The impact of spiders on aphid populations in a strip‐managed apple orchard

Abstract

Aphids and their predators were studied in an apple orchard near Berne, Switzerland. To augment the density of the predators of aphids weed strips were sown in tramlines and along the border parallel to the first and the last row of trees in one half of the orchard (the other half served as control) in April 1992. Weekly visual observations, monthly beating-tray samples, branch samples in winter, and assessment of the density of spider webs and their trapping efficiency on randomly chosen trees were carried out in 1993. During 1993, significant differences in the number of aphids, aphidophagous insects, and spiders were observed on the apple trees within both the strip-managed area and the control area. The impact on aphids by the aphidophagous insects was important during the flowering time of weeds in spring and summer. In autumn, however, spiders (i.e. Araniellu spp.) were the dominant predators of aphids on the trees; during this time of the year they were more abundant within the strip-managed area of the orchard. With a higher density of webs, spiders significantly reduced the number of aphids able to return from their summer host plants. Consequently, less hatching aphids were found on branch samples of the strip-managed area compared to the control area. The effects of the weed strips on spiders and aphidophagous insects, and the resulting impact of predation on the aphids are discussed.

Spider and Leafhopper (<I>Erythroneura</I> spp.) Response to Vineyard Ground Cover

“…Similar conclusions have been reached by others. Wyss et al (1995) found that apple trees grown with ground vegetation had higher densities of Araniella spp., and concluded that the ground cover did not provide habitat for Araniella spp. but rather increased the availability of alternate prey.…”

“…Further more, spiders have been assumed to play a role in leafhopper suppression in California vineyards (Wil son et al 1992, Roltsch et al 1998. Spider density in other agroecosystems has been increased through strip-mowing (Nentwig 1988), straw mulches (Riec hert and , Halaj et al 2000, strips of weedy vegetation (Jmhasly andNentwig 1995, Wyss et al 1995), and intercropping (Letourneau 1990), al though in contrast, Ali and Reagan (1986) did not Þnd consistent differences in spider diversity in weedy versus weed-free sugarcane.…”

The effects of plant cover on population of pear psylla (Cacopsylla pyricola) and its predators

“…Thus, plant cover had nil effect on the pear psyllid control. Some studies have reported a decrease in herbivore density in the presence of ground cover vegetation (AguilarFenollosa et al, 2011;Altieri and Schmidt, 1986;Beizhou et al, 2011;Irvin et al, 2006;Pfammatter and Vuignier, 1998;Rieux et al, 1999;Wyss, 1995;Wyss et al, 1995) et al, 1982;Meyer, 1990a, 1990b;Spellman et al, 2006). All of these studies have shown that selection of the plant cover species in the orchard is important in preventing increased pest population.…”

Comparación de la abundancia y biodiversidad de artrópodos auxiliares entre parcelas de cultivo ecológico y convencional, en plantaciones de cítricos, caqui y nectarina

“…Según estos autores el manejo del hábitat se puede abordar a nivel de la parcela, de la explotación o del paisaje. En los últimos años se ha publicado una gran cantidad de estudios sobre el papel que pueden cumplir los distintos componentes del sistema agrícola, tales como las cubiertas vegetales (Bugg y Waddington, 1994;Wyss et al, 1995;Sirrine et al, 2008;Gámez-Virués et al, 2009;Silva et al, 2010), los márgenes de los cultivos (Rieux et al, 1999;Holland y Fahrig, 2000;Olson y Wäckers, 2007), los corredores vegetales (Nicholls et al, 2001) y, en general, las denominadas áreas no cultivadas (Gurr et al, 2003;Boller et al, 2004;Bianchi et al, 2006). …”

“…El aumento de la diversidad de plantas puede producir un efecto directo de reducción de la densidad de fitófagos a través de la hipótesis de concentración de recursos. También puede incrementar el tercer nivel trófico (enemigos naturales de las plagas) y de esta manera colaborar en la disminución de los fitófagos (Hesler et al, 1993;Drinkwater et al, 1995;Wyss et al, 1995).…”