Spider Communities and Biological Control in Native Habitats Surrounding Greenhouses

Abstract

The promotion of native vegetation as a habitat for natural enemies, which could increase their abundance and fitness, is especially useful in highly simplified settings such as Mediterranean greenhouse landscapes. Spiders as generalist predators may also be involved in intra-guild predation. However, the niche complementarity provided by spiders as a group means that increased spider diversity may facilitate complementary control actions. In this study, the interactions between spiders, the two major horticultural pests, Bemisia tabaci and Frankliniella occidentalis, and their naturally occurring predators and parasitoids were evaluated in a mix of 21 newly planted shrubs selected for habitat management in a highly disturbed horticultural system. The effects of all factors were evaluated using redundancy analysis (RDA) and the generalized additive model (GAM) to assess the statistical significance of abundance of spiders and pests. The GAM showed that the abundance of both pests had a significant effect on hunter spider’s abundance, whereas the abundance of B. tabaci, but not F. occidentalis, affected web-weavers’ abundance. Ordination analysis showed that spider abundance closely correlated with that of B. tabaci but not with that of F. occidentalis, suggesting that complementarity occurs, and thereby probability of biocontrol, with respect to the targeted pest B. tabaci, although the temporal patterns of the spiders differed from those of F. occidentalis. Conservation strategies involving the establishment of these native plants around greenhouses could be an effective way to reduce pest populations outdoors.

Top-down suppression of arthropod herbivory in intercropped maize and organic farms evidenced from δ13C and δ15N stable isotope analyses

“…Therefore, such semi-natural areas are probably important to non-spider predators primarily as refuges or breeding grounds, not as foraging grounds. This finding concurs with observations by Gaigher et al (2015) and Cotes et al (2018) who reported the occurrence of parasitoids, in particular, at higher abundances and diversities in remnant vegetation surrounding agricultural field crops. Alternatively, such non-spider predators fed predominantly on crop-borne herbivore prey because these prey occur on crops at higher densities, thus easier to locate.…”

“…For example, Schmidt et al 2005reported enhanced spider densities within a plot containing a mixture of crop and noncrop plants; and noted that their ability to shuttle between the two habitat types may make them efficient at controlling aphid abundance across whole-field or whole-farm agricultural landscapes. Therefore, the ability of spiders to derive basal food source carbon from both crops and noncrops suggests the importance of using semi-natural field margins and hedgerows to facilitate herbivore suppression by these predators in both crop fields and semi-natural field edges (Schmidt et al 2005;Cotes et al 2018).…”

Variations in community assemblages and trophic networks of aphids and parasitoids in protected crops

“…Conservation biological control would thus be a way to enhance the natural regulation of aphids in greenhouses. A way to promote colonization by key indigenous parasitoid species would be to provide them with habitat and food inside or outside of greenhouses (Cotes et al 2018, Rodríguez et al 2018). Indeed, impacts of landscape complexity on the natural enemies of crop pests have been widely studied (Chaplin‐Kramer et al 2011), especially for parasitoid communities (Kruess 2003, Thies et al 2003, Rand et al 2012).…”

Food web structure of parasitoids in greenhouses is affected by surrounding landscape at different spatial scales

“…Management of the surrounding habitats may be a promising strategy to enhance biological control in greenhouses. Recently, methods involving the establishment of native plants around greenhouses have been studied for natural enemy conservation in a greenhouse-dominated landscape 56,57 . More importantly, these plants should increase the number of natural enemies in the surroundings and facilitate the migration of natural enemies to the greenhouses when necessary.…”