Bacterial volatiles attract gravid secondary screwworms (Diptera: Calliphoridae)

Authors: Chaudhury, Muhammad; Zhu, Junwei - Jerry; Skoda, Steven

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2015
Publication Date: 1/9/2016
Citation: Chaudhury, M.F., Zhu, J.J., Skoda, S.R. 2016. Bacterial volatiles attract gravid secondary screwworms (Diptera: Calliphoridae). Journal of Economic Entomology. 109(2):947-951.

Interpretive Summary: Microbial association of insects for various functions such as host seeking for feeding and egg-laying is well known. Female flies of primary screwworms are known to be attracted to volatiles produced by bovine blood inoculated and incubated with bacteria for depositing eggs. In this study, blood-bacteria preparation was tested to determine if adults of secondary screwworm would also respond to the volatiles for egg-laying. Five species of gram-negative coliform bacteria previously isolated from wounds infested by primary screwworms, when incubated singly or in combination for varying periods produced volatiles that attracted gravid flies to land on treated substrates and deposit eggs. Flies were attracted differentially and landed on the substrates containing different species of bacteria. Landing response was most significant when substrates were treated with all five species of bacteria. Substrates containing bacteria incubated for 72-hour attracted more flies than those incubated for 24, 48 or 96 hours. In 3-hour duration oviposition tests, one species of bacteria attracted more flies to oviposit than the other four species. The most eggs were recorded when substrates with all five species of bacteria were offered for oviposition and most eggs were deposited on substrates with 48 and 72-hour incubation period. It is possible that multiple active chemicals present in the volatiles of all five species result in greater response than those in a single species and at least 72-hour incubation is required to obtain most active volatile chemicals. These findings suggest that secondary screwworm females, like females of primary screwworms also use chemical cues from bacteria volatiles as oviposition attractant/stimulant.

Technical Abstract: Bovine blood inoculated and incubated with bacteria was tested to determine if adults of secondary screwworm, Cochliomyia macellaria (F.), would respond to the volatiles produced and oviposit on the incubated substrates. Five species of gram-negative coliform (Enterobacteriaceae) bacteria (Klebsiella oxytoca, Proteus mirabilis, Proteus vulgaris, Providencia rettgeri and Providencia stuartii) previously isolated from wounds infested by primary screwworms, Cochliomyia hominivorax (Coquerel), when incubated singly or in combination for varying periods with bovine blood produced volatiles that elicited gravid flies in a two-choice cage bioassay to land on treated substrates and oviposit. In 15-minute test periods, significantly more flies landed on substrates containing P. mirabilis. Klebsiella oxytoca -treated substrates attracted the least flies. Landing response was most significant when substrates were treated with all five species of bacteria. Substrates containing bacteria incubated for 72-hour attracted significantly more flies than those incubated for 24, 48 or 96-hour period. In 3-hour duration oviposition tests, substrates with P. rettgeri attracted significantly more flies to oviposit than the other four species. The most eggs were recorded when substrates with all five species of bacteria were offered for oviposition and most eggs were deposited on substrates with 48 and 72- hour incubation period. It is likely that multiple active chemicals present in the volatiles of all five species result in greater response than those in a single species and at least 72-hour incubation is required to obtain most active volatile chemicals. These findings suggest that C. macellaria females, like females of C. hominivorax, also use chemical cues from bacteria volatiles as oviposition attractant/stimulant.