Parasitisation of the spiralling whitefly, Aleurodicus dispersus Russell (Homoptera: Aleyrodidae), by Encarsia spp. (Hymenoptera: Aphelinidae) in relation to hostplant and weather factors

In Nigeria, the spiralling whitefly (SWF), Aleurodicus dispersus , is a highly polyphagous and serious pest of horticultural crops. Although its parasitoid, Encasia sp., has been accidentally introduced, information on its suitability in the ecosystem is still scanty. The study therefore investigated factors influencing whitefly parasitisation by Encasia sp, from 2014 to 2019 on Citrus sinensis (sweet orange), Acalypha wilkensiana (red acalypha), Ficus polita (fig) and Psidium guajava (guava) at two sites in Ibadan, Nigeria. SWF abundance and mummification, and weather factors were monitored monthly and correlated. Total rainfall and mean temperature were significantly associated (P < 0.05) with both SWF density and parasitisation, while Encarsia sp., the only natural enemy found during the study, improved the regulation of SWF on all the hostplants at both sites. Number of parasitoids was highly correlated and synchronized (P < 0.05) with that of SWF throughout the sampling period although the spatial patterns of parasitism distribution in relation to SWF population density were not totally directly density dependent. Local extinction of SWF was observed on Citrus, Acalypha and Ficus spp., whereas whitefly regulation with reduced and stabilized numbers and stable percentage parasitism was evident on Psidium. While there was no significant difference (P > 0.05) between parasitism indices either within or between sites on Psidium , the cumulative numbers of SWF were significantly higher (P < 0.05) than other hostplants. The continued presence of the regulated SWF number on Psidium and its extinction on Citrus, Acalypha and Ficus suggested a combination of hostplant quality and Encarsia sp. as major factors in SWF regulation.