Spider community (Arachnida, Araneae) of alfalfa crops (Medicago sativa) in Buenos Aires, Argentina. Over the last decades there has been an increasing interest in the use of natural enemies to control pest insects, including spiders. We studied a spider community in Argentina by sampling every two weeks during 2004-2006 in one-hectare lots. Soil stratum spiders were collected using nets and pitfall traps. A total of 6229 specimens were collected (15 families and 50 species). Seven families were found in the herbal stratum, the most abundant were Thomisidae (n=2012, 32.30%), Araneidae (n=1516, 24.33%) and Oxyopidae (n=604, 9.70%). The soil had 14 families, mainly: Lycosidae (n=629, 10.10%) and Linyphiidae (n=427, 6.85%). Hunting spiders predominated: ambushers (32.99 %); stalkers (11.77%) and ground-runners (10.84%) were less common. The most abundant web building spiders were the orb weavers (27.56%). The diversity indexes were: H´=2.97, Dsp=0.11 and J=0.79, evidencing a moderately diverse spider community with predominance of Misumenops pallidus, Oxyopes salticus, Lycosa poliostoma and L. erythrognatha. The spiders were present throughout the phenological development of the crop with abundance peaks in spring and summer. Rev. Biol. Trop. 58 (2): 757-767. Epub 2010 June 02.

This study analyzes predation by adult females of Misumenops pallidus (Keyserling 1880) on pairs of prey items representing non-pest insects and potential pests. The phenology of the potential pests was such that each insect guild peaked sequentially, while non-pest herbivorous and insectivorous insects were present during the entire period. Field experiments were made in a commercial 50-ha soybean plot during two successive years. Ten cages 1 3 1 3 0.5 m were placed in peripheral furrows of a soybean commercial plot. The pest species were preyed on differentially, with the order from the most favored species to the least with respect to non-pest herbivorous and insectivorous insects was as follows: defoliating lepidopterous larvae, seed feeding pentatomids in their early nymphal instars, stem boring lepidopterous larvae, and seed feeding pentatomids in older nymphal and adult instars. Adult females of M. pallidus fed on all the insect species offered, but in the presence of defoliator larvae, they hardly accepted alternative prey, whereas in the presence of other prey, they maintained a more generalized diet.

Feeding preferences of the spider Misumenops pallidus (Araneae: Thomisidae) on potential prey insects from alfalfa crops. The spider Misumenops pallidus (Thomisidae) is commonly found in alfalfa crops. We studied its predatory preferences on potential insect prey, particularly regarding agroecosystems pests. Two kinds of tests were done under normal laboratory conditions: simultaneous presentation of prey (n= 215) and alternative prey test (n= 45). The spiders preferred insects that were mobile, small, without defensive glands and with thin exoskeletons. According to the amount of prey consumed, we established four predation levels: high (> 55%, on adult Drosophila melanogaster flies); intermediate (30%-55% on the defoliator larvae of Rachiplusia nu and adult heteropterans: Horciasinus argentinus and Halticus spegazzinii); and low (10%-30% on the chrysomelids Colapsis sp. and Diabrotica speciosa). The pentatomid Piezodorus guildinii, the curculionid Naupactus sp. and the aphid Acyrthosiphom pisum were not accepted as food. Once the spider captured a prey item it did not accept another, independently of prey item species (82% of trials). Rev. Biol. Trop. 54(2): 505-513. Epub 2006 Jun 01.

Effect of spiders (Arachnida: Araneae) as predators of insect pest in alfalfa crops (Medicago sativa) (Fabaceae) in Argentina. Spiders are predators that reduce insect pest populations in agroecosystems. Trials were conducted to measure the selectivity against different insect preys, the daily consumption, effect of predators alone and together with a known number of preys, and the indirect effect of predators on vegetation. For this, experimental units (1x1m) were used covered with a fine plastic mesh. Misumenops pallidus, Oxyopes salticus and Araneus sp. were used as generalist predators, and aphids, weevils, locusts, chrysomelids and Lepidoptera larvae as their potential preys. Among the preys offered, the spiders preferred Lepidoptera larvae compared to the other two pests groups (weevils and aphids). The maximum consumption rate was of 93.33% for Lepidoptera larvae, 25.33% for aphids and 11.67% for weevils. The Q Index values for the three species of spiders showed a positive selectivity only for defoliating larvae. O. salticus showed the highest values of consumption rates while Rachiplusia nu was the most consumed. The maximum value of consumption in 24 hours was showed by O. salticus on R. nu (C)=2.8. The association of several species of predatory spiders increased the total number of insects captured, and also showed that the addition of spiders caused a decrease in the number of leaves damaged by the effect of lepidopterous larvae.

