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2002

Effect of Habitat Depth on Host Location by Five Species of Parasitoids (: , Chalcididae) of House (Diptera: Muscidae) in Three Types of Substrates

Christopher Geden USDA-ARS, [email protected]

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Geden, Christopher, "Effect of Habitat Depth on Host Location by Five Species of Parasitoids (Hymenoptera: Pteromalidae, Chalcididae) of House Flies (Diptera: Muscidae) in Three Types of Substrates" (2002). Publications from USDA-ARS / UNL Faculty. 982. https://digitalcommons.unl.edu/usdaarsfacpub/982

This Article is brought to you for free and open access by the U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Publications from USDA-ARS / UNL Faculty by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. BIOLOGICAL CONTROL Effect of Habitat Depth on Host Location by Five Species of Parasitoids (Hymenoptera: Pteromalidae, Chalcididae) of House Flies (Diptera: Muscidae) in Three Types of Substrates

CHRISTOPHER J. GEDEN1

Center for Medical, Agricultural and Veterinary Entomology, USDAÐARS, P.O. Box 14565, Gainesville, FL 32604

Environ. Entomol. 31(2): 411Ð417 (2002) ABSTRACT Four species of pteromalid parasitoids [ raptor Girault & Sanders, Spal- angia cameroni Perkins, Spalangia endius Walker, Spalangia gemina Boucek, and the chalcidid Dirhinus himalayanus (Masi)] were evaluated for their ability to locate house ßy pupae at various depths in poultry manure (41% moisture), ßy rearing medium (43% moisture), and sandy soil (4% moisture) from a dairy farm. Searching activity in manure was largely conÞned to the surface (M. raptor, D. himalayanus, and S. gemina) or to depths of up to 2 cm below the surface (S. endius, S. cameroni). S. cameroni was the most effective species at locating buried pupae in manure. All of the species searched over a wider range of habitat depths in ßy rearing medium, although M. raptor and S. gemina tended to concentrate their searching activity relatively close to the surface of the substrate. Host attacks by these species at 6 cm were 30Ð40% lower than on the surface of the medium. S. endius searched uniformly at all depths in rearing medium and S. cameroni had highest rates of host attacks 1Ð2 cm below the surface of this substrate. The parasitoids displayed considerable Þdelity to their search patterns regardless of whether or not they were given a choice of habitat depths in which they could Þnd pupae. None of the parasitoids were effective at attacking ßy pupae that were buried in sandy soil at any depth. The results suggest that ßy larvae that pupate in the sandy soils typical of FloridaÕs coastal plains are relatively impervious to attack by pupal parasitoids.

KEY WORDS Musca domestica, Muscidifurax raptor, Spalangia gemina, Spalangia cameroni, Spal- angia endius, Dihrinus himalayanus

