Intrinsic growth rate of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) feed on three sweet sorghum varieties

Study on the intrinsic growth rate of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidea) on three varieties of sweet sorghum carried out in the Entomology Laboratory of Indonesia Cereals Research Institute (ICERI) in Maros, lasted from August 2013 to April 2014. One of the basic information needed to support successful control of H. zea is knowing its bioecology. Detailed information on this is still rare in Indonesia. Integrated Pest Management (IPM) is control strategy with the ecological approach with a basic knowledge of bioecology (biotic potential) of a pest. Biotic potential of a pest can be expressed quantitatively by a parameter called the intrinsic growth rate. This study was aimed to determine the intrinsic growth rate of H. zea on 3 varieties of sweet sorghum - Sorghum bicolor L. Moench (Super 1, Super 2 and Numbu). Larvae and pupae were collected from sweet sorghum crop in ICERI Experimental Farm, and then propagated in the laboratory in plastic containers individually. Each larvae was fed according to the origin of the larvae have been collected. Larvae and pupae were maintained until become a moth, and then allowed to mate and lay eggs. The moths were feed with 10% honey solution. The mass reared insect would be used on the study of life probability and fecundity of H. zea. The life probability study performed by means of: 300 newly laid eggs (F1), kept up to become adults. Each egg put in a container and maintained until became larvae. The neonate larvae fed on Super 1, Super 2, and Numbu sweet sorghum grain (100 larvae each variety). Observations were made every day, by counting the number of eggs hatched, larvae, pupae and moths alived. The study on fecundity of H. zea moth was done by: a pair of H. zea (F1) from each variety put in container for egg laying. This activity was carried out with 5 replications. Observations were made each day by counting the number of eggs laid until the female moths were died. Sex ratio is determined by observing all the eggs are laid until they became larvae, pupae and moths from 3 pairs per variety. The analysis results showed that the intrinsic growth rate (r) of H. zea at Super 1, Super 2, and Numbu were 0.107, 0.152, and 0.149 individuals per day respectively. Net reproductive rate (R0) at Super 1, Super 2, and Numbu were 29.09, 117.45, and 104.17 times/generation respectively. Average length of life cycle (T) at Super 1, Super 2, and Numbu were 31.24, 31.32, and 31.17 days respectively. The growth rate model was Nt = N0.ert, so that a moth of H. zea can develop into 44 females for 35 days on Super 1, 206 females for 35 days on Super 2, and 184 females for 35 days on Numbu.