Effects of predator specialization, host plant and climate on biological control of aphids by natural enemies: a meta‐analysis

Abstract

Summary Aphids are among the most severe invertebrate pests of crops and cause high economic losses. The control of aphids by natural enemies is an essential ecosystem service with high relevance to management strategies applied in agricultural plant production and horticulture. However, the current knowledge on the effectiveness of specialist and generalist predators in aphid control with respect to host plants and climatic conditions has not yet been summarized in a meta‐analytical approach. We collected 60 studies providing 168 independent cases of predator exclusion experiments to analyse how predator and host plant group and climatic conditions affect aphid control by natural enemies. Effects of natural enemies on aphid populations were strongest in assemblages that included specialist predators, either alone or with generalist predators. Generalists alone also reduced aphid numbers significantly, but not to the same extent as specialists. Effects of natural enemies were weaker on aphid populations feeding on legumes compared with aphids on grasses or herbs. The percentage reduction of aphids feeding on grasses, herbs or legumes was higher in treatments with assemblages or specialists alone compared with generalists with the largest difference on grasses. According to all field studies from the temperate zone, effects of natural enemies on aphid populations were strongest in areas with high precipitation seasonality. A relationship between predator effects and temperature seasonality was only found for the USA. Synthesis and applications. Specialist predators alone or assemblages of specialists and generalists had the strongest effect on aphid populations, especially when either feeding on grasses and herbs or when exposed to extreme weather events. The control of aphids by natural enemies is most promising in grass and herb crops, whereas it is less suited for controlling aphids in legume crops. Facing climate change, the effect of extreme weather events on aphid control by natural enemies will have further implications for developing management strategies for aphid control in the future.

A Generalist Protist Predator Enables Coexistence in Multitrophic Predator-Prey Systems Containing a Phage and the Bacterial Predator Bdellovibrio

“…The strong stabilizing effects of generalist predators on predator-prey cycles were already described in a theoretical study using a reactiondiffusion-advection modeling framework (Vitense et al, 2016). In addition, a meta-analysis of 60 predator-exclusion experiments with different specialized aphid predators showed similar results (Diehl et al, 2013). Assemblages that contained either only specialists or specialists and generalists had the greatest effect on the reduction of the aphid population compared to an assemblage of only generalists.…”

“…In addition, species-specific traits, such as resource specialization, strongly affected prey biomass and diversity (Jiang and Morin, 2005;Filip et al, 2014) and induced shifts in trophic cascades (Steiner, 2001). Studies focusing on the combined effect of multiple predators with different resource utilization are unfortunately rare (Jiang and Morin, 2005;Diehl et al, 2013), but most likely better reflect natural communities and enable the direct observation of a major mediator of coexistence: resource partitioning (Chesson, 1991). Narwani and Mazumder (2010) showed that the overall consumption of specialist predators decreases at higher resource diversities, whereas generalist predators show an increase in consumption (Narwani and Mazumder, 2010).…”

Supporting Agricultural Ecosystem Services through the Integration of Perennial Polycultures into Crop Rotations

“…The control of aphids, for example, by natural enemies is most promising in grass and herb crops, and is less suited for legume crops [108]. Perennial legume-grass mixtures strongly decrease the risk of annual summer weeds and also reduce annual winter weeds, especially if grown for three years [109].…”

Ecosystem services—current challenges and opportunities for ecological research

“…Serviceproviding units* Predator density Menalled et al, 1999;Letourneau et al, 2009 Pest density Mols et al, 2007 Predator richness Duelli and Obrist, 2003 Species composition of pests and predators Bastian et al, 2013 Pest consumption rates Ingegno et al, 2013;Shrestha and Parajulee, 2013 Pest reduction Schmidt et al, 2003;Diehl et al, 2013 Ecosystem modification challenges in assessing ecosystem services arise from the need (i) to evaluate relationships between services and the kind of measures usually collected in ecological studies (e.g., species richness) and (ii) to account for the characteristics of ecological processes (e.g., dynamics, feedbacks, and uncertainties) in statistical models focusing on service provision. Final ecosystem services are often directly assessed, but such assessment does not provide information about contributing ecological processes or how management could be adapted to increase service provision.…”

“…The assessment of biological control may therefore be improved if a small set of selected measures is included that covers aspects of service and disservice-providing units (e.g., pest consumption rates), ecosystem management (e.g., insecticide applications) and landscape modification (e.g., proportion of semi-natural habitats in the surrounding landscape; Table 2). Consideration of abiotic variables such as climate (Diehl et al, 2013) or soil characteristics (Birkhofer et al, 2008) will add to the explanatory power of this set of measures.…”