PUPAL PARASITOIDS IN the family Pteromalidae are im- sitoids. Field studies have shown that parasitism rates portant natural enemies of muscoid ßies on livestock vary in different ßy breeding habitats (Petersen and and poultry farms throughout the world (Rutz and Meyer 1983; Rueda and Axtell 1985a; Smith and Rutz Patterson 1990). Augmentative releases of parasitoids, 1991c, 1991d), and substrate moisture and light levels especially in the genera Muscidifurax and Spalangia, can affect the microhabitat choices made by different can be an effective house ßy management tool when species of parasitoids (Smith and Rutz 1991a, Geden used in integrated management programs (Rutz and 1999). The depth at which parasitoids concentrate Axtell 1979, Cabrales et al. 1985, Morgan and Patterson their search effort is an another important ecological 1990, Geden et al. 1992, Petersen et al. 1992, Petersen characteristic that may vary among parasitoid species. and Cawthra 1995, Crespo et al. 1998). In some cases, Legner (1977) examined the depth at which eight disappointing results with parasitoid releases have parasitoid strains foraged in wheat ßakes in small vials been attributed to selection of appropriate species for and concluded that Muscidifurax uniraptor and M. the target ßy habitat (Rutz and Axtell 1980, Petersen zaraptor concentrated their efforts near the substrate et al. 1983). Surveillance to determine the most im- surface, whereas Spalangia spp. (S. endius, S. nigra, S. portant local species can be conducted to guide the cameroni, S. longepetiolata) were more effective at selection process, but this is labor-intensive and can locating buried hosts. He also noted that the search give different results in different years (Smith and patterns of some species were affected by the moisture Rutz 1991b, Jones and Weinzierl 1997). A better un- levels of the substrate. For example, the Muscidifurax derstanding of parasitoid niche characteristics could spp. and Sphegigaster sp. were more successful in pen- be helpful for matching appropriate parasitoid species etrating dryer than wetter media to locate buried host to different ßy breeding habitats. pupae, whereas the Spalangia spp. search patterns Little is known about the effect of microhabitat were similar at different moisture levels (Legner characteristics on foraging behavior of Þlth ßy para- 1977). Although these tests provided useful compar- isons of different species searching behavior, their 1 E-mail: [email protected]ß.edu. utility for predicting behavior in the Þeld was limited 412 ENVIRONMENTAL ENTOMOLOGY Vol. 31, no. 2 because of the type of substrate used (clean wheat of the fresh manure was 74%, pans of manure were ßakes) and because the parasitoids were restricted to partially dried in an oven at 45ЊC to achieve a moisture single burial treatments in the bioassays. King (1997) level of 41%. Moisture determinations of Þeld-col- reported that S. cameroni was more effective than M. lected manure had indicated that this moisture level raptor at locating buried host pupae in used ßy rearing was similar to that of the dry manure on the manure medium. row margins in the Þeld where naturally occurring ßy Rueda and Axtell (1985b) conducted extensive Þeld pupae were present in greatest abundance (unpub- sampling in two types of poultry houses to examine the lished data). relative abundance of parasitized pupae of six parasi- The second substrate was house ßy larval rearing toid species at various depths in poultry manure. Most medium (Hogsette 1992) that had been used for rear- (Ͼ95%) of the pupae parasitized by M. raptor, M. ing ßy immatures to the pupal stage. The resulting zaraptor, and Pachycrepoideus vindemmiae were found “spent” medium (moisture content, 39%) was frozen within the top 3 cm of the manure surface, whereas within1hofseparation of ßy pupae and frozen in pupae parasitized by S. cameroni, S. endius, and S. airtight plastic containers for up to 2 mo before testing. nigroaenea were most often collected 3Ð10 cm beneath The third substrate was sandy loam soil (moisture the surface. content, 4%) collected from under calf bedding at a In an effort to increase the efÞcacy of Þlth ßy bio- dairy farm in Bell, FL, with a history of high ßy pop- control, we have been evaluating exotic parasitoids as ulations. The soil was sifted to remove any ßy pupae candidates for possible