Tannins have been implicated in the resistance of some cotton varieties to insect attack. The relationship between tannin concentration and susceptibility of some Egyptian cotton varieties to piercing sucking insects has been undertaken in the present work. Eight Egyptian cotton derived from Gossypium barbadense and one variety from G. hirsutum were evaluated. There is a significant negative linear relationship between the concentration of tannins in two Egyptian varieties, Giza 70 and Giza 76, and the population density of piercing sucking insects. On the contrary, a positive correlation existed between piercing sucking insect infestation and tannin concentrations in the two cotton varieties, Giza 80 and Giza 81. This may be attributed to the low level of tannins in these two varieties.
Laboratory experiments were carried out to evaluate the acceptance of Trichogramma evanescens (Westwood) (Hymenoptera: Trichogrammatidae) to long and short cold storage periods of the host, the Angoumois grain moth, Sitotroga cerealella Olivier (Lepidoptera: Gelechiidae) eggs. The eggs were stored at 5°C for 5, 10, 15, 20, and 30 days, before exposing to the parasitoid. Fecundity, longevity, percentage of adult emergence, sex ratio, and general productivity (GP) were investigated. Storage period to 5 days showed the highest productivity of (28.16 females), with a parasitism efficiency of 85.64%. Increasing storage periods to 10, 15, and 20 days reduced the general productivity of the females to 22.90, 15.00, and 7.75 females, respectively, accompanied by decreased parasitization efficacy values 69.65, 46.62, and 23.57%, respectively. The 30-day storage period decreased sharply the fitness components of Trichogramma females. Generally, the results indicated that the storage period to 5 days was the most favorable.
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