incubated for 96 h. Volatiles from substrate with all species of bacteria combined attracted a significantly higher percentage of flies to land and oviposit than those from substrates prepared with single species. It is possible that multiple active chemicals present in the volatiles of all-species substrate may act as synergists resulting in greater response than those observed with volatiles from single-species substrate. Prior to oviposit the flies took a blood meal from the oviposition substrate. It is possible that the oviposition is achieved by two different factors in screwworm – first, using a chemical cue to land on a potential oviposition site and second, using a blood meal to stimulate actual oviposition.