importation and release, espe- present and frozen for up to 2 mo before being used cially in the southern United States. These exotics in the tests. include two pupal parasitoids: Spalangia gemina Bioassays. Two types of bioassays were conducted Boucek, a tropical pteromalid species collected in Bra- to determine the ability of parasitoids to locate pupae zil, and a Moroccan isolate of the chalcidid Dirhinus at different substrate depths under choice and no- himalayanus (Masi). This evaluation has included choice situations. In the Þrst type of bioassay (no- comparisons of temperature-dependent development choice situation), 1- to 2-d-old live ßy pupae were rates, rates of host attacks and fecundity, and the effect placed in small Þberglass screen bags (50 pupae per of habitat (poultry manure) moisture on host location bag) in each of the three substrates at either 0 (on the (Geden 1996, 1997, 1999). The objectives of the cur- surface), 1, 2, 4, or 6 cm from the top of the substrate rent study were to address the following questions in 350-ml plastic cups with screen lids. The height of about host-location behavior in relation to habitat the substrate column was held constant at 7 cm (ßush depth: (1) How do the exotic species D. himalayanus with the top of the assay cup) for all burial treatments. and S. gemina compare with the native species Musi- Five female parasitoids (2Ð4 d old) were introduced cidifurax raptor, S. cameroni, and S. endius, with re- into each cup and the cups were covered with spect to locating pupae at different habitat depths? (2) screened lids and held at 27ЊC, 70Ð85% RH, under Does the type of substrate (poultry manure, soil, or ßy constant light (3 cups per depth per substrate). Pupae rearing medium) affect parasitoid searching behavior? were removed from the cups after 24 h, separated from (3) Do parasitoids adjust their searching strategy any parasitoids present, and transferred to 30-cm3 when given a choice of depths at which hosts are cups with snap-on screen lids for ßy and parasitoid present? emergence. Control ßy emergence was assessed by placing ßy pupae in cups without parasitoids at depths of either 0 or 6 cm from the substrate surface (3 cups Materials and Methods each) per test date. The purpose of this bioassay was Parasitoid Colonies. Five species of pteromalid to assess host location and parasitism by parasitoids parasitoids were tested. Muscidifurax raptor Girault & when they were presented with pupae buried at a Sanders and Spalangia cameroni Perkins were from a single depth in each substrate. colony established in 1992 from a poultry farm in In the second type of bioassay (choice assays), ßy Brooksville, FL. The Spalangia endius Walker colony pupae were Þrst placed in the substrates at different was established in 1994 from a poultry farm in Zephyr depths as before (3 cups per depth), and the cups were Hills, FL; Spalangia gemina Boucek was originally col- placed in an array in a Plexiglas box (one type of lected from a poultry farm near Sao Paulo, Brazil, in substrate per box) measuring 55 cm long by 25 cm high 1991. Dhirinus himalayanus (Masi) was collected from by 37 cm wide. The substrate cups were arranged in house ßy pupae in Morocco in 1990. Parasitoids were three rows of 5, with each pupal depth treatment maintained on Ϸ1- to 2-d-old house ßy puparia in represented randomly in each row. Seventy-Þve fe- rearing rooms maintained at 27ЊC, 70Ð80% RH, under male parasitoids (2Ð4 d old) were released in the box constant light conditions. by placing them in an open 30-ml glass vial placed on Substrates. Three substrates were used in the tests. a platform suspended from the ceiling of the box 15 cm Poultry manure for the bioassays was collected by above the cup array. In this way, the host:parasitoid placing Plexiglas panels on the surface of the manure ratio used in the choice bioassays tests (75 females rows in a high-rise caged layer house in Brooksville, with 750 pupae) was the same as that used in the FL. Fresh manure accumulating on the panels was no-choice assays (5 females with 50 pupae). Pupae collected after 24 h and frozen to kill any were removed from the cups and transferred to 30 cm3 present. After determining that the moisture content cups after 24 h of exposure to the parasitoids as before. April 2002 GEDEN:HABITAT DEPTH AND HOST LOCATION BY FILTH PARASIOTIDS 413

