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1 June 2017 Effect of Host Decoys on the Ability of the Parasitoids Muscidifurax raptor and Spalangia cameroni (Hymenoptera: Pteromalidae) to Parasitize House Fly (Diptera: Muscidae) Puparia
Dana M. Johnson, Emily K. Rizzo, Caitlin Taylor, Christopher J. Geden
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Abstract

The pteromalid pupal parasitoids Muscidifurax raptor Girault & Sanders and Spalangia cameroni Perkins (Hymenoptera: Pteromalidae) are commonly released on livestock farms for management of house flies, Musca domestica L. (Diptera: Muscidae). To be effective, parasitoids must be able to locate live host puparia in complex environments that may include dead or formerly parasitized hosts and non-host physical objects. In this study, both species of parasitoids were examined for their ability to kill and parasitize live house fly puparia either alone or in mixtures with formerly parasitized (dead) hosts or similarly sized acrylic beads. Muscidifurax raptor killed significantly fewer hosts and produced fewer progeny when the parasitoids were provided with hosts that were mixed with formerly parasitized puparia. Spalangia cameroni was unaffected by the presence of formerly parasitized puparia for any of the measured variables. When beads were used as a decoy instead of formerly parasitized puparia, high bead-to-live-host ratios (90% decoys) resulted in significantly fewer numbers of hosts killed by M. raptor compared with the other treatments (50% and no decoys). Residual host mortality at the high bead-to-live-host ratio (90% decoys) was lower (31.2%) than in ratios of 50:50 and with no decoys (51.6 and 59.3%, respectively), so that progeny production by M. raptor was unaffected by the presence of beads. Spalangia cameroni killed over twice as many hosts and produced twice as many progeny in the absence of bead decoys than when beads made up 90% of the decoy—host mixture. The results support the scatter method for deploying parasitized puparia during releases, because the presence of formerly parasitized hosts did not interfere substantially with the ability of S. cameroni and M. raptor to locate and parasitize live pupae.

House flies (Musca domestica L.; Diptera: Muscidae) are worldwide pests that are an agricultural nuisance and a major public health concern. These flies have the ability to mechanically vector a wide variety of pathogenic microorganisms to humans and livestock and may have a role in the dispersal of antibiotic-resistant bacteria (Graczyk et al. 2001; Zurek & Ghosh 2014). There is critical need for house fly management tools because of increasing resistance to conventional insecticides (Malik et al. 2007; Scott et al. 2013). Pteromalid pupal parasitoids provide one of the most common and readily available biological controls for fly management (Machtinger & Geden 2017). Commercial insectaries rear and sell a variety of species, including Muscidifurax raptor Girault & Sanders and Splangia cameroni Perkins (Hymenoptera: Pteromalidae). Although releases of these species have proven effective as part of integrated pest management programs in a variety of production systems (Geden et al. 1992; Geden & Hogsette 2006; Birkemoe et al. 2009), questions remain about the numbers of parasitoids needed to provide satisfactory management and the best methods to deploy parasitized hosts in the field.

Parasitoids can be released by either scattering parasitized puparia in areas of known fly breeding (Rutz & Axtell 1981; Kaufman et al. 2002, 2012; Skovgård 2004) or by placing them in release stations that protect them from damage and accidental removal (Geden et al. 1992; Petersen et al. 1995; Crespo et al. 1998; Weinzierl & Jones 1998; Floate 2003; Skovgård & Nachman 2004; Geden & Hogsette 2006). Although release stations provide protection, scattering has the advantage of placing the parasitoids near the target fly puparia and mitigates concerns about the limited dispersal distances of some species (Tobin & Pitts 1999; Skovgård 2002; Machtinger et al. 2015). However, the scatter method results in an accumulation of formerly parasitized puparia in the habitat that must be searched through and avoided by parasitoids. Such accumulations may or may not impose increased handling time constraints on the parasitoids as they locate, inspect, and then reject unusable candidate hosts (Hubbard & Cook 1978; Waage 1979; Van Alphen & Galis 1983). The objective of the present study was to evaluate the effect of the presence of formerly parasitized hosts on M. raptor and S. cameroni parasitism of house fly puparia. We also examined whether the presence of an equivalent volume of inanimate objects roughly similar in size and shape to house fly puparia would affect the searching efficiency of both species.

Materials and Methods

INSECTS USED IN BIOASSAY

Spalangia cameroni and M. raptor females were from colonies maintained at the United States Department of Agriculture Agricultural Research Service (USDA-ARS) Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Florida. The original source material for both colonies was collected from a dairy farm in Gilchrist County, Florida. All tests with S. cameroni and the M. raptor tests involving previously parasitized puparia were conducted with colonies established in 2012. During the hiatus between tests with formerly parasitized puparia and bead decoys, the M. raptor colony developed Nosema disease and was no longer suitable for use in bioaasays, so another colony was used that had been col