Effect of sublethal concentration of <i>Bacillus thuringiensis </i>var. <i>kurstaki </i>on food and developmental needs of the American bollworm, <i><span style="font-size:14.0pt;line-height:115%;font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";color:black;mso-ansi-language:EN-IN; mso-fareast-language:EN-IN;mso-bidi-language:HI" lang="EN-IN">Helicoverpa armigera </span></i><span style="font-size:14.0pt;line-height:115%;font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";color:black;mso-ansi-language:EN-IN; mso-fareast-language:EN-IN;mso-bidi-language:HI" lang="EN-IN">(Hubner)</span>

Abstract

Effect of sublethal concentration of <i>B.thuringiensis </i>on the first, third, fourth and fifth instar larvae of the American bollworm, <i>H. armigera </i>was investigated to study their response to food consumption, digestion, utilization, and their development till adult formation. The young larvae surviving <i>B. thuringiensis </i>treatment in their first instar and third instar delayed larval period by two to three days, but did not consume more food as compared to control. However, they showed higher digestibility of food as compared to control, which was compensated by their reduced ability to utilize the digested food for body substance. Contrary to the effect on first and third instar larvae, the fifth instar larvae surviving <i>B.</i> thu<i>ringiensis </i>treatment in its fourth instar consumed less food, showed less absorption efficiency in digesting food, but compensated by increase in the utilization of ingested and digested food into body substance. Insects surviving <i>B.</i> <i>thuringiensis </i>HD-1sublethal toxicity adapted to normal larval growth when fed on untreated food, depending upon insect growth prior to treatment. The moths emerging from <i>B.thuringiensis </i>treated larvae had sex ratio favouring females, and adult pairs laid less fertile eggs than those from the untreated ones. The response of <i>B.thuringiensis </i>treated larvae to their food and developmental needs is discussed.