Controls were handled as in the no-choice assays by Table 1. Rates of host attacks and progeny production by placing pupae at either 0- or 6-cm depths in the sub- Dirhinus himalayanus when house fly pupae were placed at different depths in poultry manure, fly larval rearing medium, and soil strates in the absence of parasitoids. These assays were conducted to evaluate the ability of the parasitoids to Parasitoids not Parasitoids given locate pupae presented simultaneously at a variety of given a choice of a choice of Depth, habitat depths habitat depths substrate depths. Habitat The entire experiment was replicated twice for each cm No. No. No. No. pupae parasitoids pupae parasitoids substrate, species of parasitoid, and type of bioassay a b (choice versus no-choice). Choice and no-choice tests killed produced killed produced for a given substrate and species were conducted on Manure 0 29.5 (3.4) 18.7 (2.8) 35.3 (3.5) 21.3 (3.7) the same days to facilitate evaluation of the effect of 1 21.3 (2.9) 9.5 (2.6) 2.9 (2.0) 0.7 (0.5) 2 8.5 (3.6) 1.8 (1.1) 6.0 (3.0) 2.0 (2.0) parasitoid choice on foraging behavior. Data on num- 4 6.0 (4.0) 3.0 (2.2) 2.4 (0.7) 0.2 (0.2) bers of attacked pupae (pupae that did not produce 6 8.4 (3.2) 4.3 (1.9) 5.8 (5.3) 3.7 (1.7) ßies) and progeny production were analyzed by sep- Medium 0 23.2 (2.0) 13.8 (1.7) 28.4 (4.1) 20.8 (4.0) arate analysis of variance (ANOVA) for each substrate 1 22.6 (2.3) 15.7 (1.3) 25.4 (4.5) 17.5 (3.7) 2 19.9 (4.4) 12.8 (3.0) 15.9 (4.6) 10.2 (3.2) and parasitoid species using depth, choice and 4 19.4 (4.9) 11.3 (2.7) 14.0 (4.5) 9.2 (3.6) depth ϫ choice as model effects using the general 6 17.3 (2.2) 11.2 (1.5) 19.5 (4.5) 10.7 (2.9) linear models procedure of the Statistical Analysis Soil 0 18.4 (2.7) 13.8 (2.7) 21.8 (2.8) 12.8 (2.4) System (SAS Institute 1987). Data were normalized 1 0.9 (0.5) 0.2 (0.2) 0.9 (0.8) 0.2 (0.2) 2 1.0 (0.3) 0.2 (0.2) 1.0 (0.5) 0.0 (0.0) before ANOVA by a square-root transformation 4 0.9 (0.6) 0.0 (0.0) 1.1 (0.6) 0.0 (0.0) (Sokal and Rohlf 1981), but untransformed values 6 0.2 (0.1) 0.0 (0.0) 0.0 (0.0) 0.0 (0.0) were used to present results in tables. Control mor- tality, which averaged 3Ð16%, was used to calculate a Mean (ϮSE) number uneclosed pupae per assay cup of 50 pupae. b Mean (ϮSE) number parasitoid progeny produced per assay cup corrected percent host mortality (Abbott 1925) for of 50 pupae. presentation of data in tables but not used in con- ducting the ANOVAs. No signiÞcant differences in control mortality were observed between the 0 and 6 the surface (signiÞcant depth ϫ choice interaction, cm pupal burial treatments, and pooled control mor- Table 2). Small numbers of hosts were attacked and tality from the two burial treatments was used in the parasitized at depths greater than 1 cm in this sub- calculation of corrected mortality. strate. In ßy rearing medium, M. raptor was most ef- fective at locating pupae near the surface (36Ð48 pupae attacked in the top 1 cm) under both choice and Results no-choice conditions, but substantial numbers of pu- Dirhinus himalayanus attacked (killed) 30Ð35 of the pae were killed in this substrate even at the maximum pupae placed on the surface of poultry manure and depth of 6 cm. Attack rates at 6 cm were about half of produced 19Ð21 progeny per set of 50 host pupae those observed on the surface of the medium. There regardless of whether other burial depth treatments was no signiÞcant change in M. raptors foraging be- were present (Table 1). Host attacks and parasitism by havior in rearing medium when the parasitoids were this species in manure was lower among pupae buried given a range of burial treatments (nonsigniÞcant F for 1 cm below the surface compared with the surface choice, Table 2). Rates of host attack and parasitism on pupae, but the decline was stronger when parasitoids the surface of soil was similar to surface attack/para- were given a choice of burial treatments from which sitism rates in the other substrates, but essentially to select (signiÞcant depth ϫ choice ANOVA term, none of the buried pupae were attacked at (Table 3). Table 2). Host attacks (2Ð9 pupae killed) and progeny Spalangia cameroni was most effective at locating production (0.2Ð6.0 progeny) were low at depths of host pupae in the top 2 cm of poultry manure under greater than 1 cm in manure. In ßy larval rearing both choice and no-choice test conditions (Table 4), medium, host attacks (14Ð28) and parasitism (9Ð21) and the highest rates of host attacks (40Ð48 pupae were more evenly distributed across depths, but there killed) and progeny production (26Ð30 progeny pro- was still a tendency for somewhat higher activity at duced) were observed among pupae located on the shallower pupal depths (signiÞcant only for progeny manure surface. In ßy larval rearing medium this spe- production, Table 2). In soil, nearly all of the activity cies foraged more uniformly throughout the substrate was restricted to pupae placed directly on the surface column and easily located pupae buried 6 cm beneath regardless of the choice treatment. the surface compared with manure and soil. Highest In no-choice bioassays with manure, females of M. rates of host attacks were observed among pupae bur- raptor were only effective at locating hosts that were ied either 1 cm (37.4 pupae killed in choice assays) or present on the surface (47.0 pupae killed, 35 progeny 2 cm (35.2 pupae killed in no-choice assays) beneath produced), with negligible rates of host attacks and the medium surface. Host location in sandy soil was progeny produced at greater depths (Table 3). Fe- restricted to pupae that were placed on the surface. males that were presented with a range of burial treat- Spalangia endius had highest rates of host location ments located nearly all of the pupae on the manure (30Ð46 pupae killed, 12Ð26 progeny produced) in surface but also killed (22.4 attacks) and parasitized manure when pupae were either located on the ma- (15.7 progeny) substantial numbers at 1 cm beneath nure surface or at a depth of 1 cm (Table 5), and 414 ENVIRONMENTAL ENTOMOLOGY Vol. 31, no. 2

