Abstract
This study evaluated the parasitism of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) on eggs of Helicoverpa armigera Hubner (Lepidoptera: Noctuidae) at different ages and densities. The rates of parasitism and emergence, the number of parasitoids emerged per egg and sex ratio of offspring were evaluated in both experiments. Eggs of H. armigera up to 36 hours provided greater parasitism and emergence of adults compared to eggs up to 60 hours old. The number of parasitoids, which emerged per host egg, was greater than one and the sex ratio remained around 80% of females, regardless of the egg development stage. Females of T. pretiosum responded with superior rates of parasitism, emergence and number of parasitoids per egg at the densities of 20 and 25 eggs of H. armigera . These results indicate that T. pretiosum parasite with superior performance in eggs of up to 36h of age and densities of 20 eggs per female day -1 in laboratory conditions. These results will help to establish the intervals between releases of parasitoids, aiming to control this pest, when adjusted with knowledge of the survival of the parasitoids in the field and in pest infestation.
Highlights
The cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), which is a cosmopolite and polyphagous pest, has been introduced in Brazil (Czepak, Albernaz, Vivan, Guimarães, & Carvalhais, 2013; Specht, Sosa-Gómez, Paula-Moraes, & Yano, 2013; Gómez et al, 2016)
The larvae preferably feed on leaves, remaining exposed to agent controls in this phase (Figueiredo et al, 2006). In later instars, they attack the reproductive structure of plants, which can be located in the lower parts protected by the canopy, or even sheltered inside the fruits becoming partially protected
The average number of parasitized eggs by T. pretiosum varied depending on the eggs embryonic development stage of H. armigera (F2, 42 = 39.27; p < 0.0001) (Table 1)
Summary
The cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), which is a cosmopolite and polyphagous pest, has been introduced in Brazil (Czepak, Albernaz, Vivan, Guimarães, & Carvalhais, 2013; Specht, Sosa-Gómez, Paula-Moraes, & Yano, 2013; Gómez et al, 2016). Since it has been causing losses in the production of several crops. The main injuries are the defoliation and the attack on the reproductive structure by larvae. In later instars, they attack the reproductive structure of plants, which can be located in the lower parts protected by the canopy, or even sheltered inside the fruits becoming partially protected
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