Field margin vegetation enhances biological control and crop damage suppression from multiple pests in organic tomato fields

Abstract

Ephemeral cropping systems are characterized by frequent disturbances of ecological processes, which may compromise the conservation of plant and arthropod diversity and the ecosystem services they may provide. Conservation biological control practices include habitat manipulations that provide non-pest resources and selectively enhance natural enemies' effectiveness. This study, conducted in eight commercial fields of organically grown tomato, compared the effectiveness of sown flower strips with semi-natural margins in regulating natural enemy abundance, biocontrol, and crop damage. During repeated visits, the abundance of different arthropod groups was recorded. Crop surveys included measurement of aphid abundance, parasitism, and leaf and fruit damage from sap-sucking and lepidopteran pests. Semi-natural habitats were associated with higher vegetation diversity, but natural enemies were more strongly associated with sown strips during flowering. Sap-sucking pests were always recorded in higher abundance in flower strips, but crop damage in the plots adjacent to these strips was lower, suggesting that these strips may act as a trap-crop. The inclusion of floral supplements enhanced the parasitism rate of aphids in the crop, and reduced the rate of increase of lepidopteran-caused foliar damage with time. Early in the growing season, semi-natural strips showed significantly lower levels of crop damage and aphid counts, suggesting that these habitats may be important during early crop colonization by natural enemies. These results indicate that the inclusion of flower strips enhances the conservation of arthropod functional diversity in ephemeral crops, and that diverse mechanisms are important for controlling different pests. However, the efficacy of habitat manipulation is likely to be greater when it is complemented with the conservation of diverse semi-natural vegetation in the pre-existing field margin

Pest regulation and support of natural enemies in agriculture: Experimental evidence of within field wildflower strips

“…Whereas wheat control plots were more infested by aphids than the one in between WFS, few hoverfly larvae were observed on tillers. This indicates that hoverfly adults were first attracted by WFS in order to fulfil their need of proteins and energy, and then oviposited on adjacent wheat tillers if they were infested by aphids, which is consistent with the description given by Nevertheless, the present results are in the continuity of previous research (among others, Balzan and Moonen, 2014;Tschumi et al, 2016aTschumi et al, , 2016b, showing that implementing WFS in agricultural landscapes can benefit farmer's activities. In Europe, it can even be subsidised though the agri-environmental schemes of the Common Agricultural Policy (Haaland et al, 2011).…”

“…Some recently showed a positive effect on pest reduction (Balzan and Moonen, 2014;Tschumi et al, 2016aTschumi et al, , 2016b but previous ones recall that it may not be systematic (Hickman and Wratten, 1996;Pfiffner et al, 2009). …”

Nectar accessibility determines fitness, flower choice and abundance of hoverflies that provide natural pest control

“…). Optimal field margin strips can most easily be created by sowing annual seed mixtures (Balzan & Moonen ; Tschumi et al . ), containing, for example Fagopyrum esculentum, Centaurea cyanus , annual Apiaceae or other species with open or shallow flowers.…”

Manipulating field margins to increase predation intensity in fields of winter wheat (Triticum aestivum)

“…). The presence of flowers adjacent to crops can promote a higher level of pest control compared to grass (Blaauw and Isaacs ; Balzan and Moonen ). This is usually attributed to the presence of floral resources (pollen, nectar and sometimes extra‐floral nectar) that may be necessary during particular life stages of natural enemies such as hoverflies, lacewings, ladybirds and some spiders (Wäckers et al.…”