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 Nfertilization 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 agestage 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.

Multiple global change impacts on parasitism and biocontrol services in future agricultural landscapes

“…Phytophagous insects that feed on well-nourished host plants exhibit higher growth rates, higher efficiency of food use, higher fecundity, and higher abundance (Awmack and Leather, 2002;Chen et al 2010Chen et al , 2004Karowe and Martin, 1989;Mattson 1980;Moon and Stiling, 2000;Weibull 1987;Zhao et al 2015). An increase in nitrogen input may therefore improve the nutritional quantity (enhanced size of host) or quality of the host supporting the immature developing parasitoid and/or synovigenic species that require host feeding (i.e., feeding on host body fluids) for egg development, such effects of N may thus increase levels of parasitism (e.g., Chen et al 2010;Gharekhani et al 2020;Moon and Stiling, 2000;Pekas and Wackers, 2020;Sarfraz et al 2009). High N concentration in the soil may also disrupt the herbivore immune system promoting parasitoid development.…”