The Fluctuations of the Whitefly (Bemisia tabaci Genn) Population on Potato Plants and their Sustainable Management with Bio-Insecticides

Abstract

Potato whitefly, Bemisia tabaci (Genn.), is one of the most common insects that injure potato plants affecting the quality of potato production in Egypt. In the present study, open field experiments were conducted to study the seasonal population fluctuation of whitefly (Bemisia tabaci, Genn.) nymphs and adults on potato (Solanum tuberosum L.) during two seasons 2021 and 2022 in the Qalubia Governorate (Egypt), under protected conditions and its correlation with the environmental factors: temperature (maximum and minimum), relative humidity, wind speed, and precipitation were observed. Also, the toxicity of different essential oils (EOs) namely camphor oil (Cinnamomum camphora), citronella oil (Cymbopo gonnardus, L), geranium oil (Pelargonium graveolens L.), eucalyptus oil (Eucalyptus globulus L.), Marjoram (Origanum majorana) and thyme oil (Thymus vulgaris L.) were examined separately and as mixtures with chitosan against both B. tabaci, nymphs and adults. These were compared with imidacloprid as a positive control. The population fluctuation study of B. tabaci showed the highest mean number of adults recorded at 1.13 adults/plant and 1.1 adults/plant on November 12, 2022. While the nymph population was 2.21 nymphs/plant on November 19, 2021, and 2.413 nymphs/plant in 2022. Adult and nymph populations showed a continuous decrease until December. There was a significant correlation between the B. tabaci population (nymph and adult) and wind speed, relative humidity, and precipitation during the 2021 season. In contrast, during the 2022 season, the B. tabaci population (nymph and adult) significantly correlated with all examined environmental factors, except for precipitation levels. Also, the study tested essential oils EOs, chitosan (Ch), and their mixtures on potato plants for their effectiveness against B. tabaci infestation. Results showed the tested emulsions had a slightly lower efficacy than the conventional synthetic insecticide, Imidacloprid, in controlling B. tabaci on potato fields. Thyme and citronella were the most effective in reducing B. tabaci adult populations, followed by camphor and geranium. The highest reduction percentage was caused by
(thyme+Ch). Foliar spray of thyme, citronella, and camphor showed similar efficacy on B. tabaci nymphs. The (EOs+Ch) mixture was more effective than the EOs. Chitosan enhances the durability of essential oil emulsions and improves their adherence to leaf surfaces. Thyme and citronella oils effectively reduced B. tabaci adult populations, followed by camphor and thyme. Combining chitosan
with thyme or citronella oils enhanced their effectiveness against B. tabaci adults.