DIFFERENTIAL RESPONSE OF SELECTED WILD NICOTIANA SPECIES TO BEET ARMYWORM, SPODOPTERA EXIGUA (HUB.)

Abstract

The response of nine wild Nicotiana species to the beet armyworm, Spodoptera exigua (Hub.) was studied through construction of age-specific life tables, age-specific fertility table of female and computing the life parameters. It was observed that S. exigua could complete its life cycle only on N. eastii. The survivorship of the insect on the other species ranged from 6-26 days. Lowest survival (6 days) and life expectancy (3.44) were recorded when the insect was reared on N. acaulis. On N. eastii, the species that supported complete life cycle, agespecific life table took 30 days and the expectancy of life at the beginning of life table was 9.91. Immature stages and pre-oviposition period of female lasted 25.5 days on this species and the female survivorship was 0.02 at the beginning of fertility table of female . Potential fecundity to an extent of 78.96% was contributed during the first three days of the fertility table. The net reproductive rate (R0) was 13.32 and the potential fecundity (Pf) was 707.0 on this species. Mean generation time (Tc) was 27.24 days and an intrinsic rate of increase (rc) of 0.10 females / female / day was recorded. The weekly multiplication rate was 1.95 and the population of the insect could double itself in 7.29 days on this species. The species, N. gossei, N. acaulis and N. alata which differed the development of S. exigua with lowest life expectancy could be utilised as sources of resistance to this pest in future breeding programmes after the inheritance of resistance of this trait is established.