Virus transmission in winter wheat: Potential suppression by natural enemies

In winter wheat, aphids (Hemiptera: Aphididae) cause substantial yield loss through direct feeding but, more significantly, as vectors of Barley Yellow Dwarf virus (BYDV). They transfer the virus from infected to healthy plants as they feed, causing discoloration, stunted growth and sterility, with yield loss averaging 17% worldwide. Importantly, these aphids are preyed upon by foliage dwelling predators and, when they fall to the ground, epigeal spiders which play a major role in preventing re-colonization of the plant. In the absence of such predation, re-colonization rates are as high as 95%. Spiders are therefore important generalist predators in agroecosystems and, as part of the community of natural enemies that frequent such habitats, can help to reduce herbivorous pest populations. Thus in this system, spiders have the potential to reduce the spread of BYDV if preying selectively on infected aphids which may be more susceptible to spider predation due to changes in behavior.

A study was therefore undertaken to examine the incidence of BYDV in winter wheat and aphids (Rhopalosiphum padi, Sitobion avenae) and, to identify predation rates on infected aphids by common spiders within this agroecosystem. Enzyme linked immunosorbent assay (ELISA) was used to test for the virus throughout this food web and ultimately identify potential effects of epigeal spiders on aphid population dynamics and disease transmission. The results are discussed in the context of biological control and habitat manipulation, as we seek to reduce our reliance on chemical inputs and move towards more sustainable methods of pest control.