María Fernanda Achinelly

Susceptibility of neotropical mosquito larvae (Diptera: Culicidae) and non-target aquatic organisms to the entomoparasitic nematode Strelkovimermis spiculatus Poinar & Camino, 1986 (Nematoda: Mermithidae)

Fourteen species of mosquito and several species of non-target aquatic organisms were tested for susceptibility to the neotropical mermithid nematode, Strelkovimermis spiculatus . All species of Aedes, Anopheles, Culex, Isostomyia and Ochlerotatus, plus one of the two Psorophora species exposed to S. spiculatus preparasites, were parasitised. None of the non-target aquatic organisms exposed to S. spiculatus were infected, with the exception of Chironomidae larvae in which nematode penetration was observed although host reaction in the form of nematode melanisation occurred 24-48 h post-infection, the nematodes dying within the host.

Pre-parasitic juveniles of Strelkovimermis spiculatus Poinar & Camino, 1986 (Nematoda: Mermithidae) predated upon by freshwater copepods (Crustacea: Copepoda)

Five copepod species, Acantocyclops robustus, Macrocyclops albidus, Mesocyclops annulatus, Thermocyclops sp. (all Cyclopoidea) and Argyrodiaptomus bergi (Calanoidea), were evaluated under laboratory conditions as potential predators of preparasites of the mermithid nematode Strelkovimermis spiculatus. Adults of all five copepod species consumed 70-100% of the preparasites within 24 h. Copepodids and adults of M. annulatus predated upon 93 and 100% of the nematode pre-parasites, respectively. An average of 197 pre-parasites was daily predated upon by an adult M. annulatus. Copepod density affected prevalence and intensity of S. spiculatus on mosquito larvae. Prevalence and intensity of S. spiculatus on Aedes aegypti larvae was reduced from 98% and 2.8 nematodes per larva in control containers free of copepods to 61.4% and 1.4 nematodes per larva in containers with 50 M. annulatus females per l.

Hexamermis paranaense new species (Nematoda, Mermithidae): a parasite of Diloboderus abderus (Coleoptera, Scarabaeidae) in Argentina

A new species, Hexamermis paranaense n. sp. (Nematoda, Mermithidae), a parasite of larvae of Diloboderus abderus Sturm, 1826 (Coleoptera, Scarabaeidae) is described and illustrated. This new species is characterized by amphids small, amphidial opening pocket-shaped, the anterior portion of the vagina muscularized and slightly protruding with a descending branch forming a loop before joining the uterus, and three rows of genital papillae: the ventrolateral divided in two rows with eight papillae in the outer row and with six papillae in the inner one; the ventral row with four pairs and one single preanal papillae, and with two pairs, a triplete, one pair, a single and one pair postanal papillae.

A new Nematoda (Thelastomatidae) parasite of Coleoptera larvae from Argentina

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.

Evaluation of the mosquitoes Aedes aegypti and Culex pipiens (Diptera: Culicidae) as alternative hosts for laboratory mass-rearing of Strelkovimermis spiculatus (Nematoda: Mermithidae)

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.

Variability study of entomopathogenic nematode populations (Heterorhabditidae) from Argentina

Entomopathogenic nematodes (EPN) belonging to the Heterorhabditidae family are lethal parasites of soil-dwelling insects. Two species were reported in Argentina: Heterorhabditis argentinensis and Heterorhabditis bacteriophora characterized mainly by morphometric features. In this work a comparative and phylogenetic study between five Heterorhabditis populations from Argentina was conducted to analyze the variability between strains and to evaluate the taxonomic position of Heterorhabditis argentinensis. The PCA analyses of morphometric characters separated the larger juvenile, female and male H. argentinensis from H. bacteriophora populations. The juvenile (IJs) stage provided the clearest separation of Heterorhabditis populations presenting the least variability between strains. The variable L and MBW were highly related to H. argentinensis IJs. Three groups were separated by this stage considering PC1 and PC2: one formed by H. bacteriophora OLI, RIV and RN strains, (isolates from Córdoba and Río Negro province), one for H. bacteriophora VELI strain (Buenos Aires province) and one for H. argentinensis (Santa Fe province). Heterorhabditis bacteriophora VELI and H. argentinensis isolated from regions with more rainfalls and humidity presented larger values for morphometric features. Molecular analyses showed the Argentinian populations (H. bacteriophora VELI strain and H. argentinensis), forming a same clade, with six other H. bacteriophora populations (not from Argentina) with a genetic similarity between them of 99%. Heterorhabditis argentinensis presented one unique nucleotide that was not present in any of the other species of the clade. Considering the results of this study H. argentinensis would be conspecific to H. bacteriophora, constituting a strain with a great morphometric variation where the host and climatic conditions could have influenced on the measurements.

A new Thelastomatidae, Oryctophila bonaerensis sp. nov. (Nematoda) parasite of curculionid beetle larvae of Prosalbus rufus (Coleoptera: Curculionidae) from Argentina.

Oryctophila bonaerensis sp. nov. parasitizing curculionid beetle larvae from Argentina, is described and illustrated. The species is characterized by a prominent genital cone and a short and filiform tail appendage. Female with vulva at midlenght of body, vagina long, S-shaped, monodelphic, opistodelphic. Male with one club-shaped spicule. Genital papillae arranged as follows: one pair of large preanal papillae and three pairs of postanal papillae of various sizes: a pair of medium sized papillae is immediately posterior to the anus, followed by a pair of large papillae, and one pair of small papillae at the base of the caudal appendage.

Nematodes (Mermithidae) parasitizing grasshoppers (Orthoptera: Acrididae) in the Pampean region, Argentina

This work provides the results of a survey of entomonematodes parasites of grasshoppers in grasslands of the Pampean Region, Argentina. Nymphs of Staurorhectus longicornis Giglio-Tos, Laplatacris dispar Rhen, 1939, Dichroplus elongatus Giglio-Tos, 1894 and Metaleptea brevicornis (L.) (Orthoptera: Acrididae) were collected. Mermithidae was the only family registered with seven species: 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, and Longimermis acridophila 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.