No abstract

A census of spiders was undertaken in winter wheat fields of Buenos Aires province, Argentina, as well as from their margins and from wheat stubble. Spiders were collected weekly over 3 consecutive years using entomological sweeping and pitfall traps. Field margins were the richest and densest habitats (H'= 3.27, J'= 0.82) and registered 52 species from 14 families, while 31 species from 13 families were found in wheat. Thomisidae and Araneidae were the most abundant families in the herbaceous layer of both the margins and the crop, and Lycosidae in the soil litter. In contrast, 17 species from 8 families were recorded from wheat stubble, making it the least diverse habitat surveyed (H'= 1.67, J'= 0.72). These results could be related to repeated disturbance of wheat fields by harvest, tillage and other field work. Furthermore, the similarity observed in the families of both margin and crop communities indicates that colonization of wheat fields is from the adjacent areas.

From Martín García Island were collected 975 jumping spiders, from five environments, using beating net and manual sampling methods. Saitis variegatus Mello-Leitão, 1941 was the most abundant (24.62%). The sandy xerophilous forest had the highest species richness (23 morphospecies) and jungle showed the greatest spider abundance (n: 384). The sandy area was the least diverse and the last in relative abundance. Salticids represented 16% of the species recorded from Argentina, and the second largest family registered. The spider fauna found could be similar to that of the Southern Brasilian region, as occurs with scorpions. Two genera and two species are new records for Argentina. In addition, three new species of jumping spiders, as well as the discovery of the unknown male and female of two species, were registered. There was no record of cosmopolitan spiders or those with a large distribution range on the Island.

RESUMENLas arañas son consideradas de importancia para estudios de biodiversidad, conservación y sucesión. Presentan facilidad para dispersarse y establecerse en nuevos hábitats por lo que son buenos colonizadores de territorios insulares. La familia de arañas Theridiidae es una de las más diversas, representada por una gran variedad morfológica, etológica y ecológica. En Argentina no existen trabajos referidos a terídios de territorios insulares, por lo tanto, este trabajo consiste en el primer registro de la familia en estos ambientes. La Isla Martín García es una Reserva Natural e Histórica que se ubica en el sector noreste del Río de La Plata y presenta variabilidad ambiental y florística. Para analizar la riqueza específica, abundancia relativa y diversidad alfa y beta de terídios se realizaron muestreos durante tres años consecutivos mediante red de golpeo y muestreo manual. Se capturaron un total de 1173 individuos, pertenecientes a nueve géneros y 21 morfoespecies. La especie más abundante en todos los ambientes fue Cryptachaea hirta (61,68%). La selva fue el ambiente con mayor diversidad (H' = 1,9, J = 0,67) (S = 16), brindando una vasta vegetación, con amplios recursos para la subsistencia de estas arañas. La isla no correspondería a un área de importancia respecto a la singularidad de especies. Se encontraron tres nuevos registros para Argentina: C. altiventer, Theridion positivum y T. tinctorium.Palabras clave. diversidad alfa y beta, abundancia, riqueza específica, coeficiente de similitud. ABSTRACTSpiders are considered important for studies of biodiversity, conservation and succession. They readily disperse and become established in new habitats and are considered good colonizers of islands. The Theridiidae is one of the most diverse spider families, characterized by great morphological, ethological and ecological diversity. In Argentina, there are no studies of island theridiids, therefore, this study comprises the first record of the family in these environments. The Martín García Island is a Natural and Historical Reserve located in the northwest of the La Plata River and presents environmental and floristic variability. In order to analyse the species richness, relative abundance and alpha and beta diversity of