Semiochemicals released from five bacteria identified from animal wounds infested by primary screwworms and their effects on fly behavioral activity.

BACKGROUND: The Primary screwworm, Cochliomyia hominivorax (Coquerel), is a serious pest feeding on living flesh of any warm-blooded animal, including humans. It was eradicated from the United States in the early 1980s using the sterile male technique. However, it was recently detected in populations of wild deer and pets in the Florida Keys of the US. For monitoring purposes, screwworm flies are normally trapped using attractant bait with liver. However, there has been little effort to develop an efficient monitoring system for detection of screwworm flies using a specific synthetic attractant blend. Several studies have shown that odors from animal wound fluids attract screwworm adults, particularly gravid females. Bacteria associated with animal wounds have been identified that act as a major source for this attraction. To understand what volatiles attract screwworms we inoculated bovine blood with previously identified bacteria. We identified volatile chemicals released from the inoculated blood and other selected media over time and assessed the effect of those chemicals on behavioral activity of adult screwworm flies. METHODOLOGY/PRINCIPAL FINDINGS: A total of 7 volatile compounds were collected from bacteria incubated in either broth or blood using solid-phase microextraction, and their chemical structures were identified by their characteristic mass spectrum fragments and confirmed by retention times in comparison to those of synthetic standards via gas chromatograph combined mass spectrometry analyses. Five major volatiles including dimethyl disulfide, dimethyl trisulfide, phenol, p-cresol and indole were detected from a mixture of 5 bacteria incubated in blood. The ratios of volatiles released differed among different incubation media, time and individual bacteria. A synthetic mixture containing the five compounds was demonstrated to be attractive to adult screwworm flies both in laboratory assays and field trapping trials. CONCLUSIONS/SIGNIFICANCE: The results obtained from this study may assist in developing an efficient trapping system using the identified attractant blend to detect the infestation of primary screwworms. This is also the first study to explore the complex systems in volatile release profiles from 5 bacteria isolated from screwworm-infested animal wounds that are incubated with different media and incubation time, as well as individual and multi-species bacterial communities.

Distribution and Persistence of Sterile Screwworms (Diptera: Calliphoridae) Released at the Panama-Colombia Border.

The sterile insect technique is used by the Comisión Panamá - Estados Unidos para la Erradicación y Prevención del Gusano Barrenador del Ganado (COPEG) to maintain a barrier at the border of Panama and Colombia to prevent screwworms, Cochliomyia hominivorax (Coquerel), from South America reinfesting North America. Before studying the distribution and persistence of sterilized, mass-produced screwworms released in the barrier zone, the utility of applying fluorescent dust (∼1.0 mg/fly) to pupae and to newly emerged adults was evaluated to determine the potential effect on fly survival. The flight ability of flies collected from two adult emergence/collection systems (enclosed towers and open chambers) and treated with low (∼0.20 mg/fly) or high (∼1.0 mg/fly) amounts of fluorescent powder was compared. The distribution and persistence of sterile screwworms marked with fluorescent powder (∼0.20 mg/fly), after collection from the same two adult emergence/collection systems, was compared after their release in the barrier zone. The results demonstrated that: 1) fluorescent dust did not negatively affect sterile screwworm longevity or flight ability; 2) no differences were detected between sterile flies collected from the two emergence systems; and 3) sterile screwworms distributed evenly in the barrier zone and persisted for > 6 d. This information was useful in implementing the use of a new sterile fly emergence/collection system and deploying a new strain by COPEG for the barrier zone maintenance program; it will be valuable for evaluating alternative release strategies of sterile screwworms by the eradication and barrier maintenance program.

Identification of oviposition attractants of the secondary screwworm, Cochliomyia macellaria (F.) released from rotten chicken liver.

The secondary screwworm, Cochliomyia macellaria (F.), is an important blowfly species affecting both livestock and humans. It can transmit pathogenic disease agents mechanically and is an agent of facultative myiasis, which leads to economic losses. The adult flies are attracted to decomposing carcasses, carrion, or rotten meat in order to deposit their eggs, and the hatched larvae develop on these decaying organic materials. This research was aimed to identify volatiles emitted from rotten chicken livers that were reported previously to attract gravid females. In laboratory oviposition assays, gravid females laid significantly more eggs on rotten livers than on fresh livers, and rotten chicken liver was more attractive than rotten beef liver. Volatiles from the two livers were collected using solid phase microextraction. Significantly different volatile profiles were detected from the rotten livers of beef and chicken. Electroantennography (EAG) was performed to determine antennal responses to chemicals released from the most attractive chicken liver that are candidate oviposition attractants. Seven compounds from rotten chicken liver elicited significant EAG responses from antennae of gravid females. Oviposition assays showed that the 7-component blend stimulated gravid females to lay significantly more eggs than the other combinations tested. This 7-component blend may have potential for use in monitoring and sampling populations of secondary screwworm and their associated disease epidemiology.