Abstract
Nitrogen (N) is one of the most critical elements for plants and herbivores growth. Bottom-up effect of varying nitrogen fertilizations on demography of Habrobracon hebetor(say) on Helicoverpa armigera (Hübner) reared on different host plant treatments were investigated. Six tomato plant cultivars including Kingston (K), Riogrand (RG), Earlyurbana (E), Redston (R), Superstrain-B (SB) and Primoearly (P) ,with N fertilization regime consisted of four levels (n0 = 0, n- = 210, ns = 300, n+ = 390 kg Ha-1N as Urea 46%) , applied by fifth instar larvae of H. armigera (Hüb.) and evaluated in a factorial experiment based on a randomized complete design with 5 replications. H.armigera larvae on 24 treatments parasitized within a 24-h period were established at laboratory conditions ( 25 ± 1 °C, 60 ± 5% RH 16:8 (L:D) h). One H. hebetor egg was left on each larvae and the remaining eggs were removed. Parasitized larvae were individually kept under the same conditions as described above. The mortality, developmental time of immature stages as well as the longevity and fecundity of adult stages was recorded. Data was analyzed based on age-stage, two-sex life table theory. Developmental duration of parasitoid wasps affected by increasing nitrogen. The net reproductive rate (R0) ranged from 9.5±1.94 to 12.34±2.81 eggs on Pn0 and Kn+ treatments respectively. The lowest values of the intrinsic rate of increase (r) and finite rate of increase (λ) were 0.1058±0.0147 & 1.1013±0.0157 day-1 on En0 and the highest ones were 0.1515±0.018 & 1.1603±0.022 day-1 on Kn+. The mean generation time (T) of H. hebetor for different N levels ranged from 16.41±0.117 to 18.8 ±0.259 days on the cultivars. The life expectancy of an H. hebetor egg on H.armigera ranged from 9.1 to 9.79 days on the cultivars. Fecundity and longevity of wasps were also positively correlated with N-fertilizer application. Results of the present study demonstrated that qualitative differences in herbivore diet can affect the performance of parasitoid wasps, and bottom-up forces play noticeable role in mediating interactions involving plants–herbivores–parasitoids and should be considered in IPM and ICM programs.