Effects of environment and host on vector biology and incidence of two whitefly‐spread diseases of legumes in Nigeria

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Abstract
SUMMARY: Seasonal periodicity in the incidence of cowpea golden mosaic (CGM) and lima bean golden mosaic (LBGM), two whitefly‐spread virus‐like diseases, corresponded closely with fluctuations in population density of their vector, Bemisia tabaci, at two contrasting sites in southern Nigeria. Peak catches of the vector followed the onset of rains after very high temperatures during the dry season; populations declined abruptly with continuous, heavy rainfall. At Onne, B. tabaci infested legumes at emergence and remained and reproduced on them but at Ibadan infestation was delayed and there was no evidence of reproduction on legumes. B. tabaci preferred LBGM‐susceptible lima beans (Phaseolus lunatus) to resistant ones and more pupae of B. tabaci occurred on CGM‐susceptible cowpea (Vigna unguiculata) cultivars than on resistant ones but these observations did not relate to the yellow‐sensitivity of whiteflies. Resistance to CGM in cowpea, and to LBGM in lima bean, was identified amongst germplasm exposed to natural infection. Resistance was, in each case, associated with lower disease incidence, slower spread and milder expression of symptoms relative to susceptible cultivars. Vector non‐preference for resistant cultivars may have contributed to reduced secondary spread.

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