Biometrical Analysis of Helicoverpa armigera (Hübner) on different Hosts

To study the applicability of Dyar's principle to the larval stage of Helicoverpa armigera, when the larvae reared on pigeon pea, Indian bean and chick pea, biometrical analysis were carried out during kharif 2005–2006. The measurements of head capsule, width of the larvae fall into six well-defined groups each indicating an instar, when larvae were reared on different hosts at a constant temperature of 28 ± 1°C. The mean value of the observed (0.240 to 2.654 mm) and calculated head widths (0.230 to 2.780 mm) and progression factors were close to each other, which indicated that the width of head capsule of H. armigera was more or less constant for that particular instar. The observed and estimated progression factors were sufficiently close to indicating the increase in head width that follows Dyar's Law. The progression factors determined from body length and width indicated the great deviation. The values of R² between the variables viz., head capsule width, larval body length and larval body width ranged from 0.9713 to 0.9859 on these hosts. This indicated a very high predictability of head capsule width through larval body length and larval body width.