Spalangia endius were collected from fly pupae, primarily house fly and stable fly, from a poultry house in Indiana. Male and female wasps did not differ within and across host species in host size usage. Also, despite stable fly pupae being significantly smaller than house fly pupae, the proportion of male wasps emerging from the two host species was similar

King, B. H

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No Intersexual Differences in Host Size and Species Usage in \u3ci\u3eSpalangia Endius\u3c/i\u3e (Hymenoptera: Pteromalidae)

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The Great Lakes Entomologist Volume 24 Number 1 - Spring 1991 Number 1 - Spring 1991 Article 3 March 1991 No Intersexual Differences in Host Size and Species Usage in Spalangia Endius (Hymenoptera: Pteromalidae) B. H. King Purdue University Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation King, B. H. 1991. "No Intersexual Differences in Host Size and Species Usage in Spalangia Endius (Hymenoptera: Pteromalidae)," The Great Lakes Entomologist, vol 24 (1) Available at: https://scholar.valpo.edu/tgle/vol24/iss1/3 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 1991 THE GREAT LAKES ENTOMOLOGIST 17 NO INTERSEXUAL DIFFERENCES IN HOST SIZE AND SPECIES USAGE IN SPALANGIA ENDIUS (HYMENOPTERA: PTEROMALIDAE) B. H. Kingl ABSTRACT Spa/angia endius were collected from fly pupae, primarily house fly and stable fly, from a poultry house in Indiana. Male and female wasps did not differ within and across host species in host size usage. Also, despite stable fly pupae being significantly smaller than house fly pupae, the proportion f male wasps emerging from the two host species was similar. Early in the 1900's, entomologists observed that in some species of parasitoid wasps, males tended to emerge from smaller hosts than did females, resulting in a negative relationship between host size and parasitoid sex ratio (proportion males) (reviewed in Flanders 1939, 1946). Since then, a group of sex ratio models, the host quality models have been developed to explain this pattern (Charnov 1979, Charnov et al. 1981, Werren 1984). These models were designed for solitary species (species in which one offspring completes development per host). In these models, the predic­tion that male parasitoids should emerge from smaller hosts than females is based on the assumption that developing n a small host will be more detrimental to a female than to  male in terms of future ability to reproduce. The rationale of the assump­tion was that wasps will be smaller when developing on smaller hosts; and even small males may be able to mate successfully, whereas small females probably lay fewer eggs than large females (Charnov et al. 1981). There is some support for this idea in a few species of parasitoid wasps (Charnov et al. 1981, Jones 1982, van den Assem et al. 1989), but not in all species (King 1988). In those species or populations in which the assumption is valid, natural selection is expected to favor females that oviposit a greater proportion of males in small than in large hosts (Charnov et al. 1981). Female wasps can potentially control the sex of their offspring by controlling fertil­ization because they have haplodiploid sex determination. Under haplodiploid sex determination, males develop from unfertilized eggs and females from fertilized eggs. Here the host quality models' prediction of a greater proportion of sons from small than from large hosts is tested using field collections of the solitary parasitoid wasp Spa/angia endius Walker (Hymenoptera: Pteromalidae). The wasps emerged from house fly pupae (Musca domestlea Linnaeus) and stable fly pupae (Stomoxys ea/eitrans [LinnaeusJ) (Diptera: Muscidae) collected from a poultry house in north­ern Indiana. IDepartment of Biological Sciences, Purdue University, West Lafayette, IN 47907. Present address: Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115. 1King: No Intersexual Differences in Host Size and Species Usage in <i>SPublished by ValpoScholar, 199118 THE OREAT LAKES ENTOMOLOGIST Vol. 24, No.1 Table I. -X + SD (n) size (mm3) of house fly pupae from which male and female Spaiangia endius emerged for five collection dates. Fly Pupae Size Date Male wasps Female wasps Test Comparison" "'---:----~. Sep 03 26.24 ± 3.09 (38) 25.86 ± 3.02 (110) t = 0.66, P 0.51 Sep 10 28.15 2.27 (3) 25.16 ± 2.94 (14) t = 1.65, P 0.12 Oct 01 16.57 ± 5.04 (14) 18.51 ± 5.16 (30) t = 1.17, P 0.12 Oct 08 19.31 ± 7.19 (5) 23.94 ± 6.27 (14) t 1.37, P = 0.09 Oct 15 27.02 ± 3.21 (2) 25.81 ± 4.72 (15) 0.35, P = 0.73 *t-tests of whether females emerged from larger hosts than did males; two-tailed P values given when means were in direction opposite to that predicted MATERIALS AND METHODS Weekly from 28 May to 12 November 1985, fly pupae were collected from an enclosed, shallow-pit, egg-layer poultry house in Delphi, Indiana (the Hilltop poul­try house described in Merchant 1984, Merchant et al. 1987), using pupal traps (Hogsette and Butler 1981, Merchant et al. 1985) The pupae