Effect of Repeated Applications of Entomopathogenic Fungi on Whitefly Populations in the Greenhouse

Whiteflies (Aleyrodidae) are key pests of field and greehouse crops worldwide. There is interest in biological control tools for whitefly management. We evaluated the effect of one, two or three successive sprays of conidial suspensions of two entomopathogenic fungi in the Hypocreales, Isaria fumosorosea and Metarhizium brunneum, against cohorts of nymphs of greenhouse whitefly, Trialeurodes vaporariorum, on pinto bean plants in the greenhouse. Fungi were grown on agar media and the conidia were suspended for treatments. The fungus Isaria fumosorosea was sprayed at 1x10⁶ and 1x10⁷ spores/ml of water; likewise, Metarhizium brunneum was applied at 1x10⁶ , 1x10⁷ and 1x10⁸ spores/ml. Isaria showed more virulence against nymphs, with up to 98% mortality after two applications separated 96 hours. Metarhizium induced moderate mortality levels, ranging from 39% (one application at 1x10⁸ spores/ml) to 70% (after three applications of 1x10⁸ spores/ml). Control mortality was always below 15%. Effect on eggs will be discussed also. The potential of fungi for whitefly management in the greenhouse should be considered.