A model of temporal distribution of Aphis gossypii (Glover) (Hem., Aphididae) on cotton

The spatio-temporal distribution of Aphis gossypii (Glover) was studied for a 4-year period in a plot of Gossypium hirsutum located in Bangui, Central African Republic. A study of the temporal evolution of the number of aphids by means of non-linear regression indicated a rapid population increase during the first 8 weeks of cotton cultivation. The overdispersion of the aphids was found to be significant during most of the season. We tested three population dispersion models; Iwao's model and Taylor's power law describe the relationship between the mean m and variance sigma(2) for the number of aphids, and the Nachman's model describes the functional dependence between m and the proportion p of non-infested cotton plants. The results of these statistical tests indicate that only the Taylor's model was not rejected. The aphids' aggregation increases with population density. The regression parameter confidence intervals for each of the 4 years of observation prove the stability of the Taylor's model. The model sigma(2) = 45m(1.3) is recommended when the environmental and cultural conditions are similar to those of our study.