This work provides the results of a survey of entomonematodes parasites of grasshoppers in grasslands of the Pampean Region, Argentina. Camino and Stock, 1989. The values of parasitism ranged between 1-12%, and intensity not overcome the number of 5.0 nematodes per larva. The nematodes observed showed specificity, not registering the same species of parasite in more than one host species. The Pampean region constituted an area with high diversity of mermithids where new species could be consider as bioregulator agents of this troublesome insect pests in agricultural areas of Argentina.Keywords: nematodes, Acrididae, pest, agriculture, Argentina. Nematóides (Mermithidae) parasitando gafanhotos (Orthoptera: Acrididae) nos Pampas região, a Argentina ResumoEste trabalho apresenta os resultados de uma pesquisa entomonematode parasitando gafanhotos em pastagens da região pampeana, Argentina. Ninfas de Staurorhectus longicornis Giglio-Tos, Laplatacris dispar Rhen de 1939, Dichroplus elongatus Giglio-Tos, 1894 e Metaleptea brevicornis (L.) (Orthoptera: Acrididae) foram coletados. Mermithidae era a única família registrado com sete espécies: Agamermis decaudata Cobb, Steiner and Christie, 1923, Amphimermis bonaerensis Miralles and Camino, 1983, Amphimermis dichroplusi Camino and Lange, 1997, Amphimermis ronderosi Camino and Lange, 1997, Hexamermis coclhearius Stock and Camino, 1992, Hexamermis ovistriata Stock and Camino, 1992, e Longimermis acridophila Camino and imagem, de 1989. Os valores de parasitismo variou entre 1-12%, e intensidade não superar o número de 5,0 nematóides por larva. Os nemátodos observados demonstraram especificidade, não registar as mesmas espécies de parasita em mais do que uma espécie de hospedeiro. A região pampeana constituída uma área com alta diversidade de mermithids onde novas espécies poderiam ser consideradas como agentes bio-reguladores deste incômodos insetos pragas em áreas agrícolas da Argentina.

While conducting field survey on agricultural pests in Argentina in areas of Lincoln and Magdalena (northwest and east of Buenos Aires Province, respectively) we found adults of Gryllodes laplatae Sauss (Orthoptera: Gryllidae) parasitized by two different Rhabditida species, belonging to the families Diplogasteridae and Rhabditidae. A Diplogasteridae found in Magdalena was Cephalobium magdalensis n. sp. and a Rhabditidae found in Lincoln was Cruznema lincolnensis n. sp.; both species are here described. MATERIALS AND METHODSAdults of G. laplatae (n = 57) were hand collected and put in individual vials. According to Poinar's (1975) technique, the insect were placed at 5°C for 10 min and then disected in Petri dishes with distilled water under stereoscope microscope. The nematodes (males and females) were found in the stomodeo intestinal; they were killed in distilled water at 60ºC for 2 min. Posteriorly they were put in 50% TAF solution in water for 48 hr, finaly we finished the fixed in pure TAF.Fixed specimens were used for drawings and measurements using a camera lucida microscope, and a micrometer in a Zeiss compound microscope. Measurements are for the holotype male and allotype female and for paratypes the range is in parenthesis.

Two new species of mermithids (Nematoda: Mermithidae), Gastromermis doloresi n. sp. a parasite of Simulium wolffhuegeli Roubaud and Hydromermis doloresi n. sp. a parasite of S. jujuyense (Paterson & Shannon) from Córdoba, Argentina, are described and illustrated. G. doloresi n. sp. is characterized by having medium sized, pear-shaped and oval amphids, eight hypodermal chords all around the body, cylindrical S-shaped vagina, single long spicule 528 [mi]m, whith teh sculpture tip, three rows of genital papillae in which the middle row contains 17 pre-anal and 9 post-anal papillae, and lateral rows contain 18 papillae. Hydromermis doloresi n. sp. can be distinghished by the following: medium sized, pear-shaped amphids, eight hypodermal chords, a cylindrical, S-shaped vagina, one short curved spicule with sculpture and genital papillae in three rows. The medium ventral row of papillae has 4 double and 9 single pre-anal papillae and 3 double and 6 single port-anal papillae, lateral rows have 18 single papillae each

86 SummaryLeidynema saltense n. sp. (Nematoda, Thelastomatidae), a parasite of larvae of Cyclocephala modesta (Coleoptera, Scarabaeidae) from Salta province, Argentina, is described and illustrated. This species is characterised by the presence of an intestinal caecum in the female, and four pairs of genital papillae in the male, one pair of which is large, ventral and pre-anal and three pairs are subventral and postanal.

Gryllophila cephalobulata n. sp. (Nematoda, Thelastomatidae)

Cephalobellus cyclocephalae n. sp. (Oxyurida: Thelastomatidae), a parasite of larvae of Cyclocephala signaticollis (Coleoptera, Scarabaeidae), found in Argentina is described and illustrated. It is characterized by the cuticle striated at the anterior end in both sexes, with 15 annules, buccal cavity short and not armed, and the male with 4 pairs of genital papillae, 1 pair of preanal papillae, 3 pairs of postanal papillae.

Two different Rhabditida species (Nematoda: Rhabditidae) Parasitorhabditis platidontus n. sp. and Cruznema campestris n. sp. are described and illustrated from the larvae of Cyclocephala signaticollis (Coleoptera: Scarabaeidae) from Buenos Aires province, Argentina. Parasitorhabditis platidontus n. sp. is characterized by having 4 odontoplates in the stoma and the vulva is at 80% of the length of the body. Cruznema campestris n. sp. can be distinguished by the presence of 4 odontoplates and the arrangement of the male genital papillae, 9 pairs, of which 4 are preanal and 5 postanal.

The effect of the number of pre-parasitic juveniles of Strelkovimermis spiculatus on infection rate in larvae of the culicid mosquitoes Aedes aegypti and Culex pipiens, and the susceptibility of different larval instars of the culicids to the parasite, was studied in order to facilitate laboratory mass production of the nematode. The infection rate in each mosquito species varied between 72 and 100% for the different concentrations of pre-parasites used per host. Infection percentages in 1st, 2nd, 3rd and 4th instar larvae exposed to S. spiculatus varied from 11 to 98%. Significant differences in percentage infection were observed between 4th instar larvae and the earlier instars. The results obtained in this study demonstrate the feasibility of mass-rearing S. spiculatus in A. aegypti and C. pipiens under laboratory conditions.