An assessment of population fluctuations of citrus pest woolly whitefly Aleurothrixus floccosus (Maskell, 1896) (Homoptera, Aleyrodidae) and its parasitoid Cales noacki Howard, 1907 (Hymenoptera, Aphelinidae): A case study from Northwestern Algeria

Abstract

The aim of this study was to assess the effectiveness of the parasitoid Cales noacki Howard, 1907 (Hymenoptera, Aphelinidae) in the biological control of the citrus pest woolly whitefly, Aleurothrixus floccosus (Maskell,1896) in Northwestern Algeria. In particular the pest and parasitoid population fluctuations under different environmental conditions were investigated. The study was conducted by examination and sampling of whitefly adult populations on young shoots and catches as well as its parasitoid during a 12-month period by counting the parasite and infested-live larvae. Results showed remarkable variations in abundance indices and infestation rates of larvae and adults that depended on the growth flush in foliage and meteorological conditions of the region. The woolly whitefly manifested three flight periods coinciding with three growth flushes of orange sap; in autumn towards the end of September followed by mid-November with the highest average abundance of 10 individuals per branch and a third flight period in mid-May. Phases of growth flush seemed to have an effect on the temporal distribution of adults over the sampling period from July to June. Pest emergence appeared favorable at 12-20 °C as the minimum interval temperature whereas the maximum varied between 25-33 °C with humidity levels of 50 % and 75 %. As for the incidence of natural enemies on whiteflies, despite their abundance, their impact was not optimum due to the large fluctuations in number of whiteflies. Although the pest-parasitoid complex appears to be important in the orchard, the biological regulation exerted by C. noacki while effective is insufficient for the complete neutralization of citrus woolly whitefly A. floccosus. An integrated approach is needed using additional natural enemies associated with the woolly whitefly.

Keywords

• citrus
• biological control
• population dynamics
• Aleurothrixus floccosus
• Cales noacki
• phenology