Quantifying the harmful potential of ten essential oils on immature Trichogramma pretiosum stages

The use of chemical insecticides and non-selective natural products authorized for use in organic farming may reduce the effectiveness of egg parasitoids. The side-effects of ten plant essential oils on immature stages of Trichogramma pretiosum were evaluated. Carapa guianensis, Origanum vulgare and Zingiber officinalle during the F1 generation, and Azadirachtin and Mentha piperita in the F2 generation were slightly harmful (class II: 30-79%) to the emergence of this parasitoid. All essential oils affected the longevity of females of the F1 and F2 generations. Thymus vulgaris and Z. officinalle were the oils most harmful to female longevity. Carapa guianensis proved slightly harmful (class II: 30-79%) to parasitism in the F1 generation when applied during the egg-larval and pre-pupal stages and O. vulgare in the F1 generation in the pre-pupal stage alone, of this parasitoid. The sex ratio was lower than 0.5 during the pre-pupal stage of the F1 generation with Azadirachtin, C. guianensis, O. vulgare, Piper nigrum and Syzigium aromaticum, but this parameter was not affected for the other biological stages of T. pretiosum in the F1 and F2 generations. The Azadirachtin, C. guianensis, M. piperita, O. vulgare, T. vulgaris and Z. officinalle oils revealed a mild toxic effect to the immature stages of T. pretiosum and, therefore, it should be used according to patterns of ecological selectivity. Allium sativum and Citrus sinensis essential oils were not harmful to T. pretiosum, and can be used in Integrated Pest Management.