Development, Morphometrics and Other Biological Characteristics of the Whitefly Bemisia tabaci (Gennadius) on Cassava

The development and morphometrics of the whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) were studied on cassava and a description was made of the different nymphal instars and other biological characteristics. The nymphal instars were distinguished using easily recognisable morphological characteristics. Abnormally developing individuals were also easily recognised. Regression analysis was highly significant between the length and width of nymphal instars modelled collectively indicating two-dimensional growth at least across three nymphal stadia. Males were smaller than females on the basis of body length, wing width and width of the abdomen. The insects showed better development on a Colombian cassava variety as compared to an African variety, Ebwanateraka from Uganda, and consistently showed a higher proportion of males than females (2.33: 1) for early-emerging individuals. Mean developmental period on both varieties was 22 days and the first instars accounted for the major part of the developmental period which ranged from 19 to 29 days. The mean number of eggs/female/day was 4.89. The actual events of first instar eclosion, which can last up to approximately five minutes, were described. The intervals of honeydew flow to the vasiform orifice lasted a minimum mean time of 20.8 seconds and a maximum mean time of 123 seconds.