Tri-trophic interactions among nitrogen-fertilized tomato cultivars, the tomato fruit worm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) and the ectoparasitoid, Habrobracon hebetor (Say) (Hymenoptera: Braconidae)

Abstract

Nitrogen is one of the most critical elements for plant and herbivore growth. This research aimed to investigate the bottom-up effect of varying nitrogen fertilization on the demography of the ectoparasitoid, Habrobracon hebetor (Say) on the tomato fruit worm, Helicoverpa armigera (Hübner) reared under different host-plant treatments. Six tomato plant cultivars (e.g., Kingston, Riogrand, Earlyurbana, Redston, Superstrain-B, and Primoearly and 4 N-fertilization levels (0, 2.1, 3.0, 3.9 g/pot nitrogen as urea 46%) were tested, using 5th instar larvae of H. armigera parasitised by H. hebetor under laboratory conditions. The mortality rate and developmental time of the immature stages of the parasitoid, as well as adult longevity and fecundity, were recorded. Data were analyzed based on age-stage two-sex life-table theory. The results showed that the developmental duration of the parasitoids was affected by the increase in the levels of nitrogen. The highest value was observed at 12.83 ± 0.11 days on Earlyurbana with the lowest nitrogen level. The lowest intrinsic rates of increase (r) and finite rates of increase (λ) were 0.1058 ± 0.0147 and 1.1013 ± 0.0157 day^− 1, respectively, regarding the lowest (zero) level of added fertilizer. However, the highest rates were 0.1515 ± 0.018 and 1.1608 ± 0.013 day^− 1, respectively. The fecundity and longevity of adult wasps were positively correlated with nitrogen levels. Accordingly, differences in host-plant quality can indirectly affect the performance of parasitoids via the herbivore.