Understanding olfactory cues in host location and dispersal range of the filth fly parasitoid Spalangia cameroni (Hymenoptera:Pteromalidae) to improve the use as sustainable biological control agents for fly control on livestock operations

Final Report for GS11-101

Project Type: Graduate Student
Funds awarded in 2011: $9,828.00
Projected End Date: 12/31/2014
Grant Recipient: University of Florida
Region: Southern
State: Florida
Graduate Student:
Major Professor:
Dr. Norman Leppla
University of Florida
Expand All

Project Information

Summary:

Pupal parasitoids are often used as sustainable biological control options for filth fly pests on livestock operations. Filth flies, such as stable flies (Stomoxys calcitrans) and house flies (Musca domestica), are mechanical vectors of disease and can cause pain and losses of condition to livestock. Conventional control of these pests has relied on high doses of various insecticides. Filth fly pests are becoming increasingly resistant to many licensed insecticides and the increase of chemical use is harmful to the environment. The purpose of this project is to improve the use of pupal parasitoids of filth flies as part of a sustainable biological control program on livestock operations. Though used often, there is only limited empirical information on the microhabitat preferences and protocols for release of Spalangia cameroni Perkins (Hymenoptera: Pteromalidae) that will assure their effectiveness. The goal of this research was to (1) define the odor cues which influence host location by Spalangia cameroni, (2) assess dispersal to host sites from release locations in the field, and (3) outreach and extension activities to increase the operator awareness of biological control of filth flies. Impacts of this research include increasing the effectiveness of the parasitoids, reducing exposure of humans and animals to toxic insecticides, managing insecticide resistance by improving sustainable biological control options and ultimately reducing cost and increasing the use of these parasitoids to manage filth flies.

Introduction

The purpose of this project was to improve the use of pupal parasitoids of filth flies, such as house flies and stable flies, as part of a sustainable biological control program on livestock operations. These parasitoids in the family Pteromalidae are often used as non-chemical alternatives to chemical insecticides. Several species, including Spalangia cameroni Perkins, are commercially available and sold widely. However, there is only limited empirical information on the microhabitat preferences and protocols for release that will assure their effectiveness. The olfactory cues of host location by these wasps has been given little attention. As a consequence of this insufficient knowledge, these parasitoids have not achieved widespread success. Improvement of use is contingent upon understanding the factors influencing host location and dispersal. The proposed project will determine preferences for odor cues which influence host location as well as parasitism differences determined by dispersal range.

Biological control is an important and sustainable option for livestock operators to control their filth fly pests. Filth flies must be minimized in livestock operations primarily because they can transmit more than 100 pathogens that cause disease in humans and animals (Malik et al. 2007). Losses of physical condition have also been observed in livestock pressured by flies (Todd 1964). Field surveys of stable and house flies have revealed high levels of resistance to most commercially available insecticides due to overuse. This research will reduce the risk of transmitting diseases to humans and livestock and reduce chemicals in the environment by minimizing the size of filth fly populations using natural methods. Livestock operations will be safer and more profitable.

Increasing the knowledge of the dispersal and detection of host location  by Spalangia cameroni  has provide insight in to the post-emergence cues used by parasitoid females to locate hosts in microhabitats. With this understanding of host location and further identification of the volatile chemicals associated with attraction, livestock operators will be able to place parasitoids for release where they will be able to locate hosts, maximizing parasitoid effectiveness.

Project Objectives:

The goals of this research were to (1) define the odor cues which influence host location by Spalangia cameroni, (2) assess dispersal to hosts sites from release locations in the field, and (3) increase the operator awareness of biological control of filth flies.

Goal (1): Define the odor cues which influence host location by Spalangia cameroni

Objective 1: To assess the attraction of S. cameroni to the larvae of house flies at different concentrations.
Objective 2: To assess the attraction of S. cameroni to manures of three different farm animals and the attraction to the interaction between developing larvae in the manure.