Table 2. ANOVAs for effects of habitat depth and whether parasitoids were given a choice of habitat depths on rates of host attacks and progeny production by five species of pteromalids

ANOVA F for host attacks ANOVA F for progeny production Species and Substrate Deptha Choiceb Depth X Choicec Depth Choice Depth X Choice D. himalayanus manure 23.25** 4.06* 3.43* 21.4** 1.64NS 1.71NS medium 2.07NS 0.10NS 0.68NS 2.66* 0.14NS 0.91NS soil 87.3** 0.66NS 0.71NS 55.3** 0.11NS 0.07NS M. raptor manure 119.25** 12.93** 5.80** 98.04** 8.09** 4.94** medium 9.29** 1.97NS 0.40NS 8.52** 1.51NS 1.63NS soil 2655.44** 0.04NS 0.72NS 843.83** 1.01NS 0.73NS S. cameroni manure 78.73** 1.08NS 2.72NS 80.85** 1.34NS 1.74NS medium 3.48* 0.72NS 2.43NS 3.41* 0.25NS 2.53NS soil 755.71** 0.02NS 0.16NS 177.2** 1.24NS 1.13NS S. endius manure 70.44** 0.03NS 0.10NS 95.38** 0.15NS 1.56NS medium 5.28** 20.70** 1.91NS 8.38** 5.86* 1.77NS soil 86.45** 5.45* 1.74NS 107.99** 17.41** 1.52NS S. gemina manure 98.82** 0.61NS 0.70NS 71.93** 2.22NS 2.07NS medium 5.14** 0.02NS 0.34NS 4.85** 1.08NS 1.11NS soil 95.82** 3.75NS 2.11NS 113.42** 4.11* 2.93**

a Pupae buried 0, 1, 2, 4, or 6 cm beneath substrate surface (d ϭ 4, 50). b Choice versus no-choice bioassays (df ϭ 1, 50). c d ϭ 1, 50. responses were similar under both choice and no- no-choice test conditions (Table 6). In rearing me- choice test conditions (Table 2). In ßy larval rearing dium this species foraged throughout the substrate but medium this species foraged throughout the substrate resembled M. raptor and D. himalayanus by being but had signiÞcantly (Table 2) higher attack and par- more active closer to the surface than at greater depths asitism rates at greater depths than near the surface of in this substrate. Activity in soil was restricted to pupae this substrate. Activity in soil was restricted to pupae that were placed on the surface. that were placed on the surface. Spalangia geminaÕs search pattern in manure resem- bled that of S. cameroni, with most activity observed in Discussion the top 2 cm of the manure under both choice and Previous studies have indicated that Muscidifurax spp. tend to be superÞcial searchers that locate pupae Table 3. Rates of host attacks and progeny production by Muscidifurax raptor when house fly pupae were placed at different near the surface of test substrates, whereas Spalangia depths in poultry manure, fly larval rearing medium, and soil spp. have a tendency to search at greater depths (Leg- ner 1977, Rueda and Axtell 1985b, King 1997). Results Parasitoids not given Parasitoids given presented here support those generalizations to a de- a choice of a choice of gree, but the physical properties of various substrates Depth, habitat depths habitat depths Habitat clearly impose limits on the parasitoidsÕ innate pref- cm No. No. No. No. pupae parasitoids pupae parasitoids erences. In the most challenging substrate, sandy loam killeda producedb killed produced soil, none of the parasitoids were effective at locating pupae that were buried even by a very thin (1 cm) Manure 0 47.0 (2.2) 35.0 (1.3) 49.1 (0.6) 35.0 (1.4) 1 1.1 (0.5) 0.0 (0.0) 22.4 (6.5) 15.7 (5.7) layer of the substrate. In poultry manure we found that 2 0.5 (0.4) 0.0 (0.0) 5.0 (4.3) 2.7 (2.7) all of the species tested were primarily superÞcial or 4 0.8 (0.6) 0.0 (0.0) 0.7 (0.7) 0.2 (0.2) subsurface foragers. Although the manure in these 6 1.8 (0.8) 0.0 (0.0) 3.3 (1.4) 0.7 (0.7) tests had been dried to 43% moisture, it may have had Medium 0 48.1 (1.2) 37.7 (1.6) 47.1 (2.6) 41.3 (2.5) 1 44.2 (1.9) 36.2 (3.1) 36.1 (5.2) 27.0 (5.8) other physical characteristics (e.g., particle size) that 2 38.3 (3.6) 31.2 (2.8) 35.8 (3.2) 26.8 (3.0) inhibited parasitoids from penetrating more than a few 4 32.5 (4.9) 24.2 (4.5) 32.8 (4.8) 29.0 (5.1) cm below the surface. Under Þeld conditions, species 6 27.2 (5.6) 22.5 (5.1) 20.1 (5.4) 12.5 (2.9) that prefer to forage at greater depths may be limited Soil 0 48.8 (0.6) 39.7 (2.2) 49.2 (0.4) 37.3 (1.5) 1 0.3 (0.3) 0.2 (0.2) 0.9 (0.7) 0.0 (0.0) to surface regions in dense substrates such as soil, 2 0.0 (0.0) 0.0 (0.0) 0.3 (0.2) 0.0 (0.0) compacted silage or wet manure. It is also possible that 4 0.2 (0.2) 0.2 (0.2) 0.7 (0.7) 0.0 (0.0) naturally occurring pupae below the surface are easier 6 1.5 (1.3) 0.0 (0.0) 0.3 (0.2) 0.0 (0.0) for parasitoids to locate than our experimentally a Mean (ϮSE) number uneclosed pupae per assay cup of 50 pupae. placed pupae because of semiochemical trails and b Mean (ϮSE) number parasitoid progeny produced per assay cup break points in the substrates that may be left by the of 50 pupae. larvae before pupation. April 2002 GEDEN:HABITAT DEPTH AND HOST LOCATION BY FILTH FLY PARASIOTIDS 415

