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

Abstract

Abstract 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 × 109 infective juveniles (IJs)·hm−2, 2 × 109 IJs·hm−2, and 3 × 109 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 × 109 IJs·hm−2 was highly significant in the reduction of H. armigera larvae. However, the doses 2 × 109 IJs·hm−2 and 3 × 109 IJs·hm−2 were equally effective for E. vittella control. The S. carpocapsae APKS2 at 3 × 109 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 × 109 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 × 109 IJs·hm−2 and S. carpocapsae (APKS2) or H. bacteriophora (KKMH1) at 2 × 109 IJs·hm−2 five times at10 days intervals are the best for the management of H. armigera and E. vittella, respectively.