Goal (2): Assessment of dispersal to hosts sites from release locations in the field

Objective 3: To assess dispersal range of S. cameroni when hosts are immediately present at many distances and when hosts are not immediately available.

Goal (3): Outreach and extension activities to increase the operator awareness of biological control of filth flies.

Objective 4: Development of an extension publication to assist farmers in the use and selection of parasitic wasps for filth fly control.  

Cooperators

Click linked name(s) to expand
  • Dr. Chris Geden
  • Dr. Norman Leppla

Research

Materials and methods:

Objective 1: To assess the attraction of S. cameroni to the larvae of house flies at different concentrations. 
Objective 2: To assess the attraction of S. cameroni
 to manures of three different farm animals and the attraction to the interaction between developing larvae in the manure. 

Objectives 1 and 2 were modified to specifically define in a bioassay the attractive components of hosts in host habitat. This gave more specific results that are currently being modified to identify specific volatile chemicals used in habitat location and may lead to a monitoring tool. Bioassays for Spalangia cameroni and another common and commercially available parasitoid Mucidifurax rapor for comparison were developed to determine if it was the host habitat (horse manure and pine shavings) or hosts that were attracting the parasitoids.

House fly and parasitoid rearing. House flies were obtained from the USDA-ARS, Center for Medical, Agriculture and Veterinary Entomology (CMAVE) colony and reared as described in Machtinger and Geden (2013).  Parasitoids used for this study were from 2012 colonies of S. cameroni and M. raptor established from a source population on a dairy in Gilchrist County, Florida. Maintenance consisted of providing parasitoids with 2-day-old house fly pupae at a host: parasitoid ratio of 5:1 twice weekly in 17.5 x 17.5 x 17.5-cm cages (MegaView Science, Taiwan) and held at 25 oC and 80% RH.

Substrate. The substrate used for experiments was 3-d-old pine shavings bedding (0.1 to 0.3-cm long) bedding with horse dung and urine. Both S. cameroni and M. raptor have demonstrated the ability to locate hosts in this medium (Pitzer et al. 2011; Machtinger and Geden 2013). The substrate was collected from a private equine facility in Reddick, FL. Shavings and manure were separated then frozen at -18 oC for a minimum of one week prior to testing (Machtinger and Geden 2012). 

A standardized amount of substrate was used for each treatment totaling 20g; 15g of horse dung and 5g pine shavings. This substrate was placed in a 5.5 oz plastic cup measuring 6-cm h x 7.5-cm diam, hydrated to 70% (Machtinger 2011), and mixed thoroughly. For treatments with developing house flies, 30 house fly eggs were placed on the surface of the substrate on a moistened cloth to prevent desiccation (Machtinger 2011). Substrate was also tested without developing flies. Cups were covered with muslin and sealed with plastic rim lids. Cups were maintained at 27 0C and ~80% RH. The entire contents of each cup was used for each test and only used once.

By random assignment, a variety of odor stimuli were presented to both parasitoid species. The odor treatments of substrate alone without developing house flies (substrate), substrate with larvae that had developed from eggs to 3rd instar (substrate with larvae), and substrate in which the larvae had developed to 3rd instar but the larvae were removed (substrate, larvae removed) were tested at 4 d after initial set up in the cups. Odor treatments with house fly puparia were conducted at 8 d after cup establishment and included substrate with house flies that had developed from eggs to puparia (substrate with puparia) and substrate where house flies had developed to puparia but the puparia were removed (substrate, puparia removed). Larvae (washed larvae), and puparia (washed puparia) tested separately from substrate and were removed from either the substrate with larvae or the substrate with puparia the morning of the experiment. Individuals were rinsed twice with distilled water and air dried a minimum of 1 h prior to testing. Experiments were conducted at the USDA-ARS, CMAVE in an isolated room. The room was illuminated with a 13w CFL red light (195 lumens).