Table 4. Rates of host attacks and progeny production by Table 6. Rates of host attacks and progeny production by Spalangia cameroni when house fly pupae were placed at different Spalangia gemina when house fly pupae were placed at different depths in poultry manure, fly larval rearing medium, and soil depths in poultry manure, fly larval rearing medium, and soil

Parasitoids not given Parasitoids given Parasitoids not given Parasitoids given a choice of a choice of a choice of a choice of Depth, habitat depths habitat depths Depth, habitat depths habitat depths Habitat Habitat cm No. No. No. No. cm No. No. No. No. pupae parasitoids pupae parasitoids pupae parasitoids pupae parasitoids killeda producedb killed produced killeda producedb killed produced Manure 0 40.1 (2.3) 26.0 (1.0) 48.4 (0.3) 30.3 (1.4) Manure 0 45.0 (1.3) 28.7 (2.3) 47.7 (1.0) 25.0 (3.0) 1 18.2 (2.3) 11.2 (1.1) 27.3 (6.6) 16.0 (3.8) 1 11.8 (4.3) 3.7 (1.2) 17.3 (6.0) 6.5 (2.7) 2 15.7 (3.7) 7.8 (2.5) 9.2 (3.3) 4.3 (2.6) 2 7.3 (2.7) 1.7 (0.8) 4.2 (2.2) 0.0 (0.0) 4 1.9 (1.1) 0.0 (0.0) 1.4 (0.9) 0.8 (0.8) 4 0.9 (0.4) 0.2 (0.2) 1.2 (0.6) 0.0 (0.0) 6 1.4 (0.3) 0.7 (0.7) 0.4 (0.2) 0.8 (0.8) 6 1.2 (0.4) 0.0 (0.0) 2.4 (1.1) 0.0 (0.0) Medium 0 20.8 (1.1) 12.7 (1.1) 29.0 (4.1) 17.0 (1.6) Medium 0 46.6 (1.5) 33.5 (3.7) 46.7 (1.2) 39.2 (2.6) 1 33.2 (3.1) 18.8 (2.3) 37.4 (1.8) 23.3 (1.4) 1 36.3 (4.4) 26.3 (3.6) 39.4 (4.0) 31.5 (3.5) 2 35.2 (2.6) 21.8 (1.9) 27.0 (5.4) 15.2 (3.1) 2 31.6 (5.8) 24.2 (5.0) 24.2 (5.4) 15.2 (4.3) 4 30.5 (4.0) 16.3 (2.7) 17.6 (5.1) 10.0 (2.4) 4 29.3 (5.8) 17.3 (4.9) 29.2 (5.6) 18.5 (5.0) 6 24.5 (2.8) 15.0 (2.2) 22.7 (6.1) 15.3 (4.2) 6 29.0 (6.5) 18.8 (5.0) 30.7 (6.1) 24.6 (6.4) Soil 0 45.1 (2.0) 30.2 (2.5) 45.7 (2.5) 25.7 (3.4) Soil 0 23.1 (4.2) 19.5 (3.6) 31.2 (2.5) 27.2 (2.2) 1 0.6 (0.5) 0.2 (0.2) 0.1 (0.1) 0.0 (0.0) 1 0.3 (0.3) 0.0 (0.0) 1.9 (1.9) 1.2 (1.2) 2 0.0 (0.0) 0.0 (0.0) 0.4 (0.3) 0.0 (0.0) 2 0.3 (0.2) 0.0 (0.0) 2.0 (0.9) 0.0 (0.0) 4 0.3 (0.2) 0.0 (0.0) 0.0 (0.0) 0.0 (0.0) 4 1.0 (0.5) 0.0 (0.0) 0.7 (0.3) 0.0 (0.0) 6 0.8 (0.4) 0.0 (0.0) 0.0 (0.0) 0.0 (0.0) 6 0.8 (0.4) 0.0 (0.0) 0.1 (0.1) 0.0 (0.0)

a Mean (ϮSE) number uneclosed pupae per assay cup of 50 pupae. a Mean (ϮSE) number uneclosed pupae per assay cup of 50 pupae. b Mean (ϮSE) number parasitoid progeny produced per assay cup b Mean (ϮSE) number parasitoid progeny produced per assay cup of 50 pupae. of 50 pupae.

