Abstract
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 (1 x 1m) 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.
Highlights
Dentro de estos últimos se destacan las especies A. kondoi y A. pisum, responsables en los últimos años de graves pérdidas económicas en Argentina
Coincidentemente con LeSar & Unzicker (1978) y Young & Edwards (1990) en los cultivos estudiados predominaron también las arañas pequeñas, contando por lo tanto con una gran disponibilidad de presas potenciales
Summary
Cuatro tipos de experiencias se realizaron con las especies de arañas dominantes del cultivo de alfalfa Misumenops pallidus (Keyserling, 1880), Oxyopes salticus Hentz, 1845, Araneus sp. y Lycosa poliostoma (Koch, 1847) (Armendano & González 2010) sobre áfidos, gorgojos, larvas de lepidópteros, crisomélidos y ortópteros. Tasas de consumo: En cada jaula se ubicaron una de las tres especies de presas (A. gemmatalis, R. nu y S. frugiperda) con una densidad de 10 larvas/m2 con un ejemplar de araña de cada especie (M. pallidus, O. salticus y Araneus sp.) por separado. Efecto indirecto de los depredadores sobre la vegetación: El experimento se llevó a cabo durante 72h, con 10 réplicas para cada uno de los tres tratamientos: (i) solamente plantas de alfalfa (ii) plantas y larvas defoliadoras, (iii) plantas, larvas y arañas (10 larvas de R. nu en estadío 2 y 3 por planta, y un ejemplar de O. salticus). Los valores del Índice Q para las tres especies de arañas demostraron una selectividad positiva sólo para las larvas defoliadoras, mientras que para áfidos y curculiónidos presentaron valores entre 0 y 1 (selectividad negativa) (Test de student, p
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