Etologfa, 4:85-86 (1994)

Size-selective oviposition by phorid (Diptera: ) parasitoids on workers of the fire , Solenopsis saevissima (: Formicidae)

S. Campiolo 1 , M.A. Pesquero2 & H.G. Fowler 1

1 Dpto. de Ecologia, Inst. de Biocicncias, UNESP, 13506-900 Rio Claro, SP, . 2 Dpto. de Zoologia, Inst. de Biocicncias, UNESP, 18610 Botucatu, SP, Brazil.

ABSTRACT. Size-selective ol'iposilion by phorid (Diptera: PhoridC1e)f)arasitoids on workers of the , Solenopsis saevissima (Hymenofilera: Formicidae).- Pseudacteon tricusfiis and Pseudacteon curvatus (Diptera: Phoridae) oviposit on different sized workers of Solenopsis sunissima (Hymenoptcra: Formicidac). The phorid parasitoid, Pseudacteon tricuspis, oviposited on significantly larger workers of the fire ant Solenof)sis sael'issimu. than did another coocurring . P. curvatus. Because of the defensive posture taken hy workers and the abandonment of the foraging area hy larger workers. an array of phorid parasites might affect differentcaste components of the colony and affect their efficient deployment in exterior tasks.

KEY WORDS. Formicidac. Solenopsis, Phoridae. Pseudacteon. Oviposition, Behavior, Selection

A number of species of phorid flies have been oviposition behavior of two sympatric species of reported as probable parasitoides of a number of Pseudacteon on differing worker sizes of S. species of tropical fire , Solenopsis spp. in saevissima in the field. (Williams & Whitcomb, 1974; On July 3, 1992, between I 0:30 and I I :30 h, we Williams, et a!., 1973). Recently, Feener(l987) has placed a laboratory colony of S. saevissima in the described size-selective patterns of oviposition in field in a white plastic tray (25 X 40 X 5 cm), Pseudacreon crmvfcndi Coquillctt on Solenopsis whose sides had been covered with Teflon@ to geminara (F ), and subsequently called attention to prevent the. escape of workers. During the the fact that the presence of phorid flies results in observation period, we collected phorids after diminished ant foragingbehavior (Feener & Brown, ovipositional attempts with an aspirator, and collected the parasitizcd ant for later measurement. In south-eastern Brazil, at least 7 species of Species identification was performed with live flies Pseudacteon have been observed ovipositing on the in a glass vial after chilling on ice under a stereo fire ant Solenopsis sae1·issimct (Fr. Smith) microscope and was based upon the characteristic (Pesquero, ct al., in press). Here, we describe the ovipositor of each species. Upon identification of

Corresponding author: H.G. Fowler, Dcpartamento de Ecologia, 18, UNESP, 13506-900 Rio Claro. SP, Brazil, Tel: 195-24-2588

85 Campiolo et al.

expected when compared with our random sample (n= l 09) [Mann-Whitney U test (Siegel 1956): P. tricuspis, z=S.529, p

0.1 on workers which were significantly larger than those attacked by P. cww1t11s (fig. I) (z=6.297, 0.6 p<0.01). OA During these observations, workers of S. cu soc1·1ss1111a were observed to take a characteristic posture and other defensive behaviors described by 0 ...... _____ one.,a)o.111 Feener ( 1987). Larger workers rapidly entered the .iffl e.ead width plastic nest box whenever phorids were present. Feener ( 1987) commented that P. crawf'ordi parasitized larger workers or S. geminato. and that this might have a serious effect on the ant's foraging FIGURE. I. The distribution or ovipositional events behavior, which he later confirmed (Feen 5-13 ). by Pseuduc1eo11 cu1w1tus (N = 28) and Pseudaclcon 11irnspis (N = 27) on dillcring worker sizes of the fire ant. Soleno11sis sael'issima, and a random sample or foraging workers (N = I 09). References [La distrihuei6n de oviposiciones por Pscudodace/011 curvatus (N = 28) y Pseudace/011 tricuspis (N = 27) en ohrcras detamanos diferentes de la hormiga roja, Solenopsis sael'issima. y una eoleeei6n Pcsquero, M.A.; Campiolo, S. & Fowler, H.G., in aleatoria de obreras cxternas al nido (N = I 09).J press. Phorids (Diptera: Phoridae) associated with swarms of Solenopsis saevissima the phoricl. it was released near the tray. (Hymenoptera: Formicidac). Fla. Ent. Posteriorly, we collected a random sample of ants Siegel, S., 1956. Nonparctmetric statistics for the under the same conditions from the laboratory behcn·ioml sciences: New York: McGraw Hill. colony which were foragingduring the same time Williams, R.N., & Whitcomb, W.H., 1974. period to compare size distributions with those Parasites of fire ants in South America. Proc. which had been parasitizcd. For both parasitized m1d Tall Ti111/Jcrs Conf Ecol. Anim. random samples, we measured the maximum head Manage., 5: 49-59. width of the workers, which has been usecl Williams, R.N., Panaia. J.R., Gallo, D., & previously to index worker size variation (Wilson, Whitcomb, W.H. 1973. Fire ants attacked by 1978). phorid flies. Fla. Ent., 56:259-262. Twenty-seven workers were parasitized by P. Wilson, E.O., 1978. Division of labor in fire ants tricuspis Borgmcier, and 28 by P. curvatus based on physical caste (Hymenoptera: Borgmeier during our observation. Both phorid Formicidae: Solenopsis). J. Kansas Entomol. species oviposited on larger individual workers than Soc., 51 :615-636.

Recibido: marzo, 1993

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