Competition between the filth fly parasitoids Muscidifurax raptor and M. raptorellus (Hymenoptera: Pteromalidae)

Authors: Geden, Christopher - Chris; Johnson, Dana; KAUFMAN, P - University Of Florida; BOOHENE, C - Polk County Mosquito Control

Submitted to: Journal of Vector Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2014
Publication Date: 12/1/2014
Citation: Geden, C.J., Johnson, D.M., Kaufman, P.E., Boohene, C.K. 2014. Competition between the filth fly parasitoids Muscidifurax raptor and M. raptorellus (Hymenoptera: Pteromalidae). Journal of Vector Ecology. 39(2):278-287.

Interpretive Summary: House flies (Musca domestica L.) and stable flies (Stomoxys calcitrans (L.)) (Diptera: Muscidae) are among the most important pests of animal agriculture globally. Economic losses due to these pests in the U.S. are estimated at $375 million and $2.2 billion for house flies and stable flies, respectively (Geden and Hogsette 2001, Taylor et al., 2012). House flies are mechanical vectors of animal and human disease organisms and have provoked legal disputes between livestock producers and neighbors(Malik et al. 2007). Stable fly biting pressure on livestock results in direct production losses in the form of reduced weight gain and milk production (reviewed in Taylor et al. 2012). Effective fly management requires integration of santation, biological control, and selective use of insecticides. Insecticidal control of house flies is problematic because of the rapidity with which insecticide resistance develops, even to new products that are thought to have novel modes of action (Malik et al. 2007, Kaufman et al. 2010). Successful fly management using augmentative releases of pupal parasitoids was first demonstrated by Morgan et al. (1975). During the ensuing forty years, a vast literature on filth fly biological control has developed and many parasitoid products are commercially available. Despite the progress that has been made, it remains uncertain about which species are most effective in augmentative release programs. Spalangia spp. are valued for their ability to locate buried pupae (Geden 2002, Skovgård and Nachman 2004) and solitary Muscidifurax spp. (M. raptor and M. zaraptor) for their high attack rates and ease/economy of production (Rutz and Axtell 1981, Petersen et al. 1992). Since the 1990 discovery of the gregarious South American parasitoid M. raptorellus in the Midwestern US, this species has received considerable attention (Petersen and Currey 1996, Kaufman et al. 2012) and become one of the prominent products carried by most commercial producers of filth fly parasitoids. There has been a trend in the past 20 years away from single-species releases and towards species mixes for fly management in both the commercial and research community. In some cases, combinations of a Spalangia and Muscidifurax species have been used in the hope of exploiting between-genera niche differences to broaden the reach of the releases into a wider habitat range (Weinzierl and Jones 1998, Geden and Hogsette 2006). In others, combinations of solitary Muscidifurax species (M. raptor and M. zaraptor Kogan and Legner) and M. raptorellus have been used because of the cost-effectiveness that the latter offers (Kaufman et al. 2002, 2012). Competitive interactions between Spalangia spp. and solitary Muscidifurax are well understood, as are the life history strategies used by the parasitoids to avoid and resolve multiparasitism events (Wylie 1971, 1972, Ables and Shepard 1974, Propp and Morgan 1983, King 1997). In contrast, to our knowledge nothing is known about such interactions within the genus Muscidifurax. Perhaps one reason for this has been the difficulty in identifying the three North American species using morphological characters (Kogan and Legner 1970). A red-eyed mutant strain of M. raptor became available to us when one of the authors (CKB) noted and selected for this trait in a Florida strain maintained at the USDA-ARS, Center for Medical, Agriculture and Veterinary Entomology (CMAVE). The availability of the mutant strain raised the possibility of examining competitive interactions between M. raptor and M. raptorellus. Assays were conducted to examine competitiion under conditions in which either the order of parasitism by each species varied (sequential parasitism) or using varying ratios of the species added at the same time.

Technical Abstract: Competition bioassays were conducted with the filth fly pupal parasitoids Muscidurax raptor (Girault & Sanders) and M. raptorellus (Kogan & Legner) (Hymenoptera: Pteromalidae) with house fly Musca domestica L. (Diptera: Muscidae) hosts at different host densities. Assays were conducted by varying either the time sequence of oviposition by the two species (sequential parasitism) or the proportions of ovipositing females. A red-eyed mutant strain of M. raptor was used to facilitate species identification. Muscidifurax raptor had a significant impact on M. raptorellus when hosts were limiting in sequential parasitism tests. Fewer than 6 M. raptorellus adult progeny emerged from groups of 50 fly pupae that were parasitized at the same time or when M. raptor parasitism preceded M. raptorellus by 48 hr, respectively, compared with 42-55 M. raptorellus progeny produced when this species was tested alone. Intermediate progeny production occurred when parasitism by M. raptorellus preceded M. raptor. Production of M. raptor was significantly lower when parasitism by this species was preceded by M. raptorellus (25) than when M. raptor was tested alone (43). When the two species parasitized hosts at the same time in different proportions at low host:parasitoid densities (5:1), M. raptorellus produced 13 progeny per parent female when it was the sole species present and <2 in any of the treatments where M. raptor was present. No negative impact of M. raptorellus on M. raptor was observed in any of the species ratios tested. At the higher host:parasitoid densities of 20:1 and 40:1, neither species had a substantial effect on the success of the other. Muscidifurax raptorellus produced more progeny per parasitoid per parasitized pupa at low host:parasitoid ratios than when more hosts were available.