A glass Y-tube olfactometer was constructed with a 16-cm central arm that was connected to two 8.5-cm lateral arms. Each arm was 2-cm diam. A removable 8-cm glass adaptor was inserted into each of the lateral arms and with 100 mesh in the glass to prevent parasitoids from accessing the odor sources. The glass adaptor was connected to a 35-cm length x 4-cm diam glass chamber where each odor treatment was placed for testing with Teflon® tubing. Compressed air was humidified and purified with charcoal using a 2-port humidity and air delivery system (Model # OLFM-HAPS-ZAFMIC, Analytical Research Service, Inc, Gainesville, FL). Preliminary tests suggested that the two parasitoid species differed in behavior with varying airspeed, so airflow was optimized for each species, being introduced using a flowmeter at 200 ml/min for S. cameroni and 130 ml/min for M. raptor (McKay and Broce 2003). The olfactometer was placed in a 47.5 x 47.5 x 47.5 cm bug dorm (MegaView Science, Taiwan) with nylon (150 x 150 mesh) sides. The bug dorm sides were covered with black plastic to eliminate lateral light from the test area.

Parasitoids were standardized according to the protocol established by Mandeville and Mullens (1990). Male and female parasitoids were held in a 17.5 x 17.5 x 17.5 -cm bug dorm without hosts and with a 10% sucrose solution for 24-h prior to the experiment. Spalangia cameroni is autogenous (Gerling and Legner 1968; Morgan et al. 1989; King and King 1994) and disperses quickly after emerging (King 1990) so was standardized at 1 d-old while preliminary trials suggested M. raptor required an additional 48-h prior to responding to odor treatments so adults were 72 h-old prior to standardization. Both species were held in the experimental room at 25o C and 80% RH during the standardization period.

Females were separated from males by anesthetizing groups on a cooling table the morning of the experiment. Individual females were placed individually in size 0 gelatin capsules. Individual capsules were opened and placed in a glass inlet adaptor measuring 1.5-cm x 7-cm which served as a release chamber. The adaptor was covered with parafilm and the parasitoid given a minimum of 10 min to acclimate to the chamber prior to being inserted into the olfactometer with previously started airflow to avoid any potential movement generated by an escape response. The Y-tube was presented horizontally for S. cameroni, however, M. raptor did not respond to the horizontal orientation and remained arrested in the inlet adaptor so the Y-tube was modified to a vertical orientation which provided a greater response (Steidle and Scholler 2002; Belda and Riudavets 2010). Parasitoids were tested for 5 min and choice was recorded when an individual remained beyond a mark located 2-cm from the end of the Y-tube for 15 consecutive seconds. The time to choice was recorded for each parasitoid. If a parasitoid failed to make a choice within 5 min the parasitoid was removed and recorded as no choice. To ensure that wasps have no bias in movement toward either arm, the Y-tube was flipped for every other female. Ten parasitoids were tested individually for each odor treatment and ten replicates were completed of each odor treatment (total parasitoids, n=100). Though some females did not make a choice during the trial time, trials were continued until 10 parasitoids had made a choice for every treatment.  Those parasitoids that did not make a choice were not included in the analysis.  After each experiment, the olfactometer and used glassware was washed thoroughly with water, rinsed with acetone, and allowed to dry for a minimum of one hour before reuse (McKay and Broce 2003).                 

Statistical analysis. All odor treatments were randomly tested once as a block. Analysis revealed no effects of block, so data were pooled for further inquiry. Ten odor treatment combinations were shared between S. cameroni and M. raptor and additional treatments were tested for each individual species to further narrow odor preference. To determine differences in choice between odor attractions conspecifically, a chi-square goodness-of-fit test was used. The responses to odor treatments were compared between species using Fisher’s Exact Test (FET). To analyze the latency of females to a given odor stimuli, treatment odor and species was subjected to a two-way ANOVA and statistically separated using Student’s t-test. Time data were subjected to log transformations and back transformed for presentation in tables and figures. In all cases, the level of significance was α=0.05. Statistical analysis was performed with JMP (v. 11, SAS Institute, Cary, NC.). 

