Abstract
Cereal aphids cause economic injury to wheat crops. In Argentina,Eriopis connexais an indigenous ladybird. In the present study, the numerical response ofE. connexato changes in aphid density on wheat crops with high and low plant diversity was investigated. The study was carried out in Balcarce, Buenos Aires, Argentina, from September to December 2007 and 2008, on two wheat crops with either a higher plant diversity (HPD) with refuge strips or a lower plant diversity (LPD) without refuge strips. Crops were sampled every week and the abundance of aphids andE. connexawas recorded. The dominant aphid species wereSchizaphis graminum, Metopolophium dirhodum,andSitobion avenae.Eriopis connexashowed a linear increase in the numerical response to an increase in aphid density, which varied in space and time. The abundance ofE. connexaincreased in relation to the crop development and aphid population and was higher in the HPD than in the LPD system. This predator increased its reproductive numerical response only in 2008, with a significant liner response in the HPD system. This suggests that the potential ofE. connexaas a predator of cereal aphids also increases directly in proportion to landscape vegetal diversity.
Highlights
Cereal aphids (Hemiptera: Aphididae) are among the most important pests on wheat crops in the world, since they are found in all temperate regions and cropping systems and have the potential to reduce yields [1, 2]
The results showed that increasing the structural complexity of the habitat surrounding wheat crops resulted in a higher abundance of E. connexa that would account for the smaller abundance of cereal aphids registered in the higher plant diversity (HPD) systems
The numerical responses of E. connexa were affected by cereal aphid abundance, but the most important results of this study support the view that E. connexa dynamics is exclusively related to prey abundance and to plant diversity
Summary
Cereal aphids (Hemiptera: Aphididae) are among the most important pests on wheat crops in the world, since they are found in all temperate regions and cropping systems and have the potential to reduce yields [1, 2]. Aphid damage in wheat crops causes losses in yields and grain quality [5,6,7,8,9,10,11]. Insecticide application is the strategy selected by farmers to control aphids in wheat crops around the world. As a consequence, promoting the activity of predators and parasitoids in growing systems to maintain aphid populations below the economic injury level remains a desirable goal [15]. Several groups of natural enemies can control aphid populations in wheat crops, such as parasitoid wasps (Hymenoptera: mainly Aphidiidae) and a very large number of predators such as hoverfly larvae (Diptera: Syrphidae), lacewing larvae (Neuroptera: Chrysopidae), and ladybird adults and larvae (Coleoptera: Coccinellidae) [16, 17]
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