Ana Lía Estévez

Predation on Biomphalaria sp. (Mollusca: Planorbidae) by three species of the genus Belostoma (Heteroptera: Belostomatidae)

the voracious behaviour of water bugs is well known as they attack a great diversity of invertebrate and vertebrate organisms which may be of various sizes, even larger than they are (schnack, 1976; Menke, 1979). all of the belostomatidae family members have forelegs adapted to catch prey which are usually ambushed by bugs. after catching prey, bugs handle it in order to insert their piercing mouth parts to inject saliva and liquefy prey’s tissues to suck. the only insects that feed on snails during the larval and adult stages are belostomatids (smith, 1997). Limnogeton Mayr, 1853 is a compulsory predator of snails (voelker, 1968; tawfik et al., 1978). there are few reports on members of genera Abedus stal, 1862 and Diplonychus laporte, 1833 preying on snails in the field or in the laboratory (saha & raut, 1992; tawfik et al., 1978; okada & nakasuji, 1993; smith, 1997). somasundarao (1963), voelker (1968) and saha & raut (1992) suggested the importance of these bugs as useful snails control agents to eradicate severe worm diseases. Pointier & delplanque (1976) pointed out the importance of B. boscii as a B. glabrata predator in guadeloupe and Kesler & Munns (1989) cited B. flumineum as an important cause of snails’ mortality in the u.s.a. little is known about the alimentary preference of Belostoma species under laboratory conditions. several authors fed immature and adult stages of Belostoma species with varied prey for different purposes: Kehr & schnack (1991) fed B. oxyurum dufour 1863 with tadpoles; armua & estevez (1997) fed immature stages of B. elegans Mayr with mosquito larvae, small crustacean as Daphnia sp. and Hyalella sp., and tadpoles. some species of Belostoma latreille, 1807 have occasionally been observed feeding on snails such as B. malkini (cullen, 1969). Pereira & Melo (1998) fed specimens of B. plebejum and B. anurum under laboratory conditions, with Culex quinquefasciatus, Daphnia sp. and Biomphalaria glabrata and both species fed on all offered prey but they showed preference for mosquito larvae; B. micantulum was fed with larvae and pupae of Aedes fluviatilis and Biomphalaria glabrata, showing preference for mosquitoes in all stages (consoli et al., 1989). Presented herein is an experimental study with Biomphalaria sp. as prey for specimens of the genus Belostoma. the selected species, included in the three size categories proposed by lauck (1962), B. micantulum (small species), B. elegans (medium species) and B. elongatum (moderately large species) show different structural characteristics on their heads. the aim of this work is to compare the ability of each species with snails according to the head morphological features.

LAGUNA DON BLANCO, ARGENTINA: FIRST RECORD OF HORVATHINIA (HEMIPTERA: BELOSTOMATIDAE) AS A WETLAND DWELLER

ABSTRACT Two adult Horvathinia pelocoroides Montandon 1911 (Hemiptera, Belostomatidae, Horvathininae) are recorded for the first time in a true wetland habitat. This species, probably the only valid ones in the monobasic subfamily Horvathininae Lauck and Menke 1961, was discovered in a permanent shallow pond near the city of Corrientes, Corrientes Province (27° 28′S, 58° 50′W), Argentina, during surveys conducted on December 29, 2004, and September 23, 2005. At both dates, the specimens were taken from a fresh water marsh densely filled with floating hydrophytes dominated by water hyacinth, Eicchornia crassipes, and water lettuce, Pistia stratiotes. This is the first record of any horvathinine specimen collected in any situation other than flying to light.

Estadísticos vitales de Steatoda retorta González, 1987, y anílisis comparativo con los de Latrodectus mirabilis (Holmberg), Latrodectus antheratus (Badcock), Latrodectus corallinus Abalos, Latrodectus diaguita Carcavallo y Tidarren sisyphoides (Walckenaer) (Araneae, Theridiidae)∗

This paper completes the study of the life cycle of Steatoda retorta, which was published before (Gonzalez, 1987). The dates given in this paper were obtained from specimens reared in laboratory. Variations of mortality, survivorship and mean life expectation were studied. The survivorship curve indicates that the experimental population was affected by mortality since age 4 to 9 being this a critical period because the nymphs moult from I to II and from II to III instars. The curve shows another critical period when the population moults to adult stage. The mean life time of the cohort was 37.09 weeks. These results were compared with the data recorded for L. mirabilis, L. antheratus, L. corallinus, L. diaguita and Tidarren sisyphiodes. This analysis showed differences as: a) The survivorship curve of Steatoda retorta is more convex than the others because there is no differential mortality between males and females, b) The higher value of the mean life expectation in Steatoda retorta occurs when the fir...