Objective 3. To assess dispersal range of S. cameroni when hosts are immediately present at many distances and when hosts are not immediately available.

Substrate used as host habitat was 72 h-old pine shavings (0.1 to 0.3 cm long) soiled with horse manure and urine and containing small amounts of alfalfa hay from an equine farm in Ocala, Florida (Machtinger 2011). The substrate was frozen for a minimum of 1 week to kill any existing arthropods.

Four plastic 45L bins (55 x 25 x 33cm) were filled with 11 L of substrate (depth of 7cm). The bins were coated with Insect-a-slip (ethylene tetrafluoroethylene) (Bioquip, Inc., Rancho Dominguez, CA) to reduce potential insect predation and will have a fine mesh lid to discourage vertebrate predators (Figure 1).

Immature house fly hosts were obtained from the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology (CMAVE) insecticide-susceptible colony. Larvae were reared on the diet described in Hogsette (1992). In brief, the diet contained 5000 mL of fly diet mix, (50% wheat bran, 30% alfalfa meal and 20% fine corn meal) and 3750 mL of water.    

Larvae were separated en masse from rearing media one day from expected pupariation and 200 individuals were weighed. By extrapolation, the weight of the 200 was used to estimate approximately 2000 individual larvae. Approximately 2000 larvae were added to each of the 4 bins by scattering them over the surface of the substrate.

Fifty larvae were placed individually in a single perforated plastic snap vial with moistened vermiculite. Instead of the lid, a cotton ball were used to seal the opening. This snap vial containing larvae were buried in the center of the substrate as an environmental control. Larvae were held at 22oC and given 2 days to pupariate before placing the bins in the field.

Spalangia cameroni females established in 2010 from a large source population on a dairy farm in Gilchrist County, FL and reared on USDA-ARS, CMAVE house fly hosts were used for parasitoid releases. One-day-old virgin females were separated from males by briefly anesthetizing the flies on a cooling table. Groups of 400 females were isolated for each release, making a 5:1 host to parasitoid ratio (2000 puparia and 400 female parasitoids).

The releases occured in 2 fields at the University of Florida (Gainesville, FL). These fields did not have livestock or livestock waste in the vicinity, thus avoiding non-experimental fly attractants and parasitism by natural populations of parasitoids. The individual fields were divided into 2 plots a minimum of 100 m apart.

Bins with house fly hosts were placed at the treatment distance and protected from heavy rain and direct sunlight by a plywood roof placed approximately 30 cm from the top.

Initially, bins were placed at the experimental distances but with no release of parasitoids. This determined if there is natural parasitism. Six bins were placed individually the field at each of the treatment distances from a stationary release point: 1m, 5m, 10m, 20m, 30m, and 60m.

Parasitoids were placed in a PVC pipe (30-long and 5-cm diameter) with 3-cm holes covered with window screening and capped on both ends with the associated 5-cm diameter PVC cap (Figure 3). These PVC pipes were hung from a ground plant hook and held approximately 1-m from the ground. Bin placement and parasitoid releases were conducted at dawn on the day of release.

There was a parasitoid release in one field and a control in the other for each replication.  Releases occured 4 times at each field, location and distance.

Bins were collected 72 h after parasitoid release. Puparia were sifted from the substrate using a #8 and #12 sieve to remove small and large particles. Puparia were removed from remaining substrates by hand using soft forceps.

Puparia removed from the bins were held for emergence of parasitoids in ventilated 250-cm3 plastic cups for a minimum of 6 weeks at 27o C and 80% RH. Parasitoids are currently being identified and percent parasitism for each distance will be determined. Parasitism will be regressed against distance for each release, and for all releases combined.