were held until flies emerged and died. Then pupae from which no flies emerged and which had not been depredated (Merchant 1984) were held individually in gelatin capsules for parasitoid emergence. Wasp species were identified following Boucek (1963) and Rueda and Axtell (1985) and house fly and stable fly pupae following Skidmore (1985). Voucher specimens have been deposited at the museum of the Department of Ento­mology at Purdue University, West Lafayette, Indiana. Width of fly pupae was measured to the nearest 0.05 mm at a magnification of 360 X under a dissecting microscope. These widths were converted to volumes (m 3) using the following formulas: for house flies volume = (22.68) (width)-37.63 and for stable flies volume (11.31) (width)-11.18. These regression equations had been determined by measuring both width and length on 17 stable flies and 36 house flies, then calculating volume with the equation for a prolate spheroid (Holdaway and Smith 1932), and finally regressing volume against width. RESULTS There were no significant differences among collection dates in S. endius sex ratio (0 = 3.82, df = 6, P > 0.50). Pooling across all dates, S. endius sex ratio was 26.1070 males (n = 330 male and female wasps). There was no significant difference in the size of hosts from which male and female S. endius emerged. This was true regardless of whether one looked (I) within host species, (2) at all host species combined, or (3) between different host species. Looking at house fly hosts. among the five dates with sample sizes of greater than ten, a two-way analysis of variance on host size showed no significant effect of wasp sex (F = 0.34, P = 0.56) and no significant interaction between wasp sex and date (F = 2.26, P = 0.06). Because the interaction approached significance, I also did individual t-tests for each date, but these also revealed no significant difference in the size of hosts from which male and female wasps emerged (Table I). Looking at stable fly hosts, combining all dates, there was no significant differen£.e in host size between male and female wasps, though sample sizes are small (males: X ± SD 14.54 ± 0.73, n = 4; females 14.50 ± 0.97, n 7; t 0.07, P = 0.94). Combining host species, among the five dates with sample sizes of greater than ten, a two-way analysis of variance on host size showed no significant effect of wasp sex (F = 0.51, P = 0.48) and no significant interaction between sex and date (F = 1.57, P 0.18). Looking between host species, though stable fly pupae are on average smaller than 2The Great Lakes Entomologist, Vol. 24, No. 1 [1991], Art. 3https://scholar.valpo.edu/tgle/vol24/iss1/31991 THE GREAT LAKES ENTOMOLOGIST 19 house fly pupae (Skidmore 1985, King 1991), the sex ratio of S. end/us n stable fl es (36010 males, n = 11 wasps) was not significantly greater than on house flies (25% males, n 264 wasps) (G 0.67, P > 0.30). DISCUSSION The absence of host size differences between the sexes for S. ndius in this study is consistent with results of laboratory experiments by Donaldson a d Walter (1984). Their experiments indicated that S. en ius females do not manipulate the sex of th ir offspring in response to the size of house fly hosts. The lack of any significant relationship between host size and parasitoid sex ratio for S. end/us contrasts both with the pattern observed in most other species of parasitoid wasps that have been examined and with the prediction of the host quality models. In mo t, though not all, species of parasitoid wasps that have been examined, females emerge from larger hosts than do males (about 44 of 65 parasitoid wasp species (reviewed in King 1987, 1989, in press). Results with other species of Spalangia besides S. endius have been mixed. These other species of Spaiangia are also parasitoids of fly pupae. Legner (1969) found the predicted negative relationship between host size and offspring sex ratio for S. nigra, but not for S. cameroni or S. drosophilae (statist cal analyses of his results in Table 7 of King 1987). King's (1988) laboratory results support the prediction for S. cameroni parasitizing house flies. However, field results with S. cameroni are more complicated: the prediction is supported on a within host species basis for two ofthree dates - two dates on which S. cameroni emerged only from house fly pupae­but not on the date when stable fly pupae were also parasitized by S. cameroni (King 1991). Looking just at stable fly pupae, S. cameroni males actually emerged from significantly larger hosts than did females, opposite the prediction. As was the case with S. endius, S. cameroni sex ratio did not differ between small and large host species (Le., stable fly and house fly pupae) (King 1991). Because the members of the genus Spaiangia exhibit such a variety of relation­ships between sex ratio and host size, it is a promising group for a comparative study. A comparison of behavioral, ecological, and life history factors among he species may help to explain the interspecific differences in sex ratio patterns. One