Alternative insecticides to control cereal aphids, Sitobion avenae, that are resistant to pyrethroids.
Cereal aphids, Sitobion avenae, have developed resistance to pyrethroids in the last few years, culminating in control failure at some locations in England 2011 and 2012, associated in the latter year with local epidemics of barley yellow dwarf virus (BYDV). Studies by Rothamsted Research and Syngenta have shown this to be due to target site resistance, which can be detected in populations by using a vial test, and in individual aphids using a DNA diagnostic test. Field trials in autumn 2012 using inoculations of a clone of S. avenae that was resistant to pyrethroids showed that cypermethrin at 25 g a.i./ha and deltamethrin at 7.5 g a.i./ha gave significantly poorer control than chlorpyrifos at 450 g a.i./ha, but not lambda-cyhalothrin at 7.5 g a.i./ha. In two trials to test alternative products, the carbamate pirimicarb at 120 g a.i./ha gave moderate control at one site, but good control at another; with neonicotinoids, thiacloprid gave good control at both sites, while acetamiprid at 50 g a.i./ha was relatively poor. Pymetrozine at 100 g a.i./ha plus adjuvant oil gave good control at the one site it was tested. Chlorpyrifos gave best control. None of these alternatives are currently approved for use against aphids in cereals in the autumn, but these results will give regulators some evidence for their activity against resistant grain aphids, should alternatives be required.