Resistance and Synergism of Novel Insecticides in Field Populations of Cotton Bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) in Pakistan.

The cotton bollworm Helicoverpa armigera (Hübner) is still a serious pest of non-Bt crops in Asia and Africa. It has been a notorious pest in developing resistance to all the insecticide classes applied for its control. Response of field populations of H. armigera to new chemistries having novel modes of action was monitored during 2003-2016 using a leaf-dip bioassay. No or very low level of resistance was found to newer insecticides, such as spinetoram, chlorantraniliprole, and flubendiamide during 2008-2016. There was also no or very low resistance to chlorfenapyr from 2003 to 2016. Resistance to spinosad, abamectin, and emamectin benzoate was none or very low as well during 2003-2013 and then it rose to a low level for spinosad and to a high level for avermectins by the year 2016. Methoxyfenozide resistance was very low during 2003-2010, low during 2011-2013, and moderate during 2014-2016. Resistance to thiocyclam was very low to low during 2009-2011, but it increased to moderate to high levels during 2012-2016. Resistance to indoxacarb was moderate during 2003-2006, which then decreased to low level during 2007-2010, very low level during 2011-2014, and no resistance during 2015 and 2016 corresponding to the reduced use of indoxacarb in the Pakistani agriculture. Piperonyl butoxide and tribufos exhibited a good synergism with indoxacarb and chlorfenapyr but not with spinosad in H. armigera populations. Rotation of new insecticides, having no, very low, and low resistance along with other IPM practices, is recommended to manage resistance to insecticides in H. armigera.