The results with rearing medium were similar to were observed by Rueda and Axtell (1985). The latter those of Rueda and Axtell (1985b) for the three spe- authors hypothesized that the Spalangia spp. may seek cies that the two studies had in common; M. raptor, S. pupae at greater depths to avoid superparasitism en- endius, and S. cameroni. M. raptor foraged to depths of counters with Muscidifurax spp., who are generally the 5Ð6 cm with little difÞculty in both studies, although victors in such encounters (Propp and Morgan 1983). proportionally greater activity was observed closer to If this is the case, then Spalangia spp. may search the surface. Similarly, S. endius and S. cameroni in both surface regions more thoroughly in the absence of studies displayed a tendency to search across a wide heterospeciÞc competitors. Indeed, King (1997) range of depths. We observed considerably higher found that S. cameroni reproduction on buried hosts rates of attacks on the surface by Spalangia spp. than was higher when M. raptor were included in the assay arenas. It is possible that Spalangia spp. under Þeld conditions can detect the presence of competitively Table 5. Rates of host attacks and progeny production by Spalangia endius when house fly pupae were placed at different superior Muscidifurax spp. and reÞne their search pat- depths in poultry manure, fly larval rearing medium, and soil terns to minimize competition events that would work to their disadvantage. Further research would be re- Parasitoids not given Parasitoids given quired to evaluate the impact of the presence of het- a choice of a choice of erospeciÞc competitors on the search patterns of these Depth, habitat depths habitat depths Habitat parasitoids. cm No. No. No. No. pupae parasitoids pupae parasitoids Spalangia gemina displayed search pattern charac- killeda producedb killed produced teristics that were most similar to those of S. cameroni. These two species resemble each other morphologi- Manure 0 43.6 (2.7) 28.5 (3.5) 45.5 (1.8) 23.3 (1.4) 1 33.1 (5.9) 10.0 (2.5) 32.5 (4.7) 12.8 (2.6) cally and in their manure moisture preferences, de- 2 6.4 (2.3) 0.0 (0.0) 5.4 (1.1) 0.3 (0.2) velopment times, and attack rates (Geden 1996 1997, 4 9.4 (3.1) 0.0 (0.0) 7.6 (2.4) 0.0 (0.0) 1999). Little is known about the biology of this tropical 6 4.2 (2.1) 0.0 (0.0) 4.0 (1.6) 0.0 (0.0) species in the Þeld, but it has been found parasitizing Medium 0 45.5 (0.9) 26.3 (2.0) 33.0 (4.7) 12.3 (3.4) 1 44.5 (2.5) 24.2 (4.1) 30.4 (4.9) 21.2 (4.5) house ßies on poultry farms in Brazil sympatrically 2 48.5 (0.7) 32.8 (2.7) 45.8 (2.0) 31.5 (2.3) with S. cameroni at the same times of year (Ferreira de 4 47.8 (0.7) 31.8 (1.2) 45.2 (3.0) 31.2 (2.1) Almeida and Pires do Prado 1998). The other exotic 6 48.9 (0.7) 32.7 (2.5) 41.5 (2.7) 29.5 (2.5) species tested, D. himalayanus, attacks a wide range of Soil 0 27.0 (1.8) 16.0 (2.0) 17.8 (2.2) 6.8 (0.9) 1 0.9 (0.8) 0.0 (0.0) 1.6 (0.7) 0.0 (0.0) hosts and has lower overall attack rates than the other 2 1.3 (0.7) 0.0 (0.0) 1.2 (0.8) 0.0 (0.0) species studied here (Geetha-Bai 1990). This species 4 1.2 (0.8) 0.0 (0.0) 1.1 (0.6) 0.0 (0.0) appears to be similar to M. raptor with regard to 6 1.3 (0.6) 0.0 (0.0) 1.7 (0.7) 0.0 (0.0) searching behavior as a function of habitat depth (this study) and manure moisture preferences (Geden a Mean (ϮSE) number uneclosed pupae per assay cup of 50 pupae. b Mean (ϮSE) number parasitoid progeny produced per assay cup 1997). No information is available on the outcome of of 50 pupae. competition between these two species, but it is likely 416 ENVIRONMENTAL ENTOMOLOGY Vol. 31, no. 2 that M. raptor would overwhelm D. himalayanus in the Geden, C. J. 1996. Modeling host attacks and progeny pro- Þeld because of its faster development rate and ag- duction of Spalangia gemina, Spalangia cameroni, and gressive larvae. Muscidifurax raptor (Hymenoptera: Pteromalidae) at None