ارزیابی اثر هم افزایی میزان نیتروژن گیاه میزبان و پارازیتوئید های تخم و لارو روی پویایی جمعیت کرم میوه خوار گوجه فرنگی Helicoverpa armigera

The tomato fruitworm, Helicoverpa armigera (Hübner), is the most important pest in decreasing quality and quantity of tomato. This study examined the effect of nitrogen fertilization, as the bottom-up force, and egg and larval parasitoids (Trichogramma principium Sugonjaev & Sorokina and Habrobracon hebetor say), as top-down forces on the population dynamics of H. armigera. Treatments included 6 tomato cultivars (Kingston, Riogrand, Earlyurbana, Redston, Superstrain-B and Primoearly) fertilized by 4 nitrogen levels (0, 2.1, 3.0, 3.9 g/pot N as Urea 46%) replicated 5 times via a factorial experiment based on the randomized complete design The fruitworm, H. armigera, fed on 8-week-old tomato plant cultivars and after one generation a pair of one day old wasp, T. principium or H. hebetor were added to its colony in each treatment., under a standard condition (25 ± 1 °C, 60 ± 5% RH and 16:8 (L: D) h) photoperiod. The number of live wasps and H. armigera was daily recorded during one generation of the parasitoids. Log-linear models showed extreme host plant fertilization significantly affected the tomato fruitworm mean population size. According to the two sex life table analysis, the intrinsic rate of increase (r) of the wasps and H. armigera were significantly different among 24 treatments, moreover, r parameter of the insects increased as the level of fertilization increased. The intrinsic rate of increase were 0.1255±0.005, 0.1961±0.013 and 0.1491±0.010 day-1 for H. armigera, T. principium and H. hebetor, respectively, on the Kingston cultivar plus 3 g nitrogen per pot. However, fertilization has synergist effects on the finite parasitism rate (ω) of the parasitoids that resulted in multiplication of parasitism rate. Based on the findings, the parasitoids performance were positively influenced with optimum nitrogen fertilization. Therefore, the synergistic effects of bottom-up and top-down factors can be used for improving management practices.