Within-plant distribution of Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) on cassava: effect of clone and predation on aggregation

Abstract

A presence-absence sampling procedure is presented which relates the proportion of leaves infested with the mite Mononychellus tanajoa (Bondar) at a given node of cassava to the mean number of mites per leaf at that node. The procedure incorporates Taylor's variance-mean density relationship, taking into account mite aggregation behaviour. Aggregation of M. tanajoa was greater in plants where mite predators were excluded, on a resistant (CG5-79) rather than a susceptible cassava clone (MCol 22) and on leaves arising from the lower nodes rather than the higher ones. The implications of the effect of mite mortality factors on aggregation are discussed.