Quantifying the prevalance of intraguild predation in winter wheat: impact on biological control

Aphids (Hemiptera:Aphididae) are pests of multiple cropping systems, primarily due to the viruses they vector and their rapid rate of population growth.  In Kentucky winter wheat, grain aphids (Rhopalosiphum padi and Sitobion avenae) cause significant yield loss as vectors of Barley Yellow Dwarf virus (BYDV), prompting the routine application of insecticides.  Coupled with increasing human populations and decreasing arable land, it is becoming evident that biological control services provide by natural enemies represent viable management options.  Aphids are preyed upon by a diverse array of natural enemies in winter wheat and these species can be exploited in conservation biological control.  This research utilized extensive field sampling and molecular techniques to examine specific relationships between aphids and their predators.  PCR-based gut content analysis and species-specific aphid primers (R. padi and S. avenae) were used to identify key aphid predators, revealing adult and larval ladybeetles (Coccinellidae:Coleoptera) and green lacewings (Chrysopidae:Neuroptera) as the most abundant predators over two field seasons.  However, these predators are known to consume the same resources and exhibit considerable spatial and temporal overlap, thus making them competitors.  This potential for intraguild predation can reduce the effectiveness of aphid suppression, so additional species specific primers were used (Coleomegilla maculata and Coccinella septempunctata) to identify predation by lacewings on ladybeetles.  Our research shows that there is IGP by lacewings, but it occurs after aphid populations decline, therefore not hindering aphid biological control.