 Objective 4: Development of an extension publication to assist farmers in the selection and use of parasitic wasps for filth fly control.

Literature reviews of previous studies and the results from this research are being compiled to create a single reference document on the use of pupal parasitoids for filth fly control on equine farms in Florida. It is expected that this document will be published in 2014 in the University of Florida Electronic Delivery Information System (EDIS) and potentially in the Journal of Integrated Pest Management, a national publication through the Entomological Society of America.

 

Research results and discussion:

Goal (1): Define the odor cues which influence host location by Spalangia cameroni

Objectives 1 and 2:

Results: In the Y-tube olfactometer, the two species of parasitoid exhibited different responses to many of the shared treatments. Spalangia cameroni positively responded to all odor treatments that included substrate when they were tested against clean air (Chi-square test: substrate: c2 = 6.76, P = 0.0093; substrate with puparia: c2 = 6.76, P = 0.0093; substrate, puparia removed: c2 = 12.96, P = 0.0003; Figure 1) and was particularly attracted to the substrate with larvae (c2 = 43.56, P = <0.0001). There was a significant difference in response found between the two species to this particular treatment, as M. raptor did not distinguish between the substrate with larvae and the clean air control (P = 0.0001; Fisher’s Exact Test, FET).  Similarly, M. raptor did not distinguished between the substrate and clean air control, but this species was attracted to the substrate with puparia over clean air (c2 = 11.56, P = 0.0007) and the substrate with the puparia removed over clean air (c2 = 4.00, P = 0.0455). Neither species differentiated between the washed larvae and the clean air control, though unlike S. cameroni, M. raptor was attracted to the washed puparia over the clean air control (c2 = 5.76, P = 0.0164). However, there wasn’t a significant heterospecific difference in choice with this odor treatment.

When odor treatments were compared against other odors in lieu of clean air the responses of S. cameroni and M. raptor to shared treatments revealed opposite preferences for each of the comparisons but with similar magnitudes of response. Following the trend demonstrated against the clean air control, S. cameroni was significantly attracted to the substrate with larvae over the clean air (c2 = 43.56, P = <0.0001) as well as the substrate with larvae over the substrate with puparia (c2 = 11.56, P = 0.0007). Muscidifurax raptor did not distinguish between the clean air and the substrate with larvae and the substrate with puparia was found to be more attractive than the substrate with larvae (c2 = 4.00, P = 0.0455). When washed larvae and washed puparia were compared, S. cameroni preferred the washed larvae (c2 = 4.84, P = 0.0278) while M. raptor continued to preferred the washed puparia (c2 = 4.84, P = 0.0278). Spalangia cameroni preferred the substrate with the larvae over the substrate alone (c2 =4.00, P = 0.0455). Conversely, M. raptor preferred the substrate over the substrate with larvae (c2 = 4.00, P = 0.0455). All of these comparisons were significantly different between species (substrate with larvae versus substrate with puparia: P = 0.0002, FET; washed larvae versus washed puparia: P = 0.0028, FET; substrate with larvae versus substrate: P = 0.0071, FET). 

   When the preference of S. cameroni to treatment odors with substrate with larvae were further analyzed independently of M. raptor, S. cameroni was highly attracted to the odor of the substrate with the 3rd instars removed over the control as well as over the washed larvae (Table 1). Females did not differentiate between the substrate with larvae over the substrate with larvae removed or between just substrate and the washed larvae.

The species preferences of M. raptor further demonstrated this species attraction to host puparia. Muscidifurax raptor females were significantly attracted to odors of the washed puparia over the substrate with larvae, even though the latter contained host habitat substrate (Table 1). However, M. raptor was found to be more attracted to the substrate with the puparia removed over the washed puparia.This species was also attracted to the substrate with puparia over the substrate alone. The latency (time-to-choice) of S. cameroni varied somewhatamong some odor treatments (F = 2.10; df = 9, 90; P = 0.0371) (Table 2); responses were significantly slower to the washed puparia versus the control (mean latency 112.20 sec + 1.09 SE) than to the substrate with larvae versus substrate alone (mean 70.79 + 1.08 sec). There were no significant differences in latency time for M. raptor for any odor treatment.

