Effect of Bt-cotton on biodiversity of natural enemies.

Abstract

Studies on the biodiversity of natural enemies on Bt (RCH 134) and non-Bt (RCH 134 and LHH 144) cotton hybrids were curried out during Kharif 2003 at Punjab Agricultural University, Ludhiana. Overall population of natural enemies remained low during the season. Pooled data of all the observations revealed that Bt cotton hybrid KCH 134 recorded significantly higher population of Chrysoperla carnea , spiders, Geocoris bug and yellow wasps, Polistes hebraeus (Fabricius) (0.76, 1.87, 1.45 and 0.65/plant) than non-ltt hybrid RCH 134 (0.43, 1.05, 0.89 and 0.46/plant) and LHH 144 (0.44, 1.08, 1.12 and 0.47/plant). The population of coccinellid beetles was very low and there was non-significant differences in its populations in Bt and non-Bt cotton hybrids. The value of general diversity index (Shannon Weaver's index) was comparatively higher in Bt cotton hybrid RCH 134 as compared to non-Bt hybrids RCH 134 and LHH 144 in most of the observations. However, higher value of diversity index was recorded in LHH 144 i.e. 1.349 and 1.340 on Sept 1 and 10, respectively. Higher population of natural enemies recorded in Bt cotton hybrids may be ascribed to reduction in number of insecticidal sprays (only one application) as compared to non-lit hybrids, which received higher number of insecticidal sprays (six applications).