of the parasitoids were able to forage below constant and variable temperatures. Biol. Control 7: 172Ð the surface of sandy loam soil from a dairy farm. Large 178. numbers of pupae were present in the soil when it was Geden, C. J. 1997. Development models for the Þlth ßy collected and had to be removed before the soil was parasitoids Spalangia gemina, Spalangia cameroni, and Muscidifurax raptor (Hymenoptera: Pteromalidae) under used in the tests. In regions with extensive coastal constant and variable temperatures. Biol. Control 9: 185Ð plains such as Florida, ßy pupae can be found 15Ð30 cm 192. below the soil surface near ßy breeding areas Geden, C. J. 1999. Host location by house ßy parasitoids (Hogsette 1996). Our data suggest that such pupae are (Hymenoptera: Pteromalidae and Chalcididae) in poul- well protected from parasitoid attacks, although Þeld try manure at different moisture levels and host densities. surveys for pupal parasitism at different depths in soil Environ. Entomol. 18: 755Ð760. are needed to conÞrm this. Geden, C. J., D. C. Steinkraus, R. W. Miller, and D. A. Rutz. Most of the species tested, especially the Spalangia 1992. Suppression of house ßies on New York and Mary- spp., displayed considerable Þdelity in their search land dairies using Muscidifurax raptor in an integrated patterns and located pupae in different depth zones at management program. Environ. Entomol. 21: 1419Ð1426. similar rates regardless of whether they were in choice Geetha-Bai, M. 1990. Host-parasite relationship of Dirhinus or no-choice situations. This was surprising because it pachycerus Masi (Hymenoptera: Chalcididae), with par- ticular reference to its house ßy control potential, pp. was anticipated that the parasitoids would be more 11Ð28. In D. A. Rutz and R. S. Patterson [eds.], Biocontrol willing to search outside their preferred zones if the of arthropods affecting livestock and poultry. Westview, only hosts available to them were outside those zones Boulder, CO. (no-choice tests). The only time that this hypothesis Hogsette, J. A. 1992. New diets for production of house ßies was borne out was in the manure tests with D. hima- and stable ßies (Diptera: Muscidae) in the laboratory. J. layanus, which located more pupae below the surface Econ. Entomol. 85: 2291Ð2294. in no-choice tests than it did in tests where the para- Hogsette, J. A. 1996. Development of house ßies (Diptera: sitoids were presented with a range of host burial Muscidae) in sand containing varying amounts of manure treatments. In a related study, the same Þve species of solids and moisture. J. Econ. Entomol. 89: 940Ð945. parasitoids were found to be comparatively ßexible in Jones, C. J., and R. A. Weinzierl. 1997. Geographic range their manure moisture preferences; females would and temporal variation in pteromalid (Hymenoptera: Pte- switch over to less-preferred moisture zones when romalidae) parasitism of stable ßy and house ßy (Diptera: Muscidae) pupae collected from Illinois cattle feedlots. hosts in the preferred zones were in short supply Environ. Entomol. 26: 421Ð432. (Geden 1999). King, B. H. 1997. Effects of age and burial of house ßy In summary, the Þve species tested showed distinct (Diptera: Muscidae) pupae on parasitism by Spalangia search patterns with regard to habitat depth, but these cameroni and Muscidifurax raptor (Hymenoptera: Ptero- patterns were modulated by the type of substrate malidae). Environ. Entomol. 26: 410Ð415. tested. Because ßy pupae can occur in a wide range of Legner, E. F. 1977. Temperature, humidity and depth of habitats within individual farms, the results also sup- habitat inßuencing host destruction and fecundity of port the suggestion of Rueda and Axtell (1985b) that muscoid ßy parasites. Entomophaga 22: 199Ð206. releases of multiple species with complimentary for- Morgan, P. B., and R. S. Patterson. 1990. 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