 There were significant differences found between species in latency time for various odor treatments (Table 3). Overall, S. cameroni had a longer overall mean response time to odors (90.37 + 1.03 sec) than M. raptor (77.09 + 1.04 sec) (t = 3.01; df=1,198; P=0.0030). When analyzed by odor treatment, M. raptor was significantly faster than S. cameroni at responding to the substrate with the puparia against the control (t = 2.41,df = 1,18, P = 0.0132), the washed puparia against the control (t = 2.77; df = 1,18; P = 0.0062), the substrate with the puparia removed against the control (t = 2.41; df = 1,18; P = 0.0294) and the washed larvae against the washed puparia (t = 2.34; df = 1,18; P = 0.00312). All of these quicker responses were with treatment combinations that included an odor source containing puparia, either washed or in the substrate. The anomaly was the latency time in the substrate with larvae against the substrate with puparia where there was no difference between the two species.

Discussion: This study showed that Spalangia cameroni and Muscidifurax raptor, two common and commercially available pupal parasitoids of filth flies, substantially differed in their odor responses to house flies hosts and substrates associated with developing hosts. Though these two species share a similar ecological niche, competition between parasitoids does not mean that coexistence is not possible (Harvey et al. 2008) but may rely on different methods of host-seeking and relatively plastic foraging behavior as observed here (Vet at al. 1993, Wiskerke and Vet 1994, Geervliet et al 1996, Cortesero et al. 1997). Spalangia cameroni was more attracted to odor cues originating from substrate and substrate with interactions with larvae while M. raptor preferred odor cues associated with host puparia.

Spalangia cameroni and M. raptor share many of the same habitat and host preferences; however, differences in life history traits, such as ovarian development and adult dispersal, may allow for temporal and spatial resource partitioning. Spalangia cameroni was very attracted to the odors of substrate and larvae within the substrate. Similar positive responses to larvae in dry cattle manure over manure alone were observed with S. endius (Stafford et al. 1984), though larval concentration was a factor. Spalangia cameroni emerges as an adult with mature eggs and both males and females have demonstrated a quick dispersal instinct in the laboratory, leaving the site of emergence within 3-h (Myint and Walter 1990).  Additionally, S. cameroni is sensitive to host age, preferring to oviposit on young hosts (King 1997). Because they are autogenous, S.cameroni does not need to immediately host-feed and thus locating host puparia to feed before oviposition is not necessary. Females can disperse quickly from emergence sites and seek habitats with developing larvae, ensuring the location of newly pupariated hosts. Spalangia spp. have shown flexibility in locating hosts within development habitats, parasitizing hosts at depths up to 10–cm (Rueda and Axtell 1985). After locating the appropriate habitat, S. cameroni may forage using close-range or contact chemicals to locate hosts, ensuring optimal parasitism of newly formed puparia. 

Unlike S. cameroni, the dispersal behavior of M. raptor after emergence is not known. Preliminary tests from this bioassay suggest that this species requires a short latency period before responding to odor cues, then preferring odors associated with the puparia. The primary attraction to host puparia was observed with another Muscidifurax spp., M. zaraptor Kogan and Legner, by McKay and Broce (2003).  Mucidifurax zaraptor was found to be somewhat repelled by fresh and aged cattle manure alone but strongly attracted to host puparia. Unlike S. cameroni, both M. zaraptor and M.raptor parasitizes older hosts, showing flexibility in offspring production in puparia from 1- to 8-d, in the case of M. zaraptor (Mandeville et al. 1988; King 1997).  Volatiles from host puparia are likely not strong and identifying hosts may be time-consuming. The flexibility to parasitize hosts at a range of development stages may have developed to accommodate the use of very specific cues to locate host puparia. Muscidifurax spp. have been documented to primarily parasitize puparia near the substrate surface (Legner 1977) and will only forage for hosts primarily around 3-cm of the host habitat (Rueda and Axtell 1985). As suggested by McKay and Broce (2003), the odors of habitat may mask the preferred odors of the puparia at greater depths, further separating hosts accessible for Spalangia spp. and Muscidifurax spp. spatially. Opposing strategies for host-seeking would diversify the search for hosts and avoid direct competition between not only the two species observed in this study, but perhaps between the two genera of Spalangia and Muscidifurax.

