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Background The bollworm complex consisting of  Helicoverpa armigera  and  Earias vittella  is a major threat in cotton production globally. The habit of developing resistance to many insecticides including  Bt  transgenic cotton necessitates the exploration of an alternate strategy to manage bollworms. The entomopathogenic nematodes (EPN)  Steinernema carpocapsae  strain APKS2 and  Heterorhabditis bacteriophora  strains KKMH1 and TRYH1 at different concentrations of 1 × 10 9  infective juveniles (IJs)·hm −2 , 2 × 10 9  IJs·hm −2 , and 3 × 10 9  IJs·hm −2  in 500 L of water were evaluated as a foliar spray in fields naturally infested with  H. armigera  and  E. vittella  located at Eastern Block and and Cotton Research Farm of Tamil Nadu Agricultural University, Coimbaotre, India during October 2010–February 2011 and October 2011–February 2012, respectively. Results In general, all three tested EPN strains reduced the larval population of  H. armigera  and  E. vittella ; reduced square and boll damage; and subsequently increased cotton yield compared with the untreated control. The  S. carpocapsae  APKS2 is most effective against  H. armigera  whereas both  S. carpocapsae  APKS2 and  H. bacteriophora  KKMH1 were equally effective against  E. vittella.  The higher dose of 3 × 10 9  IJs·hm −2  was highly significant in the reduction of  H. armigera  larvae. However, the doses 2 × 10 9  IJs·hm −2  and 3 × 10 9  IJs·hm −2  were equally effective for  E. vittella  control. The  S. carpocapsae  APKS2 at 3 × 10 9  IJs·hm −2  caused a 62.2% reduction of  H. armigera  larvae, 34% reduction of square damage, 58.5% reduction of boll damage, and yielded 45.5% more seed cotton than the untreated control plots. In  E. vittella  infested field,  S. carpocapsae  strain APKS2 and  H. bacteriophora  strain KKMH1 at 2 × 10 9  IJs·hm −2  resulted in 60.6%~62.4% larva reduction, 68.4%~70.7% square damage reduction, 66.6%~69.9% boll damage reduction and 45.9% yield increase over the untreated control. The effective EPN treatments were comparable to the chemical insecticide chlorpyriphos 20% emulsifiable concentrate spraying at 2 mL·L −1 . Conclusions This study has shown that EPN have great potential in the management of the bollworm complex in cotton. Foliar spraying EPN strain  S. carpocapsae  (APKS2) at 3 × 10 9  IJs·hm −2  and  S. carpocapsae  (APKS2) or  H. bacteriophora  (KKMH1) at 2 × 10 9  IJs·hm −2  five times at10 days intervals are the best for the management of  H. armigera  and  E. vittella , respectively.

Management of cotton bollworms Helicoverpa armigera and Earias vittella by entomopathogenic nematodes