The impact of cold storage durations on Trichogramma evanescens (Westwood) (Hymenoptera: Trichogrammatidae) during their pupal stage

This experimental study was done at the Biological Control Laboratory, Sakha Agricultural Research Station, Sakha, Kafrelsheikh, Egypt. We aimed to estimate the impact of different cold (10 °C) storage durations [0 (non-cold-stored parasitized eggs), 3, 6, 9, 12, 15, 18, 21, 24, 27, and 30 days], on Trichogramma evanescens (Westwood) (Hymenoptera: Trichogrammatidae) during the pupal stage using the eggs of Sitotroga cerealella after exposing to T. evanescens. The emergence percentage of non-cold-stored eggs of S. cerealella was higher than all cold-stored durations. Also, the female’s percentages of T. evanescens in the cold storage durations were lower than the non-cold storage one, and they were influenced by extended cold storage durations. There were non-significant differences in the female’s longevity of T. evanescens obtained from 0, 3, and 6 days cold-stored parasitized eggs of S. cerealella at 10 °C, but it began to decrease from those produced after 9 days of cold-stored eggs. In addition, the emergence percentage in F1 progeny of T. evanescens was greater than 50% until 21 days of cold storage. It could be concluded that cold storage reduced the % emergence, % females, female’s longevity, and emergence percentage in F1 progeny of T. evanescens. For a successful biological control program, the decrease of T. evanescens performance after cold storage durations should be considered in mass production, and the release percentage should be increased by the equivalent of a lack of % emergence. Also, the economic importance of using cold storage periods in commercial mass rearing should be assessed in the biological control program.