Both S. cameroni and M. raptor had the strongest cumulative responsesto cues produced either directly or indirectly by the developing hosts. Directly responding to odor cues of host puparia, as found with M. raptor, would provide a reliable indicator of host presence (Vet et al. 1991) but may be more difficult to perceive from a distance. Spalangia cameroni was not attracted to cues produced by washed puparia or washed larvae, but highly attracted to odors from the substrate with larvae. Additionally, this species did not differentiate between the substrate with the larvae and the substrate with the larvae removed further suggesting that the washed larvae were not the source of the attractant, but instead some interaction between the developing larvae and the substrate. Though S. cameroni does not appear to be using odors emitted directly from the host, this speciesmay be using indirect cues from the developing larvae. Kairomones produced by bacteria and fungi have been documented as attractors to several species of parasitoids in various systems (Davis et al. 2013). It is not known if S. cameroni responses were to volatile cues emitted from larval frass or microbial activity associated with fly larvae; however, fungal volatiles were found to play an important role host-location of several species of pteromalids, the stored product pests parasitoid Lariophagus distinguendus Forster and bark beetle parasitoids Rhopalicus pulchripennis (Crawford) and Heydenia unica Cook and Davis. (Steiner et al. 2007; Boone et al. 2008). In the absence of substrate with larvae, S. cameroni was still attracted to substrate alone whereas M. raptor was not, suggesting some odor cue from substrate alone is still favorable over clean air. Spalangia cameroni may be more mobile than M. raptor after dispersing and may be more plastic in odor response.  Interestingly, M. raptor was slightly more attracted to odors of the washed puparia than the puparia with the substrate which suggests that odor cues directly from host puparia are important for attraction for this species.  However, the attraction to the substrate, without puparia over clean air provides some evidence that this species is somewhat attracted to volatiles associated with interactions between the substrate and developing flies or aging substrates.  The behaviors of these parasitoids were observed from a relatively short distance from the odor source and M. raptor may be more sensitive to short-range odors produced by puparia.  Separation of short- and long-range odor attraction may be possible with bioassays conducted at a greater distance. Confirmation and identification of the source of the volatiles, whether from microorganism or development habitat, used in host-location by S. cameroni and M. raptor should could be explored to improve biological control using these parasitoids.

Fly control programs using biological control rely on effective ways to monitor the natural enemies released. Effective monitoring techniques for pteromalid parasitoids could improve biological control programs by identifying endemic species and accurately predicting baseline parasitism. Currently, parasitoid monitoring is conducted using sentinel puparia or wild caught puparia, but bias by genera has been observed with Muscidufrax spp. recovered more frequently from the sentinel puparia and Spalangia spp. more common in the wild caught puparia (Petersen and Watson 1992). The attraction of M. raptor to puparia and substrates with puparia in the laboratory supports these field observations. When laboratory reared puparia are placed in the field, M. raptor likely is capable of using puparial odors to locate them whereas S. cameroni may only parasitize sentinels accidentally, unless they are placed near developing larvae or younger substrates. Though S. cameroni and M. raptor are related species utilizing the same host resource, monitoring techniques should be defined that integrate host puparia and developing larvae in substrate to recover the widest range of parasitoid fauna.