possibility is that the species that do not upport the host quality models' prediction may not meet the models' assumption of a more positive effect f host size onfemale than male reproduction. For example, competition among males for mates may increase the importance of large male body size in some species. In general, among parasitoid wasps, the importance of size on male reproductive success has been little studied (Char nov et al. 1981, Jones 1982, King 1988, van den Assem et aI. 1989), especially relative to the attention given females (e.g., Charnovet aI. 1981, Jones 1982, King 1988, van den Assem et al. 1989; 14 references in Table 6 of King 1987). ACKNOWLEDGMENTS I thank R. Flanders for introducing me to parasitoid wasps, the Brubakers of Hilltop Egg Farm for the use of their poultry house, M. Merchant for helpful tips on identification, R. Howard for valuable discussions in the planning, analyzing, and writing of this research, and R. King for comments on the manuscript. This research was aided by a National Science Foundation Graduate Fellowship and by Grants-in­Aid of Research from Sigma Xi, The Scientific Research Society. 3King: No Intersexual Differences in Host Size and Species Usage in <i>SPublished by ValpoScholar, 199120 THE GREAT LAKES ENTOMOLOGIST Vol. 24, No. I LITERATURE CITED van den Assem, 1., J. J. A. van lersel, and R. L. Los-den Hartogh. 1989. Is being large more important for female than for male parasitic wasps? Behavior 108:160-195. Boucek, Z. 1963. A taxonomic study in Spalangia Latr. (Hymenoptera, Chalcidoidea). Acta Entomo\ogica Musei Nationalis Pragae 35:429-497. Charnov, E. L. 1979. The genetical evolution of patterns of sexuality: Darwinian fitness. Am. Nat. 113:465-480. Charnov, E. L., R. L. Los-den Hartogh, W. T. Jones, and J. van den Assem. 1981. Sex ratio evolution in a variable environment. Nature 289:27-33. Donaldson, J. S., and O. H. Walter. 1984. Sex ratios of Spalangia endius (Hymenoptera: Pteromalidae), in relation to current theory. Eco!. Entomol. 9:395-402. Flanders, S . E . 1939. Environmental control of sex in hymenopterous insects. Ann. Entomol. Soc. Am. 32:11-26. Flanders, S. E. 1946. Control of sex and sex-limited polymorphism in the Hymenoptera. Q. Rev. BioI. 21:135-143. Hogsette, J. A., and J. F. Butler. 1981. Field and laboratory devices for manipulation of pupal parasites. pp. 90-94 In: Proceedings Workshop on Status of Biological Control of Filth Flies. U.S.D.A. Holdaway, F. T., and H. F. Smith. 1932. A relation between size of host puparia and sex ratio of Alysia manducator. Aust. J. Exp. BioI. Med. Sci. 10: 247-259. Jones, W. T. 1982. Sex ratio and host size in a parasitoid wasp. Behav. Eco!. Sociobiol. 10:207-210. King, B. H. 1987. Offspring sex ratios in parasitoid wasps. Quart. Rev. BioI. 62:367-396. ___. 1988. Sex ratio manipulation in response to host size by the parasitoid wasp Spalangia cameroni: A laboratory study. Evolution 42: 1190-1198. ___. 1989. Host-size-dependent sex ratios among parasitoid wasps: does host growth mat­ter? Oecologia 78:420-426. ___. 1991. A field study of host size effects on sex ratio of the parasitoid wasp Sp langia cameroni. Am. MidI. Nat. 125:10-17. Sex ratio manipulation by parasitoid wasps. In: Evolution and Diversity of Sex Ratio: Insects and Mites (D. L. Wrensch and M. Ebbert, eds.). Chapman and Hall, New York, in press. Legner, E. F. 1969. Adult emergence interval and reproduction in parasitic Hymenoptera influenced by host size and density. Ann. Entomo!' Soc. Am. 62:220-226. Merchant, M. E. 1984. House flies and their parasitoids in egg-layer poultry houses in Indiana: ecology and sampling method comparisons. M.S. thesis, Purdue Univ., West Lafayette, IN. Merchant, M. E., R. V. Flanders, and R. E. Williams. 1985. Sampling method comparisons for estimation of parasitism of Mu ca domestica (Diptera: Muscidae) pupae in accumulated poultry manure. J. Econ. Entomol. 16:716-721. Merchant, M. E., R. V. Flanders, and R. E. Williams. 1987. Seasonal abundance and parasit­ism of house fly (Diptera: Muscidae) pupae in enclosed, shallow-pit poultry houses in Indiana. Environ. Entomol. 16:716-721. Rueda, L. M., and R. C. Axtell. 1985. Guide to common species of pupal parasites (Hymenop­tera: Pteromalidae) of the house fly and other muscoid flies associated with poultry and livestock manure. Technical Bulletin 278. North Carolina Agricultural Research Service, North Carolina State University, Raleigh, North Carolina. 88 pp. Skidmore, P. 1985. The biology of the Muscidae of the world. Junk Publishers, Dordrecht, Netherlands. 550 ppWerren, J. H. 1984. A model for sex ratio selection in parasitic wasps, local mate competition and host quality effects. Neth. J. Zool. 34:81-%. 4The Great Lakes Entomologist, Vol. 24, No. 1 [1991], Art. 3https://scholar.valpo.edu/tgle/vol24/iss1/3

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No Intersexual Differences in Host Size and Species Usage in \u3ci\u3eSpalangia Endius\u3c/i\u3e (Hymenoptera: Pteromalidae)

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