The Entomology of Swollen Shoot of Cacao

Abstract

The entomology of swollen shoot of cacao is a complex and unique problem involving the inter-relations in the field of over 120 insect species of four insect and two arachnoid orders. Briefly, there are 17 species of pseudococcids, 75 species of ants, 16 species of hymenopterous parasites, three predatory beetles, one predatory dipteran, and three arachnid species involved in vector relationships directly, with a further 18 Coccid species involved indirectly (it is possible, of course, that further work will show that some of these 18 species are directly concerned as vectors).In the present paper an attempt has been made to reduce this assemblage of insect material to some semblance of order. The Coccid species are named and a series of preliminary observations on their biology and field behaviour detailed. The ant species, some of which are obligatorily associated with certain vector species, have been sorted into groups where specific determination has proved impossible or unnecessary and information has been included on their field habits and relative abundance.There are three distinct but complementary ecological niches involved in the problem. The first, and most important, is the association between the mealybug virus vectors and the Myrmicine coccid-tending ants. The second is the association between mealybugs of the generaParaputoandFormicococcusand the wild forest tree hosts of swollen shoot virus, and the third is the negative association between the mealybug tending Myrmicine ants andOecophyllaandMacromischoides, the latter species acting in certain circumstances as barriers to the spread of the mealybugtending species and hence to the spread of mealybugs and virus. These problems will be dealt with on a quantitative basis in a further paper.