We demonstrated that two pupal parasitoid species coexisting in similar habitats have evolved very different strategies for host-seeking. Our results suggest these parasitoids minimize negative effects of competition by shifting the temporal and/or spatial pattern of resource exploitation (Chesson 2000; Chase and Leibold 2003). The differences between S. cameroni and M. raptor are likely adaptations to avoid competition that may allow each species to exercise host partitioning in ephemeral habitats. Further identification of the source of the volatile cues and isolation of these volatiles could lead to useful monitoring techniques to improve the use of these parasitoids as biological control agents of filth flies on livestock facilities.

Goal (2): Assessment of dispersal to hosts sites from release locations in the field

Objective 3: The results of the dispersal experiment are currently being analyzed. It appears as though S. cameroni females will travel up to 60 m from a release site, though parasitism did decline the farther removed from the release site the bin was. The majority of the recovered parasitoids are S. cameroni, though a few unidentified parasitoids have been found as well.

Goal (3): Outreach and extension activities to increase the operator awareness of biological control of filth flies.

Objective 4: The Extension document detailing the use of biological control agents on horse farms is currently being produced.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Results of the current research have been presented at two professional conferences.

Machtinger, E.T., P.E. Teal, C.J. Geden, N.C. Leppla. 2014. Differential host-seeking cues used by the filth fly parasitoids Spalangia cameroni and Muscidifurax raptor (Hymenoptera: Pteromalidae). Annual meeting of the Southeastern Branch of the Entomological Society of America, Greenville, SC, March 1-5.

Machtinger, E. T., C. J. Geden, P. E. Teal, N. C. Leppla. 2013. Understanding olfactory cues in host location of the filth fly parasitoid Spalangia cameroni (Hymenoptera:Pteromalidae) to improve monitoring and release methods on livestock operations. Annual meeting of the Entomological Society of America, Austin, TX, November 10-13.

It is expected that three manuscripts resulting from this research will be submitted this year.

Submitted to Environmental Entomology (Journal of the Entomological Society of America); Comparison of Host-seeking Strategies Used by the Filth Fly Pupal Parasitoids Spalangia cameroni and Muscidifurax raptor (Hymenoptera: Pteromalidae).

To be submitted to the Florida Entomologist: Linear dispersal of the pupal parasitoid Spalangia cameroni.

To be submitted to the Journal of IPM (Journal of the Entomological Society of America): Use of pupal parasitoids as biological control agents on livestock facilities. 

Project Outcomes

Project outcomes:

Impacts of this research include increasing the effectiveness of the parasitoids, reducing exposure of humans and animals to toxic insecticides, managing insecticide resistance by improving sustainable biological control options and ultimately reducing cost and increasing the use of these parasitoids to manage filth flies. Owners and operators of livestock facilities tend to be good stewards of the land but they need assistance in determining which integrated pest management practices will reduce filth fly numbers under threshold levels while remaining safe and cost effective.

Economic Analysis

No economic analysis was done for this study.

Farmer Adoption

This project did not directly involve farmer partners for on-farm research or aim to immediately initiate adoption of chemical cues as a management practice. However,  results concerning the use of biological control agents of filth flies have been communicated to horse owners through a presentation at the health horses conference at the University of Florida and will continue to be distributed through Extension material.

Recommendations:

Areas needing additional study

Additional research using various livestock waste in the bioassay could further our knowledge on the chemical cues used by these parasitoids to identify host material. Identification of the volatile cue associated with host habitat location is currently being researched for Spalangia cameroni, but this research could continue for several other species of different genera that are currently sold as biological control agents of filth flies on equine farms.
Dispersal of parasitoids still needs attention for many situations on various livestock facilities. Dispersal from release points likely differs based on the surrounding landscape and environmental effects. All of these factors should be analyzed to improve release strategies of pupal parasitoids as biological control agents of filth flies on livestock facilities. 

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.